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The intensity of upconversion luminescence (UCL) poses a significant challenge for oxides characterized by high phonon energy. Herein, a significant enhancement of red UCL is achieved through the introduction of an intermediate band (IB) in α-Ba 2 ScAlO 5 : Yb3+/Er3+ by Ca2+ ions doping. The absorption spectra verify the existence of the IB. The IB of α-Ba 2 ScAlO 5 : Yb3+/Er3+/Ca2+ increases the host's absorption of excited photons, provides more electrons for the excitation of Er3+, and realizes the enhancement of UCL emission. The optimal concentration of Ca2+ in α-Ba 2 ScAlO 5 : 0.2Yb3+, 0.03Er3+ is 0.15. Compared with undoped Ca2+ samples, the red and green UCL intensity of α-Ba 2 ScAlO 5 : Yb3+, Er3+, 0.15Ca2+ increased by 48.2 and 10.6 times, respectively. The mechanism of Ca2+ enhanced UCL was investigated by analyzing the UCL spectra, absorption spectra and lifetime decay curves of α-Ba 2 ScAlO 5 : Yb3+/Er3+/Ca2+. The temperature-dependent UCL properties of α-Ba 2 ScAlO 5 : Yb3+/Er3+/Ca2+ were also studied by the 2H 11/2 (525 nm) and 4F 9/2 (667 nm) energy level radiation transitions. The observed linear correlation between luminescence intensity and temperature, coupled with its high sensitivity, indicates the promising potential for temperature sensing applications. This study not only opens a new avenue for enhancing UCL but also holds significant implications for sparking widespread interest in non-contact temperature sensing applications leveraging UCL. [Display omitted] • α-Ba 2 ScAlO 5 :Yb3+/Er3+/Ca2+ with strong upconversion red emission was prepared by high temperature solid phase method. • A significant enhancement of UCL red is achieved through the introduction of an intermediate band. • α-Ba 2 ScAlO 5 :Yb3+/Er3+ phosphor enhances red light by 48.2 times and green light by 10.6 times after doping with Ca2+. • α-Ba 2 ScAlO 5 :Yb3+/Er3+/Ca2+ phosphor have broad application in non-contact temperature sensing applications. [ABSTRACT FROM AUTHOR]

Single doped Mg 0.388 Al 2 O 3.408 O 4 phosphor was prepared and multivalent Mn ion (Mn2+ and Mn4+) emission was achieved in a single host. The structure, morphology, and luminescence characteristics of Mn ions in Mg 0.388 Al 2 O 3.408 O 4 were discussed in detail, especially the temperature dependent emission characteristics of Mn ions. Based on the fluorescence intensity ratio (FIR) of Mn2+ versus Mn4+ and the decay lifetime of Mn4+ emission as the temperature readout, a dual-mode optical temperature-sensing mechanism was proposed and studied in the temperature range of 293–473 K. The maximum relative sensitivities (S r) are derived as 2.83 % K−1 (at 373 K based on FIR) and 3.40 % K−1 (at 473 K based on decay lifetime), respectively. The temperature sensing characteristics of Mg 0.388 Al 2.408 O 4 : Mn2+/Mn4+ powders in a full fiber system were studied, which can provide thermal-sensitive emissions at dual-wavelengths for stable ratiometric temperature sensing with good precision and repeatability. The constructed all fiber temperature sensing system has been applied in the on-line monitoring of CPU temperature. • Emission of multivalent Mn ions (Mn2+ and Mn4+) phosphor in Mg 0.388 Al 2 O 3.408 O 4 host. • A dual-mode optical temperature sensing based on FIR and the decay lifetime as the temperature readout. • Optical thermometry with high relative sensitivity based on FIR (2.83 % K−1) and decay lifetime (3.40 % K−1). • The constructed all fiber temperature sensing system for the on-line monitoring of CPU temperature. [ABSTRACT FROM AUTHOR]

In this paper, a very simple method was used to synthesize ligand-free luminous hydrogels doped with Tb3+ and Eu3+. The hydrogels exhibit red (615 nm), green (544 nm) and blue (425 nm) emissions derived from Tb3, Eu3+ and defects, respectively. Effective energy transfer from Tb3+ to Eu3+ is observed. We apply these ligand-free luminous hydrogels for temperature sensing for the first time. In surprise, the relative sensitivities are all very high (>2 %/K) by using many kinds of fluorescence intensity ratios. In addition, with the increase of temperature, the emission color of the samples changes significantly (from orange-red to blue) which can be applied for visual temperature sensing. The above results infer that the ligand-free luminous hydrogels can be used as an eco-friendly visual temperature sensing material. • Temperature sensing of ligand-free luminous hydrogels is reported firstly. • High sensitivities are obtained by using many kinds of FIRs. • Emissions color changes sharply with temperature for visual temperature sensing. • These hydrogels can be made into flexible transparent films for wearable devices. [ABSTRACT FROM AUTHOR]

