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Mn4+/Tb3+ doped CaAl 2 Si 2 O 8 (CASO) phosphors were synthesized using high temperature solid-state method. Crystal structure and lattice parameters were acquired through X-ray diffraction technique and Rietveld refinement. Energy band and density of states of CASO host were given by density functional theory calculations. By calculating the bond lengths and total energies of Mn4+ doped CASO, the results show that Mn4+ occupies the Ca2+ site with six coordinating oxygen atoms in the phosphor. The CASO:Mn4+,Tb3+ phosphors exhibit two major emission bands originating from the red emitting of Mn4+ (2E g → 4A 2g) and the green emitting of Tb3+ (5D 4 → 7F 5). Due to the emitting intensity of Mn4+ and Tb3+ varies differently with temperature, the temperature sensing study was carried out adopting the fluorescence intensity ratio of Tb to Mn. The relative sensitivity of CASO:1.5%Mn4+,6%Tb3+ achieves a peak value of 3.38 % K−1 at 423 K. The repeatability was tested and the result showed that the sample exhibits excellent repeatability. The luminescence color of the employed phosphors transitions from orange to green as the temperature increases. These findings uncover potential applications of CASO:Mn4+,Tb3+ phosphors in temperature sensing and multicolor-tunable emitting. [ABSTRACT FROM AUTHOR]

Using the melt quenching crystallization technique, Er3+-Yb3+ co-doped glass-ceramics with NaLaSiO 4 crystalline phase have been successfully prepared. The optimal heat treatment condition was identified to be 605 °C/90 min. Optical band gap and Urbach energy changes were analyzed. Additionally, J-O parameters, radiative transition probabilities, fluorescence branching ratios, and stimulated emission cross sections for Er3+ were also calculated. The results of XRD refinement and crystal locality optimization verify that Er3+ is located with a low-symmetry site. The optimal emission intensity was achieved at Yb3+ doping concentration of 0.7 %. Temperature sensing was accomplished using FIR, with S a-max of 1.15 x 10−2 K−1 (498 K) and S r-max of 1.34 % K−1 (298 K). This Er3+-Yb3+ doped silicate glass-ceramic has potential applications in up-conversion green lasers and optical thermometers. [ABSTRACT FROM AUTHOR]

Melt-curing-crystallization was used to synthesized a series of Tb3+/Dy3+ doped glass ceramics (GCs) with a crystalline phase of Bi 2 Ti 2 O 7. The optimal treatment with heat conditions is 570 °C for 60 min. The emission spectra of Tb3+-Dy3+ co-doped GCs contain four separate emission peaks at 485 nm (5D 4 →7F 6 and 4F 9/2 → 6H 15/2), 545 nm (5D 4 →7F 5), 575 nm (4F 9/2 → 6H 13/2) and 612 nm (5D 4 →7F 3), proving existence of an energy transfer Dy3+→Tb3+. Concentration quenching dominated by dipole-dipole interactions appears as concentration of Dy3+ exceeds 0.4 %, So the optimum dopant concentration is 0.4 % Dy3+. Thermal quenching activation energy (ΔE) is 0.320 eV for Tb3+ at 545 nm and 0.383 eV for Dy3+ at 575 nm. The Tb3+-Dy3+ co-doped GCs showed a highest absolute sensitivity S a of 7.96 × 10−2 K−1 and a greatest relative sensitivity S r of 3.19 % K−1 at temperatures between 298 K and 458 K, indicating GCs has potential application value in the field of temperature sensing. [ABSTRACT FROM AUTHOR]

Fluorescence intensity ratio (FIR) technique has been a promising non-contact thermometry method owing to the characteristics of rapid response and exceptional resolution. In this study, a new iodate phosphor NaYI 4 O 12 :Er3+ (NYIO:Er3+) is synthesized via a microwave-assisted hydrothermal method. It exhibits bright green emission under 380 and 980 nm excitations. The power-dependent upconversion and Er3+ content-dependent downshifting performances are investigated. Excited by 380 nm, the temperature-dependent FIR originating from thermally coupled levels of Er3+ are discussed in detail. The resulting material displays outstanding temperature sensing properties across the temperature range of 298–523 K. The absolute and relative sensitivities can reach the maximum values of 0.51 × 10−2 K−1 and 1.3 % K−1, separately. Meanwhile, the reliability and repeatability of the temperature sensing characteristics are verified. The result demonstrates that the Er3+-activated iodate phosphor NaYI 4 O 12 :Er3+ is a promising candidate in non-contact optical thermometry domain. [Display omitted] [ABSTRACT FROM AUTHOR]

