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With the development of new energy vehicles, the safety concern of power batteries has become urgent, making the exploitation of new temperature sensors for the batteries important. In this paper, persistent luminescence nanoparticles (PLNPs) of Bi 1.91 Ga 4 O 9 : 0.04 Er3 +, 0.05 Eu3+ with up- and down-conversion luminescence were prepared by a simple and low-cost co-precipitation method. Single rare earth element doping of Er3+ achieves up-conversion luminescence at 526 nm/550 nm under 980 nm excitation. After co-doping with rare earth element Eu3+, it can realize the down-conversion luminescence at 590 nm/614 nm under 254 nm excitation. They showed obvious temperature dependence at 293–503 K and 423–573 K, respectively. The corresponding maximum relative sensitivities are 0.98 % K−1 and 0.55 % K−1. Interestingly, all temperature ranges cover the spontaneous ignition point of the power battery at 473 K. Thus, the PLNPs-based sensor was successfully validated for monitoring overheating and spontaneous combustion of power battery with the dual-channel temperature measurement modes. The two kinds of temperatures were verified with each other for the improved sensitivity and accuracy, so they were used to accurately measure the temperature of the power battery in real time for early warning and the improved safety. Thus, we provided a new application scenarios of PLNPs in the field of temperature sensing for monitoring the temperature of battery. • Er-Eu co-doped Bi2Ga4O9 persistent luminescence nanoparticles with up- and down-conversion luminescence was prepared. • The material for dual-mode temperature measurement. • Accurately measuring the temperature of the power battery for the improved safety. [ABSTRACT FROM AUTHOR]

The self-assembly mechanism of porous materials has always been a hot topic and a challenging issue in research. What factors induce the self-assembly process, and how is the temperature sensing performance related to it? Innovatively, in this paper, Gd 2 O 2 S:Er3+/Yb3+ phosphors with different morphologies were synthesized, and elucidated the formation mechanism of flower-like structures through relevant theorems, formulas, and experiments, proposing that polar molecules and dipole-dipole interactions guide the synergistic effect of van der Waals forces and hydrogen bonding, which ultimately induces the self-assembly of spherical structures into flower-like ones. In addition, four representative intermediates were selected to investigate their luminescence and temperature sensing properties. The results show that the flower-like sample can respond more effectively to changes in ambient temperature because of its rich pore structures, and thus exhibit better temperature sensing performance. In-depth research on the self-assembly mechanism of materials helps to predict and regulate their properties, and the unique characteristics of flower-like sample provide new ideas for material selection in the field of high-precision temperature measurement. • Successfully synthesized flower-like porous Gd 2 O 2 S:Er3+/Yb3+ phosphor for the first time. • The formation mechanism of self-assembly of spherical structures into flower-like structures was deeply investigated. • The up-conversion luminescence and thermometric performance of samples with different morphologies were studied. • The flower-like sample can respond more effectively to temperature changes, with its highest sensitivity reaching 0.089 K−1. [ABSTRACT FROM AUTHOR]

A simple and rapid grinding method for preparing Er3+-doped and Er3+/Yb3+co-doped Cs 3 Bi 2 Cl 9 upconversion phosphors was developed. We avoid to employ strong acids as reaction solvents, aligning with the principles of green chemistry. By controlling the thermal treatment temperature and adding BiCl 3 , a reversible phase transformation process between Cs 3 Bi 2 Cl 9 and Cs 3 BiCl 6 perovskite phosphors was achieved. The Er3+/Yb3+ co-doped Cs 3 Bi 2 Cl 9 phosphors emit green light under 980 nm excitation, whereas Cs 3 BiCl 6 phosphors emit red light. Their temperature sensing performance was tested through variable-temperature processes. Compared to Er3+-doped Cs 3 Bi 2 Cl 9 phosphors, the co-doped Er3+/Yb3+ phosphors have a higher relative sensitivity of 1.60 % K−1. Compared to previously reported materials, Cs 3 Bi 2 Cl 9 phosphors show enhanced sensitivity in temperature sensing. The study demonstrates that lead-free halide perovskites' unique color-tunability not only underscores the innovativeness of this synthetic strategy but also provides a significant technological foundation for temperature sensing applications. Given their environmental friendliness and facile preparation process, these phosphors possess notable advantages for industrial production and hold promise as potential candidates for next-generation high-performance phosphor materials. • A grinding method for preparing Cs 3 Bi 2 Cl 9 phosphors using a green chemistry approach. • Reversible phase transitions between Cs 3 Bi 2 Cl 9 and Cs 3 BiCl 6 can be controllinged by thermal treatment and BiCl 3 addition. • Er3+/Yb3+ co-doped Cs 3 Bi 2 Cl 9 emit green light under 980 nm excitation, while phase-transformed Cs 3 BiCl 6 emit red. • Cs 3 Bi 2 Cl 9 phosphors co-doped with Er3+/Yb3+ show improved sensitivity compared to Er3+single doping. [ABSTRACT FROM AUTHOR]

In this paper, Cs 2 NaErCl 6 double perovskites microcrystals (MCs) co-doped with Yb3+ and Bi3+ are successfully synthesized by a simple "dissolving-drying" method. When excited at 379 nm, 808 nm and 980 nm, the MCs show strong red, green and yellow light, respectively, which can be well distinguished by the naked eyes. On this basis, two kinds of systems are designed with doped/undoped MCs for triple-mode fluorescent anti-counterfeiting and information encryption of numbers and characters. The results indicate that our MCs are not only beneficial to the application of fluorescent anti-counterfeiting, but also greatly improve the security of anti-counterfeiting. In addition, we evaluate the temperature sensing performance of these MCs by fluorescence intensity ratio technique. The samples show a high relative sensitivity as 3.8 %/K at 243 K. The results show that the samples have multi-functional applications in the fields of fluorescent anti-counterfeiting and temperature sensing, and this work will broaden the application fields of lead-free double perovskites in fluorescent anti-counterfeiting and temperature sensing. • Novel Yb3+/Bi3+ co-doped Cs 2 NaErCl 6 double perovskites microcrystals (MCs). • Multifunctional applications in anti-counterfeiting and temperature sensing. • Triple-mode anti-counterfeiting and information encryption. • A high relative sensitivity of temperature sensing as 3.8 %/K. [ABSTRACT FROM AUTHOR]

All-inorganic perovskite QDs, such as CsPbX 3 (X = Cl, Br, I), have garnered significant attention in the field of optoelectronics as emerging photonic materials. Rare-earth (RE) doping is an effective strategy for enhancing the optical properties of CsPbX 3 perovskite quantum dot glasses. Therefore, investigating the crystallization behavior of rare-earth ion-doped CsPbX 3 glass and the energy transfer mechanisms between rare-earth ions and CsPbX 3 is crucial for advancing the development of rare-earth-doped perovskite glass materials. The paper systematically introduces the preparation methods, structural characteristics, and applications of CsPbBr 1.5 Cl 1.5 QDs in optoelectronic devices. Firstly, the detailed effects of Eu3+ and F⁻ doping on the structure and optical properties of CsPbBr 1.5 Cl 1.5 quantum dot glass are discussed. Subsequently, the crystal structure, size distribution, and morphology of CsPbBr 1.5 Cl 1.5 QDs are characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Furthermore, the application of CsPbBr 1.5 Cl 1.5 QDs in LEDs and temperature sensing optoelectronic devices is explored, highlighting their performance and potential value in these applications. This study provides important references and guidance for further research and application of CsPbBr 1.5 Cl 1.5 QDs in the field of optoelectronics. • Eu³⁺ doping enhances spontaneous crystallization, improving material structure and properties. • Eu³⁺ doping greatly boosts luminescence intensity and displays characteristic emission peaks. • Eu³⁺ doping enhances the sensitivity and resolution of temperature sensing in glass ceramics, making them ideal for precise applications. [ABSTRACT FROM AUTHOR]

Rare earth-doped nanomaterials can achieve diverse upconversion luminescence by changing doping ions, presenting them as promising candidates for rapid temperature measurement. However, most upconversion luminescent phosphors have a thermal quenching effect, which greatly weakens the luminous intensity of the material and impairs thermometry performances. Here, we studied the synthesis of Bi 4 Ti 3 O 12 nanosheets tridoped with Er3+, Yb3+, and Nd3+ ions using molten salt method. Notably, this luminescent material demonstrates both thermal quenching and thermal enhancement effects. The unusual phenomenon results in a high sensitivity of the optical temperature sensor based on the inter-ion energy level between Er3+ and Nd3+. At 523 K, this sensitivity reaches 5.94×10−2 K−1, surpassing that of sensors relying on the thermal coupling of only Er3+ ions by nearly ninefold. Our findings suggest a promising strategy to augment the temperature sensing sensitivity of luminescent materials, paving the way for potential applications in precise temperature monitoring. [Display omitted] • The nanosheets are very sensitive to temperature. • Combination of positive and negative thermal quenching effects improves sensitivity. • The temperature measurement accuracy is up to ± 0.5 K. [ABSTRACT FROM AUTHOR]