Long-afterglow luminescent materials has undergone extensive research in sensing and anti-counterfeiting. However, the complex preparation process, single luminescence with low quantum yields, potential biological toxicity and harsh application conditions limited the widespread use of these materials. In this work, 3-APBA CDs@MA was obtained by 3-aminophenylboronic acid, sulfuric acid and melamine via a one-pot hydrothermal process. The as-designed 3-APBA CDs@MA exhibit dual emission with quantum yields of 15.74 % and lifetime of 1.39 s for thermally activated delayed fluorescence and 1.63 s for room temperature phosphorescence. The afterglow of carbon dots can be observed by the naked eye for about 24 s and 13 s after turning off the 365 nm UV lamp and visible light lamp, respectively. Furthermore, the as-obtained 3-APBA CDs@MA show potential for temperature sensing and advanced anti-counterfeiting. Visible light-excited carbon dots with dual emission long-afterglow were synthesized by 3-aminophenylboronic acid, sulfuric acid and melamine via one-pot hydrothermal method. The as-designed 3-APBA CDs@MA exhibits dual emission with room temperature phosphorescence and thermal activated delayed fluorescence, 15.74 % quantum yields, 1.39 s and 1.63 s lifetime (TADF and RTP, respectively).Then the as-obtained 3-APBA CDs@MA was applied in anti-counterfeiting and temperature sensing. [Display omitted] • A new type of dual emission long-afterglow carbon dots-MA composite (CDs@MA) via one pot hydrothermal method. • Afterglow CDs@MA can be excited by UV and visible light. • Afterglow with long lifetime and can be seen by naked eye about 24 s. • Afterglow of CDs@MA can be maintained under water or other organic solvents. • A method of regulating afterglow dual emission is proposed. [ABSTRACT FROM AUTHOR]

The objective of this work was to investigate the thermoluminescence (TL) properties of lanthanide-doped CaSO 4 synthesized by co-precipitation for particle temperature sensing applications. Desirable properties for temperature sensing include high TL intensity, stability of the TL signal against light exposure, low room temperature fading, UV emission, and multiple TL peaks over a wide range of temperatures. CaSO 4 was synthesized with one or more lanthanides and characterized using x-ray diffraction (XRD), radioluminescence (RL), and TL using both broad-band or wavelength resolved detection. We focused particularly in samples containing blue and UV emitting centers (e.g. Ce3+, Tm3+), because of the possibility of better discriminating the TL emission against the blackbody background emission in the high temperature region of the TL curves. TL emission was observed mostly for trivalent states of the lanthanides (Ce3+, Pr3+, Sm3+, Gd3+, Tb3+, Dy3+ and Tm3+), except in Eu-doped samples, in which both Eu2+ and Eu3+ emissions were observed. A variety of TL peaks was observed with emission from <100 °C to almost 600 °C with relative intensities that varied according to the dopants. Samples doped with Ce and co-doped with either Pr, Gd or Tb were particularly interesting for temperature sensing, because they showed TL emission in the UV region with higher intensity than the single-doped samples, and TL peaks in the high temperature range of the TL curve. The results demonstrate the possibility of synthesizing CaSO 4 samples with high TL intensity and TL peaks distributed over a wide temperature range, which can be controlled by the appropriate choice of dopants. This can be useful for temperature sensing applications, because materials with TL peaks in specific temperature regions are required depending on the intended temperature range of measurement. • Structure of TL peaks in CaSO 4 can be controlled by lanthanide doping. • TL from room temperature up to 600 °C can be introduced. • TL emission spectra provided evidence of the recombination mechanism. [ABSTRACT FROM AUTHOR]