A series of Y 2 MoO 6 :0.01Er3+/0.09 Yb3+ upconversion phosphors doped with different concentrations of Li + ions (0.05, 0.10, 0.15, 0.20, 0.25, and 0.30 mol) were prepared by the high temperature solid phase reaction method, and their physical phase structures and upconversion luminescence were analyzed. At the excitation wavelength of 980 nm, the addition of Li+ sharply increased the upconversion luminescence intensity. With the increase of Li+ ion content, the luminescence intensity first increases and then decreases. When the doping amount reaches 0.25 mol, the luminescence intensity reaches the maximum, and the sample emits green light in the two-photon process. Y 2 MoO 6 :0.01Er3+/0.09 Yb3+/0.25Li + exhibits excellent temperature sensing properties. Its absolute sensitivity S a reaches up to 0.012 K-1, the relative sensitivity S r is 0.017 K-1 and the measurement error δ T is less than 0.3 K at room temperature. Its temperature sensing performance is far superior to similar materials. In addition, Judd-Ofelt theory calculations revealed that in comparison with Y 2 MoO 6 :0.01Er3+/0.09 Yb3+, its Ω 2 increased from 0.56 × 10−20 cm2 to 3.68 × 10−20 cm2, and the spectroscopic quality factor Ω 4 /Ω 6 ratio reached 4.09, which is much higher than that of the other fluorescent materials. The main reason is that Li + replaces the Y3+ ion lattice site, causing lattice distortion and reducing the lattice symmetry around the active ion. The increase in asymmetry increases the possibility of spontaneous radiative transitions. It is shown that the prepared upconversion luminescent materials have potential applications in the field of solid-state lasers and optical sensing. [ABSTRACT FROM AUTHOR]

In recent years, people have higher requirements for temperature measurement with the development of optical temperature measurement. Meanwhile, the emission intensity of most fluorescent materials is quenched by thermal effects as the temperature rises, making it challenging to meet the specifications of fluorescent materials employed in the field of pyrometry. In this work, the pure phase of Yb3+/Er3+ ions co-doped Sc 2 W 3 O 12 phosphor was successfully prepared. Sc 2 W 3 O 12 : Yb3+, Er3+ samples showed strong green emission and weak red emission. The optimal doping concentrations of Yb3+ and Er3+ ions are 0.3 and 0.02, respectively. The potential upconversion luminescence (UCL) mechanism was investigated by analyzing the UCL spectra, downshift emission spectra and power dependence spectra of Yb3+/Er3+ ions co-doped Sc 2 W 3 O 12. The upconversion emission excitation path is mainly through Er3+ ions from 4I 11/2 absorption photon excitation to 4F 7/2 energy level, then the photons of 4F 7/2 relaxes to green and red emission energy levels and returns to ground state for emitting green and red light. In addition, according to the UCL green light intensity increasing with temperature, it serves as an optical temperature sensor. The temperature sensitivity of the sample was explored in the temperature range of 298 K–673 K. This study provides new materials and ideas for non-contact temperature sensing. [ABSTRACT FROM AUTHOR]

The redshift of the charge transfer band (CTB) edge of phosphor induced by temperature rise is pervasively accompanied by antithermal quenching. Accordingly, exploring the mechanism of the CTB redshift is thus not only propitious for optimizing the sensitivity of optical thermometry but also tenders a new idea for the design of antithermal quenching phosphors. Herein, a family of YP 1-x V x O 4 :Eu3+ phosphors were designed via the V5+/P5+ ion substitution strategy. With the increase of the V5+ ratio, the relative integral intensity of the 5D 0 →7F 2 transition multiplies from 1.25 to 28.67 times under CTB edge excitation. Moreover, by Gaussian fitting, the reduction degree of vanadate band gap energy 1E (1T 1)→1B 2 (1T 2), 1A 2 (1T 1)→1B 2 (1T 2) increased from 0.122 eV and 0.065 eV to0.162 eV and 0.083 eV, respectively, in the range of 303–523 K. Both reveal an enhance in redshift of the excitation spectra. The decrease of charge transfer state (CTS) energy level and the alteration of photoelectron thermal population are two mechanisms that induce CTB redshift. Specifically, the decrease of the CTS level is dominant in the YPO 4 :Eu3+ sample, and the thermal population of the higher vibrational levels of the VO 4 3−ground state is dominant in the presence of a tiny amount of V5+ doping. In addition, according to the experimental phenomenon, a dual-mode temperature sensing scheme based on excitation intensity ratio (EIR) and single band ratiometric (SBR) is proposed. Y 0.9 P 0.1 V 0.9 O 4 :0.1Eu3+ achieves a maximum sensitivity of S r-max = 4.040 % K−1 and a minimum temperature determination uncertainty of δT = 0.124 K at 323 K, which excellent performance indicates that this is a promising non-contact optical thermometer. [Display omitted] [ABSTRACT FROM AUTHOR]

Upconversion luminescence presents obvious advantages in optical temperature sensing, nevertheless the application in complex scenarios is limited by luminescence thermal quenching. Herein, NaYS 2 :Yb3+,Nd3+ phosphors are synthesized by the solid-gas reaction method and used for temperature sensing. A series of emissions for Nd3+ from visible to near-infrared region are achieved based on energy transfer from Yb3+ to Nd3+ under 980 nm excitation. With elevating the temperature, significant thermal enhancement effect of nearly three orders of magnitude is detected in near-infrared emission of 4F 7/2 → 4I 9/2 , which is attributed to phonon-assisted energy transfer of Yb3+→Nd3+ and the corresponding thermal population effect. The thermal behaviors of thermally coupled energy levels for 4G 7/2 /2G 9/2 and 4F 7/2 /4F 5/2 in NaYS 2 :Yb3+,Nd3+ are evaluated by luminescence intensity ratio technique. Remarkably, the optical thermometer based on the enhanced emission of 4F 7/2 /4F 5/2 shows excellent temperature measurement performance, which is expected to be applied in wide-temperature-range and highly-sensitive temperature sensing. These results not only provide a pathway to realize high performance temperature sensing, but also heighten the understanding of UC emission thermal enhancement. [ABSTRACT FROM AUTHOR]