Rare earth doped up-conversion materials play an important role in information security, colorful display and temperature sensing. In this work, the up-conversion luminescence of NaYF 4 :0.2Tm/20Yb@NaYF 4 :20Yb@NaYF 4 :2Er/20Yb phosphors, synthesized by typical co-precipitation method, are investigated under different excitation condition. The emission color of sample can be tuned from yellow to blue-green through changing pump laser from 1550 to 980 nm because the Tm3+ ions in the core cannot be excited by 1550 nm laser. More interesting, the value of red-to-green (R/G) and blue-to-green (B/G) can be finely manipulated by tuning the excitation pulse width and frequency. This phenomenon can be interpreted by different rising processes of the green, red and blue up-conversion emission. In addition, the core-shell structured sample displays a temperature-dependent color change, ranging from blue-green to purple. The green emissions, radiated from thermal coupled levels (2H 11/2 4S 3/2), are used in thermometry and the max relatively sensing sensitivity reaches 0.01 K−1 at 303 K. The findings indicate that the core-shell Tm@Yb@Er phosphors, with excitation-dependent and temperature-dependent up-conversion luminescence, have potential applications in information security and temperature sensing. [Display omitted] • The emission color of sample can be tuned from yellow to blue-green through changing pump laser from 1550 to 980 nm. • The value of red-to-green and blue-to-green can be finely manipulated by tuning the excitation pulse width and frequency. • The different temporal response of up-conversion luminescence is originated to the different rise time of green, red and blue emissions. [ABSTRACT FROM AUTHOR]

A series of spherical Er3+/Yb3+ doped Lu 2 O 3 and Lu 2 O 2 S phosphors co-doping with varying concentrations of Li+ (0, 1, 3, 5, and 7 mol%) were synthesized by homogeneous precipitation method followed by direct calcination or sulfurization. The crystal structure and morphology of the as-prepared phosphors were characterized by XRD, FTIR and SEM. Meanwhile, the upconversion (UC) luminescence spectra were recorded under 980 nm laser excitation at temperatures ranging from 303 to 573 K. The incorporation of lithium ions led to an enhancement of UC luminescence intensity by about 15 times at room temperature. The introduction of Li+ could also affect the temperature sensitivity of the samples. Furthermore, optical temperature sensing of the phosphors was achieved by analyzing the fluorescence intensity ratio (FIR) of thermally coupled levels (TCLs) and nonthermally coupled levels (non-TCLs). Impressively, utilizing the non-TCLs approach resulted in maximum S a values of 8.80 %K−1 and 11.06 %K−1 for the Er3+/Yb3+/5 % Li+ doped Lu 2 O 3 and Lu 2 O 2 S phosphors, leading to an approximately 17-fold and 23-fold increase compared to that of TCLs-based approach, respectively. The results of this work demonstrate the great potential of Er3+/Yb3+/Li+ doped Lu 2 O 3 and Lu 2 O 2 S phosphors for optical thermometers. • Monodisperse spherical Er3+/Yb3+/Li+ doped Lu 2 O 3 and Lu 2 O 2 S phosphors were successfully synthesized. • A simple, accurate, low cost and large-scale production method for rare earth doped Lu 2 O 3 and Lu 2 O 2 S phosphors was proposed. • The effects of Li+ on enhancement of upconversion luminescence and thermometric performance were investigated systematically. [ABSTRACT FROM AUTHOR]

A series of NaGd(MoO 4) 2 glass ceramics containing Eu3+-Tb3+ were fabricated using the melt-curing crystallization method. These glass ceramics were subjected to various analyses, such as differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and light transmittance curve analysis, to determine the optimal heat treatment conditions, which were determined to be 680 ℃/1.5 h. The XRD Rietveld analysis results confirmed the successful incorporation of Eu3+ and Tb3+ ions into the NaGd(MoO 4) 2 lattice structure. Moreover, the glass ceramics exhibited a smaller optical bandgap than the precursor glass, as observed by absorption spectroscopy. The energy transfer from Tb3+ to Eu3+ was demonstrated through the excitation spectra, emission spectra, and fluorescence decay curves. The primary mechanism responsible for this energy transfer was identified as a dipole dipole interaction. The ability to produce multicolor tunable emission was achieved by varying the Eu3+ doping concentration at a fixed Tb3+ concentration. The fluorescence intensity ratio and temperature dependence of Tb3+ and Eu3+ were used to calculate the relative sensitivity (S r), which reached a maximum of 3.34 % K−1 at 458 K. In conclusion, Eu3+-Tb3+ co-doped glass ceramics have promising potential for application in the fields of light-emitting diodes and temperature sensing. • Eu3+-Tb3+ co-doped NaGd(MoO 4) 2 glass ceramics were prepared. • The transmittance of glass ceramic can reach 80 % in the visible region. • The maximum relative sensitivity of the glass ceramics were obtained to be 3.34 % K−1 at 458 K. [ABSTRACT FROM AUTHOR]

The quenching of luminescence in Er3+/Yb3+ co-doped with Tm3+ presents a dilemma as it substantially diminishes thermometric performance. In this study, Y 2 O 2 S: Er3+/Yb3+/Tm3+ phosphors were synthesized using a homogeneous precipitation method combined with a sulfurization process. In addition, three sets of fluorescence intensity ratio (FIR) models were designed, which have self-calibration function. The effects of incorporation of Li+ or Li+/Ba2+ on the up-conversion luminescence (UCL) intensity and thermometric performance of the phosphors were systematically studied. The results show that the introduction of Li+ or Li+/Ba2+ co-doping leads to lattice distortion and the formation of oxygen ion vacancies in the lattice, which further accelerates the energy transfer process and mixes the charge transfer states, and ultimately dramatically improves the UCL and thermometric performance. The introduction of Li+ and Li+/Ba2+ co-doping enhanced the UCL of the materials by about 3.7 times and 5.6 times compared to Y 2 O 2 S: Er3+/Yb3+/Tm3+. When based on nonthermally coupled levels (NTCLs), the S r-max of Li+/Ba2+ co-doped sample is 0.080 K−1 at 573 K, which is 87 % higher than that based on TCLs. These findings not only provide a new avenue for improving the UCL and thermometric performance but also provide an accurate self-calibration FIR model over a wide temperature range. • Monodisperse spherical Y 2 O 2 S:Er3+/Yb3+/Tm3+ phosphors were successfully synthesized. • A simple, accurate, low cost and large-scale production method for rare earth doped Y 2 O 2 S phosphors was proposed. • The effects of Li+ and Li+/Ba2+ ions on enhancement of optical performance were investigated systematically. • Three sets of fluorescence intensity ratio models were designed and a self-calibration function was obtained. [ABSTRACT FROM AUTHOR]

Lanthanide upconversion luminescent materials featuring multi-peak and tunable emissions allow for ratiometric luminescence thermometry in a remote detection manner. However, wide explorations are still required to develop relevant materials for efficient thermometric performances. Herein, Yb3+/Er3+ co-doped non-stoichiometric analogues of bismuth oxyfluoride were obtained by simply tuning the F−/(Bi3+ + Ln3+) molar ratio of the reactants in a solid-state reaction method, for the first time. We achieved simultaneous regulations in composition, structure, morphology, and upconversion luminescence properties of BiO x F y :Yb/Er (2/1 mol%) microcrystals. Compositional analysis revealed not only the predictable increase of fluorine content, but also the constant O/(Bi + Ln) atomic ratios in all nominal BiO x F y :Yb/Er. Experimental results showed the structure and morphology evolutions from hexagonal-phase micro-flowers, to tetragonal-phase microplates, and further to orthorhombic-phase irregular microcrystals. Benefiting from adjustable composition, structure and morphology, up-conversion luminescence with adjustable intensity and color was obtained. Temperature dependent upconversion properties and ratiometric thermometric performances based on the thermally coupled levels, 2H 11/2 and 4S 3/2 of Er3+, were explored. BiOF:Yb/Er, BiO 0.67 F 1.66 :Yb/Er, and BiF 3 :Yb/Er microcrystals were found as suitable temperature sensing candidates with operating temperature range as wide as 298−673/723 K, high relative sensitivity up to 1.24% K-1, and minimum temperature uncertainty of 0.15 K. These results benefit not only further explorations for high-performance lanthanide-based luminescence thermometers, but also the chemistry of fluorides made from the solid-state reaction method. [Display omitted] • Non-stoichiometric analogues of BiOF obtained by controlling the amount of NH 4 F. • Evolutions in structure and morphology of BiO x F y :Yb/Er were revealed. • O/(Bi + Ln) atomic ratios remain constant in all nominal BiO x F y :Yb/Er. • BiO x F y :Yb/Er show intensity-varied and multicolor upconversion luminescence. • BiO x F y :Yb/Er permit wide temperature detection range, high S r and low uncertainty. [ABSTRACT FROM AUTHOR]

Mechanochemical has emerged as an eco-friendly, efficient, and upscalable tool for the synthesis of perovskite quantum dots (PQDs). However, achieving control over the size and ensuring good mono-dispersion of PQDs by mechanochemistry, while simultaneously increasing their stability remains a great challenge. Herein, we specifically chose a lead bromine-based MOF (PbBr-MOF) with [Pb 2 Br 3 ]+ nodes and utilized the uniform distribution of [Pb 2 Br 3 ]+ to induce the in-situ confined growth of Cs 4 PbBr 6 QDs via bottom-up mechanochemical approach for the first time, denoted as Cs 4 PbBr 6 @PbBr-MOF. The Cs 4 PbBr 6 QDs uniform and firmly anchor in PbBr-MOF through [Pb 2 Br 3 ]+ nodes, preventing their aggregation and enhancing quantum confinement effects. Highly dispersed Cs 4 PbBr 6 QDs (3.86 ± 0.61 nm) exhibit high photoluminescence quantum yield (31%) and notable durability in various solvents. Furthermore, Cs 4 PbBr 6 @PbBr-MOF demonstrates excellent performance as a temperature sensor, with maximum absolute (Sa) and relative (Sr) temperature sensitivities of up to 0.013 K−1 and 3.41% K−1, respectively. [Display omitted] • [Pb 2 Br 3 ]+ nodes in PbBr-MOF as Cs 4 PbBr 6 QDs precursors. • Enhancing Cs 4 PbBr 6 's confinement effect through controlled CsBr and nodes dispersion. • Cs 4 PbBr 6 QDs have 3.86 ± 0.61 nm size with high photoluminescence yield (31%). • PbBr-MOF boosts Cs 4 PbBr 6 QDs stability in harsh conditions. • Cs 4 PbBr 6 @PbBr-MOF shows impressive temp sensitivity. [ABSTRACT FROM AUTHOR]