Abstract We present a simple design of a six-band terahertz metamaterial absorber (MMA). The unit-cell of the MMA consists of a metallic cross-cave-patch (CCP) structure and an InSb dielectric spacing layer stands on a ground-plane. The permittivity of the InSb dielectric layer can be adjusted efficiently by the variation of external temperature. The numerical simulation results show that the MMA has six distinct absorption peaks from 0.4 THz to 2.2 THz, and the absorption peak frequencies can be tuned easily by changing the external temperature. The surface current distributions of the top layer and back layer of the unit-cell structure are studied to better understand the physical mechanism of the proposed MMA. The six-band strong absorption of the MMA is originated from the excitations of high-order magnetic resonance. In addition, the sensitivity S is investigated to explore temperature sensing performance of the device, and the value of S is 10.3 GHz/K, 8.1 GHz/K, 6.7 GHz/K, 6.4 GHz/K, 5.5 GHz/K and 5.4 GHz/K, respectively. The design of the MMA could find potential applications in temperature sensing or other optoelectronic related areas in terahertz region. Highlights • A simple design of a six-band terahertz metamaterial absorber (MMA) was proposed. • The absorbance of MMA is over 97.8% on average at six different resonance frequencies. • Physics origin of MMA is studied by surface current distributions. • The MMA can achieve a sensitivity of about 10.3 GHz/K, 8.1 GHz/K, 6.7 GHz/K, 6.4 GHz/K, 5.5 GHz/K and 5.4 GHz/K, respectively. [ABSTRACT FROM AUTHOR]

In this study, a multifunctional Ba 2 GdF 7 :Yb3+, Er3+/Ag 2 S NCs was synthesized, which could realize temperature measurement and photothermal conversion. The temperature sensing properties of Ba 2 GdF 7 :Yb3+, Er3+/Ag 2 S NCs based on FIR technology were investigated in the range of 300K–360K. The results indicate that the maximum values of S a and S r are 0.073 K−1@360K and 1.406%K−1@300K, respectively. Next, the photothermal effect of the content of Ba 2 GdF 7 : Yb3+, Er3+ on Ag 2 S in the composites was evaluated. Appropriate amount of Ba 2 GdF 7 : Yb3+, Er3+ can enhance the photothermal efficiency of Ag 2 S, which is attributed to Ag 2 S absorbing visible light emitted from the up-conversion process of Ba 2 GdF 7 :Yb3+, Er3+ and releasing heat. Then, in egg white, Ba 2 GdF 7 :Yb3+, Er3+ based on FIR technology can monitor temperature of Ag 2 S photothermal therapy. Ultimately, the cytotoxicity test on HeLa cells using methyl thiazolyl tetrazolium (MTT) assay showed good biocompatibility of the Ba 2 GdF 7 :Yb3+, Er3+/Ag 2 S NCs. • The S a of Ba 2 GdF 7 :Yb3+, Er3+/Ag 2 S NCs is superior to others. • Ba 2 GdF 7 : Yb3+, Er3+ can promote the PTT of Ag 2 S. • Ba 2 GdF 7 NPs can monitor temperature in the process of Ag 2 S PTT. [ABSTRACT FROM AUTHOR]

Abstract Optical thermometry based on the adjacent thermally coupled levels of rare earth ions has been widely studied in the high temperature range, and shows unobvious effect at low temperature range. In this work, we propose a new method to achieve optical thermometry in 10˜300 K range through manipulating the energy transfer from WO 6 6− to Ho3+. A comprehensive five-level rate-equation model is developed to establish the relation between lifetime ratios and temperature. It is found that the lifetime ratios of 540 nm (Ho3+) and 471 nm (WO 6 6−) emissions are dependent on the phonon energy of Y 2 WO 6 host and temperature. The values of sensor sensitivity reach the maximum 2.1% K−1 at 211 K in 30%Ho3+ doped Y 2 WO 6 , which is higher than the maximum of the reported phosphors at low temperature. It overcomes the shortcoming of unobvious thermal population of thermally coupled levels in low temperature range through traditional Boltzmann distributing method. Highlights • Energy transfer process between host and Ho3+ was analyzed. • Temperature dependent emission spectra of Ho3+ doped Y 2 WO 6 were studied. • A new method to achieve optical thermometry through manipulating the energy transfer from WO 6 6− to Ho3+ is proposed. [ABSTRACT FROM AUTHOR]

