Optical Thermometry Research Articles

Tunable multicolor-emission in Eu3+ and Tb3+ codoped Cs2NaInCl6:Sb3+ double perovskite nanocrystals and its dual-model anti-counterfeiting and temperature-sensing applications

Lead-free metal halide double perovskites with non-toxicity and stable self-trapped excitons (STEs) have received considerable attention in the field of photoelectric applications. However, it is difficult to achieve independent control of its photoluminescence performance to meet the requirements of multi-band emission. Herein, a doping strategy was employed to introduce lanthanide ions (Ln3+) into Cs2NaInCl6:Sb3+ nanocrystals (NCs), enabling the multicolor emission modulation ranging from blue to red and even white light. Benefiting from the efficient energy transfer from Sb-related self-trapped excitons to Ln3+ ions, green and red emissions originate from the 5D0→7FJ (J = 1, 2, 3, 4) transition of Eu3+ ions and 5D4-7FJ (J = 6, 5, 4, 3) transition of Tb3+ ions, respectively. According to the tunable polychromatic photoluminescence characteristics of doped NCs, the dual-mode fluorescent anti-counterfeiting applications were exhibited. Furthermore, the distinct temperature sensitivities exhibited by blue (453 nm) and red (617 nm) emission in Cs2NaInCl6:Sb3+/Eu3+ NCs provide the opportunity for the optical thermometry, which demonstrates the maximum absolute and relative sensitivity are 0.0018 and 0.43 % K−1, respectively. These results indicate that the synthesized codoped NCs have the potential applications in multifunctional fields, such as optical thermometer, fluorescence anti-counterfeiting, and multicolor-LEDs.

Up-conversion luminescent properties of CaGdAl3O7: Er3+, Yb3+, Lu3+ as a ratio optical thermometer

Rare earth doped up-conversion luminescent materials have been extensively studied for ratio optical thermometry. Compared with commonly used fluorides, oxides have low up-conversion luminous efficiencies but good thermal stability and are more suitable for high temperature environments. In this paper, a series of CaGdAl3O7: x% Er3+, y% Yb3+, z% Lu3+ phosphors were successfully prepared by high temperature solid-state reaction. Upon 980 nm laser excitation, the optimal CaGdAl3O7: 5 % Er3+, 35 % Yb3+, 1.5 % Lu3+ shows bright characteristic emission peaks of Er3+. CaGdAl3O7: 5 % Er3+, 35 % Yb3+, 1.5 % Lu3+ shows good temperature sensing performance from 303 K to 503 K. The absolute sensitivity reaches the maximum value at 428 K (Sa = 0.292 % K−1). The maximum relative sensitivity is 0.917 % K−1 at 303 K. Moreover, CaGdAl3O7: 5 % Er3+, 35 % Yb3+, 1.5 % Lu3+ shows superior repeatability and reversibility. The results suggest that it is potential candidates as temperature sensors.

In-situ embedding of carbon dots in perovskite GdAlO3:Eu3+/Li+ composite: Boosting phosphor stability, optical thermometry, flexible displays and data protection applications

Phosphors that are highly fluorescent have shown considerable promise in applications like flexible displays and enhancing data security. Still, the task of boosting their fluorescence attributes, especially in the realm of phosphors, remains an ongoing challenge. Precisely, the luminescent properties of GdAlO3:Eu3+ (GAO:Eu3+) phosphors co-doped with lanthanide (Ln) and alkali ions (M+) are successfully synthesized using a solution combustion method. The integration of fluorescent carbon dots (CDs) onto the GAO:7Eu3+/Li+ phosphor surface notably enhanced their luminescent characteristics. Incorporating CDs into GAO:7Eu3+/Li+ resulted in a decrease in both positive and negative defects within the phosphor, consequently enhancing its crystalline structure. Particularly noteworthy is the substantial spectral alignment observed between the emission of CDs and the absorption of GAO:7Eu3+/Li+. When excited by 395 nm UV light, the GAO phosphors displayed the distinctive emission associated with the doping ions. The emission intensity of GAO:7Eu3+/Li+, and CDs(7 wt%)@GAO:7Eu3+/Li+ composite rises by 18 and 66.23 folds, respectively, in comparison to the corresponding samples lacking the inclusion of CDs. The enhanced photoluminescence (PL) intensity observed can be attributed to the Förster resonance energy transfer (FRET) mechanism. In comparison to its emission intensity at room temperature, the CDs@GAO:7Eu3+/Li+ composite retains 95.6% of its intensity, while GAO:7Eu3+ retains 88.5% and GAO:7Eu3+/Li+ retains 91.2% at 400 K, showcasing remarkable thermal stability. The finely optimized CDs(7 wt%)@ GAO:7Eu3+/Li+ combination displays an impressive color purity (CP) of 98.15 %. Furthermore, this NCs demonstrates significant potential for optical thermometry across a broad temperature spectrum ranging from 300 to 480 K. The brush mode is utilized to create anti-counterfeiting (AC) labels using the optimized composite ink on various surfaces. The resulting AC tags exhibit high resolution and durability. The fabricated flexible films exhibit remarkable flexibility, and foldability significantly broaden the scope of potential applications in the field of AC. These results suggest that CDs(7 wt%)@ GAO:7Eu3+/Li+ have potential for multifaceted applications in flexible luminescent films, AC, and optical thermometry.