In the pursuit of optical thermometers, the fluorescence intensity ratio technique has aroused much interest because of the urgent need for noncontact thermometers driven by technological development. Here, an optical thermometer BaLaGa 3 O 7 :Bi3+,Eu3+ based on different thermal responses of Eu3+ and Bi3+ emissions had been reported. The structure, morphology, luminescence properties, and optical thermometric behavior were investigated by experimental data comprising X-ray diffraction patterns, microscopy, and luminescence spectroscopy. The dopants with eight oxygen ligands in the melilite-type host form emission centers. The Bi3+ singly doped, and Eu3+ singly doped phosphors can have intense blue and red emissions due to the 3P 1 -1S 0 and 5D 0 -7F J(0−4) electron transitions, respectively. In the Bi3+-Eu3+ codoped phosphors, tunable emission colors were obtained owing to Bi3+→Eu3+ energy transfer and doping concentration variation. Moreover, the intensity ratio of Bi3+ and Eu3+ emissions varied with the temperature in the range of 298 − 523 K. The relative and absolute sensitivities of the as-prepared phosphor were determined to be 0.29%K−1 and 0.20%K−1, respectively, manifesting that the prepared BaLaGa 3 O 7 :Bi3+,Eu3+ has the potential to serve as phosphors for optical thermometers. • The novel optical thermometer BaLaGa 3 O 7 :Bi3+,Eu3+ based on FIR technique had been reported for the first time. • Photoluminescence static and dynamic properties of BaLaGa 3 O 7 :Bi3+ at 300 K and 77 K had been investigated in detail. • Tunable emission colour of BaLaGa 3 O 7 :Bi3+,Eu3+ had been realized by Bi3+→Eu3+ energy transfer and doping content variation. • The as-prepared BaLaGa 3 O 7 :Bi3+,Eu3+ possesses good temperature resolution and high sensitivity.. [ABSTRACT FROM AUTHOR]

This paper reports on microcrystals with deep tissue penetration depth, strong red light emission, and thermometric function. The red light emission of NaLuF 4 :20 % Er3+/1 % Tm3+/10 % Yb3+ microcrystals is exceptionally strong, thanks to the introduction of Tm3+ and Yb3+ ions energy capture centers. In bioimaging, the 1532 nm laser exhibits deeper imaging depth due to weak photon scattering and autofluorescence. Furthermore, red light emission has the greatest tissue penetration depth in the visible region. The luminescence intensity and tissue penetration depth of both the excitation and emission light make them suitable for deep tissue imaging. We investigated temperature sensing performance of NaLuF 4 :20 % Er3+/1 % Tm3+/10 % Yb3+ microcrystals, and found that the maximum relative sensitivity of LIR (I 521 /I 540) reaches 0.92 %K−1. The microcrystals NaLuF 4 :20 % Er3+/1 % Tm3+/10 % Yb3+ are anticipated to have application in deep tissue imaging and temperature sensing. • The red light of NaLuF 4 : Er3+ microcrystals is enhanced by the introduction of Tm3+ and Yb3+ ions. • The microcrystals NaLuF 4 :Er3+/Tm3+/Yb3+ exhibit weak photon scattering and deeper imaging depth. • The microcrystals NaLuF 4 :Er3+/Tm3+/Yb3+ exhibit favourable temperature sensing properties. • The microcrystals NaLuF 4 :Er3+/Tm3+/Yb3+ exhibit favourable properties for red light imaging. [ABSTRACT FROM AUTHOR]

Eu2+/Eu3+ co-doped Sr 3 P 4 O 13 phosphors were prepared by high temperature solid stated method in air atmosphere and studied in detail their luminescent properties in order to investigate the possible applications in temperature sensors. The broadband emission of Eu2+ ions and the linear emission band of Eu3+ ions can be observed in the photoluminescence (PL) spectra of Sr 3 P 4 O 13 : Eu2+/Eu3+ phosphors due to the self-reduction effect. X-ray photoelectron spectroscopy (XPS), PL spectra, and time-resolved fluorescence lifetime confirm the formation of double emission centers of Eu2+ and Eu3+ ions in Sr 3 P 4 O 13 because of the self-reduction by charge compensation. In the Eu2+/Eu3+ co-activated Sr 3 P 4 O 13 thermometric phosphor, the blue emission of Eu2+ ions and red emission of Eu3+ ions, can be used as fluorescence intensity ratio (FIR) signals. In addition, the mechanism is discussed in detail based on the experimental data, and the strong temperature dependence is explained from the point of view of thermal quenching. Additionally, benefited from their diverse thermal quenching behavior, the FIR of Eu3+ to Eu2+ is fitted very well, and S a reached a maximum 0.008 K−1 at 573 K, while S r reached a maximum of 1.06% K−1 at 353K. As a consequence, this work indicates that Sr 3 P 4 O 13 : Eu2+/Eu3+ phosphors could be widely applied in optical temperature sensors. The Eu2+/Eu3+ co-doped Sr 3 P 4 O 13 thermometric phosphors is synthesized by solid-state reaction. the blue emission of Eu2+ ions and red emission of Eu3+ ions, can be used as fluorescence intensity ratio (FIR) signals. The dual-emissions has different thermal dependencies due to the competition between thermal-activated energy transfer and thermal quenching, thus enabling their intensity ratio to be highly sensitive to the temperature variation, which makes this phosphor a good candidate as ratiometric and colormetric temperature sensor. Image 1 • The emission of Eu2+ and Eu3+ ions can be observed Sr 3 P 4 O 13 : Eu2+/Eu3+ phosphors due to the self-reduction influence. • The blue emission of Eu2+ and red emission of Eu3+ ions can be used as fluorescence intensity ratio signals. • S a reached a maximum 0.008 K−1 at 573 K, while S r reached a maximum of 1.06% K−1 at 353K. [ABSTRACT FROM AUTHOR]

Research on near-infrared (NIR) emission of Tm3+ and Yb3+ co-doped upconversion (UC) materials has accepted many interests owing to delightful features for frontier applications. In this work, we focus on the preparation of pure NIR emission and the improvement of absolute sensitivity (S A) on temperature in Tm3+ and Yb3+ co-doped novel double perovskite Gd 2 ZnTiO 6 (GZT) phosphors. Upon 980 nm excitation, these phosphors perform dramatical NIR emissions, and the integral intensity percentage of NIR emission versus total visible emissions reaches up to 99.88%. A high S A value with 1.7351 K−1 at 473 K for the I 801 /I 650 is obtained via introducing excellent NIR emission. Besides, the S A value of non-thermally coupled levels is higher than that of thermally coupled levels. These results suggest that this kind of UC material may be a candidate for NIR imaging and temperature detection applications. Image 1 High sensitivity based on non-thermally coupled levels is received via utilizing intense NIR emission in Tm3+ and Yb3+ co-doped double perovskite GZT phosphors. • Upconversion properties of Tm3+ and Yb3+ co-doped novel double perovskite Gd 2 ZnTiO 6 phosphors are investigated in detail. • Intense and nearly pure NIR emission with high integral intensity percentage that achieves 99.88% is obtained. • High S A with 1.7351 K−1 at 473 K for N-TCLs is received via utilizing intense near-infrared emission. [ABSTRACT FROM AUTHOR]

NaYF 4 :Yb3+/Ho3+/Ce3+ upconversion phosphors were synthesized by using a citric acid assisted hydrothermal method. Both increasing the concentration of Ce3+ and decreasing the Yb3+ content are beneficial to the formation of cubic NaYF 4. When the concentration of Yb3+/Ho3+/Ce3+ were 20/1/20 and 5/1/10, respectively, a pure cubic phase was obtained. The spectral conversion from green to red was achieved by first increasing Ce3+ concentration to 10% and then decreasing the Yb3+ concentration to 5%. In the first half, the two cross relaxation processes between Ho3+ and Ce3+ were responsible for the modulation of the luminescence, while in the latter half, the enhanced intensity ratio of red to green emission was related to the decreased energy transfer from Ho3+ to Yb3+. Except for the sample doped with 5% Yb3+, 1% Ho3+ and 10% Ce3+, the total emission intensity of other samples decreased linearly with increasing sample temperature. The maximum responsibility was obtained in the case of 20% Yb3+, 1% Ho3+ and 5% Ce3+ doping. Compared to the Er3+ based luminescent temperature sensing, this novel temperature sensing not only shown little impact from pump power, but also had the identical sensitivity at various temperatures, and thus being a promising candidate for temperature sensing. • A simple method for regulating phase structure of NaYF 4 :Yb3+,Ho3+,Ce3+ was reported. • Spectral conversion was achieved by adjusting the content of Ce3+ and Yb3+. • The luminescent temperature sensing was investigated. [ABSTRACT FROM AUTHOR]