Abstract In this paper, Nd3+/Yb3+ codoped SrWO 4 phosphors for temperature sensing are investigated. Firstly, the doping ratio of Nd3+ and Yb3+ was optimized. Then, under a 980 nm excitation, the temperature response of the near infrared (NIR) upconversion emission spectra in the temperature range of 313 K–453 K was characterized. The results show that the NIR emission peaks increase notably with the increase of temperature. With the fluorescence intensity ratio (FIR) technique, thermal sensing property of the optimized phosphor was investigated. A maximum thermal sensitivity of 0.02857 K−1 (I 801 / I 869) at 453 K was achieved, which is higher than that of the other previously reported similar materials. The minimum temperature uncertainty is about 1 K at 453 K. The results reveal that SrWO 4 : Nd3+/Yb3+ is a promising material for optical thermometry. Highlights • The optical temperature sensing properties of the SrWO 4 :Nd3+/Yb3+ phosphor are demonstrated for the first time. • Optical thermal sensing was demonstrated in the first biological window. • Nd3+/Yb3+ codoped SrWO 4 for temperature sensing based on the FIR method was proposed and experimentally investigated. • The thermal sensitivities of thermally coupled levels of Nd3+ (4F 7/2 /4F 5/2 , F 7/2 /4F 3/2 and 4F 5/2 /4F 3/2) were investigated. [ABSTRACT FROM AUTHOR]

To explore new upconversion (UC) phosphor materials for optical temperature sensing, a series of Er 3+ /Tm 3+ -Yb 3+ doped Ca 4 Y 6 Si 4 O 24 samples were designed by using solid-state reaction method. The phase purity was examined via XRD patterns, which indicates the obtained phosphors are single-phase. The UC spectra of CYS:1%Er 3+ ,xYb 3+ (0 ≤ x ≤ 20%) reveal the green and red emission peaks of Er 3+ show different change rate in intensity when the Yb 3+ concentration increases, which can be owing to the cross-relaxation between Er 3+ and Yb 3+ . For the Tm 3+ -Yb 3+ doped CYS, the optimal Yb 3+ concentration was determined to be 10 mol%. Different strategies were employed for temperature sensing behavior. The investigation indicates that the best sensor sensitivity was obtained in the CYS:1%Er 3+ ,10%Yb 3+ sample by employing the fluorescence intensity ratio technique with non-thermally coupled levels. The above results could be instructive to the development of new luminescent materials with high sensitivity. [ABSTRACT FROM AUTHOR]

Rhodamine B(RhB) was encapsulated in Tb(btc) (btc = 1,2,4-benzene tricarboxylic acid) frameworks by "one-pot" method, and the complex RhB@Tb(btc) with host-guest dual fluorescence emissions was synthesized. Compared with the stability of Tb3+ emission, the characteristic emission of RhB at 620 nm showed a more sensitive response to ambient temperature. By integrating the different temperature dependence of Tb3+ and RhB emissions, the temperature sensing of RhB@Tb(btc) was determined with relative sensitivity ranging from 0.43 to 0.59% K−1 (temperature range 298–353 K). Among several common antibiotics, RhB@Tb(btc) showed fluorescence quenching response to metronidazole (MDZ) and color transition to levofloxacin (LOFX) respectively with stable reusability. The combination of photoinduced electron transfer and internal filtration effect was confirmed as the contributor to MDZ induced fluorescence quenching. Furthermore, hydrogels and milk, which were added antibiotics on purpose for simulating unsafe foods, were detected at in situ temperature by RhB@Tb(btc) test paper, which achieved highly sensitive and highly selective detection to MDZ and LOFX with limit of detection reaching 10−6 M. [Display omitted] • Dye@Tb(btc) composite is constructed by encapsulating dye molecules, which showed emission of both dye and Tb(btc). • Dye@Tb(btc) can serve as a highly sensitive ratiometric temperature sensing platform. • Dye@Tb(btc) is a highly sensitive and selective sensor for detecting antibiotics in aqueous solution and hydrogel. • A portable assay test paper was designed for visual and in situ temperature testing of antibiotics. [ABSTRACT FROM AUTHOR]

The YAG:Pr transparent ceramic was fabricated using a conventional solid-state reactive method to explore its possible application in optical thermometry. Photoluminescence and temperature-dependent luminescence were elaborately investigated under 452 nm excitation. The ceramic showed two intrinsic emission bands at 488 and 594 nm, which were attributed to characteristic Pr 3+ : 3 P 0 → 3 H 4 and 3 P 1 → 3 H 6 transitions, respectively. Down-conversion emissions from the two thermally coupled excited states of Pr 3+ were recorded in the temperature range of 293–593 K. The Boltzmann distribution theory was adopted to interpret the temperature-dependent luminescence of Pr 3+ . The temperature sensitivity exhibited an increasing trend with the increase of temperature, typically, 0.0025 K −1 at 593 K. The results indicated that the present ceramic was a promising candidate for optical temperature sensor. [ABSTRACT FROM AUTHOR]