Cryolite-type materials have advantages of low phonon energy, easy rare-earth ion doping, and stable physicochemical properties, and they are considered ideal matrices for up-converting luminescent materials. In this paper, a series of K 3 LuF 6 :Er3+,Yb3+ up-converting materials with cryolite structure were prepared for the first time by high-temperature solid-phase method. The compositions, structures and luminescent properties were systematically characterized by X-ray powder diffractometry (XRD), field emission scanning electron microscopy (SEM) and fluorescence spectroscopy (PL). Under 980 nm excitation, the sample emission spectra mainly consisted of green and red emission bands with peaks at 525, 546 and 662 nm, corresponding to the 2H 11/2 -4I 15/2 , 4S 3/2 -4I 15/2 and 4F 9/2 -4I 15/2 electron transitions of Er3+, respectively. In addition, the temperature sensing characteristics of two thermally coupled energy levels (2H 2/11 and 4S 3/2) were studied based on the fluorescence intensity ratio (FIR) technique in the range of 79–579 K. All the results show that K 3 LuF 6 :Er3+/Yb3+ up-converting luminescent materials have excellent temperature sensing performance in the ultra-wide temperature range and have broad application prospects in the field of temperature sensing. [ABSTRACT FROM AUTHOR]

Optical temperature sensing based on luminescence intensity ratio shows significant potential in achieving accurate temperature detection. In this work, Sb3+/Mn2+ co-doped Cs 2 NaYCl 6 double perovskites were synthesised via a hydrothermal method. Introducing Sb3+ ions to the host significantly enhances the radiative recombination of self-trapped excitons (STEs), resulting in a broad blue emission. The co-doping of Mn2+ ions to the composition leads to a tunable dual-emission in the spectra, originating from the energy transfer between the STEs and Mn2+ ions. The dependence of the dual-emission on temperature is employed for optical temperature sensing. The maximum relative sensitivity, optimal thermal resolution, and optimal thermal repeatability are determined as 1.40 % K−1, 0.002 K and 99.3% at 250 K, respectively. The results indicate that the synthesised Cs 2 NaYCl 6 : Sb3+/Mn2+ double perovskites are promising candidates for high-sensitivity optical thermometers. [ABSTRACT FROM AUTHOR]

Although upconversion luminescence (UCL) materials have attracted considerable attention in biomedical, lighting, anti-counterfeiting, and solar cells due to their excellent fluorescence properties, reports of the dibarium gadolinium aluminum oxide (Ba 2 GdAlO 5) are scarce. Herein, we synthesized the single-phase Ba 2 GdAlO 5 material with non-stoichiometric Ba 2 Gd 1.06 Al 0.94 O 5 (denoted as BGAO, hereafter). The X-ray Rietveld refinement reveals that the substitution of Gd for Al accounts for the non-stoichiometry. Notably, the UCL properties of BGAO are realized by doping with Yb3+ and Er3+ ion pair, and it can be further enhanced significantly by co-doping with appropriate Zn2+ ions. The SEM images show that the particle size increases as the concentration of Zn2+ ions increases. The X-ray Rietveld refinement results of the Zn-doped BGAO: 0.1 Yb3+, 0.03Er3+ phosphor indicate the substitution of Zn2+ for Ba2+ and Al3+ ions simultaneously. Grain growth and lattice distortion account for the improvement of UCL properties after Zn2+ ions doping. In addition, the temperature sensing performance of the Zn2+-doped sample has been researched based on the fluorescence intensity ratio (FIR) technique, and the maximum absolute and relative sensitivities (S A-max and S R-max) are obtained to be 4.8 × 10−3 K−1 at 498 K and 1.1% K−1 at 298 K, respectively. This work provides a candidate with high UCL intensity for potential applications in optical temperature sensors. [ABSTRACT FROM AUTHOR]

Polymer-derived SiBCN ceramics with good high-temperature stability and temperature-sensitive properties can be used in real-time temperature monitoring in the aeronautical industry. However, previous investigations mostly focus on the temperature sensitivity of SiBCN ceramics but neglect the fast temperature conversion of the real operating environment and its effect on the temperature sensitivity, which hinders their further practical application. In this study, the response to rapid temperature changes of polymer-derived SiBCN was studied. SiBCN ceramics maintain excellent high-temperature semiconductor performance under rapid heating, and its direct-current (DC) conductivity increases with increasing temperature. The conductive mechanism conforms to the amorphous semiconductor formula, following three different transition mechanisms in different temperature regions. The resistance of SiBCN increases with the number of cycles during 100 cycles of 500–1200 °C, presenting excellent temperature-sensitivity and relatively good sensing stability. This work demonstrates that SiBCN ceramics can maintain excellent temperature-resistance under extreme environments with rapid heating and cooling, and it is hoped that this work could guide the development of temperature sensors for extreme environments in the future. [Display omitted] [ABSTRACT FROM AUTHOR]