Abstract To develop new upconversion (UC) phosphors of high sensitivity for temperature sensing, a series of Yb3+-Er3+ and Yb3+-Ho3+ doped NaLaMgWO 6 (NLMW) samples were designed via solid-state reaction method. The phase purity was examined by XRD patterns, indicating the obtained samples are all single-phase. The morphology was characterized by SEM and TEM techniques, revealing smooth particle surface. The electronic structure of NLMW was analyzed theoretically, and the optical bandgap obtained was compared with the experimental results. Upon 980 nm excitation, the characteristic transitions of Er3+ and Ho3+ were found, and their optimal concentrations were determined to be 2 and 3 mol%, respectively. By investigating the temperature-dependence of NLMW:0.1 Yb3+,0.02Er3+, it was found that the thermally-coupled 2H 11/2 and 4S 3/2 levels of Er3+ cause a large fluorescence intensity ratio (FIR) for 528 and 550 nm emissions, which can generate a high absolute sensitivity (0.0107 K−1 at 508 K). The corresponding explanation was given by using the dependence of UC emissions on excitation power density. For the NLMW:0.1 Yb3+,0.03Ho3+ phosphor, the non-thermally-coupled (5F 4 ,5S 2) and 5F 5 levels were employed to character the temperature-sensing behavior of Ho3+. High absolute sensitivity of 8.9 × 10 − 3 K−1 was gained at 548 K. The reason for the different change of 543 and 658 nm emissions intensities with temperature was conducted by the phonon-electron coupling. Highlights • Different strategies for temperature sensing were studied in NLMW:Yb3+-Er3+/Ho3+. • The NLMW:Yb3+-Er3+/Ho3+ phosphors show high sensitivity for temperature sensing. • The phonon-electron coupling was proposed to explain the change of I 658 /I 543 of Ho3+. • The present phosphors could have potential application in optical temperature sensors. [ABSTRACT FROM AUTHOR]

Abstract Er3+/Yb3+-doped Pb(Zn 1/3 Nb 2/3)O 3 -9PbTiO 3 ferroelectric crystals were grown by the high-temperature solution method. The micromorphology, phase structure, and upconversion photoluminescence of obtained crystals were analyzed and investigated. As the results suggest, the crystals displayed typical lamellar growth and possessed a pure perovskite structure. Excited by a 980 nm laser, the characteristic upconversion (UC) emissions of Er3+ were observed at room temperature. The luminescence intensity improved with the increasing of excitation power and reached its maximum at 1056 mW. Two-photon process was demonstrated at lower power range. As the temperature increased from 213 to 493 K, the luminescence intensity weakened continuously. An apparent difference in variation trend between two thermally coupled levels (2H 11/2 and 4S 3/2) was also observed, which was ascribed to the redistribution of electrons at two levels at the heating process. Based on this dependence, the temperature sensing abilities were examined with the help of the fluorescence intensity ratio (FIR) technique. The absolute sensitivity S A increased in the measurement temperature range and its maximum of 0.0033 K-1 was obtained at 493 K. Moreover, low conversion from incident light into heat was also demonstrated, which indicates the feasibility for crystal luminescence at high power pumping. These results make Er3+/Yb3+-doped Pb(Zn 1/3 Nb 2/3)O 3 -9PbTiO 3 crystals become a promising candidate in optical devices and temperature sensors. Highlights • Frequency and temperature dependence of UC PL was investigated for grown crystals. • Two-photon process at lower power range was demonstrated. • The maximum S A of 0.0033 K-1 was obtained. • Low conversion from incident light into heat was also demonstrated. [ABSTRACT FROM AUTHOR]

Abstract Phytochromes P R and P FR are distributed in various organs of plant, phytochrome P R absorbs red light and phytochrome P FR absorbs far-red light, respectively, so the flower induction, etc. can be controlled by changing the ratio of red light to far-red light. The emission of Eu3+ (transition from 5D 0 →7F 2) is located at the red range and matches with the absorption band of P R. Herein, we synthesized successfully NaYb(MoO 4) 2 : Eu3+ phosphors with the high doping concentration (50%) by hydrothermal method with further calcinations. The LED device was also fabricated by the blue InGaN chip combined with the red phosphors NaYb(MoO 4) 2 : 50%Eu3+ based on the excellent luminescent intensity. Moreover, the effect of temperature on the excitation intensity ratio of MoO 4 2− to Eu3+ has also been studied, which provided the possibility of simultaneous luminescence and temperature measurement. This work is the first time to use Eu3+ as a red source matching P R , and the red phosphors have potential value to control plant growth. Graphical abstract Image 1 Highlights • High concentration of Eu3+ doped NaYb(MoO 4) 2 phosphors have strong red luminescence. • The 395 nm chip combined with NaYb(MoO 4) 2 : 50%Eu3+ was used to fabricate LED device. • The EL spectrum of the LED device matched with the absorption band of phytochrome P R. • The excitation intensity ratio of MoO 4 2− and Eu3+ can be used to measure temperature. • The highest sensitivity is 0.01136 K−1 at 498 K. [ABSTRACT FROM AUTHOR]

Abstract A series of Ca 8 ZnLa(PO 4) 7 (CZLPO) phosphors doped with Tb3+ and Tb3+, Eu3+ have been synthesized using a high-temperature solid-state method. The XRD pattern verifies that all prepared samples are attributed to whitlockite-type structure of β-Ca 3 (PO 4) 2 with R3c (161) space group. Under 366 nm excitation, the CZLPO: Tb3+, Eu3+ phosphors exhibit a tunable multi-color emission owing to energy transfer from Tb3+ to Eu3+ via a quadrupole-quadrupole interaction mechanism. The emission colors of the phosphors could be modulated from green to red under NUV (366 nm) excitation due to efficient Tb3+→Eu3+ energy transfer. The fluorescence intensity ratio (I 542nm /I 611nm) for the Tb3+→Eu3+ of this material displayed excellent temperature sensing properties between 298 and 498 K. Moreover, it was found that the intensity ratio was unchanged when the temperature was cycled between 298 and 498 K, thus demonstrating the recyclability of this system. These results show that CZLPO: Tb3+, Eu3+ phosphors have potential as high performance multifunctional materials for solid state lighting and temperature sensing applications. Graphical abstract Image 1 Highlights • Whitlockite-type Ca 8 ZnLa(PO 4) 7 :Tb3+, Eu3+ phosphors were designed. • Ca 8 ZnLa(PO 4) 7 :Tb3+, Eu3+ phosphors exhibit a tunable multi-color emission. • The energy transfer mechanism from Tb3+ to Eu3+ were investigated. • Ca 8 ZnLa(PO 4) 7 :Tb3+,Eu3+ phosphors display excellent temperature sensing property from 298 K to 498 K. • This work provides an effective and feasible pathway for the exploration of mmultifunctional applications materials. [ABSTRACT FROM AUTHOR]

A series of Pr3+ doped SrWO 4 phosphors were synthesized using solid-state reaction routes. The phase composition, photoluminescence and temperature sensitivities of as-prepared materials were investigated. Rietveld refinement of measured XRD data was applied to analyze the lattice parameters. The optical transition was elaborated using UV–visible diffuse reflectance spectra and photoluminescence spectra. The photoluminescence measurements confirmed the strong visible light emission from the developed phosphors under both UV excitation at 250 nm and blue excitation at 450 nm. Notably, the maximum emission intensity was observed at a Pr3+ doping concentration of 2 mol%. Furthermore, the fluorescence intensity ratio (FIR) technique was employed, focusing on the emissions originating from the 3P 0 and 1D 2 state of Pr3+ within the temperature range of 298–598 K. Two FIR groups were adopted in this case, which can verify each other to achieve self-calibration. Typically, SrWO 4 :0.02Pr3+ exhibited remarkable performance as a temperature sensor, displaying an absolute sensitivity (Sa) of 3.11%K−1 and a relative sensitivity (Sr) of 0.81%K−1. As a result, the significant temperature-dependent PL and remarkable down-conversion luminescence make the SrWO 4 :Pr3+ material a promising candidate for optical thermometers and UV to visible converters of solar cell applications. • Intense visible emission of SrWO 4 :Pr3+ excited by 250 nm and 450 nm was observed. • FIR from non-thermally coupled energy levels was used for temperature sensing. • The wide-range and highly-sensitive of optical temperature sensing were realized. • The self-calibration of temperature measurement was achieved by two FIR groups. [ABSTRACT FROM AUTHOR]

Optical temperature sensors have become a research hotspot in recent years due to their non-contact feature. In this study, Er3+/Yb3+ co-doped ZnS phosphors (1:3, 1:6, 1:9, 1:12, 1:15, 1:19) were prepared by co-precipitation method. The up-conversion and down-conversion luminescence performance of the phosphors was studied. It was found that the luminescence performance is optimized when the doping molar ratio is 1:9. Based on the fluorescence intensity ratio technology of non-thermal coupling energy level, the temperature sensing characteristics of ZnS:Er3+/Yb3+ (1:9) phosphors were studied in the temperature range of 313–533 K. The results show a maximum absolute sensitivity of 1.9 % K−1 and a maximum relative sensitivity of 2.7 % K−1. In terms of multifunctionality, this work also designed a flexible film based on thermoplastic polyurethane (TPU) to explore its anti-counterfeiting properties. The results of this work demonstrate the great potential of ZnS:Er3+/Yb3+ phosphors for optical temperature measurements and anti-counterfeiting. • Doping Er/Yb in ZnS produces dual-mode luminescence. • ZnS: Er/Yb phosphors achieve an excellent relative sensitivity S a of 1.90 % K-1 and a maximum relative sensitivity S r of 2.7 % K-1. • Flexible films based on thermoplastic polyurethane (TPU) provide effective protection against counterfeiting. [ABSTRACT FROM AUTHOR]