Ho 3+ /Yb 3+ codoped Gd 2 O 3 phosphor has been synthesized by solution combustion method. The concentrations of Ho 3+ and Yb 3+ were optimized to be 0.3 and 2.0 mol% respectively for maximum emission intensity. The effect of Li + ion co-doping on phase structure and photo luminescence were investigated. It is found that there is no change in phase of the sample due to Li + ion co-doping. However the Upconversion (UC) and Downshifting (DS) emission show a remarkable enhancement in intensity. It is concluded that, this enhancement in the emission intensity is mainly due to the change in crystal field around the Ho 3+ ion and reduction in quenching centers. The optimum doping concentration of Li + ion was found to be 20 mol%. We have further explored the temperature sensing behavior using the FIR technique. The maximum sensitivity is found to be 0.0092 K −1 at 505 K. [ABSTRACT FROM AUTHOR]

For the first time, lanthanide co-doped self-activated Ca 9 Y 1 − x − y Er x Yb y ( VO 4 ) 7 phosphors have been investigated for bearing dual-mode emission: downshifting and upconversion emission behavior. The Ca 9 Y 1 − x − y Er x Yb y ( VO 4 ) 7 phosphor, under 379 nm excitation evinces two bright green emission peaks at 525 nm and 553 nm, which corresponds to H 11 / 2 2 , S 3 / 2 4 → I 15 / 2 4 transitions of Er3+ ion, this transition is sensitized by an efficient energy transfer from the ( V O 4 ) 3 − group to Er3+ ions. Irradiated with a 980 nm power tunable laser, it shows strong green and comparatively weak red emissions bands. The upconversion emission can be enhanced enormously with the introduction of Li+ ions in the optimized C a 9 Y 0.847 E r 0.003 Y b 0.15 ( V O 4 ) 7 phosphor. Furthermore, utilizing the well-known fluorescence intensity ratio (FIR) technique, optimized C a 9 Y 0.647 L i 0.20 E r 0.003 Y b 0.15 ( V O 4 ) 7 phosphor has been explored for optical temperature sensors also. The maximum absolute sensitivity and relative sensitivity are obtained to be 0.0125 K−1 at 513 K and 0.012 K−1 at 300 K, respectively. The acquired result reveals that the phosphor C a 9 Y 0.647 L i 0.20 E r 0.003 Y b 0.15 ( V O 4 ) 7 can be a worthy material for temperature sensing application. [Display omitted] • Synthesis of Li + doped Ca 9 Y 1-x-y Er x Yb y (VO 4) 7 by sol-gel combustion method. • Charge transfer transition of (VO 4)3- group in Ca 9 Y 1-x-y Er x Yb y (VO 4) 7. • First observation of upconversion emission in Ca 9 Y 1-x-y Er x Yb y (VO 4) 7 phosphor. • The influence of Li + doping on the upconversion emission. • Li + doped Ca 9 Y 1-x-y Er x Yb y (VO 4) 7 shows high optical temperature sensitivity. [ABSTRACT FROM AUTHOR]

Different concentrations of Er 3+ doped Y 2 O 3 ceramics are synthesized. Under the 966 nm excitation, it is found that the ratios of red to green emissions are obviously enhanced with temperature for high doped sample, which is attributed to the combined temperature-dependent processes. Besides that, variations of fluorescence intensity ratio of green upconversion emissions in Er 3+ :Y 2 O 3 ceramics have been studied as a function of temperature. A maximum sensitivity of less than 0.003 K −1 is obtained in the high doped sample, whereas it is above 0.005 K −1 in the low doped sample. Concentration effects on the temperature sensing behaviors are discussed. In addition, similar phenomenon is found in Er 3+ /Yb 3+ codoped NaYF 4 nanocrystals. [ABSTRACT FROM AUTHOR]

