Maximum Relative Sensitivity Research Articles

Optical temperature sensing properties of novel RE3+ (RE=Er, Ho) doped BaLa2Ti3O10 phosphors

A novel luminescent material of BaLa2Ti3O10:RE3+ was synthesized by the high-temperature solid phase method, with a typical layered structure belonging to a special crystal system. Under the excitation of 980 nm, BaLa2Ti3O10:4%Er3+ exhibits characteristic emissions centered at 531 nm, 551 nm and 668 nm. It is noteworthy that the color of BaLa2Ti3O10:3%Ho3+ shows a strong green emission at 551 nm and a weak red emission near 664 nm, also represents adjustable yellow-green light with the change of 980nm laser pumped powers. The optical temperature sensing properties were checked by employing different strategies, relating to the thermally-coupled-levels (TCLs) and nonthermally-coupled-levels (NTCLs). The results show that the maximum relative sensitivity of TCLs based on BaLa2Ti3O10:Er3+ is 0.68% K-1(305 K). Similarly, the maximum sensitivity of TCLs is 0.89% K-1(313 K) in BaLa2Ti3O10:Ho3+, which performs well from 313 K to 513 K. It has been found the samples using FIRs of TCLs can produce higher absolute (Sa) and relative (Sr) sensitivities compared with those using Fluorescence Intensity Ratios (FIRs) of NTCLs. The multiple FIRs also achieved superior levels of temperature resolution and repeatability in all cases. Generally, this work provides favorable candidates for the temperature sensors.

Prominent cryogenic fluorescence temperature sensing and superior room-temperature photochromism in Bi/Eu codoped KNN transparent-ferroelectric ceramics

The growing demand for the miniaturization and multifunctionality of optoelectronic devices has promoted the development of transparent ferroelectrics. However, it is difficult for the superior multiple optical properties of these materials to be compatible with the excellent ferroelectricity and piezoelectricity in transparent ceramics. Here, we successfully synthesized Bi/Eu codoped eco-friendly K0.5Na0.5NbO3 transparent-ferroelectric ceramics with photoluminescence (PL) behavior, photochromic (PC) reactions and temperature-responsive PL. Based on the distinct optical properties of ceramics at different temperature ranges (room temperature and ultralow temperature), high utilization of multiple optical functions was realized. At room temperature, the PC behavior induced PL modulation contrast reaches 75.2% (at 592 nm), which can be applied in the optical information storage field. In the ultralow temperature range, the ceramics exhibit excellent sensitivity (with a maximum relative sensitivity of 26.32%/K) via fluorescence intensity ratio technology and exhibit great application potential in noncontact optical temperature measurements. Additionally, the change in the PL intensity at different wavelengths (I614/I592) can serve as a reliable indicator for detecting the occurrence of the phase transition from rhombohedral to orthorhombic at low temperature. This work provides a feasible paradigm for realizing the integration of ferroelectricity and multifarious optical properties in a single optoelectronic material.

Pyrazine Dicarboxylic Acid and Phosphite-Bridging Lanthanide-Incorporated Tellurotungstates and Their Fluorescence Performances.

Two pyrazine dicarboxylic acid and phosphite-bridging lanthanide-incorporated tellurotungstates [H2N(CH3)2]12 Na4[Ln4(H2O)2(H2PDBA)2(HPO3)2W6O10][B-α-TeW8O31]4 · 70H2O [Ln = Eu3+ (1), Tb3+ (2); H2PDBA = 2,5-pyrazine dicarboxylic acid) were prepared, which contain four [B-α-TeW8O31]10- subunits and a deca-nuclear heterometallic [Ln(H2O)2(HPO3)2 (H2PDBA)2(W3O5)2]24+ cluster. Strikingly, two H2PDBA ligands connect two equivalent {W3Eu2O5(H2O)(B-α-TeW8O31)2(HPIIIO3)}8- moieties to form the polyanion skeleton, while the phosphite plays a bridging role in joining two lanthanide centers in the {W3Eu2O5(H2O)(B-α-TeW8O31)2(HPIIIO3)}8- moiety. In addition to the fluorescence (FL) properties of 1 and 2 at room temperature, their temperature-dependent FL properties were also investigated. In 80-298 K, FL intensities of 1 and 2 decrease as temperature increases, and their maximum relative sensitivities (Sr) are 3.70 and 1.99% K-1, whereas the minimum temperature uncertainties (δT) are 1.25 and 1.18 K for 1 and 2. In 298-973 K, upon increasing temperature, FL intensities of 1 and 2 initially rise to their maxima at 373 K and subsequently decrease. This is because samples of 1 and 2 undergo dehydration together with amorphization below 473 K and decomposition above this temperature. This work lays a foundation for the development for luminescent thermometers based on lanthanide-incorporated polyoxometalates.

