Thermometric Materials Research Articles

Energy-Transfer-Enhanced Cr3+/Ni2+ Co-doped Broadband Near-Infrared Phosphor for Fluorescence Thermometers and Near-Infrared Window Imaging.

Here, near-infrared broad dual-band emission phosphors were achieved through energy transfer between Cr3+ and Ni2+ ions in the β-Ga2O3 host. All samples co-doped with Cr3+ and Ni2+ exhibit dual-band emission covering 600-1700 nm under 430 nm excitation. Thanks to the doping of Cr3+ ions, the emission intensity of Ga2O3:Cr3+, Ni2+ phosphors has increased by about 2.4 times and the internal quantum efficiency has increased by 83.2% compared to Ga2O3:Ni2+ phosphors. Meanwhile, when the fluorescence lifetime was monitored at 745 nm, an efficient energy transfer between Cr3+ and Ni2+ ions in the β-Ga2O3 host was verified. Due to the significant differences in the emission temperature-sensitive properties of Cr3+ and Ni2+ ions, a thermometer was designed utilizing fluorescence intensity ratio technology, achieving a maximum relative sensitivity of 5.26% K-1, which surpasses most optical temperature measurement phosphors. This suggests that Ga2O3:Cr3+, Ni2+ samples hold promise as potential candidates for optical thermometer materials. Additionally, the broadband near-infrared emission of the Ga2O3:Cr3+, Ni2+ sample has been investigated for potential applications in component analysis and night vision, demonstrating its versatility for multifunctional applications.

Up/down-conversion luminescence and optical thermometry of Er3+-activated bismuth tellurium borate

Base on up/down-conversion luminescence with thermally coupled energy levels, Er3+-activated phosphors have been significantly promising in non-contact optical thermometry technology. In this study, a new bismuth tellurium borate-based phosphor was synthesized via replacing Bi3+ with Er3+. The structure, morphology, photoluminescence, and concentration quenching are elucidated thoroughly. Particularly, according to the temperature-dependent up/down-conversion luminescence behaviors of Er3+, the fluorescence intensity ratio (FIR, 2H11/2→4I15/2 /4S3/2→4I15/2) of thermally coupled energy levels is investigated. the maximum absolute/relative sensitivities of 0.38 % K−1/0.87 % K−1 (λex = 380 nm), 0.33 % K−1/1.01 % K−1 (λex = 453 nm), and 0.37 % K−1/1.19 % K−1 (λex = 980 nm) is determined. The findings indicate that the resulting phosphor is a promising optical thermometric material.

Promising lanthanide- NaYbF4:Er3+@NaYbF4:Tm3+ micro-phosphors for highly efficient upconversion luminescence and temperature sensing

In recent years, the fluorescence intensity ratio (FIR)-based technique for optical non-contact temperature measurement is of great interest to researchers due to its promising wide range of applications in high-voltage electricity fields, fires, corrosive environments, biological tissues, as well as other fields. Unfortunately, the FIR techniques based on thermally coupled energy levels (TCLs) often have the problem of low sensitivity as a result of the narrow energy gap. In contrast to FIR techniques with TCLs, the FIR technique with non-thermal coupled energy levels (NTCLs) is no longer restricted by the energy gap and is expected to achieve high signal resolution. In this study, we attempted to acquire a thermometric material that possesses high sensitivity as well as high signal resolution with the help of NTCLs. We successfully prepared NaYbF4:Er3+@NaYbF4:Tm3+ core-shell microcrystals by solvothermal technique using NaYbF4 as matrix and Er3+ and Tm3+ as luminescent centers and made necessary investigations on their crystal structures, microscopic morphologies, intrinsic mechanisms, and thermometric properties. The sample phosphors in a 980 nm laser show bright upconversion (UC) luminescence with emission peaks corresponding to the characteristic energy level jumps of Er3+ as well as Tm3+, respectively. The temperature sensing characteristic parameters have been investigated by FIR techniques with TCLs (2H11/2 → 4I15/2(Er3+)/4S3/2 → 4I15/2(Er3+)) & NTCLs (3H4→3H6(Tm3+)/1G4→3H6(Tm3+),3H4→3H6(Tm3+)/2H11/2 → 4I15/2(Er3+),3H4→3H6(Tm3+)/4S3/2 → 4I15/2(Er3+) and 3H4→3H6(Tm3+)/4F9/2 → 4I15/2(Er3+)), respectively. It is shown that the maximum absolute & relative sensitivities are 0.5677 K-1(495 K) as well as 1.20 % K−1(445 K) respectively with good thermal stability. In addition, the NTCLs have good separation of the emission bands, which enables the material to have excellent signal discrimination in temperature detection. These results indicate that the material is expected to be a potential candidate for optical thermometers.