A material-modified Fresnel reflection enhancing high-sensitive fiber-tip temperature sensing method is theoretically proposed and experimentally demonstrated. High refractive index semiconductive nano-ZnO and nano-TiO 2 as doping materials enhance the Fresnel reflection in fiber tip probes, and the interference spectrum of these reflected light shows better sensing performance than when undoped. On this basis, the sensitivity is further improved by utilizing ultraviolet (UV) irradiation due to the UV sensibility of the modified materials. By comparing the sensing performance of different material-doping sensing probes, the ZnO-doped fiber tip sensor witnesses the highest temperature sensitivity, which is 94.1 pm/°C. Thanks to the positive role of UV irradiation, this number increases to 141 pm/°C. The proposed fiber tip sensor has a sturdy structure, simple and economical preparative process, competitive sensitivity, high linearity, satisfactory repeatability, and stability. The micron-scale reflective probe enables better detection of extreme environments and can be expected to conduct high-sensitivity temperature sensing in industrial, biomedical, chemical, environmental, and military regions. [ABSTRACT FROM AUTHOR]

A facile one-step non-contact process was developed for preparing the substrates for Fabry-Perot-based side-polished optical fiber sensors. A carbon dioxide (CO 2) laser cladding removal technique was used to control the profile of the polished fiber surface and to introduce two reflective cavities. The substrates were characterized for a range of cavity lengths and their thermal response was studied. This device added a degree of freedom to the design of optical fiber based Fabry-Perot sensors and its potential was demonstrated by coating the substrate with polydimethylsiloxane (PDMS). The resulting sensors had a three-order of magnitude increase in sensitivity when compared to the substrate. The polished flat surface provided a route for the integration of novel materials for sensing applications, particularly those where polarization control was vital for light-matter interaction, for example, low dimensional materials such as graphene or MXene. The inherent simplicity, mechanical stability, and scalability of this approach are important steps for the realization of practical devices of this type. [Display omitted] • The in-fiber resonator and side-polished fiber were fabricated with a CO 2 laser in one single step. • The large evanescent field of the side-polished fiber treated with 2D PDMS induced a change in the effective refractive index. • The FPIR-PDMS demonstrated excellent sensitivity, with the dip wavelength shifting by 1.27 nm/℃. [ABSTRACT FROM AUTHOR]

A composite fiber Fabry-Perot interferometer (FPI) -based optical fiber temperature sensor is theoretically proposed and practically demonstrated in this work, in which the composite FPI is formed by covering the end face of single-mode fiber with ultraviolet (UV) adhesive and nano-TiO 2 coating using the dip-coating method. With the superior thermo-optic characteristic of UV adhesive and the UV absorption of nano-TiO 2 , the sensitivity of the composite FPI temperature sensor can be effectively enhanced by UV irradiation. After five times of TiO 2 dip-coating processes, the composite FPI has a higher temperature sensitivity of 75.3 pm/°C (R2 = 0.9754) under 365 nm UV light, in which the measurement range is from 25 °C to 130 °C and the detection accuracy is 0.66 °C. The proposed sensor has a simple structure and preparation process, competitive sensitivity, high linearity, and satisfactory repeatability and stability, which can be an appropriate candidate to realize high-precision temperature sensing in industrial, chemical, biological, and environmental applications. [ABSTRACT FROM AUTHOR]

Pr3+-Er3+ co-activated glass-ceramics containing Ba 3.75 Gd 0.833 Nb 10 O 30 crystalline phase were prepared as a multifunctional material. The optimum heat treatment condition was determined to be 750 °C/90 min, as this condition is most favorable for luminescence. As the Pr3+ concentration increases, the emissions of 3P 0 and 1D 2 energy levels show different trends, leading to a shift in luminescence from orange to yellow. With the introduction of Er3+, the co-doped sample achieves orange-yellow-green tunable luminescence. The 0.3%Pr3+-0.3%Er3+ co-doped sample exhibits alternating yellow-orange-green luminescence during continuous excitation in the range of 250–500 nm, which has potential applications in optical anti-counterfeiting. In the temperature interval of 298–458 K, the maximum temperature sensitivities based on the NTCLs of Pr3+ and Er3+ were 0.82 × 10−2 K−1 (S a) and 1.40 % K−1 (S r). Meanwhile, the thermal repeatability ratio is higher than 92.3 %, which proved that it is a potential temperature sensing material. In addition, the concentration quenching, energy transfer and luminescence phenomena involved were analyzed in depth and their mechanisms were explained. [ABSTRACT FROM AUTHOR]

Optical temperature sensing based on fluorescence intensity ratio (FIR) technology has become a potential temperature measurement method due to its fast response, non-invasive and high accuracy. In order to improve the efficiency of development, a multi-strategy combination method was used to study the multi-mode temperature sensing performance of optical temperature sensing materials. Bi3+ doped, Sm3+ doped materials and K 3 YSi 2 O 7 :Bi3+,Sm3+ materials have been successfully prepared and multi-mode temperature sensing models have been established. According to FIR sources, the strategies used are classified according to Bi3+ occupying two sites, energy level thermal coupling of Sm3+ and Bi3+-Sm3+ dual center. The relative sensitivity of the material is up to 0.705% K−1, which adds a new member to the high-performance optical temperature sensing materials family. More importantly, the multi-strategy combination method based on one system opens up an effective way for the rapid development of inorganic optical temperature sensing materials. [ABSTRACT FROM AUTHOR]