The traditional preparation methods of quantum dots (QDs) for temperature sensing are limited to self-crystallization and secondary heat treatment processes, which requires precise control of the experimental equipment and conditions. In this paper, CsPbBr 3 QDs are successfully obtained by friction crystallization in the prepared precursor glass. The results show that when the glass network structure is subjected to continuous mechanical impact, the thermal kinetic energy of the fracture surface increases. Therefore, the combination of relatively loose structure and local thermal energy supply more excellent space for the nucleation and growth of CsPbBr 3 QDs. Furthermore, the PL enhancement is confirmed to be occur in Sm3+ ions doped CsPbBr 3 QDs, which is due to the increase of density of exciton states near the edge of the band, thus facilitating radiative recombination. Significantly, this material has a favorable performance of temperature sensing and thermal stability, with the maximum relative sensitivity of 3.09 % K−1. This work provides an energy-saving and green way for the preparation of Sm3+ ions doped QDs, and the materials provide potential applications in the field of temperature sensing. • Sm3+ ions doped CsPbBr 3 quantum dot glass are successfully prepared by mechanical crystallization method. • The loose structure is conducive to ions migration and recombination, thus promoting crystallization. • The material shows good thermal stability and temperature sensing performance, with a Sr of 3.09 % K -1. [ABSTRACT FROM AUTHOR]

Abstract Upconversion (UC) nanophosphors of Lu 2 TeO 6 :Yb3+/Er3+ as temperature sensing material have been successfully synthesized via hydrothermal method followed by a subsequent heat treatment process. The phase and micrographs of the as-prepared phosphors were characterized by XRD, SEM, and TEM. Results indicate that the phosphors of hexagonal Lu 2 TeO 6 :Yb3+/Er3+, formed after heat-treatment at 800 °C for 5 h, consist of rice-like nanoparticles with size mostly distributed less than 200 nm in length. Under the 980-nm NIR excitation, the tellurite nanophosphors exhibit strong green and red UC emissions. The optimum Yb3+ and Er3+ concentrations for UC luminescence are determined to be 10% and 1%, respectively. The possible energy transfer mechanism implicated in the nanophosphors is discussed based on the pump power dependence of UC emissions. Furthermore, temperature sensing ability of Lu 2 TeO 6 :Yb3+/Er3+ (10/1) is investigated by employing the temperature dependent fluorescence intensity ratio (FIR) of two emission bands (2H 11/2 /4S 3/2 → 4I 15/2) of Er3+ ion. The maximum sensitivity achieved in this developed material is as high as 0.0103 K−1 at 623 K. This work provides a new qualified UC nanomaterial for application in optical remote temperature sensing. Highlights • Yb3+/Er3+ co-doped Lu 2 TeO 6 nanophosphors were synthesized by hydrothermal reaction accompanying with post-heat treatment. • The nanophosphors exhibited single crystal nature. • Optimal concentration of Yb3+/Er3+ for upconversion luminescence was confirmed. • Optical temperature sensing ability of nanophosphors was investigated based on FIR technique. [ABSTRACT FROM AUTHOR]

Abstract A series of Yb3+-Er3+, Yb3+-Ho3+, and Yb3+-Tm3+ doped Ca 2 Gd 8 (SiO 4) 6 O 2 (CGS) phosphors were synthesized by solid-state reaction method, and their upconversion (UC) luminescence properties for temperature sensing were studied. Upon 980 nm excitation, the green and red emissions of Er3+ were observed, and the optimal Er3+ concentration was determined to be 3 mol%. For the CGS:10%Yb3+,yHo3+ phosphors, three emission peaks in the green, red and near-infrared region appear. It was found that the relative intensities of Ho3+ different emissions change with Ho3+ concentration, which has been explained by the cross-relaxation process. The strongest Tm3+ emission appeared at 790 nm, attributed to the 3H 4 -3H 6 transition. The optimal Tm3+ concentration was determined to be 0.5 mol%. The temperature sensing behavior was evaluated by employing the thermally-coupled or non-thermally coupled levels of Er3+, Ho3+ and Tm3+. The maximum sensitivities obtained are 3.71 × 10 − 3 and 1.12 K-1 for CGS:10%Yb3+,3%Er3+, 0.111 K-1 for CGS:10%Yb3+,3%Ho3+ and 3.3 × 10 − 4 K−1 for CGS:10%Yb3+,0.5%Tm3+, respectively. The high sensitivities indicate the present phosphors could have potential application in temperature sensing. Highlights • Different strategies for temperature sensing were introduced in the present phosphors. • The present phosphors show smooth particle surface that benefits the UC luminescence. • High sensor sensitivity has been obtained in the CGS:Yb3+-Er3+/Ho3+/Tm3+. • The present phosphors could have potential application in optical temperature sensors. [ABSTRACT FROM AUTHOR]

Abstract High luminescence intensity is crucial for realizing luminescent temperature sensing with a large signal-to-noise ratio. In this work, the temperature sensing behavior of Ca 1-x Na x MoO 4 :Yb3+,Er3+ with intense green up-conversion luminescence was studied. It has been demonstrated that the single-band green emission was dependent on the Yb3+-MoO 4 2- dimer sensitization as well as the low multi-phonon relaxation rate of 4S 3/2 → 4F 9/2. In addition, it was found that the uncorrected thermometer could not accurately measure temperature due to thermal effects. A simple method for calibration of up-conversion temperature sensing was reported. Due to high luminescence intensity and temperature sensitivity, Ca 1-x Na x MoO 4 :Yb3+,Er3+ is a promising candidate for up-conversion temperature sensing. Highlights • The ratiometric temperature sensing behavior of Ca 1-x Na x MoO 4 :Yb3+,Er3+ upconversion phosphor is investigated. • It is found that the temperature sensing suffers from the problem of temperature measurement accuracy. • A simple and reliable method of correction is reported. [ABSTRACT FROM AUTHOR]

Ho 3+ /Yb 3+ co-doped YNbO 4 phosphor was synthesized via a high-temperature solid-state reaction technique. Excitation power density and temperature dependent up-conversion (UC) luminescence properties were systematically investigated. Under 980 nm excitation, intense green UC emissions accompanied with weak red and near infrared UC emissions were observed, which were attributed to the transitions of 5 S 2 / 5 F 4 → 5 I 8 , 5 F 5 → 5 I 8 and 5 S 2 / 5 F 4 → 5 I 7 , respectively. Varied population paths for generating the green and the red UC emissions were found from the analyses on the temperature and excitation power density dependent UC emissions. It was confirmed that 2-photon processes were responsible for both the green and the red UC emissions at room temperature. However, with an increase in temperature, the green UC emission still kept 2-photon process, and 1.5-photon process for the red UC emission occurred. In addition, the temperature dependent UC luminescence spectra displayed that the luminescence intensity ratio of the red to the green UC emissions was sensitive to both the excitation power density and the sample temperature. Thus, it was concluded that the dependence of the luminescence intensity ratio of the red to the green UC emissions of Ho 3+ on temperature might not be suitable for accurate temperature sensing for YNbO 4 : Ho 3+ /Yb 3+ phosphor. [ABSTRACT FROM AUTHOR]

A series of Yb 3+ -Er 3+ /Ho 3+ /Tm 3+ doped K 3 Y(PO 4 ) 2 (KYP) phosphors were synthesized by solid-state reaction method. Several effective strategies for temperature sensing were introduced based on their upconversion (UC) luminescence properties. For Yb 3+ -Er 3+ codoped KYP, it was found the relative intensities of different emissions of Er 3+ change with temperature, and the repeatability of measurement was evaluated. The sensor sensitivities were calculated and compared based on the thermally coupled and non-thermally coupled levels of Er 3+ . For Yb 3+ -Ho 3+ codoped KYP, red emission was obtained due to the strong 5 F 5 - 5 I 8 transition of Ho 3+ . With increasing temperature, the 5 F 5 - 5 I 8 and ( 5 F 4 , 5 S 2 )- 5 I 8 emissions show different decrease rates in intensity. The high absolute sensitivity of 0.078 K −1 was obtained from the dependence of the fluorescence intensity ratio (FIR) on temperature, but the relative sensitivity is low compared with that of Er 3+ activated KYP. For Yb 3+ -Tm 3+ codoped KYP, various emission peaks of Tm 3+ have been found from the near-ultraviolet to near-infrared range. The temperature dependence of the FIR for ( 3 F 2 , 3 F 3 )- 3 H 6 and 3 H 4 - 3 H 6 transitions of Tm 3+ reveals the relative sensitivity is more than twice as much as that of the Yb 3+ -Er 3+ codoped KYP, but it shows a much lower absolute sensitivity due to the low FIR value. [ABSTRACT FROM AUTHOR]

RE 2 O 3 (RE = La, Gd, Lu) co-doped with Yb 3+ and Er 3+ nanocrystals were synthesized by sol-gel method. Phase evolutions upon the calcination temperature were studied. The structural parameters of the RE 2 O 3 systems were refined by the Rietveld method based on the powder XRD data. Upconversion (UC) properties with 980-nm NIR excitation as well as the mechanism were investigated. The temperature dependent UC behaviors and the optical temperature sensing properties based on the fluorescence intensity ratio (FIR) of the Er 3+ green UC emissions were studied comparatively. Result reveals that the Lu 2 O 3 system exhibits the strongest UC luminescence while the La 2 O 3 system exhibits the highest temperature sensitivity among the three nanocrystals, and the Gd 2 O 3 system exhibits an intermediate performance among the three systems. However, taking into account of the preparation, emission intensity, and sensor sensitivity, the Gd 2 O 3 system in between should be the optimum candidate for optical temperature sensing application among the three systems. [ABSTRACT FROM AUTHOR]