Doping-mediated thermal control of phase transition for supersensitive ratiometric luminescence thermometry

Intelligent luminescent materials, characterized by optical switching in response to thermal stimulation, are highly attractive for cutting-edge temperature sensing technologies. However, the exploration of sensitive and reliable thermometric materials remains challenging. Herein, we establish a phase-transition-driven thermometric model that relies on the reversible transition between the monoclinic (β) and tetragonal (α) phase of LiYO2:Dy3+ crystals under controlled thermal stimulations. Accordingly, the ratiometric emissions from hypersensitive electric diploe transitions (4F9/2 → 6H13/2) drastically varied across the phase-transition temperature range, rendering remarkable thermal sensitivity and resolution (Sr-max = 35.24% K−1, δTmin = 0.009 K). We further demonstrate the extended control of phase-transition temperature and thermal hysteresis by a partial substitution approach. These findings highlight an endogenic approach to constructing customized luminescence thermometers via local crystal-field engineering, which raises new possibilities for practical sensing applications.

Novel Photoluminescence and Optical Thermometry of Solvothermally Derived Tetragonal ZrO2:Ti4+,Eu3+ Nanocrystals

In this paper, we report on the solvothermal preparation and detailed characterization of pristine and intentionally doped zirconium dioxide (ZrO2) nanocrystals (NCs, ~5 nm) with Eu3+ or Ti4+/Eu3+ ions using alkoxide precursors. The results indicated that the ZrO2 NCs were dominantly of a tetragonal phase (t-ZrO2) with a small proportion of monoclinic ZrO2 (m-ZrO2). The high purity of t-ZrO2 NCs could be synthesized with more Eu3+ doping. It was found that the as-obtained ZrO2 NCs contain some naturally present Ti4+ ions originating from precursors, but were being overlooked commonly, and some carbon impurities produced during synthesis. These species showed distinct photoluminescence (PL) properties. At least two types of Eu3+, located at low- and high-symmetry sites (probably sevenfold and eightfold oxygen coordination), respectively, were demonstrated to build into the lattice structure of t-ZrO2 NCs together. The cationic dopants were illustrated to be distributed non-randomly over the sites normally occupied by Zr, while Ti impurities preferentially occupied the sites near the low-symmetry site of Eu3+, yielding efficient energy transfer from the titanate groups to the neighboring Eu3+. Luminescence nanothermometry could measure temperature in a non-contact and remote way and could find great potentials in micro/nano-electronics, integrated photonics, and biomedicine. On the basis of the dual-emitting combination strategy involving the white broadband CT (Ti3+→O−) emissions of the titanate groups and red sharp Eu3+ emissions, t-ZrO2:Eu3+ nanophosphors were demonstrated to be ratiometric self-referencing optical thermometric materials, with a working range of 130–230 K and a maxima of relative sensitivity of ~1.9% K−1 at 230 K.