Remote and noncontact surface temperature measurements are frequently required yet challenging to execute. One the most promising options consists in using rare earth or transition metal doped materials as optical (luminescence) temperature sensors. In this paper, a series of novel Tb3+/Mn4+ co-doped SrLaMgNbO 6 (SLMN) phosphors have been synthesized and thoroughly investigated for their structural, luminescence spectroscopic and decay kinetics properties as well as for temperature sensing performance. X-ray powder diffraction (XRD) analysis has shown that the prepared sample presents a double perovskite structure. Upon the UV excitation, emission spectra of SLMN:Tb3+, Mn4+ exhibit green and red emission bands for Tb3+ and Mn4+ dopants, respectively. Temperature-dependent photoluminescence (TD-PL) studies revealed sever thermal quenching of Mn4+ emission while that of Tb3+ was moderate providing well pronounced difference in fluorescence intensity ratios (FIR) of the ions. The maximum relative sensitivity (Sr) was found to be 3.27% K−1 and 1.92% K−1 for Mn4+ and Tb3+, respectively. This implies that SLMN: Tb3+, Mn4+ phosphor is a viable candidate material for a dual-mode optical temperature detection. [ABSTRACT FROM AUTHOR]

Upconversion nanoparticles have emerged as promising materials for non-contact temperature sensors due to their unique detection capabilities and low interference, so it is valuable to explore simple and effective approaches to enhance the temperature measurement sensitivity. In this study, we employed a special sol-gel method to prepare NaGd(MoO 4) 2 powder by calcining the precursor mixture, and the fluorescence properties as well as thermal sensitivity were investigated. Analysis based on XRD, SEM and energy transfer modes revealed that the enhancement in temperature sensitivity resulted from the increased distance between the sensitizer and activator ions as well as changes in crystallinity, compared with normal sol-gel method. By optimizing the doping of rare earth ions, the highest sensitivity reached 3.34 %K−1. Additionally, fluorescence spectra analysis of NaGd(MoO 4) 2 samples synthesized via different methods demonstrated that energy transfer between the sensitizer and activator ions can be achieved through high-temperature calcination. Moreover, LiGd(MoO 4) 2 samples prepared using the unique sol-gel method exhibited similar enhancements in temperature sensitivity as NaGd(MoO 4) 2 powder. These findings imply that the samples prepared through the unique sol-gel synthesis method exhibit significant potential in terms of their fluorescence and temperature detection capabilities. [Display omitted] • NaGd(MoO 4) 2 :Er3+-Yb3+ sample was prepared by a special sol-gel method which were calcined after precursor mixing. • The method of calcining after precursor mixing increases the distance between ions and affects crystallinity. • The mixing ratio of the Er3+-Yb3+ doped precursor can be adjusted to achieve higher upconversion. • The temperature sensitivity of the special sol-gel sample prepared in the manuscript is higher, reaching 3.34 %K−1. • Er3+/Yb3+ doped LiGd(MoO 4) 2 prepared by the special sol-gel method also showed similar enhancement in temperature sensitivity. [ABSTRACT FROM AUTHOR]

In recent years, lanthanide doped materials have been extensively studied in the field of fluorescence temperature sensing due to their abundant emission levels and sensitive thermal response. Temperature sensing based on fluorescence intensity ratio (FIR) of upconversion nanoparticles has the advantages of fast temperature response, non-aggressiveness, and high spatial resolution. However, the most reported FIR sensing has limited sensitivity, probably due to the use of thermal coupling levels. Herein, we report a novel FIR temperature measurement based on non-thermal coupling levels of NaGdF 4 :Yb3+/Er3+@NaGdF 4 @NaGdF 4 :Yb3+/Tm3+ core-shell-shell nanostructure, which has high sensitivity and robustness simultaneously. The relative sensitivity based on I 801 / I 654 and I 801 / I 841 of Tm3+ to Er3+ can reach up to 4.56 (303 K) and 3.82% K−1 (313 K), respectively. Between them, FIR of I 801 / I 841 is independent of excitation power and time. These results show the great potential of FIR based on non-thermal coupling levels in high-sensitive and robust temperature sensors. [ABSTRACT FROM AUTHOR]

Most thermometers suffer from thermal quenching resulting in low signal to noise ratio at elevated temperature. To overcome thermal quenching, we fabricated a negative thermal expansion (NTE) thermometer based on Sc 2 Mo 3 O 12 :Nd3+/Yb3+/Er3+ phosphor. Under 808 nm excitation, the upconversion (UC) emissions of Er3+ ions show the thermal enhancement and its 524 nm emission increases 10-fold as the temperature increased from 310 to 670 K. Furthermore, the temperature sensing behaviors are investigated. It is found fluorescence intensity ratio (FIR) of 524–559 nm is linear with temperature over a wide range of 310–790 K. The maximum relative sensitivity is 0.84% K−1 at 310 K. These results indicate such phosphor not only achieves a high sensitivity, but also exhibits excellent performances at high temperature due to its thermal enhancement. [ABSTRACT FROM AUTHOR]