The practical application of light thermometer based on the FIR (520/540) has been greatly limited due to the strong absorption of green light by biological tissues. The sensitivity of the temperature sensor located in a biological window (FIR-BW) also needs to be improved. Based on this, we designed and synthesized an upconversion nanoparticles (UCNPs) with suitable R/G ratio and red visual output to prebreaking the limitation of strong absorption of biological tissue, while improving the sensitivity of temperature sensor and in vivo fluorescence imaging. In this paper, NaErF 4 :40%Tm@NaYF 4 , a high efficient red UCNPs with R/G ratio (6.86), is first utilized as an optical thermometer, accomplished through the fluorescence intensity ratio (FIR) of thermally coupled stark sublevels of 4S 3/2 /4F 9/2 (FIR(540/654)). In the studied temperature range, the maximum absolute and relative sensitivity (S a and S r) is 0.47% K−1 and 2.61% K−1 at 298 K, respectively, which is much higher than most previous reports about FIR-based temperature sensors. Additionally, we investigated the in vivo bioimaging behavior of NaErF 4 :40%Tm@NaYF 4 in detail. The superior biocompatibility, the distribution to the main organs with the blood circulation system, and the bright red fluorescence signals were observed under 980 nm laser radiation. All the results imply that NaErF 4 :40%Tm@NaYF 4 is a promising candidate for optical thermometry and in vivo bioimaging with high sensitivity. [Display omitted] • The practical application of light thermometer based on the FIR (520/540) has been greatly limited due to the strong absorption of green light by biological tissues. • The sensitivity of the temperature sensor located in a biological window (FIR-BW) also needs to be improved. • Based on this, a high efficient red upconversion nanoparticles (UCNPs) with suitable R/G ratio (6.86), is first utilized as in vivo bioimaging and an optical thermometer, accomplished through 4S 3/2 /4F 9/2 with S a (0.47% K−1) and S r (2.61% K−1), which is much higher than most previous reports about FIR-based temperature sensors. [ABSTRACT FROM AUTHOR]

Abstract: Fluorophosphates glasses YF3–BaF2–Ba(PO3)2 doped with Er3+ and Er3+–Yb3+ were prepared and the structures of the samples were briefly investigated. The experimental intensity parameters were calculated according to the Judd–Ofelt theory, from which the radiative transition probabilities, fluorescence branching ratios, and radiative lifetimes of Er3+ were obtained. Bright green and red upconversion emissions was observed in Er3+–Yb3+ co-doped samples excited by 980nm laser diode, and two-photons absorption processes were determined for the emissions by examining the dependence of the emission intensity on the excitation power. The concentration effects on the intensity and decay time of the upconversion emission revealed that growing Er3+ concentration declined the probability of sequential energy transfer from Yb3+ to Er3+, and thus increasing the intensity ratio of the red emission to the green ones. The temperature effects on the intensity ratios of different emission bands showed that the maximum transducer sensitivity based on the fluorescence intensity ratio (FIR) was calculated to be 0.0015/°C at 6°C. [Copyright &y& Elsevier]

Temperature sensing technology is of great siginificance in scientific research, agricultral production and industrial manufacture. In this work, the sub-10 nm NaYbF 4 : Nd@NaYF 4 : Nd active-core/active-shell NPs are employed for near-infrared (NIR) temperature sensing. Compared with the core-only and core/inert-shell NPs, the downshifting emission intensity of the NaYbF 4 : Nd@NaYF 4 : Nd active-core/active-shell NPs is greatly enhanced. Upon 808 nm excitation, the Yb3+ emission intensity at ∼975 nm decreases evidently while that of Nd3+ ions at ∼1055 nm only slightly decreases with the rising of temperature from 293 K to 493 K. The maximum S a of 1.27*10−3 K−1 at 470 K and S r of 0.7%/K at 293 K are achieved. The NIR emission studied in this work show deep penetration depth more than 4 mm. • Sub-10 nm NaYbF 4 : Nd@NaYF 4 : Nd active-core/active-shell NPs are prepared. • The active NaYF 4 : Nd shell greatly enhances the Yb3+ NIR intensity. • The Yb3+ emisison decreases evidently while that of Nd3+ slightly decreases at higher temperature. • The maximum S a of 1.27*10−3 K−1 at 470 K and S r of 0.7% K−1 at 293 K are achieved. [ABSTRACT FROM AUTHOR]

In this work, a series of Nd3+ and Yb3+ codoped SrF 2 nanocrystals (NCs) were synthesized by the hydrothermal method. The TEM results show that the average size of these NCs is approximately ∼50 nm. The structure of SrF 2 NCs and its optical properties of near-infrared (NIR) downconversion luminescence (DCL) are systematically characterized. Under the excitation of 808 nm laser, intense NIR DCL centered at 976 nm from Yb3+ ions is experimentally determined. The mechanism of the DCL is further interpreted based on the efficient energy-transfer (ET) processes from Nd3+ to Yb3+. In addition, utilizing the fluorescence intensity ratio (FIR) technique, the temperature sensing behaviors of SrF 2 :Nd3+/Yb3+ (15/4 mol%) are also investigated through the heterogeneously coupled states between Nd3+ (4F 3/2 → 4I 11/2) and Yb3+ (2F 5/2 → 2I 7/2) in a temperature range of 298–573 K. The results confirm that the maximum thermal sensitivity is up to 0.00346 K−1 at 473K. The excellent thermal sensitivity of these NCs, particularly the DCL located at the NIR region, have the potential for biological applications and temperature measurement at the nanoscale. • Efficient near-infrared downconversion of Yb3+ was achieved in Nd3+-sensitized SrF 2 nanocrystals under 808 nm excitation. • The thermometric performances located in near-infrared range were systematically investigated. • A maximum thermal sensitivity up to 0.00346 K-1 is obtained at 473 K. [ABSTRACT FROM AUTHOR]