A novel ultrahigh-sensitive optical thermometer based on inverse thermal responses of Nd3+ and Yb3+ emissions in BaGd2(MoO4)4 phosphor

Nowadays, lots of efforts have been vested on the exploitation of novel luminescent thermometric materials to achieve remote temperature readout with ultra-high sensitivity and sub-degree resolution. Herein, the BaGd2(MoO4)4: Yb3+, Nd3+ phosphors were successfully prepared via a solid-state reaction method, and their concentration/temperature-dependent luminescence behaviors were investigated systematically. Upon 980 nm excitation, the photoluminescence (PL) spectra consisted of three emission bands centered at 754 nm, 805 nm and 872 nm from Nd3+, together with an emission band peaked at 1008 nm from Yb3+. As the temperature elevated, the Yb3+: 2F5/2 → 2F7/2 emission weakened sharply, whereas the promoted phonon-assisted energy transfer process from Yb3+ to Nd3+ and excited-state absorption process of Nd3+ led to an intense thermal enhancement of the Nd3+: 4Fj → 4I9/2 (j = 7/2, 5/2, 3/2) transitions. Moreover, the thermally enhancing factor was found to depend on the Nd3+ concentration. By utilizing the luminescence intensity ratio (LIR) technique, the temperature sensing behaviors based on thermally coupled levels (Nd3+: 4Fj, j = 7/2, 5/2, 3/2) and non-thermally coupled levels (Nd3+: 4Fj and Yb3+: 2F5/2) were studied at the different doping concentrations. When the temperature sensing was based on LIR between Nd3+: 4F3/2 → 2I9/2 and Yb3+: 2F5/2 → 2F7/2 transitions, the BaGd2(MoO4)4: 3 mol%Nd3+, 15 mol%Yb3+ sample displayed excellent thermal sensitivity (2.28–8.42 %K−1) and temperature resolution (0.1–0.22 K) at temperatures ranging from 298 K to 573 K, which were superior to those of many other reported luminescence materials. The present work might give a new input for developing near-infrared (NIR) luminescence materials with desirable temperature sensing performances.

A strategy for enhancing luminescence thermometry via Ta5+-triggered K0.5Na0.5NbO3: Er3+ transparent ceramics

Luminescence thermometry is a reliable approach for remote thermal sensing, and extensive studies have been devoted to designing a luminescence thermometer with heightened thermal sensitivity. Herein, we report a promising luminescence thermometric material, Ta5+-substituted K0.5Na0.5NbO3:0.003Er3+ transparent ferroelectric ceramics. The temperature sensing sensitivity is significantly improved by adjusting the concentration of Ta5+ in the material. Specifically, utilizing the fluorescence intensity ratio from the 2H11/2 and 4S3/2 thermally coupled states of Er3+ as a detecting signal within the temperature range of 273–543 K, an optimal maximum absolute sensitivity of 0.0058 K–1 and relative sensitivity of 0.0158 K–1 are achieved for K0.5Na0.5NbO3: 0.65Ta5+/0.003Er3+. Simultaneously, as the concentration of Ta5+ increase, a unique evolution of structural phase transitions is observed from orthorhombic to tetragonal and then to cubic. This is accompanied by an improvement in luminescence temperature sensing properties, and the best sensitivity is demonstrated in the cubic-phase region. Intriguingly, a huge change in infrared luminescence properties as a function of temperature is found around the structure transition temperature of the samples. These results indicate a promising potential for achieving highly sensitive thermometry or monitoring phase structure transitions through luminescence thermometry behavior in the K0.5Na0.5NbO3 host.

Spectroscopic and temperature sensing properties of Sm3+ in self-activated CsLu(WO4)2 phosphors

In this research, a series of Sm3+ doped CsLu(WO4)2 phosphors was prepared via high temperature solid phase technique to design new red phosphors and optical thermometric materials. Their structures, morphology, band gap and luminescence properties were characterized by X-ray diffraction, scanning electron microscopy, diffuse reflection and luminescence spectra, respectively. Under UV excitation, CsLu(WO4)2 gives rise to a blue broad emission band between 350 and 700 nm, which stems from the 3T1u → 1A1g transition of WO66− groups. When Sm3+ is introduced into CsLu(WO4)2, energy transfer between WO66− groups and Sm3+ ions takes place in CsLu(WO4)2:Sm3+ phosphors, and color-tunable luminescence from blue to red is realized by controlling the Sm3+ doping concentration. The energy transfer efficiency between WO66− groups and Sm3+ ions was analyzed, and the energy transfer mechanism was determined to be dipole–dipole interactions. According to the temperature-dependent luminescence spectra, WO66− groups and Sm3+ ions exhibit large discrepancy in thermal quenching rates, and thus the temperature sensing properties of CsLu(WO4)2:Sm3+ in the temperature range of 283–403 K were analyzed. Based on the framework of fluorescence intensity ratio theory, the basic optical thermometry parameters including absolute and relative sensitivity of CsLu(WO4)2:Sm3+ were calculated and the results show that it has great potential for application in optical thermometry.