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.

Dy3+-doped niobate phosphor based on charge transfer band red-shift effect: Luminescence thermal stability and temperature sensing performance

The thermal quenching behavior seriously limits the application prospect of phosphors, so it is urgent to improve the thermal quenching behavior of phosphors. It is expected that the red-shift of charge transfer band (CTB) caused by temperature can be used to improve the luminescent stability of phosphor. Therefore, we designed a family of LuNbO4:x%Dy3 (x = 0.25, 1, 2, 5) phosphors based on the characteristic of the red-shift of CTB edge, and investigated the relationship between the red-shift of the CTB edge and the luminescence thermal stability of the phosphor, further broadening the application of this phosphor in temperature sensing. The effects of three different excitation positions, CTB (260 nm), CTB edge red-shift (288 nm) and Dy3+ 4f-4f transition (354 nm), on the luminescence thermal stability of phosphors were also investigated. It was found that only excitation in the red-shift range of CTB edge showed complete antithermal quenching behavior. The LuNbO4:2 %Dy3+ phosphor showed complete antithermal quenching under the excitation of CTB edge, and the comprehensive emission intensity at 573 K is 741 % of that at 298 K. According to the above characteristics, a dual-mode optical thermometry based on fluorescence intensity ratio (FIR) and International Commission on Illumination (CIE) chromaticity coordinates is proposed, in which the maximum relative temperature sensitivity of LuNbO4:x%Dy3+ is 5.04 % K−1 (298 K, FIR) and 3.14 % K−1 (573 K, CIE). Interestingly, when constructing CIE temperature measurement model, we found that LuNbO4:0.25 %Dy3+ phosphor at 260 nm excitation position has obvious color change at each temperature stage, showing temperature visualization characteristics. At 354 nm excitation position, it shows constant white light emission. The excellent optical temperature measurement performance and temperature visualization characteristics of the phosphor shows that it has excellent application potential in optical sensing.

Ultrasensitive and Adjustable Nanothermometers Based on Er3+-Sensitized Core@Shell Nanoparticles for Use in the First Biological Window.

In recent years, intensive research has focused on lanthanide-doped nanoparticles (NPs) used as noncontact temperature sensors, particularly in nanomedicine. These NPs must be capable of excitation and emission within biological windows, where biological materials usually show better transparency for radiation. In this article, we propose that NPs sensitized with Er3+ ions can be applied as temperature sensors in biological materials. We synthesized the NPs through a reaction in high-boiling solvents and confirmed their crystal structure and the formation of core@shell NPs by using X-ray diffraction, high-resolution transmission electron microscopy, and element distribution mapping within the NPs. NaErF4@NaYF4, NaYF4:12.5% Er3+, 2.5% Tm3+@NaYF4, NaYF4:7.5% Er3+@NaYF4, and NaYF4:12.5% Er3+, 2.5% Ho3+@NaYF4 exhibited intense upconversion (UC) emission under 1532 nm laser excitation detectable also in the whole human blood. We propose that this UC results from energy transfer between Er3+ ions and from Er3+ to Tm3+ or Ho3+ codopants. To determine the mechanism of UC, we measured the dependence of the emission band intensities on the laser power densities. Importantly, we also analyzed the temperature-dependent emission of the NPs within the 295-360 K range. Based on the collected emission spectra, we calculated the luminescence intensity ratios (LIRs) of the emission bands to assess their potential for optical temperature sensing. The temperature-sensing properties varied with the concentration of Er3+ ions and the presence of additional Tm3+ or Ho3+ codopants. Depending on the NP composition and the emission bands used for luminescence ratio calculations, the maximum relative temperature sensitivity ranged from 4.55%·K-1 to 1.12%·K-1, with temperature resolution between 0.05 and 2.53 K at room temperature. Finally, as proof of using NPs as temperature sensors in biomedicine, we successfully measured the temperature-dependent emission of NaYF4:7.5% Er3+@NaYF4 NPs dispersed in whole blood under 1532 nm excitation. We demonstrated that the ratio of Er3+ ion emission bands changes with temperature, indicating that these NPs have potential applications in temperature sensing within biological environments. We also confirmed the properties of NPs as temperature sensors by measuring the temperature reading uncertainty and the repeatability of the LIR readings during heating-cooling cycles, thereby confirming the excellent properties of the studied systems as temperature sensors.