A series of Sm 3+ activated Lu 2 MoO 6 phosphors were synthesized by high-temperature solid-state reaction method. The X-ray diffraction (XRD) patterns, excitation spectra, emission spectra and decay lifetime of the phosphors were measured to characterize the structural and luminescent properties. The crystal structure of Lu 2 MoO 6 :Sm 3+ has been defined by the Rietveld method, and it is shown that Lu 2 MoO 6 :Sm 3+ belongs to the monoclinic system. The photoluminescence (PL) excitation spectra revealed that the obtained phosphors can be efficiently excited by both near-ultraviolet and blue light. Under 360 and 402 nm excitation, four dominating emission bands corresponding to the 4 G 5/2 → 6 H J (J = 11/2, 9/2, 7/2, and 5/2) transitions of Sm 3+ ions were detected. The emission intensity was strongly dependent on Sm 3+ concentration and the optimal doping concentration in the Lu 2 MoO 6 :Sm 3+ phosphor was determined to be 5 mol%. The concentration quenching mechanism was investigated using the Van Uitert equation and Inokuti-Hirayama (I-H) model. In addition, the thermal quenching mechanism of Sm 3+ activated Lu 2 MoO 6 has been proposed. The Lu 2 MoO 6 :Sm 3+ phosphors have potential application in temperature sensors based on luminescent intensity and lifetime. [ABSTRACT FROM AUTHOR]

A series of LuAG: 5 mol%Yb3+/0.5 mol%Ho3+/x mol%Ce3+ (x = 0, 0.2, 0.5, 1.0, 2.0) up-conversion (UC) fluorescent materials were prepared using CO 2 laser heating zone melting method. The X-ray diffraction (XRD) patterns confirm that the prepared samples have a pure LuAG crystal phase. Under excitation of a 980 nm laser, the up-conversion luminescence (UCL) spectra of the prepared samples were obtained. Two UCL emission bands of Ho3+ ions were observed, including green emission band of the 5F 4 /5S 2 →5I 8 transition, and red emission band of the 5F 5 →5I 8 transition. Due to the cross-relaxation (CR) processes between Ce3+ ions and Ho3+ ions, the doping of Ce3+ ions can effectively improve the UCL efficiency of Ho3+ ions, and the emission intensity reaches maximum when doped with 1 mol% Ce3+. The temperature sensing characteristics of LuAG: Yb3+/Ho3+ and LuAG: Yb3+/Ho3+/Ce3+ from 303 K to 723 K were studied by fluorescence intensity ratio (FIR) method. By doping 1 mol% Ce3+ ions, the absolute sensitivity of the sample has been significantly improved, with the maximal absolute sensitivity of 0.0951 K−1 (303 K), and the maximal relative sensitivity of 0.0103 K−1 (343 K). The high sensitivity and wide measurement range make LuAG: Yb3+/Ho3+/Ce3+ UCL material ideal for temperature sensing. [Display omitted] • LuAG: Yb3+/Ho3+ doped with Ce3+ ions fluorescent materials were prepared by CO 2 laser zone melting method. • The doping of Ce3+ ions can effectively improve the emission intesnity of LuAG:Yb3+/Ho3+ materials. • The temperature sensing characteristics of LuAG: Ho3+/Yb3+/Ce3+ and LuAG: Yb3+/Ho3+ materials were compared by FIR method. • The LuAG: Yb3+/ Ho3+/Ce3+ has a temperature measurement range from 303 K to 723 K, and absolute sensitivity of 0.0951 K−1. [ABSTRACT FROM AUTHOR]

In this paper, the multi-functional multi-layer core-shell structure NaYF 4 : Ce3+/Eu3+@NaYF 4 @NaYF 4 : Ho3+/Yb3+ nanoparticles (NPs) were prepared. These multi-layer NPs can be applied in temperature sensing with high relative sensitivity. Moreover, these NPs can be used in multimode optical anti-counterfeiting. Based on structure design and doped earth ions optimized, the maximum relative sensitivity is further promoted from 0.9 %·K−1 at 234 K (Eu/Ho) to 5.1 %·K−1 at 113 K (Ce/Eu@Y@Ho/Yb) by the blocking effect of the inter layer and by cross-relaxation of introducing Ce3+ and Yb3+ ions. Meanwhile, by introducing Ce3+ and Yb3+ ions, the NPs provide multimode emissions under multiple excitations, which are beneficial for the application of optical anti-counterfeiting. The NPs present increased sensitivity of temperature sensing and improved security of optical anti-counterfeiting, which has promising applications in biological cell calibration, micro-integrated circuits, etc. • High relative sensitivity (5.1 %·K−1) is obtained in multi-layer nanoparticles. • Sensing performance is improved by the blocking effect and cross-relaxation. • Anti-counterfeiting is achieved by multimode emissions under multiple excitations. [ABSTRACT FROM AUTHOR]

The mono-dispersed hexagon microcrystal of KLuF 4 :24%Yb 3+ /0.5%Tm 3+ with an average particle size of 5 μm has been synthesized by a facile hydrothermal method. Based on the fluorescence intensity ratio (FIR) technique, the dependence of the up-conversion (UC) emission intensity of a single KLuF 4 :24%Yb 3+ /0.5%Tm 3+ particle on the ambient temperature ranging from 303 to 503 K has been studied in detail. The sensitivity of the 1 G 4 (a)/ 1 G 4 (b) and 3 F 2,3 / 3 H 4 thermally coupled levels (TCLs) is calculated, and the maximum sensitivity of which is 2.101 × 10 −3 K −1 at 303 K and 1.451 × 10 −4 K −1 at 503 K, respectively. Furthermore, the temperature of KLuF 4 :24%Yb 3+ /0.5%Tm 3+ single-particle rise from 347 to 366 K when the pump power increases from 168 to 1145 mW. It proves the heating effect of 3 F 2,3 / 3 H 4 TCLs is induced by 980 nm laser excitation. Compared with 1 G 4 (a)/ 1 G 4 (b) TCLs, the sensitivity of 3 F 2,3 / 3 H 4 TCLs exhibits better accuracy at high temperature. Moreover, the excellent thermal stability of the KLuF 4 :24%Yb 3+ /0.5%Tm 3+ microcrystal for temperature detection in the range of 303–503 K is proved. The Yb 3+ /Tm 3+ co-doped KLuF 4 single-particle shows promising applications in the fields of compact optical thermometers and optical heaters. [ABSTRACT FROM AUTHOR]

Investigating and understanding temperature-dependent photoluminescence (PL) properties of inorganic phosphors are of vital importance to optimize their performance and expand their application. Recently, K 2 SiF 4 :Mn 4+ phosphors have attracted intense attention as a red phosphor candidate for white LED applications because of their extremely narrow emission peaks in the red spectral region. Here, temperature-dependent (20–200 °C) diffuse reflection spectra and steady and transient PL spectra of K 2 SiF 4 :Mn 4+ were systematically investigated. Both the emission intensities and spectral characteristics of the phosphor showed excellent thermal stability at temperatures from 20 to 150 °C, ensuring its great potential for practical white LED applications. An abnormal PL enhancement was found at elevated temperatures that differed from the thermal quenching behavior of common phosphors and could be attributed to enhanced phonon-assisted radiative transitions at higher temperatures. We further successfully tested and verified that the intensity ratio of anti-Stokes and Stokes emission peaks of Mn 4+ ions was sensitive to temperature and followed a Boltzmann-type distribution function very well, making the K 2 SiF 4 :Mn 4+ phosphor a good candidate for temperature sensing, especially for investigating the thermal distribution of white LEDs. [ABSTRACT FROM AUTHOR]

A new type of thermally sensitive fibers with an antimony selenide (Sb 2 Se 3 ) core and phosphate glass cladding is demonstrated. The fibers were fabricated by a molten core method and maintained overall diameters ranging from 250 to 800 μm and core diameters of 35–200 μm. A 2.8 cm long Sb 2 Se 3 core fiber, electrically contacted to external circuitry through fiber end facets, exhibited a four orders of magnitude change in conductivity after the whole fiber was heated from 25 to 195 °C. In addition, the fiber exhibited enhanced photoconductivity under illumination. These results indicate that Sb 2 Se 3 core multimaterial fibers have promising applications in temperature sensing, optical switches and photodetectors. [ABSTRACT FROM AUTHOR]

Single-doped manganese with two luminous centers of MgGa 2 O 4 fluorescent powder was generated through a solid-state reaction. It goes into great detail about the optical characteristics and temperature sensitivity of MgGa 2 O 4 :Mn2+, Mn4+. The emission spectrum activated by 322 nm UV light showed a sharp green peak for Mn2+ at 502 nm and a red peak for Mn4+ at 694 nm. Additionally, Mn4+ emission reduces as temperature rises, but Mn2+ emission increases initially before declining, demonstrating that Mn2+ and Mn4+ have differing temperature sensitivity in the MgGa 2 O 4 host. The performance of temperature sensor capability at 80–500 K was investigated by the fluorescence intensity ratio (FIR) technology. The sample's maximal relative sensitivity (Sr) value is calculated as 1.64% K−1 at 260 K, indicating that MgGa 2 O 4 :Mn2+, Mn4+ have considerable potential for optical thermometry. [Display omitted] • MgGa 2 O 4 :Mn2+, Mn4+ phosphors were synthesized by solid state reaction method. • This work highlights the presence of two easily detected emission peaks signals caused by different valence states of the same element in the same matrix. • Mn2+ emission shows anti-thermal quenching in the 80–350 K temperature range in this material. The Mn2+ and Mn4+ react differently to temperature presenting good temperature sensing ability. • The maximum Sa is 8.15% K−1 and Sr is 1.64% K−1 in the 80–500 K. The broad detection area and high relative sensitivity demonstrate that MgGa 2 O 4 :Mn2+, Mn4+ phosphors can be a potential material for optical thermometry. [ABSTRACT FROM AUTHOR]