Designing multi-mode optical thermometers via Sb3+/Er3+ co-doped Cs2NaInCl6 lead-free double perovskite microcrystals

Contactless optical thermometers are widely studied in scientific research and technology because of their apparent advantages. The combination of multi-mode thermometric techniques can realize self-referenced temperature sensing, making temperature monitoring signals more accurate. Herein, a series of Cs2NaInCl6: Sb3+, Er3+ microcrystals (MCs) were prepared via the ligand-assisted reprecipitation method. Under 320 nm excitation, the energy transfer from the self-trapped excitons (STEs) to Er3+ is established, which leads to the blue emission of STEs and intrinsic emissions of Er3+. Additionally, the MCs can also produce up-conversion green emissions under the excitation of NIR laser. Based on this, a multi-mode thermometer is developed, including the luminescence intensity ratio of two thermally coupled levels of Er3+ (2H11/2/4S3/2), the luminescence intensity ratio of a non-thermally coupled system of STEs and Er3+(4S3/2), and fluorescence lifetime of Er3+(4S3/2). Moreover, the MCs exhibit thermochromic properties, the luminescent color changes from blue to green as the temperature increases. To monitor the temperature more objectively by color variation, a novel sensing mode is constructed via the relationship between chromatic coordinates and temperature. The favorable thermometry performances for four-mode temperature sensing reveal that Cs2NaInCl6: Sb3+/Er3+ MCs are good candidates for thermometric materials for the novel multi-mode design.

Thermometric properties of Na 2Y 2TeB 2O 10:Tb 3+ green phosphor based on fluorescence/excitation intensity ratio

For noncontact optical thermometry, in contrast with fluorescence intensity ratio (FIR) technology, excitation intensity ratio (EIR) technology has been seriously limited due to low sensitivity. Moreover, by exploring all possible temperature-dependent response, developing multimode optical thermometry is of great importance. In this work, a new Na₂Y₂TeB₂O₁₀ (NYTB):Tb³⁺ phosphor is obtained by a solid-state reaction. Based on FIR and EIR models of Tb³⁺, thermometric properties are studied thoroughly. Excellent relative and absolute sensitivity (<i>S</i>_R and <i>S</i>_A) are acquired due to the significant difference in emission/excitation lines in response to temperature. Meanwhile, Tb³⁺ content-dependent luminescence quenching mechanism is discussed. This study shows a feasible route for exploiting well-performing FIR-/EIR-based thermometric materials.

ЧУТЛИВІ ЕЛЕМЕНТИ ПЕРЕТВОРЮВАЧІВ ТЕМПЕРАТУРИ НА ОСНОВІ ТЕРМОМЕТРИЧНОГО МАТЕРІАЛУ HfNi1-xCuxSn

ЧУТЛИВІ ЕЛЕМЕНТИ ПЕРЕТВОРЮВАЧІВ ТЕМПЕРАТУРИ НА ОСНОВІ ТЕРМОМЕТРИЧНОГО МАТЕРІАЛУ HfNi1-xCuxSn

Microstructure and Photoluminescence of ZrTiO4:Eu3+ Phosphors: Host-Sensitized Energy Transfer and Optical Thermometry