Ratiometric temperature sensing with non-thermally coupled levels from Pr–Al co-doped MgGa2O4

Fluorescence intensity ratio (FIR) technique demonstrates significant potential for non-contact temperature sensing with rapid response time, while the design of FIR probes is particularly intriguing. Herein, we report Pr–Al co-doped MgGa2O4 persistent luminescence nanoparticles (PLNPs), as MgAl0.04Ga1.96O4: 0.1 % Pr3+ (MAGP), for ratiometric temperature sensing application. Pr3+ ions function as the emission centers for dual-emission at 612 and 494 nm, while Al3+ ions adjust the lattice environment around Pr3+ ions to enhance the luminescence. Consequently, 274 nm excitation induces the emissions at 494 and 612 nm, as the transitions of Pr3+ for 3P0→3H4 and 1D2→3H4, respectively. The emission mechanism is substantiated by density functional theory calculations, regarding the electronic transitions of Pr3+. Ratiometric temperature sensing is achieved over the temperature range of 303–573 K with the thermally non-coupled mechanism of the 3P0/1D2 energy levels by FIR at 612 and 494 nm, respectively. The maximum relative sensitivity was 0.91 %. The mechanism is corroborated as the non-thermally coupled energy levels through intervalence charge transfer. Thus, the reversible and sensitive response was illustrated for temperature measurement and the non-thermally coupled mechanism is efficient for the design of ratiometric temperature sensors.

Upconversion luminescence and thermosensitive properties of NaGd(PO3)4:Yb3+/Er3+

High-sensitivity optical temperature measurement has attracted extensive attention in both fundamental studies and practical applications. In this study, a series of upconversion (UC) luminescence phosphors composed of NaGd(PO3)4 (NGP) doped with 20 at% Yb3+ and various concentrations of Er3+ (0.5 at% as the optimal concentration) was synthesized by high-temperature solid-state method. And their crystal structure and the distribution of lanthanide dopants were analyzed using X-ray diffraction with Rietveld refinement verifies. Under 980 nm laser excitation, the obtained phosphors show the characteristic Er3+ upconversion green and red emission bands through two-photon processes. The fluorescence intensity ratio (FIR) based on the thermal coupled states demonstrates the thermal sensing ability in a wide temperature range of 200–573 K. The thermal sensitivity is relatively high with the maximum absolute thermal sensitivity Sa of 0.53 % K−1 (523 K) and the maximum relative thermal sensitivity Sr of 2.60 % K−1. The phosphor NGP:Yb/Er also exhibits high repeatability as the thermal sensors reach 97 %. These findings postulate the potential of NGP:Yb/Er as a promising candidate in optical thermal sensing applications.

Optimizing the thermal stability of Tb3+-based phosphor through intervalence charge transfer compensation and charge transfer band edge red-shift