Simultaneous modulation of multicolor upconversion emission and thermal‐sensing performance of Ba5Zn4Y8O21 phosphors

AbstractIn this study, we report the modulation of the emission color and optical temperature‐sensing properties of Er3+ in Ba5Zn4Y8O21 crystals. Er3+ single‐doped Ba5Zn4Y8O21 phosphors showed green emission under 980 nm excitation. When codoping with Yb3+ ions, the red emission component from the Er3+ ions increased significantly, and the sample emission turned orange. Yb3+–Er3+ codoped Ba5Zn4Y8O21 samples exhibited bright red emission with a maximum IR/IG value of 89.30 when excited with a longer wavelength, 1550 nm. A broad range of emission colors could be modulated by adjusting the dopant concentration. The possible modulation mechanisms and upconversion processes were analyzed based on the luminescence decay curves and power‐dependent emission intensities. Furthermore, the optical temperature‐sensing properties of Ba5Zn4Y8O21:Er3+ and Ba5Zn4Y8O21:Er3+, Yb3+ phosphors with thermal coupled energy levels (TCELs) and nonthermal coupled energy levels (N‐TCELs) of Er3+ ions were investigated using fluorescence intensity ratio technique. Based on the TCELs (2H11/2/4S3/2), the Er3+ single‐doped and Yb3+–Er3+ codoped Ba5Zn4Y8O21 phosphors present the similar optical thermometry behaviors under 980 and 1550 nm excitation. The highest absolute (Sa) and relative sensitivity (Sr) are 3.95 × 10−3 K−1 at 573 K and 1.31% K−1 at 303 K, respectively. Based on N‐TCELs (4F9/2/2H11/2), the temperature‐sensing performance depends on the Yb3+ dopant and excitation wavelength. The highest values for Sa and Sr reached 5.46 K−1 at 303 K and 1.38% K−1 at 573 K for the Ba5Zn4Y8O21:Er3+, Yb3+ phosphor under 1550 nm excitation, respectively. In addition, the present phosphor exhibited high stability and repeatability over a wide temperature range. These results indicate that the multicolor modulation upconversion Ba5Zn4Y8O21‐based phosphor can be considered a potential reusable optical thermometer for noncontact temperature detection.

Remote optical thermometry by two-dimensional LiAl5O8:Cr3+ luminescence sensor probe

Pure-phase LiAl5O8:Cr3+ leaf-like particles were synthesized by combustion synthetic route at various concentrations. Both sharp peaks and broad emission photoluminescence are apparent even at room temperature. The most optimum doping concentration of 0.75 % based on lifetime and emission intensity was chosen. Peaks of different configurations were separated by deconvolution from 120 K to 680 K, where 4T2 peak increases in temperature to the expense of the sharp 2E emissions, giving luminescence intensity ratio (LIR) relative sensitivity of 2.8 % K−1 at room temperature. Large separation between Cr3+ R lines marks their LIR as perspective at low temperatures. At high temperatures luminescence lifetime provided for 0.8 % K−1 sensitivity, while line-shift and bandwidth methods are not sensitive enough for thermometric applications. Deconvolution of peaks enabled for 10 % more precise estimation of Debye temperature (679 K).