Orthorhombic ZrTiO4 is an attractive dielectric material; its optical properties are, however, less known. In this paper, we reported on the microstructure and luminescence studies of pristine ZrTiO4 and Eu3+-doped ZrTiO4 phosphors. The results indicated that two types of TiO6 octahedra, the isolated/ localized and coupled/delocalized, coexisted in host matrix. Eu3+ doping could induce oxygen vacancy defect states located below the bottom of the conduction band. Pristine ZrTiO4 showed bright yellow luminescence via STEs recombination at defects sites at low temperatures, but significant thermal quenching occurred due to STEs migration to quenching centers at elevated temperatures. Effective host sensitized energy transfer to Eu3+ was observed in ZrTiO4:Eu3+ phosphors and yielded the red characteristic emissions of Eu3+. Anomalous STEs luminescence enhancement and spectral blue-shift in the excitation spectra with higher Eu3 + concentration appeared and were explained by considering three factors: competitive absorption between electron transitions from the top of the valence band to the defect states and host conduction band, Eu3+ doping driving the production of more isolated TiO6 octahedra, and energy back-transfer from Eu3+ activators to other titanate groups. On the basis of the dual-emitting combination strategy involving host STEs and Eu3+ luminescence, ZrTiO4:Eu3+ phosphors were demonstrated to be ratiometric self-referencing optical thermometric materials, with a working range of 153–313 K and a maxima of relative sensitivity to ~1.1% K−1 at 243 K.

Fluorescence Lifetime-Based Luminescent Thermometry Material with Lifetime Varying over a Factor of 50.

Recently, the growing demand for temperature detection is pushing forward the flourishing development of noncontact optical thermometry. Herein, a new red phosphor Sr2InTa1-xO6:xMn4+ (SIT:xMn4+) was first constructed and systematically investigated. Based on the fairly rapid decline of the lifetime from 0.403 to 0.008 ms by increasing the temperature from 25 to 450 K, a noncontact optical thermometer can be made from phosphor SIT:0.003Mn4+ with Sr = 1.396% K-1 at 375 K and Sa = 0.0012 K-1 at 300 K. Because the luminescence is based on the outermost 3d orbits of Mn4+, the lifetime of SIT:xMn4+ is quite sensitive to the temperature, leading to a rapid decline of the lifetime with the increase in temperature. Moreover, multiple rounds of variable-temperature studies were performed to demonstrate the stability and reversibility of SIT:0.003Mn4+. This work suggests that Mn4+-phosphors are promising candidates for application as optical thermometric material.

Multipath luminescent thermometry inCs3GdGe3O9:Yb3+, Er3+ phosphor

Nowadays, luminescent thermometry appeals the eyes of researchers more and more on account of the unique merits including non-invasive, fast response and relatively high sensitivity. However, most of reported up-conversion optical thermometric materials based on fluorescence intensity ratio (FIR) from thermal couple energy levels (TCELs) usually suffer from the overlap of two luminescence signals, leading to the deviation of the temperature readout. Herein, Cs3GdGe3O9:Yb3+,Er3+ phosphors were successfully synthesized. Multiple sharp peaks from green and red luminescence of Er3+ are observed. The emission signals even from the TCELs are well separated, enabling the accuracy of temperature detection to some extent. With the aid of the different thermo-responses of luminescence centered at 534, 559, 660 nm and their splitting peaks of Er3+, multi-mode optical thermometric techniques based on fluorescence decay time (4S3/2), FIR from TCELs, non-TCELs and their sub-energy levels in Cs3GdGe3O9:Yb3+,Er3+ upon single-beam light stimulation were designed. The resultant sample reveals excellent signal discernibility, eminent relative sensitivities, outstanding reversibility and glorious thermal resolution. Such results infer that Cs3GdGe3O9:Yb3+,Er3+ phosphors have the promising prospect in temperature monitoring fields.

Designing Color-tunable luminescent thermometers and information encryption based on Pr3+ or Sm3+ doped SrNb2O6: Tb3+ phosphors via energy transfer

Color-tunable luminescence intensity ratio thermometers and information encryption are firstly designed through different energy transfer mechanism. Herein, two types thermometric materials, SrNb2O6: Tb3+, Pr3+ and SrNb2O6: Tb3+, Sm3+ are prepared. The Tb3+ and Pr3+ typical emissions show luminescence mechanism between two intervalence charge transfer states. Whereas, Tb3+ and Sm3+ emissions are related to energy migration from intervalence charge transfer state to 4f level. Interestingly, (5D4→7F5)Tb3+/(1D2→3H4)Pr3+ or (5D4→7F5)Tb3+/(4G5/2→6H7/2)Sm3+ have different temperature sensing properties due to distinct energy transfer processes and provide visualization of temperature measurement. The former gains high sensitivity (Sa = 0.012 K−1) at high temperature region, and the latter reach as high as Sa = 0.028 K−1 at low temperature. Besides, using multi-mode color emission of Tb3+ or Pr3+ doped SrNb2O6 achieves information hiding. This work not only shows new strategy to develop high-efficiency luminescent thermometers but also develop flexible optical encryption technology.