Thermal quenching (TQ) limits the large-scale practical application of most luminescent materials, so the investigation on thermal quenching phenomenon of phosphors has emerged as a prominent research area, garnering significant attention in academic circles. The thermal quenching performance is closely related to the charge transfer band (CTB) and intervalence charge transfer (IVCT) band. Herein, we study the correlation between CTB edge red-shift, IVCT band position and the thermal stability of Tb3+-based lithium tantalate phosphors, aiming to regulate the thermal quenching performance. The results show that totally anomalous thermal quenching (TATQ) was found to exist in LiTaO3:xTb3+ phosphors during the process of temperature rising, and the whole CTB edge absorption showed a red-shift and enhance with increasing temperature. Based on this characteristic phenomenon, under the excitation of CTB edge (270 nm), the phosphor exhibits obvious antithermal quenching. In addition, the existence of the Tb3+-Ta5+ IVCT band can be used as a compensation channel for Tb3+ 5D3 → 5D4 transition, which makes the phosphor produce stronger antithermal quenching performance. Accordingly, the co-regulation of the CTB edge red-shift and IVCT compensation effect was proposed. Modulation of Tb3+ concentration revealed that during thermal activation (λem = 547 nm), LiTaO3:0.005Tb3+ luminescence integral intensity (423 K) reaches 255.6% of the initial intensity, phosphor achieves the most excellent performance. The maximum absolute sensitivity (Sa) and relative sensitivity (Sr) for temperature sensing scheme based on the intensity ratio of excitation spectrum CTB and CTB-IVCT reaches 0.996%@523 K and 0.927%@523 K, respectively. The co-regulation strategy of thermal activation-induced CTB edge red-shift and IVCT compensation channel provides a promising research idea for developing Tb3+-based antithermal quenching luminescent materials.

A “turn-on” polymer nanothermometer based on aggregation induced emission for intracellular temperature sensing

Temperature measurements at the nanoscale facilitate the understanding of physiological processes related to heat in cells. Herein, we prepare a tetraphenylethylene-functionalized fluorophore (TPPEBr) with dual characteristics of twisted intramolecular charge transfer (TICT) and aggregation induced emission (AIE). It is polymerized with a thermo-responsive unit NIPAM to construct a fluorescent polymer nanothermometer (PNIPAM-TPPEBr). The phase transition behavior of PNIPAM from dispersed chains to dense spheres in aqueous media promotes the aggregation of TPPEBr fluorophores, which makes the fluorescence of PNIPAM-TPPEBr enhance with increasing temperature. Furthermore, the phase transition of PNIPAM is accompanied by a significant decrease in the polarity of the microenvironment, resulting in a blue shift in the emission wavelength of TPPEBr. Varying the ratio of NIPAM and TPPEBr can regulate the thermo-responsiveness of PNIPAM-TPPEBr in the physiological temperature range (31–38 °C), and the maximum relative thermal sensitivity reaches 13.2 % °C−1. The thermo-responsive performance of this nanothermometer is independent of the intracellular microenvironment, and it is successfully applied in the temperature imaging of A549 cells. Under the stimulation of ionomycin and oxidative phosphorylation inhibitor, the cell temperature increased by ca. 1.5 °C and ca. 1.0 °C, respectively.

Double perovskite CaSrMSbO6(M = La, Gd, Y): Bi3+ phosphors for multifunctional application

Bi3+-doping luminescent materials have recently evoked considerable interest in versatile applications. In this work, we have developed a series of Bi3+-activated CaSrMSbO6(M = La, Gd, Y) phosphors with double perovskite structures, exhibiting blue emission from 350 nm to 500 nm. The emission spectral position and intensity of Bi3+ ions can be tuned by changing excitation wavelength and doping concentrations. The relationship between the local crystal field environment and the luminescence properties is comprehensively analyzed. Importantly, optical temperature properties of CaSrLaSbO6: Bi3+ were investigated and were found to reach a maximum relative sensitivity of 4.57 % K−1 at 298 K. Furthermore, the anti-counterfeiting ink was prepared using CaSrLaSbO6: Bi3+ phosphors, and it showed tunable emission under different light stimulation. These results indicate that CaSrLaSbO6: Bi3+ phosphors have application potential in optical temperature sensing and anti-counterfeiting.