Dy3+-doped borogermanate glass-ceramics with CsPbBr 3 quantum dots (QDs) were synthesized by the high-temperature melting and heat treatment methods. The structural, morphology, and luminescence temperature-sensitive properties of QDs in glass hosts were investigated using XRD, the high-resolution transmission electron microscopy (HR TEM), and temperature-dependent photoluminescence (PL) emission spectra, respectively. Strong green emission from CsPbBr 3 QDs was observed. The optimal concentration of Dy3+ ions in borogermanate glasses was also determined. The activation energy (E a) is estimated as 337.7 meV from the fitting curve of integrated PL emission intensity of CsPbBr 3 versus the reciprocal temperature. The relative sensitivity maximum value of the 0.4 mol% Dy3+-doped CsPbBr 3 QDs (CDy0.4) glasses reaches 2.39% K−1 at 298 K. The results indicate that CDy0.4 borogermanate glass-ceramics could be potentially used for high-sensitivity optical temperature sensing applications. • Dy3+-doped CsPbBr 3 quantum dots in borogermanate glasses have been fabricated. • The optical properties and microtopography of Dy3+-doped CsPbBr 3 QDs glasses is investigated. • The maximum relative sensitivity of 0.4 mol% Dy3+-doped CsPbBr 3 QDs glasses reaches 2.39% K−1 at 298 K. [ABSTRACT FROM AUTHOR]

Detecting structural damage in the form of geometrical defects in materials that operate under extreme conditions or serve as critical structural components is essential. In this work, the feasibility of using thermographic phosphors as a non-destructive, remote, instantaneous, and customizable sensing mechanism for detection of structural damage was investigated. The two materials studied were (1) Sylgard 184 elastomer and (2) silica aerogels. Two different types of structural damage were investigated in samples of increasing thickness, up to a maximum of 18 mm. To accurately interpret the results, heat flux measurements were also collected from both material types. The changes in the thermal profile of the material as a result of material defects were used to infer information about the structural health of the material. La 2 O 2 S:Eu and Mg 3 F 2 GeO 4 :Mn were chosen for the study since their temperature sensitivity range complemented one another and allowed for measurements from cryogenic to 200 °C. It was determined that fracture and failure in both aerogels and Sylgard 184 could be detected by phosphor thermometry and the limit of its resolution was ultimately determined by the thermal properties of the material, the choice of phosphor, and ambient temperature. • Successfully applied remote optical sensing to identify geometrical defects in aerogels and elastomers. • Two different types of structural damage was investigated as a function of increasing thickness. • The damage geometry was chosen to resemble established fracture geometries. [ABSTRACT FROM AUTHOR]

The far-red emitting phosphor plays a significant role in the agricultural lighting application. Herein, we present the temperature-dependent luminescent characteristic of Cr3+ doped ZnGa 2 O 4 (ZGO) phosphor, which was synthesized using the conventional high temperature solid-state reaction. The prepared ZGO:Cr3+ sample was evidenced through the analyses of X-ray diffraction technique and X-ray photoelectron spectroscopy. Photoluminescence phenomena present an expected sharp R line origin from the spin forbidden transition of 2E → 4A 2 in Cr3+ ion. In the matrix of ZGO, the R line was divided into R1 and R2 lines as a result of the splitting of 2E level into 2E (Ē) and 2E (2Ā) levels at the distorted crystal field environment. Electron paramagnetic resonance spectrum of Cr3+ proved that g = 3.63 and 1.92 are attributed to the isolated Cr3+ ions and exchange coupled Cr3+-Cr3+ ion pairs. The red-shift of R1 and R2 lines were observed with the temperature rising from 140 K to 440 K. The Debye temperature estimated from the shift of R1 lines was 690 K. The luminescence decay curves of the ZGO:Cr3+ sample show long-lived lifetimes changing from 5.83 ms to 2.16 ms in the range of 140–440 K. Besides, the temperature sensing relative sensitivity increases with the elevation of temperature and reaches the maximum value of 0.582% K−1 at 400 K. The obtained results could promote the performance of Cr3+ doped phosphors for the applications in phosphor-converted light-emitting diodes and temperature sensing. • The temperature-dependent luminescent characteristic of ZnGa 2 O 4 :Cr3+ phosphor was performed. • The red-shift of R1 and R2 lines were observed and Debye temperature of R1 lines was estimated to be 690 K. • The temperature sensing relative sensitivity reaches the maximum value of 0.582% K-1 at 400 K. [ABSTRACT FROM AUTHOR]