Charge Transfer-Triggered Bi3+Near-Infrared Emission in Y2Ti2O7for Dual-Mode Temperature Sensing

Trivalent bismuth is a popular main group ion showing versatile luminescent behaviors in a broad spectral range from ultraviolet to visible, but barely in the near-infrared (NIR) region. In this study, we have observed unexpected NIR emission at ∼744 nm in a Bi3+-doped pyrochlore, Y2Ti2O7 (YTOB). Our first-principles electronic structure calculation and analysis of the Bi local structure via extended X-ray absorption fine structure indicate that only Bi3+ species appears in YTOB and it has a similar local environment to that of Y3+. The NIR emission is assigned to a Ti4+ → Bi3+ metal-to-metal charge transfer process. Moreover, we have demonstrated dual-mode luminescence thermometry based on the luminescence intensity ratio (LIR) and lifetime (τ) in 0.5% Bi3+ and 0.5% Pr3+ co-doped Y2Ti2O7 (YTOB0.5P0.5). It exhibits high thermometric sensitivity simultaneously in the cryogenic temperature range from 78 to 298 K based on τ of the NIR emission of Bi3+ at 748 nm and in the temperature range of 278-378 K based on the LIR of Bi3+ to Pr3+ emissions (I748/I615). As a novel LIR-τ dual-mode thermometric material over a wide temperature range, the maximum relative sensitivities of the YTOB0.5P0.5 reach 3.53% K-1 at 298 K from the τ mode and 3.52% K-1 at 318 K based on the LIR mode. The dual-mode luminescence thermometry with high responsivity from our Bi3+-based pyrochlore Y2Ti2O7 phosphor opens a new avenue for more luminescent materials toward multi-mode thermometry applied in complex temperature-sensing conditions.

La2Zr2O7:Pr3+ nanoparticles for luminescence thermometry based on a single parameter over a wide temperature range of 620 K

Luminescence thermometry based on the variation of the fluorescence intensity ratio (FIR) of rare-earth materials has become fascinating owing to their applicability in chemically and electromagnetically harsh environments. Relevant to their practical applicability, a wide temperature sensing range is urgently required for luminescent thermometric materials besides possessing a high relative sensitivity. Herein, we have demonstrated that pyrochlore La 2 Zr 2 O 7 :Pr 3+ (LZOP) nanoparticles (NPs) can serve as a promising optical temperature sensing material over a wide temperature range of 620 K. Specifically, we have taken advantage of the intervalence charge transfer state (IVCT) of Pr 3+ doping ion for luminescence temperature sensing and confirmed excellent optical thermometric performance from the LZOP NPs in a temperature sensing range of 85–705 K. The thermal sensing here could be measured by exploiting one thermometric parameter, i.e. the FIR between 1 D 2 → 3 H 4 and 3 P 0 → 3 H 4 transitions of Pr 3+ , and thus we only need to use one calibration formula for the whole temperature range. A maximum relative sensitivity of> 0.4%·K −1 from 165 to 205 K and a low temperature uncertainty of 1.21 K at 185 K is obtained. Based on the proposed configurational coordinate diagrams, A high-lying IVCT state was demonstrated to be the cause for slow thermal quenching at high temperatures, which broadened the working range of our thermometric sensing materials. This work provides a useful inspiration for exploring appropriate host materials with slow thermal-quenching channels to develop optical thermometric materials over a wide temperature sensing range. • Synthesized La 2 Zr 2 O 7 :0.1%Pr 3+ (LZOP) NPs by a low temperature molten salt method. • Demonstrated an excitation band at ~256 nm from the 4f-5d and IVCT transitions. • Confirmed their wide range thermal sensing potential using a single parameter.