Structural analysis, fluorescence characteristics, and thermal radiation phenomena of Y2O3:Al3+/Er3+ materials doped with varying concentrations of Al3+ ions

In this study, Y2O3: Al3+/Er3+ crystals materials (AYE) were synthesized through laser annealing. The structure and spectral characteristics of Al3+ ions doping in Y2O3: Er3+ crystals are discussed in detail. With the incorporation of Al3+ ions, the AYE structure experiences a phase transformation characterized by a sequence of monophasic and biphasic states: monophasis-biphase-biphase-monophasis-biphase. When the concentration of Al3+ ions is 0–50 %, AYE has fluorescence characteristics under 980 nm excitation, and its I563 nm/I799 nm shows non-thermal coupling phenomenon at low temperature and thermal coupling phenomenon at high temperature, with a maximum relative sensitivity of 1.643 %K−1. When the concentration of Al3+ ion is 60 %-98 %, AYE shows a strong thermal radiation phenomenon under the excitation of a 980 nm laser. Its initial laser power density is as low as 0.71 W/mm2. This is about three times lower than the initial power density of thermal radiation generated by the same level of material. In summary, Y2O3: Al3+/Er3+ crystals materials have a broad application prospect in the field of temperature sensing and thermal radiation materials.

Luminescence properties of Sr2Ga2GeO7:Bi3+ phosphors and temperature sensing characteristics of co-doped Sm3.

As one of the fundamental physical quantities, temperature is extremely important in various fields. In order to study the temperature sensing characteristics of dual-emitting center phosphors, Bi3+-doped and Bi3+/Sm3+-doped Sr2Ga2GeO7 phosphors were synthesized by high-temperature solid-phase method. Under 312 nm excitation, the Sr2Ga2GeO7:Bi3+ phosphor exhibits a blue broadband emission corresponding to the 3P1 → 1S0 transition of Bi3+ ions. By testing the temperature change spectrum of phosphors, it was found that Bi3+ exhibited strong thermal sensitivity. However, due to the fact that single ion doped phosphors are easily affected by other factors when applied to the field of temperature sensing, based on the thermal sensitivity of Bi3+, Sm3+ with low temperature sensitivity was selected as the co-doped ion, and it was found that the two ions had different thermal quenching characteristics when the temperature change spectrum was tested. Using the temperature detection method based on the fluorescence intensity ratio (FIR) of the dual emission centers, it was found that the best absolute sensitivity Sa was 3.125% K-1 and the maximum relative sensitivity Sr was 1.275% K-1 in the range of 303-423 K. These results show that Sr2Ga2GeO7:Bi3+/Sm3+ phosphors have broad application prospects in the field of optical temperature sensing.

Unraveling the photophysical response of BaLaLiTeO6:Dy3+ double perovskites with excellent thermal stability for colour tunable LEDs and optical thermometry

The quest for reliable phosphors has accelerated amidst a growing demand for cost-effective, high-performance multifunctional phosphors. Incorporating thermometric application into double perovskite phosphors can enhance their multifaceted features for diverse applications. The present work endeavours to develop a series of BaLaLiTeO6:Dy3+ double perovskites via a solid-state reaction route, stressing their application in next-generation colour-tunable LEDs and non-contact luminescence thermometry. X-ray diffraction, Raman and FTIR spectroscopy analysis were done to make inferences about the structural modifications induced by the substitution of Dy3+ at the La3+ site of BaLaLiTeO6. An extensive investigation of optical characteristics was carried out by diffuse reflectance spectroscopy, photoluminescence spectroscopy and decay curve analysis. Prominent photometric parameters were also evaluated to assess the commercial feasibility of the developed phosphors in photonic applications. Judd-Ofelt parameters were estimated from the photoluminescence excitation spectra of BaLaLiTeO6:Dy3+ for the first time. Furthermore, the values of radiative parameters, fluorescence decay time and quantum efficiency suggested the suitability of the developed phosphor as a competent material. A comprehensive analysis of BaLaLiTeO6:Dy3+ as a thermographic phosphor was done by temperature-dependent photoluminescence spectroscopy. The potential use of this material in luminescence temperature sensing was probed by estimating the thermometric figures of merit based on the fluorescence intensity ratio (FIR). An absolute sensitivity of 22.17 × 10−4 K−1 was achieved at a temperature of 500 K and a remarkable maximum relative sensitivity of 2.34 %K−1 was attained at 250 K, which is much higher than other Dy3+ substituted thermographic phosphors. All these culminated features of BaLaLiTeO6:Dy3+ phosphor proved their prospective applications in thermally stable colour-tunable LEDs, wLEDs and as non-contact optical temperature sensors.