In this paper, a temperature sensor based on fluorescence intensity ratio (FIR) technique is prepared by the dual curing method. The pumping threshold is only 0.1 mW for the application of real-time thermal monitoring on small transformers. This not only greatly reduces the thermal effects accumulated by laser irradiation but also contributes to the integration and portability of the light source. Based on the FIR, the temperature information could be demodulated through tracking the fluorescence spectral changes. The basic temperature sensing characteristics of this sensor were evaluated, which showed that the maximum stability deviation and reproducibility error were within ±1.1 K and ±0.8 K, respectively. Notably, it has a maximum measurement error of only 0.61 K when applied to the temperature monitoring of transformers. And a fast time response of 2.1 s was exhibited in the cyclic exhalation experiment. This proposed sensor is suitable for mass production due to its resistance to electromagnetic interference, low pumping power, fast time response, excellent stability and reproducibility. [ABSTRACT FROM AUTHOR]

Transparent glass ceramic with Ba 2 NaNb 5 O 15 as the main crystal phase was prepared, and the appropriate heat treatment condition was selected as 710 °C/150 min through various characterizations. The luminous intensity and thermal stability were enhanced significantly when the glass ceramic was used as the luminous matrix. After introducing Ti4+ ions as charge compensators, the luminescence performance and thermal stability were further improved, and the reasons for this were analyzed. At 458 K, the luminous intensity of 0.5%Eu3+ doped glass ceramic containing 0.5%Ti4+ can maintain about 65% of room temperature with a chromaticity shift of 5.16 × 10−2. The relative and absolute sensitivities of 0.7%Er3+ doped glass ceramic were 4.04 × 10−3 K−1 and 1.31% K−1. Introducing Ti4+ ions would weaken the population redistribution ability of 2H 11/2 and 4S 3/2 levels and reduce the temperature sensitivity. However, the sample containing Ti4+ shows good thermal stability, its green emission at 458 K has a small chromaticity shift of 6.45 × 10−3. The research shows that the glass ceramic can be used as a good luminescent host material, and Eu3+/Er3+ doped glass ceramic can be used in the fields of LEDs or temperature sensing. [ABSTRACT FROM AUTHOR]

We have fabricated CsPb(Cl/Br) 3 quantum dots (QDs) and Tb3+ co-doping glass and comparatively investigated four-mode temperature sensing of fluorescence intensity ratio (FIR), full width at half maximum (FWHM), lifetime and chromatic coordinate. Temperature dependent photoluminescence (PL) spectra are measured. The Tb3+ ions and CsPb(Cl/Br) 3 QDs have independent luminescence and FIR of Tb3+ to QDs has obvious decrease with temperature, which is used for FIR temperature sensing. The PL and PL decay of QDs are used for FWHM and lifetime temperature sensing. The change of FIR with temperature leads to the change of luminous color and chromatic coordinate with temperature. A new chromatic temperature sensing method is established, which utilizes linear relation of chromatic coordinate and temperature. Temperature dependence for FIR, FWHM, lifetime and chromatic coordinate has been fitted. Absolute sensitivity, relative sensitivity, temperature accuracy and repeatability have been evaluated. Among the four sensing modes, the FIR and chromatic coordinate modes have large sensitivity and small accuracy. The FIR mode is better than chromatic coordinate mode in absolute sensitivity and relative sensitivity, whereas the chromatic coordinate mode is better in its good linear relation. The four sensing modes have excellent repeatability due to the stability of QDs-Tb3+ co-doping glass. [ABSTRACT FROM AUTHOR]

Rare earth ions doped upconversion materials have an extensive range of utilizations because of their exceptional luminescence properties. Here, scheelite type Yb3+, Er3+ co-doped KBi(MoO 4) 2 nanomaterials were produced by means of a conventional co-precipitation method at room temperature with a typical crystallite size of 13 nm. 980 nm excitation aided in the investigation of the concentration and power-dependent upconversion emission. The optimum upconversion emission is obtained with Er and Yb concentrations of 0.035 and 0.125 mol%, respectively in KBi(MoO 4) 2 nanomaterials. The intensity ratio of upconversion emission bands based on 529 and 551 nm is investigated in the temperature range of 200–550 K and the theoretical function is used for fitting the exploratory information. The absolute sensitivity is found to be of maximum value of 0.0123 K-1, indicating that this double molybdate can be utilized as a potential probe for luminescence-based temperature sensing. [ABSTRACT FROM AUTHOR]

Researches on fluorescence intensity ratio (FIR) based temperature sensors have become more and more popular in recent years. Herein, we co-doped Pb2+ and Sm3+ into the host material Ba 2 MgY 2 (BO 3) 4 (BMYB) to prepare a new series of phosphors. The Pb2+ activated phosphor BMYB:0.03 Pb2+ presents a wide blue emission band centered at 416 nm under 278 nm laser excitation with internal quantum efficiency of 46%. In the presence of both Pb2+ and Sm3+, energy transfer will occur between them, resulting in tunable color emission. Besides, the phosphor has an absolute sensitivity of 0.96% K−1 at 575 K, which makes it an excellent candidate for temperature sensing. These findings suggest that prepared phosphor is a potential candidate for color tunable phosphor and temperature sensing material. [ABSTRACT FROM AUTHOR]