(Digital Presentation) La2Zr2O7:Pr3+ Nanoparticles for Luminescence Thermometry Based on a Single Parameter

Luminescence thermometry based on the variation of the fluorescence intensity ratio (FIR) of rare-earth materials has become fascinating owing to their applicability in chemically and electromagnetically harsh environments. Relevant to their practical applicability, a wide temperature sensing range is urgently required for luminescent thermometric materials besides possessing a high relative sensitivity. Herein, we have demonstrated that pyrochlore La2Zr2O7:Pr3+ (LZOP) nanoparticles (NPs) can serve as a promising optical temperature sensing material over a wide temperature range of 620 K. Specifically, we have taken advantage of the intervalence charge transfer state (IVCT) of Pr3+ doping ion for luminescence temperature sensing and confirmed excellent optical thermometric performance from the LZOP NPs in a temperature sensing range of 85-705 K. The thermal sensing here could be measured by exploiting one thermometric parameter, i.e. the FIR between 1D2 → 3H4 and 3P0 → 3H4 transitions of Pr3+, and thus we only need to use one calibration formula for the whole temperature range. A maximum relative sensitivity of > 0.4%·K−1 from 165 to 205 K and a low temperature uncertainty of 1.21 K at 185 K is obtained. Based on the proposed configurational coordinate diagrams, a high-lying IVCT state was demonstrated to be the cause for slow thermal quenching at high temperatures, which broadened the working range of our thermometric sensing materials. This work provides a useful inspiration for exploring appropriate host materials with slow thermal-quenching channels to develop optical thermometric materials over a wide temperature sensing range. Figure 1

Novel optical temperature sensors based on the emission of the Pr3+ ions doped Ca3(M,Ga)5O12 (M5+ = Nb, Ta) garnet phosphors

Pr3+-doped Ca3(Nb,Ga)5O12 (Pr:CNGG) and Ca3(Ta,Ga)5O12 (Pr:CTGG) phosphors with garnet structure have been systematically investigated as optical thermometric materials for potential applications in the field of sensing technology, for the first time to our knowledge. The ceramic samples of Pr:CNGG and Pr:CTGG with different concentrations of Pr3+ ions have been obtained by the solid-state reaction method. A comparative analysis to evidence the influence of the position of the inter-valence charge transfer (IVCT) states on the excited-state dynamics of Pr3+ ions in CNGG and CTGG materials is presented. The optical thermometric properties of the Pr:CNGG and Pr:CTGG samples were studied. The luminescence thermal quenching mechanisms of the 3P0 and 1D2 levels were investigated in detail based on the luminescence intensity ratio (LIR) of 1D2→3H4 / 3P0→3H4 (I606/I487) transitions over an extended temperature range (10–700 K). The maximum relative sensitivities were determined to be 1.64% K−1 at 10 K for 7 at% Pr:CTGG and 2.4% K−1 at 430 K for 1 at% Pr:CNGG, thus proving their potential as high-sensitivity temperature sensors in cryogenic and high-temperature domains, respectively.

Yb/Er: Cs2Ag(In/Bi)Cl6 lead-free double perovskite for dual-modal optical temperature sensing

Exploring new optical thermometric materials is important to realize highly accurate temperature detecting. Herein, Yb/Er activators are successfully doped into Cs2Ag(In/Bi)Cl6 lead-free double perovskite (DP) semiconductor, providing dual-modal photoluminescence originated from self-trapped exciton recombination and 4f-4f transitions of Yb/Er dopants as well as Er3+ upconversion emissions. Remarkably different temperature-dependent emissive behaviors from DP host and Yb/Er activators are experimentally demonstrated, which enables to design novel fluorescence intensity ratio (FIR) between DP and Yb/Er based thermometric technology. In addition, upconversion FIR-based temperature sensing via thermal population between the 2H11/2 level and 4S3/2 one of Er3+ dopants in DP host is also realized. It is believed that the present Yb/Er: Cs2Ag(In/Bi)Cl6 DP with excellent long-term stability and dual-functional temperature detecting is a suitable candidate as the self-calibrated optical thermometric material.