Improved broadband luminescence in Gd2GaSb1-xTaxO7:Cr3+,Yb3+ pyrochlore phosphors: Near-infrared spectroscopic applications and dual-mode optical thermometry

The growing demand for spectroscopic applications in the fields of night vision monitoring, non-destructive analysis and bioimaging has led to extensive research into near infrared (NIR) light sources. Thus, the design of high-performance broadband Cr3+-doped NIR phosphors is of urgent and critical importance. Herein, novel Gd2GaSb1-xTaxO7:Cr3+,Yb3+ NIR-emitting pyrochlore phosphors were successfully explored. Via partly substituting Sb5+ by Ta5+ and tuning Cr3+ amount, a significant enhancement, broadening and redshift of Cr3+ NIR luminescence are exhibited under the radiation of 460 nm light. Moreover, higher thermal stability and wider NIR luminescence are realized by the proper introduction of Yb3+. A satisfactory NIR output power of 46.51 mW @ 300 mA and photoelectric efficiency of 10.82 % @ 10 mA of the fabricated NIR phosphor-converted light-emitting diodes (NIR pc-LEDs) based on Gd1.96Ga0.97Sb0.9Ta0.1O7:3%Cr3+,4%Yb3+ phosphor enable the demonstration in night vision and bioimaging applications. Besides, superior dual-mode optical thermometry was successfully constructed on fluorescence intensity ratio (Cr3+/Yb3+) and fluorescence lifetime (4T2) of Cr3+ in Gd2GaSb1-xTaxO7:Cr3+,Yb3+. These results confirm that Gd2GaSb1-xTaxO7:Cr3+,Yb3+ can serve as inspiring luminescent converters employed in NIR pc-LEDs and non-contact temperature sensing.

Fractional thermal load in cryogenically cooled Yb:YLF and Yb:YAG lasers

We present a method for the direct measurement of the fractional thermal load (FTL) in cryogenically cooled laser crystals. The experimental methodology involves characterizing the liquid nitrogen evaporation rate in a dewar containing the laser crystals, allowing for the accurate determination of FTL. The FTL is measured to be 1.7 × quantum defect (QD) for Yb:YLF and 1.5 × QD for Yb:YAG under continuous wave lasing conditions. The measured FTL values are then used to calculate the temperature distribution inside the crystals as a function of pump power, and the simulation results are found to be in very good agreement with the in-situ temperature measurements using contactless optical luminescence thermometry. The method and findings presented in this work hold great potential to benefit laser engineers and scientists working with cryogenic lasers to address and overcome temperature-dependent handicaps.

Calcination-free crystallization of rare earth double tungstate Na(La1 − xEux)(WO4)2 by sacrificial-template hydrothermal reaction, restrained concentration quenching, and optical thermometry

Calcination-free crystallization of rare earth double tungstate Na(La1 − xEux)(WO4)2 by sacrificial-template hydrothermal reaction, restrained concentration quenching, and optical thermometry

Delineating Dy3+ and Sm3+ in thermally stable strontium silicate apatites for multifunctional applications

The structural, optical and temperature dependent luminescence properties of a series of Sr2Y8-xREx(SiO4)6O2 (RE=Dy and Sm) silicate phosphors are investigated for their multifunctional applications. The phosphors were synthesized using the solid-state reaction route with varying doping levels and characterized for phase purity. X-ray Diffraction analysis revealed the hexagonal crystal structure of (Sr2RE2)(RE6)(SiO4)6O2, indicating the incorporation of rare earth (RE) ions into two distinct crystallographic sites, thereby augmenting the luminescence properties. Dy3+ doped compounds exhibit intense yellow emission, promising white light generation when paired with InGaN blue LED chips. Sm3+ doped samples show orange-red emission around 601 nm, attributed to multipole-multipole interactions, with rapid decay curves suitable for high-speed response LEDs. Correlated Color Temperature (CCT) values were computed to assess the commercial viability of these phosphors in luminescence applications and the role of lighting in the growth of indoor plants and office spaces is discussed. The Sr2Y7.8Dy0.2(SiO4)6O2 phosphor with remarkable quantum yield of 63.56% demonstrated a thermal stability of 0.27 eV with enhanced sensitivity of about 0.39% K−1 and Sr2Y7.8Sm0.2(SiO4)6O2 with stability around 0.31eV with sensitivity of 1.11% K⁻¹ at 100K reveals them as potential candidates for optical temperature sensing. These results declare the competence of synthesized novel silicate apatites in solid-state lighting and optical thermometry.