A zincate material, BaLa 2 ZnO 5 was successfully synthesized by a high-temperature solid-state method as a host for Bi3+. All the peaks in the X-ray diffraction patterns of the obtained material could be attributed to single phase BaLa 2 ZnO 5. The BaLa 2 ZnO 5 host exhibited strong band-to-band absorption in the range of 200–290 nm. After the doping of Bi3+, the absorption band due to band-to-band transition decreased, and three new absorption bands appeared. Upon monitoring the luminescence of Bi3+ at 407 nm, three excitation peaks were observed for BaLa 2 ZnO 5 : Bi3+, which could be attributed to A, C and metal-to-metal charge-transfer states by analyzing its excitation and absorption spectra. When codoped with Bi3+ and Sm3+, BaLa 2 ZnO 5 : Bi3+/Sm3+ exhibited strong energy transfer process from Bi3+ to Sm3+. Variable-temperature emission spectra revealed that the luminescence intensity of Bi3+ decreases rapidly with the increase in temperature, while that of Sm3+ ions decreases slowly. The relative sensitivity (S R) values of the BaLa 2 ZnO 5 : Bi3+ and BaLa 2 ZnO 5 : Bi3+/Sm3+ phosphors to temperature (1.77 and 1.12% K−1, respectively) were high and extremely stable in the range of 293–423 K. Therefore, the Bi3+-doped BaLa 2 ZnO 5 phosphor has great application potential for biological temperature sensing. [ABSTRACT FROM AUTHOR]

• A bent fiber-optic interferometer for measurement of temperature and refractive index is proposed. • Calibration of the sensor's performance by manipulating the birefringence is explained. • A theoretical model considering the elastic optical properties of bent fiber is presented. • Experimental findings validate proposed theoretical sensing characteristics. • Repeatability and reproducibility of the sensor have been verified. A macehead-shaped bent polarization-maintaining fiber-based interferometric sensing structure called MBPIS is described and experimentally demonstrated for precise temperature and refractive index measurement. The sensor's working principle is explained by simulating the spatial distribution of the field intensity in straight and bending PANDA fibers. A maximum extinction ratio (∼21 dBm) for the interference dip wavelength (1527.825 nm) in the sensor's output spectrum was optimized by manipulating the birefringence of propagating fiber modes by adjusting PMF's bending diameter from 17 to 11 mm. The phase difference changes between these fiber modes due to temperature and RI-induced birefringence cause a shift in the interference spectrum. The sensor's highest RI sensitivity has been seen at −259.32 nm/RIU for a wide range of analytes from 1.3333 to 1.3579. In contrast, the highest temperature sensitivities evaluated for the temperature range of 0 ∼ 100 ℃ are −220 pm/℃ and −0.139 dBm/℃, respectively. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a novel ammonia gas and temperature sensor based on a femtosecond laser inscribed small-period long-period fiber grating (SP-LPG) coated with a nano-assembled polyelectrolyte thin film composed of poly(diallyldimethylammonium chloride) (PDDA)/poly(acrylic acid) (PAA). The PDDA/PAA film is deposited onto the SP-LPG via layer-by-layer electrostatic self-assembly. The SP-LPG is inscribed in a single mode fiber with a period of 30 μm and the total length is only 3 mm. The designed period is much smaller than that of the conventional long period fiber grating (LPFG) of several hundred microns, so we can not only see high-order cladding modes in the transmission spectrum, but also a series of Bragg resonance peaks in the reflection spectrum. The concentration of ammonia gas is detected by the wavelength shift of the transmission resonance dip. The ambient temperature is monitored by the wavelength shift of the Bragg resonance peak. Because the Bragg resonance peak is insensitive to refractive index, we can measure ammonia gas and temperature simultaneously. The experimental results show that the detection limit of the sensor is less than 0.1 ppm. The sensor is sensitive only to ammonia when exposed to different gases. The temperature sensitivity of the sensor is about 8.7 pm/℃ from 30℃ to 70℃. Compared with traditional LPFG, SP-LPG has a more compact structure and the special ability to monitor temperature in real time, which makes the device more advantageous in practical applications. • The proposed SP-LPG was first ever applied to gas sensing. • The SP-LPG was fabricated efficiently and economically by femtosecond laser writing. • Simultaneous detection of ammonia gas and temperature was achieved. • The SP-LPG was easier for integration and miniaturization. [ABSTRACT FROM AUTHOR]

• The Sc 6 WO 12 : Yb3+/Er3+ with strong upconversion red emission were prepared by high-temperature solid phase method. • The optimal doping concentrations of Yb3+ and Er3+ ions in Sc 6 WO 12 were determined to be 0.05 and 0.02, respectively. • The strong red upconversion emission mechanism of the Sc 6 WO 12 : Yb3+/Er3+ phosphor was confirmed as Yb3+(2F 5/2) + Er3+(4I 13/2) → Yb3+(2F 7/2) + Er3+(4F 9/2). • Sc 6 WO 12 : Yb3+/Er3+phosphors have a broad prospect for non-contact temperature sensing applications. Herein, a strong red upconversion phosphor of Yb3+/Er3+ co-doped Sc 6 WO 12 was prepared by employing an equivalent substitution approach. When irradiated by 980 nm near-infrared laser, the phosphor emits strong 660 nm red light. The main excitation mechanism for its red upconversion luminescence emission is the energy transfer process, through which the Er3+ ions is promoted from the 4I 13/2 energy level to the 4F 9/2 energy level. In addition, it is noteworthy that the multimode upconversion luminescence phosphor exhibits three different trends upon temperature change, and its upconversion emission integral intensity ratio exhibits a linear relationship with temperature in the range of 298 K–623 K. This special property makes the phosphor promising for applications in optical temperature measurement. [Display omitted] [ABSTRACT FROM AUTHOR]