An optical thermometer Bi3+, Eu3+ co-doped Sr 3 La 2 Ge 3 O 12 (SLGO) phosphor with dual-emitting centers was synthesized in high-temperature condition. The X-ray diffraction patterns, SEM, EDS, luminescent properties and optical temperature sensing characteristics were exhaustive investigated. Under UV excitation, the SLGO: Bi3+ phosphor exhibits the 3P 1 →1S 0 blue luminescence of Bi3+ peaked at 400 nm and SLGO: Eu3+ phosphor shows the 5D 0 →7F 2 red luminescence of Eu3+ peaked at 612 nm. The ET behavior was proved by spectrum overlap between the PL spectrum of Bi3+ and PLE spectrum of Eu3+. Moreover, the decay time of Bi3+ could be verified the conclusion. Under UV excitation of 291 nm, the maximal value of absolute sensitivity (S a) of SLGO: Bi3+, Eu3+ was 0.079 %K−1 at 573 K, and relative sensitivity (S r) was 0.831 %K−1 at 473 K. The results proved that SLGO: Bi3+, Eu3+ phosphor could have a good performance in the field of optical thermometer. • The Sr 3 La 2 Ge 3 O 12 : Bi3+, Eu3+ phosphors can conquer the inherent defects of TCL-based phosphors. • The Sr 3 La 2 Ge 3 O 12 : Bi3+, Eu3+ phosphors have high temperature sensitivity and signal discriminability. • The ET behavior and temperature-dependent sensing properties of Bi3+ and Eu3+ are discussed. [ABSTRACT FROM AUTHOR]

Upconversion (UC) luminescence properties are of great significance in realizing good performances on practical display and sensing applications and that can be tuned by adjusting UC energy transfer (ET) processes. In this work, we devoted to gaining UC white emission and achieving high sensing sensitivity by manipulating ET processes in the Er3+/Tm3+/Yb3+ tri-doped double perovskite Gd 2 ZnTiO 6 (GZT) phosphors. Nearly standard UC white emission with the CIE coordinate of (0.333, 0.331) was obtained based on effective ET processes between Er3+, Tm3+ and Yb3+ in the GZT: 0.5%Er3+/3.5%Tm3+/15%Yb3+ sample. The maximum absolute sensitivity of 5.02 K-1 (473 K) of non-thermally coupled levels (I 635 − 685 ∕ I 500 − 540 ) and another the maximum absolute sensitivity of 84.6 × 10−4 K−1 (473 K) of thermally coupled levels (I 500 − 540 ∕ I 540 − 600 ) were gained. The two absolute sensitivities both are higher than that in Tm3+/Yb3+ and Er3+/Yb3+ co-doped double perovskite GZT phosphors, respectively. The enhancements of sensitivities are due to the effective ET processes between Er3+, Tm3+ and Yb3+. This work reveals not only certified UC processes for UC white emission but also a valid idea on the manipulation of UC processes towards high absolute sensitivity in phosphors. High sensitivity and standard white emission are gained based on complex energy transfer processes in the Er3+/Tm3+/Yb3+ tri-doped double perovskite Gd 2 ZnTiO 6 phosphors. Image 1 • An idea on the manipulation of energy transfer processes to enhance the absolute sensitivity was proposed. • An ultrahigh absolute sensitivity of 5.02 K−1 at 473 K of non-thermally coupled levels (I 635 − 685 ∕ I 500 − 540 ) was obtained. • A high absolute sensitivity of 84.6 × 10−4 K−1 at 473 K of thermally coupled levels (I 500 − 540 ∕ I 540 − 600 ) was gained. • Standard upconversion white emission with the CIE coordinate of (0.333, 0.331) was achieved. • Crucial energy transfer processes for color-tunable emissions were discussed and certified. [ABSTRACT FROM AUTHOR]