Optical thermometry based on the stark sub-levels of Er3+ in Y2Mo3O12: Yb3+, Er3+ particles synthesized by sol–gel method

Optical thermometry based on the stark sub-levels of Er3+ in Y2Mo3O12: Yb3+, Er3+ particles synthesized by sol–gel method

Remote temperature sensing in microelectronics: optical thermometry using dual-center phosphors

Remote thermal sensing has emerged as a temperature detection technique for tasks in which standard contact thermometers cannot be used due to environment or dimension limitations. One of such challenging tasks is the measurement of temperature in microelectronics. Here, optical thermometry using co-doped and mixed dual-center Gd2O3:Tb3+/Eu3+ samples were realized. Ratiometric approach based on monitoring emission intensities of Tb3+ (5D4–7F5) and Eu3+ (5D0–7F2) transition provided sensing in the range of 30 °C–80 °C. Dispersion system type only slightly affected relative sensitivity, accuracy and precision. The applicability of phosphors synthesized to be utilized as remote optical thermometers for microelectronics has been proved with an example on a surface mount resistor and microcontroller.

Optical Phenomena in Molecule-Based Magnetic Materials.

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Tunable emission and improved sensitivity of optical thermometry in Ca2+/Sr2+ doped Ba2GdNbO6:Yb3+, Er3+ phosphors

Many efforts have been devoted to contactless optical thermometry because of their apparent advantages. The phosphors with double perovskite structure are considered good hosts for luminescence according to many related research. Herein, Yb3+/Er3+ co-doped Ba2GdNbO6 phosphors were successfully prepared and showed good up-conversion performance. Furthermore, the phosphors could achieve tunable luminescence by adjusting the calcination temperature or introducing proper Ca2+/Sr2+ ions. The intensity of green emissions increases with calcination temperature, while the red emissions increase by incorporating Ca2+/Sr2+ ions. The properties of optical thermometry based on the fluorescence intensity ratio (FIR) method of Er3+ at thermally coupled levels (2H11/2/4S3/2) were also explored in the range of 300–570 K. The maximum relative sensitivity (SR) of Yb3+/Er3+/Sr2+ tri-doped Ba2GdNbO6 sample reach 1.01 % K−1, which is higher than that of Yb3+/Er3+ co-doped Ba2GdNbO6 sample (0.78 % K−1). The research shows that the phosphors are prospective applications in temperature sensing.

Optimizing optical thermometry with tri-doped Ba2GdV3O11 phosphors: Ratiometric and fluorescence lifetime analysis

Optical sensor technology has undergone a transformative evolution with the advent of fluorescence ratio techniques (FIR) and fluorescence lifetime (FL) strategies, revolutionizing precision, performance, and reliability. This study delves into the synthesis of Ba2GdV3O11 phosphors doped with Ho3+/Nd3+, Er3+, and Yb3+, employing the sol-gel method for upconverting material fabrication. A thorough investigation into the structural, morphological, and optical properties of the synthesized phosphors is conducted. Excitation at 980 nm unveils upconversion (UC) emissions across green and red spectra. The intensities of the observed emission bands for Ho3+, Nd3+, and Er3+ demonstrate significant sensitivity to fluctuations in temperature. Temperature sensing relies on the 4S3/2 and 2H11/2 upconversion emissions bands, in addition to the emission lifetimes at 4S3/2. Enhanced thermal sensitivity values are attained, reaching up to 1.03 % K−1 and 1.07 % K−1 using the FIR strategy, and up to 0.146 % K−1 and 0.47 % K−1 with the FL strategy for Ho3+/Er3+/Yb3+ and Nd3+/Er3+/Yb3+ tri-doped Ba2GdV3O11 phosphors, respectively. Furthermore, the studied phosphors exhibit remarkable precision in detecting minute temperature changes (0.3 K), positioning them as promising candidates for precise temperature sensing. This study pioneers innovative methodologies to advance optical thermometry techniques, offering promising prospects for scientific and industrial applications reliant on precise optical temperature sensing.