Textile-integrated wearable sensors have exhibited an immense potential to transform human life by fetching safety and comfort at the forefront. This work underscores a novel design approach to fabricate textile-integrated multimodal sensors using a conductive ink coated bi-stretch nylon fabric. Conductive ink has been formulated by dispersing high aspect ratio silver nanowires into water-dispersed PEDOT: PSS solution with polyvinylpyrrolidone that allows sensing of various stimuli, including mechanical strains, temperature, humidity, etc. The fabrication of sensing elements involves the interleaving of screen-printed conductive ink into flexible coats, using water-borne polyurethane, achieved by the facile pad-dry-cure technique on bi-stretch fabric like a sandwich. Remarkable mechanical strain sensing performance in terms of sensitivity, repeatability, and stability has been demonstrated along with flexibility, bendability, and compliant form factor, making them suitable for applications in wearable technology and smart textiles. Moreover, the temperature and humidity sensing exhibit rapid response and wide detection ranges, making the sensor adaptable to diverse environmental conditions. The sensing fabric responds well to different strain and compression conditions. The as-developed fabric can also operate as an IR heating element when biased at certain operating conditions. These attributes make such elements an ideal candidate for various applications, such as human motion tracking, environmental monitoring, and healthcare devices. The sensor's low-cost, solvent-free production and scalability make it a practical choice for mass adoption. [Display omitted] • Silver nanowires integrated functional ink was synthesized using polyol method. • PEDOT: PSS was used as a conducting polymer blend to impart resilient sensing performance. • The conductive ink interleaved between the two coats of water-borne polyurethane. • Functional ink coated on nylon fabric exhibited extreme sensitivity to various stimuli. • Multimodal sensor performance in terms of environment, health, etc as a wearable patch is projected. [ABSTRACT FROM AUTHOR]

In recent years, non-contact temperature reading sensors based on carbon quantum dots (CQDs) have attracted a lot of attention, most researchers have studied them at room temperature and high temperature. In this paper, red-CQDs (R-CQDs) was synthesized by hydrothermal method using o -phenylenediamine and chemically characterized by transmission electron microscopy, Fourier transform spectroscopy and X-ray photoelectron spectroscopy. The bandgap energy of R-CQDs was calculated from the absorption spectra, and the photoluminescence (PL) spectra at different laser powers showed that the PL of the R-CQDs were single-photo absorbing process. For better application, R-CQDs/polyvinyl alcohol (PVA) films were prepared. The PL properties of the film were studied. Experiments show in temperature range of 190∼260 K, the PL intensity decreases linearly with increasing temperature. Relative sensitivities of temperature sensing were calculated to be about −0.62% K−1. This work demonstrates the feasibility of its application in low temperature sensing. • We have synthesized R-CQDs with good photoluminescence properties using a simple method. • In the low temperature range of 190 ∼ 260 K, the R-CQDs/PVA film's have good temperature-dependence. • Relative sensitivities of temperature sensing were calculated to be about −0.62% K−1. [ABSTRACT FROM AUTHOR]

We have fabricated Sm3+ doped glasses, CsPb(Br/Cl) 3 quantum dots (QDs) glasses and CsPb(Br/Cl) 3 -Sm3+ codoped glasses by melt-quenching and subsequent heat treatment for optical temperature sensing. Photoluminescence (PL), photoluminescence excitation (PLE) spectra and PL decay have been measured. Two CsPb(Br/Cl) 3 -Sm3+ samples with different PL peaks of QDs at 486 nm and 503 nm have been studied for fluorescence intensity ratio (FIR) and chromatic coordinate sensing. The CsPb(Br/Cl) 3 QDs and Sm3+ ions exhibit distinguished spectral components and they are dynamically independent. PL intensity of QDs rapidly decreases with temperature, whereas PL intensity of Sm3+ slowly decreases with temperature. PL intensity of Sm3+ ions and CsPb(Cl/Br) 3 QDs have been independently fitted. Then, FIR sensing has been studied. The different variation in PL intensity with temperature for Sm3+ and CsPb(Cl/Br) 3 leads to the change of luminescent color and chromatic coordinate. The chromatic coordinate sensing has also been studied. Absolute sensitivity (S a) and relative sensitivity (S r) have been analyzed for both FIR and chromatic coordinate sensing. Compared with the chromatic coordinate mode, FIR mode has the larger S a and S r. But the chromatic coordinate method is more convenient for application, which does not require separating two spectral components. Both FIR and chromatic coordinate sensing modes show outstanding temperature cycling characteristics. [ABSTRACT FROM AUTHOR]