Eu2+/Eu3+ co-activated luminescence as a key technology has gradually attracted attention in many research and application fields, including solid-state lighting, printing and dyeing, temperature sensing, etc. Here, by virtue of the unique self-reduction characteristics of Eu3+ in certain host lattices, Eu2+/Eu3+ co-activated luminescent material of SrAl 2 O 4 :Eu2+/3+ with single host lattice was prepared by solid-state reaction in the ambient atmosphere. The phase composition and crystal structure were determined by X-ray powder diffraction and Rietveld refinement. The micromorphology was observed by scanning electron microscope and transmission electron microscope. From the perspective of applied science, the dual-driven luminescence behavior and temperature-sensing properties of the material were studied and discussed. The ratiometric luminescence of Eu2+ and Eu3+ in SrAl 2 O 4 can be regulated by the excitation wavelength from ultraviolet to visible light. The luminescent material shows temperature-sensing performance superior to other similar Eu2+/Eu3+ co-activated luminescent materials, with absolute sensitivity of 0.067 K−1 and relative sensitivity of 1.6% K−1. The development of this luminescent material provides a unique insight for designing novel Eu2+/Eu3+ co-activated luminescent materials for multifunctional applications. [Display omitted] • The SrAl 2 O 4 :Eu2+/3+ phosphor was obtained through the solid-state reaction in ambient air. • The doping site of Eu was determined by Rietveld refinement and bond energy theory. • The dual-driven luminescence behavior of Eu2+ and Eu3+ in SrAl 2 O 4 :Eu2+/3+ was studied. • The SrAl 2 O 4 :Eu2+/3+ phosphor with superior temperature-sensing properties (S a = 0.067 K−1 and S r = 1.6% K−1) was developed. [ABSTRACT FROM AUTHOR]

Efficient deep-penetrating red upconversion luminescent nanoparticles with ultra-small size are promising biological temperature probes. Herein, bright red upconversion luminescence are achieved in NaErF 4 @NaYF 4 core-shell nanoparticles under multi-wavelength excitation of 808 nm, 980 nm, and 1550 nm. The core-shell structure engineering is constructed to minimize energy dissipation by surface quenchers. Furthermore, the established model explains the temperature dependence of thermally coupled energy levels in detail, confirming that the non-radiative relaxation is responsible for the quenching processes. Based on the luminescence intensity ratio technique, optical temperature sensing characteristics of thermally coupled (2H 11/2 /4S 3/2) and non-thermally coupled energy levels (4F 9/2 /4S 3/2) are investigated under the excitation of a relatively safe near-infrared wavelength for 1550 nm. The thermometer can maintain a maximum sensitivity of 35 × 10−3 K−1 over the entire temperature measurement region by fitting the non-thermally coupled energy levels, which is conducive to temperature monitoring in vivo due to high sensitivity and relatively safe excitation wavelength. • Bright red upconversion luminescence under multi-wavelength excitation (808, 980 and 1550 nm) are achieved in NaErF 4 @NaYF 4 core-shell nanoparticles. • The core-shell structural engineering and upconversion luminescence mechanism of NaErF 4 @NaYF 4 are investigated in detail. • The established temperature-dependent model proves that non-radiative relaxation is the main reason for the luminescence quenching process. • LIR from thermally coupled and non-thermally coupled energy levels of NaErF 4 @NaYF 4 are used for temperature sensing. • Highly-sensitive and stable optical temperature sensing behavior is realized under the excitation at relatively safe near-infrared wavelength of 1550 nm. [ABSTRACT FROM AUTHOR]

BiTa 7 O 19 :Er3+/Yb3+/Mo4+ phosphors with excellent upconversion luminescence (UCL) intensity were synthesized by high temperature solid state method. The crystal structure, grain morphology and valence states of molybdenum ions were determined by X-ray diffraction (XRD), field emission scan electronic microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) technologies, respectively, and the UCL properties were studied by spectroscopy under 980 nm laser excitation. The green UCL intensity of BiTa 7 O 19 :0.1Er3+/0.4Yb3+/0.4Mo4+ is 1.66 times higher than that of commercial NaYF 4 :Er3+/Yb3+ under 980 nm laser excitation with 18.09 W/cm2. The UCL intensity of BiTa 7 O 19 :Er3+/Yb3+ phosphors increased first and then decreased with the increase of 980 nm laser excitation power density (0.38–56.69 W/cm2), while the UCL intensity of BiTa 7 O 19 :Er3+/Yb3+/Mo4+ phosphors can keep increasing with the increase of excitation power density. Based upon the luminescence intensity ratio (LIR) technique, the maximum absolute sensitivity (S A) is 0.01046 K−1 at 401 K. The experiment proved that BiTa 7 O 19 :Er3+/Yb3+/Mo4+ phosphors had strong acid and alkali resistance compared with NaYF 4 :Er3+/Yb3+. It indicates that BiTa 7 O 19 :Er3+/Yb3+/Mo4+ can replace NaYF 4 :Er3+/Yb3+ to be applied as luminescence imaging and temperature sensors in complex environments under high 980 nm laser excitation power density. • BiTa 7 O 19 :Er3+/Yb3+/Mo4+ phosphors exhibited outstanding UCL intensity. • Green UCL intensity of BiTa 7 O 19 :Er3+/Yb3+/Mo4+ is higher than that of NaYF 4 :Er3+/Yb3+. • Green UCL intensity increases with the increase of excitation power. • Maximum absolute sensitivity is 0.01046 K−1 under 980 nm laser excitation. • Compared with NaYF 4 :Er3+/Yb3+, it has better chemical stability. [ABSTRACT FROM AUTHOR]

High thermal stability, high bandgap, and low phonon energy (452 cm−1) of GdScO 3 perovskite make it ideal for optical applications, particularly for infrared (IR)-to-visible photon upconversion (UC) emission. This phase has been typically synthesized either in single crystal or in thin film forms which require high temperatures and a longer time. Thin films/single crystals of GdScO 3 have limited optical application mostly as lasing material. Unexpectedly, the photon UC-based emission and correlated applications are completely ignored in this host so far. Herein, we have successfully synthesized pristine and Yb3+, Er3+ co-doped GdScO 3 nanocrystals (powder) at low temperatures and further analyzed their crystal structure, phase, and optical absorption and emission properties at length. The photon-UC property in GdScO 3 nanocrystal has been studied for the first time. Further, the material has been used for the non-contact luminescence-based temperature sensor application also. Our study shows that the maximum relative sensitivity (S r) and absolute sensitivity (S a) obtained for Yb3+, Er3+: GdScO 3 nanocrystal is better than most of the reported oxide-based perovskite materials. • Low temperature synthesis of Gadolinium Scandate for optical emission. • First observation of upconversion emission in Er/Yb co-doped of Gadolinium Scandate. • Non-contact based optical temperature sensing. • Improved thermal sensing using Er/Yb lanthanides in oxide perovskites. [ABSTRACT FROM AUTHOR]

Indoor plant growing requires the creation of artificial light that meets the needs of future agriculture. The majority of research focuses on various phosphors that generate red or far-red light. The enhancement of the blue component in LEDs for plant development is underappreciated. In this work, Bi3+/Mn4+ co-doped CaYAlO 4 phosphors were synthesized. Two distinct emission bands in the blue (400 nm) and deep red (710 nm) regions, corresponding to Bi3+ ions and Mn4+ ions, were observed under 290 nm excitation. Energy transfer efficiency from Bi3+ to Mn4+ ions was confirmed to be ∼75 % by photoluminescence and decay curve measurements. The EL spectra of the manufactured LED device overlap with the absorption spectra of the principal plant pigments, indicating that the synthesised phosphors are promising for indoor plant growth. In a proof-of-concept experiment, the potential of the synthesised phosphors for temperature monitoring was investigated. The smallest percentage temperature variation between prediction and measurement is approximately 0.5 %, indicating that the synthesized materials are also promising candidates for ratiometric temperature sensing. • Two emission bands located at the blue and deep red regions were observed when the phosphors were under 290 nm excitation. • Energy transfer from Bi3+ to Mn4+ ions was verified by PL and decay curve measurements. • Varying doping concentrations or excitation wavelengths readily achieved adjustments of emission colour. • The materials show promising application in indoor cultivating lighting and ratiometric temperature sensing. • In a proof-of-concept experiment, the potential of the synthesised phosphors for temperature monitoring was investigated. [ABSTRACT FROM AUTHOR]

The cerium, manganese solely and co-doped MgAl 2 O 4 have been synthesized via traditional solid-state reaction. XRD refinement and the first-principle calculation indicate that the Mn2+ preferentially substitutes for Mg2+ while Ce3+ is more preferential for the substitution of Al site in MgAl 2 O 4 matrix. Effective energy transfer enables the photoluminescence spectra of the co-doped phosphors to show both ultraviolet (UV) emission of Ce3+ at around 359 nm and green emission of Mn2+ peaked at 516 nm. The separated emission bands of Ce3+ and Mn2+ indicate the good signal resolution. Due to relative thermally stable of Mn2+ and huge thermal quenching of Ce3+, the temperature sensing performance of the prepared phosphor was evaluated by measuring fluorescent intensity ratio (FIR) of Ce3+ to Mn2+ and lifetime of Ce3+. The maximum of the S r values is 0.59%K−1 at 448 K for FIR mode and 0.40%K−1 at 523 K for lifetime mode, respectively. Satisfactory repeatability makes it suitable for dual-mode optical thermometry. • First-principle calculation indicates Ce3+ preferentially substitutes Al3+ site. • The energy transfer mechanism from Ce3+ to Mn2+ in MgAl 2 O 4 was demonstrated. • The potential of MgAl 2 O 4 :Ce3+, Mn2+ for dual-mode thermometry was evaluated. • MgAl 2 O 4 :Ce3+, Mn2+ shows high repeatability by both FIR and lifetime technologies. [ABSTRACT FROM AUTHOR]

In this work, Er 3+ /Yb 3+ :CaMoO 4 upconversion phosphor is fabricated, and its temperature dependent luminescent performance is investigated. Using fluorescence intensity ratio of the Er 3+ 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 emissions in CaMoO 4 as thermometric index, the temperature sensitivity is found to be above 0.0095 K −1 in the whole temperature range of 303–873 K, while the maximum value reaches as high as 0.0143 K −1 at 573 K, revealing this phosphor to be a very promising optical temperature sensing material. [ABSTRACT FROM AUTHOR]