Investigation of Ca2Al2SiO7: Pr3+/Gd3+ UVB upconverting phosphor and its optical thermometric properties

On basis of fluorescence intensity ratio (FIR) over certain narrow coupled levels of rare-earth ions, up-conversion of RE-doped materials perform excellent temperature-sensing abilities for thermometry applications. A series of Pr3+/Gd3+ co-doped Ca2Al2SiO7 phosphors (Ca2Al2SiO7:Pr3+/Gd3+) were prepared by a conventional high-temperature solid-state reaction. Under excitation of blue ∼445 nm, the Ca2Al2SiO7:Pr3+/Gd3+ phosphor yields intense photoluminescence (PL) bands around 489, 528, 537, 580, 604, 613, and 646 nm due to electronic transition of 3P0 → 3H4, 3P0 → 3H5, 3P1 → 3H5, 3P1 → 3H6, 1D2 → 3H4, 3P0 → 3H6, and 3P0 → 3F2 of Pr3+, respectively. Their relative intensities are sensitively determined by Pr3+ contents, which, from 0.1 % to 5 %, tune the emission color from pink to warm white under excitation of 445 nm. It is of great interest that intense irradiation using a blue ∼445 laser does make efficient ultraviolet B (UVB) up-conversion at about 297, 306, and 313 nm, just stemming from the 6P3/2 → 8S7/2, 6P5/2 → 8S7/2, and 6P7/2 → 8S7/2 of Gd3+, respectively. A typical two-photon absorption process was proved to account for the UVB up-conversion, i.e. successive absorption of two blue ∼445 nm photons populating Pr3+ 4f5d excited state, which further efficiently transfer its energy to the 6IJ/6PJ states of Gd3+ neighbor for UVB emission. Moreover, the thermally coupled levels (TCLs) of Gd3+: 6P3/2-6P7/2, and Gd3+: 6P5/2-6P7/2 were thoroughly investigated for temperature sensing in 298–598 K. Maximum relative sensitivity of the 6P3/2-6P7/2 TCLs, i.e. Sr(I306/I313), is proved to be 0.96 % K−1 at 298 K, and that of the 6P5/2-6P7/2 TCLs, i.e. Sr(I297/I313), is 1 % K−1 at 373 K. The relevant thermal stabilities of the Ca2Al2SiO7:Pr3+/Gd3+ thermometric candidate was well validated with 10 cycles of heating and cooling processes in 298–598 K. Such continuous explorations of Pr3+/Gd3+ co-doping system will significantly promote the development of robust UVB up-converting phosphors as well as their practical applications in the field of high-resolution optical thermometry.

Erbium‐Induced Boost in Self‐Trapped Exciton Emission of Double Perovskites for Highly Sensitive Multimodal and Multiplexed Optical Thermography

AbstractSelf‐trapped excitons (STEs) of lead‐free perovskites have aroused tremendous interest in remote optical thermometry due to strong exciton–phonon coupling and large Stokes shifts. Herein, a bright multimodal and multiplexed optical thermometer is constructed with high sensitivity (Sr) and self‐calibrating ability based on Cs2NaInCl6:Er3+ double perovskite, allowing for fast and simplified reading via mobile devices. Intriguingly, Er3+ doping not only shows the characteristic green emissions but also introduces nanoelectronic domains through a new localized valance band maximum and breaks the symmetry of In3+ site, which facilitates the generation of more STEs. The temperature‐sensitive blue emission of STEs and temperature‐insensitive green emission of Er3+ endow multimodal optical thermometry including time‐resolved and ratiometric readout schemes with a maximum Sr of 3.8% K−1, where an upconversion primary thermometry serves as a reference to calibrate other modes. Meanwhile, the designed thermometers show robust photostability, repeatability, and structural stability for long‐time working and storage. In addition, the remarkable thermochromic phenomenon from blue to green enables a quick color‐multiplexed thermography on a smartphone, which is utilized to capture real‐time 2D thermal imaging of microelectronic devices. This work demonstrates the great potential of lead‐free double perovskite for low‐cost and portable optical thermometry.

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.