Enhancing upconversion luminescence intensity of BiTa7O19:Er3+/Yb3+/Mo4+ by doping Sc3+ or Sb

AbstractBased on the previous optimal concentration of Er3+/Yb3+/Mo4+ co‐doped BiTa7O19 (BTO) samples, Sc3+ or Sb is planned to be doped into BTO:Er3+/Yb3+/Mo4+ for further improving the upconversion luminescence (UCL) intensity under 980‐nm laser excitation. A series of BTO:Er3+/Yb3+/Mo4+/Sc3+ and BTO:Er3+/Yb3+/Mo4+/Sb samples are prepared by high‐temperature solid‐phase sintering method. The microstructure and UCL properties are investigated by X‐ray diffraction, Raman, X‐ray photoelectron spectroscopy (XPS), diffuse reflection, and luminescence spectrum. The green UCL intensity of BTO:Er3+/Yb3+/Mo4+/Sb is little better than that of BTO:Er3+/Yb3+/Mo4+/Sc3+, which reaches 2.40 times than that of β‐NaYF4:Er3+/Yb3+. XPS results show that Sc is 3+, Mo is 4+, and Sb is 3+ and 5+. Raman spectra show that BTO:Er3+/Yb3+/Mo4+/Sb has lower phonon energy and more disorder than BTO:Er3+/Yb3+/Mo4+/Sc3+. The maximum relative temperature sensitivity is got as 0.01012 K−1 at 303 K based on luminescence intensity ratio technology. BTO:Er3+/Yb3+/Mo4+/Sb has outstanding pure green UCL intensity, which can be applied to luminescence display and temperature sensing.

Fiber temperature sensor based on dual-wavelength emitting Mg0.388Al2.408O4: Mn2+/Mn4+ phosphors for real-time temperature monitoring

Single doped Mg0.388Al2O3.408O4 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 Mg0.388Al2O3.408O4 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 (Sr) 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 Mg0.388Al2.408O4: 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.

Mn2+ doped Zn2SiO4 phosphors: A threefold-mode sensing approach for optical thermometry in the visible region at 525 nm

Optical functional materials such as nanostructured silicates have been studied for photonics applications involving energy conversion. In this scenario, we studied Zn2SiO4:Mn2+ nanostructured powders prepared by combustion synthesis for optical thermometry based on photon downshifting. The structural analysis showed that Zn2SiO4 particles were found embedded in clustered silica nanoparticles. The photoluminescence analysis showed that the samples exhibit intense green emission (centered around 525 nm), corresponding to the electronic transition 4T1 → 6A1 of Mn2+, when exposed to a low power ultraviolet lamp (centered around 255 nm). The temperature sensing performance of this material was evaluated using three different methodologies, i.e. the luminescence decay time constant, the spectral full width at half maximum, and the luminescence peak intensity from the 4T1 → 6A1 radiative transition. The thermometric analysis based on luminescence peak intensity provided a maximum relative sensitivity of ∼4.9x10−3 K−1 at 498 K, while the decay lifetime and the spectral width at half maximum provided maximum relative temperature sensitivities of ∼2.9x10−3 K−1 at 523 K and ∼1.7x10−3 K−1 at 298 K, respectively.

Photoluminescence properties and Mn4+ → Tm3+ energy transfer of La0.557Li0.33TiO3: Mn4+, Tm3+ for thermometry and NIR-LED applications

Over the span of years, Mn4+-doped red phosphors have been utilized to meaningful optoelectronic devices due to their outstanding optical properties, and Tm3+ usually is used for activator ion because of its efficient up-conversion emission, but the down-conversion processes are rarely used. Herein, we have successfully synthesized a series of novel La0.557Li0.33Ti1-xO3:xMn4+ (x = 0.1–7 %) phosphors. The photoluminescence properties have been analysis in detailed. Using Mn4+-Tm3+ co-doped strategy, we successfully synthesis La0.557-yLi0.33Ti0.993O3:0.7 %Mn4+, yTm3+ phosphors. Upon excitation with 360 nm light, this phosphor exhibits two distinct emission peaks at 729 nm and 806 nm. The emission intensity of Tm3+ is greatly improved after Mn4+ doping, which is attributed to the energy transfer of Mn4+ to Tm3+. In terms of potential applications, utilizing fluorescence intensity ratio technology, La0.551Li0.33Ti0.993O3:0.7 %Mn4+, 0.6 %Tm3+ exhibits maximum absolute and relative sensitivities of 3.25 % K−1 at 523 K and 3.49 % K−1 at 298 K, which demonstrating its potential for application in optical thermometry. Furthermore, The NIR-LED using phosphor and 365 nm chips reveals potential applications of the La0.551Li0.33Ti0.993O3:Mn4+, Tm3+ phosphor in NIR night vision and biosensing.