Flexible piezoelectric nanogenerators (PENG) have attracted wide attention because of their great potential in solving the power supply problem of wearable electronic devices. In order to expand the applications of PENG, high quality (Na 0.5 Bi 0.5)TiO 3 -0.06BaTiO 3 (NBT-0.06BT: x Er3+) nanofibers doped with different Er3+ concentrations were prepared by the gel-sol electrostatic spinning method. The morphology and phase structure of the prepared nanofibers were characterized. Dense nanofibers with good crystallization have been obtained. The local ferroelectric properties of the nanofibers were characterized by PFM. It is found the prepared nanofibers have a strong upconversion (UC) photoluminescence (PL) property. Utilizing the fluorescence intensity ratio (FIR) technique, the temperature sensing properties of the nanofibers has been investigated, showing a maximum sensitivity of 0.0043 K−1. Finally, the flexible PENG was prepared by encapsulating NBT-0.06BT:0.01Er3+ nanofibers, interdigital electrode and PDMS. The maximum voltage output of PENG is 97 V. The present investigation integrates the luminescence characteristics and electrical properties of nanofibers into the flexible PENG, which may greatly expand its application field. • NBT-0.06BT: x Er3+ nanofibers with high quality have been successfully prepared. • NBT-0.06BT: x Er3+ nanofibers have excellent temperature sensing properties. • The present PENG has a potential application in optics. • The output voltage of the PENG reaches a high value of 97 V. [ABSTRACT FROM AUTHOR]

The advanced new Er3+/Yb3+: Na 3 Zr 2 (SiO 4) 2 PO 4 (NASICON) monoclinic phosphors prepared by solid state reaction technique has been analyzed as upconverting materials. The crystal phase, structural parameters, surface morphology, different functional groups and bandgap of the synthesized phosphors have been analyzed. Under 980 nm continuous wave diode laser excitation, the codoping of Yb3+ ions in the Er3+ doped phosphors exhibit fascinating results. Stark sublevels observed in the upconversion emission have been used for the fluorescence intensity ratio (FIR) based thermometry. Relative & absolute sensitivity, thermal stability and temperature dependent CIE have been determined. The thermally stable Na 3 Zr 2 (SiO 4) 2 PO 4 : Er3+/Yb3 phosphors with high color purity can be utilized in sensing, display and security purposes. Upon 980 nm excitation the UC emission obtained from Er3+/Yb3+ doped Na 3 Zr 2 (SiO 4) 2 PO 4 phosphors have been utilized for temperature sensing and security ink application. [Display omitted] • UC intensity enhancement of ~ 13 times has been observed with incorporation of Yb3+ in Er3+ doped Na 3 Zr 2 (SiO 4) 2 PO 4 upconverting phosphors. • Maximum absolute and relative sensitivity of the developed phosphor have been found to be 6.4 @ 393 K and 9.3 @ 303 K respectively with thermal resolution± 0.30 K at 303 K. • Thermal stability with activation energy ~ 0.30 eV has been studied upto 508 K. [ABSTRACT FROM AUTHOR]

Hexagonal (β)-phase NaYF 4 :Yb 3+ , Er 3+ upconversion nanoparticles (UCNPs) with or without a protection shell are successfully synthesized. Effects of inert (undoped NaYF 4 ) and active (NaYF 4 :10% Yb 3+ ) shells on their upconversion luminescence (UCL) and temperature sensing properties are studied. Well-fitted exponential relations between the intensity ratio ( R HS ) of the green fluorescence bands of Er 3+ ions ( 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 ) and temperature are obtained for core-only and core–shell UCNPs, showing their potential applications as temperature sensing probes. Heating–cooling cycle tests show that all the samples have high thermal stability. Both inert and active shells can obviously improve the UCL properties of UCNPs, and do not affect their R HS values and thermal sensitivity. However, compared with the active shell, the inert shell can significantly reduce the thermal effect of UCNPs caused by laser excitation, which is beneficial for practical applications by avoiding the interference of excitation light and reducing the measuring errors. Temperature sensing properties of UCNPs are insusceptible to different dispersion mediums and show high stability in a broad range of pH values and salt conditions, indicating their availability for temperature sensing in the biomedical field. [ABSTRACT FROM AUTHOR]

• Novel codoping strategy – Bi3+, Pr3+ doped Li 3 Gd 3 Te 2 O 12 is investigated in detail. • White light emission is achieved together by combining emissions of Bi3+ and Pr3+. • A maximum temperature sensitivity of 0.672% K−1 in the range of 100–300 K. [Display omitted] Crystal structure and photophysical response of Bi3+ and Pr3+ co-doped Li 3 Gd 3 Te 2 O 12 system was investigated for lighting and ratiometric temperature sensing applications. The double substitution at the dodecahedral site was confirmed via Rietveld refinement and Raman spectra analysis. Considering the full advantage of distinct and characteristic cyan and orange emissions of Bi3+ and Pr3+, the emission tunability towards white region was achieved by the proposed co-doping combination. The as-prepared Li 3 Gd 3 Te 2 O 12 : Bi3+, Pr3+ phosphor exhibited characteristic and enhanced emission of Pr3+ under the excitation of 297 nm. The activation energy of 0.29 eV was obtained for the co-doped matrix, exhibiting better thermal stability. Further, the temperature sensing properties were evaluated based on the temperature dependent photoluminescence emission and decay curves in the range 100–300 K. Notably, the as-prepared Li 3 Gd 3 Te 2 O 12 : Bi3+, Pr3+ phosphor showed a maximum relative sensitivity of 0.672% K−1, as based on decay curve method, indicating that the phosphor can act as a potential candidate for optical temperature sensing in the physiological range. These findings demonstrate the efficiency of new co-doping combination Bi3+-Pr3+ for designing multifunctional phosphors. [ABSTRACT FROM AUTHOR]

• Pb2+ and Sm3+ doped CaZrO 3 perovskite phosphor have been successfully synthesized. • The absorption edge shows a red shift with the increase of Pb2+ doping concentration. • Analysis shows C state of Pb2+ is the reason for the red shift of the absorption edge. • The relative sensitivity of the phosphors is stable with temperature. [Display omitted] Based on high temperature solid state technique, a series of Pb2+/Sm3+ doped CaZrO 3 perovskite phosphors have been successfully synthesized. Comparing with CaZrO 3 host, the absorption edge of CaZrO 3 :x%Pb2+ samples exhibits a red shift with the increase of Pb2+ ions doping concentration. Analysis shows that the red shift of absorption edge can be attributed to the 1P 1 level of Pb2+ ions which is just below the bottom of conduction band. By comparing the absorption and excitation spectra of CaZrO 3 :x%Pb2+ samples, it is found that the excitation band at 286 nm should be composed of two parts, MMCT and 1S 0 →3P 1 transitions, respectively. The normalized excitation and emission spectra of CaZrO 3 :x%Pb2+ samples also confirm that the excitation band at 286 nm should be composed of MMCT and 1S 0 →3P 1 transitions, and the emission band at 370 nm should come from the 3P 1 →1S 0 transition. Based on the analysis of the absorption and excitation spectrum of CaZrO 3 :Sm3+, it indicates that the excitation band of CaZrO 3 :Sm3+ sample at 231 nm should be the O2--Sm3+ charge transfer state. In addition, the characterization of the temperature sensing properties demonstrates that the relative sensitivities of CaZrO 3 :Pb2+ and CaZrO 3 :Pb2+/Sm3+ samples have high stability. In the temperature range of 303–443 K, the relative sensitivity for CaZrO 3 :Pb2+ and CaZrO 3 :Pb2+/Sm3+ materials is in the range of 1.03%−1.32% K−1 and 0.89%−1.13% K−1, respectively. Therefore, the CaZrO 3 :Pb2+/Sm3+ material has great potential and application value in temperature sensing. [ABSTRACT FROM AUTHOR]

• A citrate-based sol-gel strategy was used to synthesize NGVO phosphors. • The TCL and non TCL temperature sensing techniques were investigated and compared. • NGVO: Yb3+-Er3+/Ho3+ phosphors could be used for optical temperature sensor applications. [Display omitted] In several scientific and technical fields, contactless optical thermometry has been successfully used for precise local temperature sensing. One of the primary goals at the moment is to enhance sensitivity and resolution. In this work, we report the synthesis of crystalline Yb3+-Er3+ and Yb3+-Ho3+ co-doped Na 3 Gd(VO 4) 2 (NGVO) microparticles by a citrate-based sol-gel method. The phase purity, vibrational modes, morphology and luminescence characteristics were evaluated by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), and Photoluminescence (PL). Temperature sensing in the visible region is allowed by an effective upconverted emission from rare-earth ions (Yb3+, Er3+, Ho3+) codoped into matrix. The luminescence intensity ratio (FIR) technique is used to record temperature sensing behaviors based on UC luminescence in Yb3+/Ln3+-codoped NGVO phosphors and high sensitivities were obtained. The S r value of the NGVO Er3+/Yb3+ as a function of temperature are calculated to be 0.83% K−1. For the NGVO: Yb3+/Ho3+ phosphors, the S r values were determined for TCLs and non-TCLs and reaches 1.37% K−1, and 1.90% K−1, respectively. These particles have a sub-degree thermal resolution at 295 K, making them excellent materials for accurate temperature sensing. The temperature-induced multicolor emissions in the analyzed samples suggest that the Er3+, Ho3+/Yb3+ co-doped NGVO crystals could have promising applications as a safety sign in high-temperature environments. [ABSTRACT FROM AUTHOR]