Probing multifunctional applications of LiCa2Mg2V3O12: Sm3+ phosphor using Judd-Ofelt analysis and dual mode non-contact optical thermometry

LiCa2Mg2V3O12:Sm3+ phosphors have been prepared by solid state method and analysed by X-ray diffraction, EDX-elemental mapping, UV–VIS-NIR spectroscopy, photoluminescence (PL) and temperature dependent photoluminescence (TDPL). The absorption spectra analysis using Judd-Ofelt theory provides the intensity parameters and manifest the covalent nature of Sm-O bond. The PL spectra monitored at 338 nm excitation exhibits emission peaks of Sm3+ at 567, 617 and 651 nm in addition to the broad band emission of LiCa2Mg2V3O12 host. The Commision Internationale deL’Eclairage (CIE) coordinates, correlated color temperature (CCT) and color rendering index (CRI) values elucidate the efficient yellow emission of phosphors. The radiative parameters are evaluated and have outrageous branching ratio and cross section that aids in visible laser applications. The optical thermometry of phosphor is carried out by utilizing FIR method through selecting spectral modes 6H5/2/VO43-, 6H7/2/VO43- and 6H9/2/ VO43-. The mode 6H9/2/ VO43- have higher absolute sensitivity (Sa) and relative sensitivity (Sr) values of 0.4418 K−1 and 1.6079% K−1. The temperature resolution of modes are 0.1633, 0.1677 and 0.1563 K respectively. The thermochromic study reveals the high chromaticity shift (Δs = 0.1869) of phosphor and the Sa(x) and Sr(x) values evaluated based on CIE coordinates are 0.0011 K−1 and 0.2407% K−1 respectively. The PL and TDPL characteristics of prepared phosphor suggest that it have multifunctional application in the fields of lasers, thermo-sensors, thermochromic displays and LEDs.

Luminescence-Monitored Progressive Chemical Pressure Implementation Realized through Successive Y3+ and Mg2+ Doping into Ca10.5(PO4)7:Eu2.

Chemical pressure generated through ion doping into crystal lattices has been proven to be conducive to exploration of new matter, development of novel functionalities, and realization of unprecedented performances. However, studies are focusing on one-time doping, and there is a lack of both advanced investigations for multiple doping and sophisticated strategies to precisely and quantitatively track the gradual functionality evolution along with progressive chemical pressure implementation. Herein, high-valent Y3+ and equal-valent Mg2+ is successively doped to replace multiple Ca sites in Ca10.5(PO4)7:Eu2+. The luminescence evolution of Eu2+ serves as an optical probe, allowing step-by-step and atomic-level tracking of the site occupation of Y3+ and Mg2+, interassociation of Ca sites, and ultimately functionality improvement. The resulting Ca8MgY(PO4)7:Eu2+ displays a record-high relative sensitivity for optical thermometry. Utilization of the environment-sensitive emission of Eu2+ as a luminescent probe has offered a unique approach to monitoring structure-functionality evolution in vivo with atomic precision, which shall also be extended to optimization of other functionalities such as ferroelectricity, conductivity, thermoelectricity, and catalytic activity through precise control over atomic diffusion in other types of substances.

Ratiometric thermometry using down-conversion luminescence and solid-state lighting application of Er3+ activated strontium tungstate phosphor

Er3+ activated Sr3WO6 double perovskite crystallized in triclinic structure was synthesized via the solid-state reaction method at 1200 °C for non-contact optical thermometry and solid-state lighting. The phosphors under study were characterized via X-ray diffraction, scanning electron microscopy, diffusion reflectance spectra, and photoluminescence techniques. When excited with 380 nm, the Sr3WO6:Er3+ phosphors exhibited intense green emission, corresponds to 2H11/2/4S3/2-4I15/2 transitions of Er3+. The fluorescence intensity ratio of thermally coupled energy levels were computed within 303–513 K and subsequent relative sensitivity (0.56% K−1 at 303 K) was determined. Moreover, the PL intensity maintained 76.28% at LED burning temperature (150 °C) compared to PL intensity observed at room-temperature, denotes good thermal stability. Additionally, the fluorescent behaviour of the phosphors was examined via PL decay lifetime study. The PL quantum efficiency of the phosphor is computed via the Auzel's model using PL decay lifetime, and was obtained to be 80.32% for Sr3WO6:2% Er3+ phosphor.