Single-Band Ratiometric Thermometry Strategy Based on the Completely Reversed Thermal Excitation of O2- → Eu3+ CTB Edge and Eu3+ 4f → 4f Transition.

Single-band ratiometric (SBR) strategies present huge potential in the field of luminescence intensity ratio thermometry owing to their excellent signal discrepancy and appealing simplicity. Herein, we employ the approach of Na replacing Li in the LiYGeO4:Eu3+ phosphor to regulate the thermal stability of the O2- → Eu3+ charge-transfer band (CTB) and obtain significant thermal enhancement of luminescence under CTB edge excitation. Combined with the obvious thermal quenching of luminescence under ground-state absorption excitation, the ratio of the single emission band increases by 18 times when the temperature increases from 300 to 570 K. Therefore, such excitation-wavelength-dependent diametrically opposite thermal luminescence behaviors enabled SBR thermometry, whose maximum relative sensitivity can reach up to 3.6% K-1. We demonstrate that the O2- → Eu3+ CTB thermal red-shifts and enhancements are particularly attractive for SBR thermometry with high sensitivity by utilizing the diametrically reversed thermal excitation between the O2- → Eu3+ CTB edge and the 4f → 4f transition of Eu3+. These advances have opened up a novel horizon for the development of high relative sensitivity and performance of the SBR thermometry strategy.

Thermal-dependent luminescence in Er³⁺-doped BaHfO₃ and SrHfO₃ perovskites: Improve temperature sensing via Ba-Sr exchange

The luminescence process behavior stimulated by temperature changes is examined by using the theory of thermally coupled energy levels of erbium ion (Er3+) 2H11/2 and 4S3/2. The different mechanisms and environments are compared and elucidated in crystalline structures of BaHfO3 and SrHfO3 as a product of the atomic exchange of Ba2+ for Sr2+ respectively. The undoped and erbium-doped materials were synthesized by hydrothermal route, the erbium-doped materials were impurified with different Er3+ concentrations; 0.25, 0.5, 1, 3, and 5 at.%. X-ray diffraction (XRD) patterns of both materials present a cubic perovskite-type phase, with space group Pm-3m. High-resolution transmission electron microscopy (HRTEM) micrographs show for both materials the presence of nanocrystals with straight profiles and with an approximate size of 36 nm for BaHfO3 and 32 nm for SrHfO3. The room temperature photoluminescent emission spectra shows the highest luminescent intensity at 1 % Er3+ for both materials, showing different spectral characteristic shapes for each material, due to the different electrostatic forces produced by either Ba2+ or Sr2+ ions surrounding Er3+. Using the “Fluoresce Intensity Ratio” (FIR) technique, the temperature sensing properties of these materials were analyzed and compared from 290 to 330 K covering the well-known physiological range (298.15 K–318.15 K). Both materials, BaHfO3:1%Er3+ and SrHfO3:1%Er3+, show dependence to temperature changes, and the experimental energy gap (ΔE) was used to improve (or decrease) the temperature sensing properties. The theoretical ΔE, maximum relative sensitivity (SRMAX), and the resolution in temperature (δT) were obtained, for BaHfO3: 1 % Er3+ these values were: ΔE = 505.73 cm−1, SRMAX = 0.87 % K−1 at 288.5 K and δT = 0.02 K, while for SrHfO3: 1 % Er3+ the values were: ΔE = 649.21 cm−1, SRMAX = 1.12 % K−1 at 288.5 K and δT = 0.01 K.