Strategies for Designing Antithermal-Quenching Red Phosphors

Luminescence, temperature sensing and Judd-Ofelt analysis of Bi2Mo3O12:Eu3+ phosphors and the application in latent fingerprint visualization

Eu3+-activated materials have garnered significant attention due to their outstanding optical characteristics. In this work, the sol-gel method was successfully used to prepare Bi2Mo3O12 phosphors doped with different amounts of Eu3+. The generated samples were identified as orthorhombic Bi2Mo3O12 with a scheelite-like structure by X-ray diffraction analysis of the crystal structure. The sample's morphology and size were examined using scanning electron microscopy and transmmission electron microscopy, which revealed irregular block morphology and tens to hundreds nanometers scale dimension. From the analysis of the concentration-dependent luminescence intensity of Eu3+, it was confirmed that the exchange interaction was responsible for the quenching of 5D0 fluorescence of Eu3+. When excited at 374 nm, the phosphor emitted brilliant red light, with the highest emission occurring at 616 nm (5D0→7F2 transition), and the calculated color coordinates of the sample were (0.663, 0.336). By examining the temperature dependence of the emission spectra, the temperature sensing performance of the sample and the thermal quenching behavior of Eu3+ luminescence was explored. Furthermore, the optical transition property of Eu3+ was investigated by using the emission spectra and fluorescence lifetime within the context of Judd-Ofelt theory. Ultimately, latent fingerprint visualization of the sample on various object surfaces was studied, thanks to the intense luminescence and small particle size of the Bi2Mo3O12:Eu3+ phosphor. The results indicated that the sample can clearly display the different hierarchical features of fingerprint on different object surfaces.

Wide Range Near-Zero Thermal Quenching of Orange-Yellow Phosphor via Impeding Self-Oxidation of Eu2+ for Versatile Optoelectronic Applications

Li2SrSiO4:Eu2+ is a promising substitute for traditional Y3Al5O12:Ce3+ (YAG:Ce3+) owing to its strong orange-yellow emission of 4f-5d transition originating from Eu2+ dopant, covering the more red-light region. However, its inevitable luminescence thermal quenching at high temperatures and the self-oxidation of Eu2+ strongly impede their applications. Their remediation remains highly challenging. Herein, an anti-self-oxidation(ASO) concept of Eu2+ in Li2SrSiO4 substrate by adding trivalent rare-earth ions (A3+: A = La, Gd, Y, Lu) for highly efficient and stable orange-yellow light emission have been proposed. A significantly increased orange-yellow emission (202% improvement) from Li2Sr0.95A0.05SiO4:Eu2+ with a wide range near-zero thermal quenching is obtained, superior to other Eu2+ activated phosphors. The presence of A3+ ions with various radii modifies the ASO degree of Eu2+ ions, achieving the tunable chemical state, composition, electronic configuration, crystal-field strength, and luminescent characteristics of the developed phosphors. For the proof of the concept, a W-LED device and a PDMS (Polydimethylsiloxane) luminescent film are fabricated, endowing excellent luminescence performance and thermal stability and the huge application prospects of Li2SrSiO4:Eu2+ in lighting and display fields.

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.

An efficient rare-earth free deep red-emitting GdGeSbO6:Mn4+ phosphor for white light-emitting diodes

Red phosphors play an important role in improving the light quality and color rendering index of white light-emitting diodes (WLEDs) for lighting. In this paper, we report the transition ion Mn4+-activated deep red phosphor GdGeSbO6:x%Mn4+ and analyze its crystal structure, composition and luminescence behavior in detail. Its optimal doping concentration of Mn4+ is 0.3%. Under ultraviolet (UV) excitation, GdGeSbO6:0.3%Mn4+ produces a narrow emission peak centred at 682 nm in the range of 650-800 nm with a full width at half maximum (FWHM) of 25 nm, which is attributed to the spin-prohibited 2Eg → 4A2g transition of Mn4+ ions. Notably, the optimal phosphor GdGeSbO6:0.3%Mn4+ has a high internal quantum efficiency (IQE ≈ 65%) and excellent thermal stability performance (I423 K/I303 K ≈ 62%). The synthesis of high-performance warm WLEDs and full-spectrum WLEDs was achieved by combining and coating GdGeSbO6:0.3%Mn4+ phosphors with commercial phosphors on the surface of a 365 nm UV chip.

Luminescence center modulation for the synthesis of a narrow-band green phosphor: mechanism and backlighting display application

A highly efficient and stable green phosphor with a narrow emission-band in a hexagonal aluminate was synthesized based on the energy transfer between Eu2+ and Mn2+ luminescence centers. The related mechanism was elucidated from the viewpoints of the crystal structure and energy level, providing insights for designing novel phosphors with high performance.

Thermal activation induced charge transfer state absorption redshift realizes strong anti-thermal quenching in Pr3+-activated phosphor

In our work, a totally anomalous thermal quenching phenomenon of red-shifted and enhanced charge transfer state (CTS) absorption is found for the first time in LiTaO3:xPr3+ phosphors. The crystal structure, luminescent properties and the mechanism of abnormal thermal quenching were investigated in detail.

Negative Thermal Quenching of Photoluminescence: An Evaluation from the Macroscopic Viewpoint

Negative thermal quenching (NTQ) denotes that the integral emission spectral intensity of a given phosphor increases continuously with increasing temperature up to a certain elevated temperature. NTQ has been the subject of intensive investigations in recent years, and a large number of phosphors are reported to have exhibited NTQ. In this paper, a collection of results in the archival literature about NTQ of specific phosphors is discussed from a macroscopic viewpoint, focusing on the following three aspects: (1) Could the NTQ of a given phosphor be reproducible? (2) Could the associated data for a given phosphor exhibiting NTQ be in line with the law of the conservation of energy? (3) Could the NTQ of a given phosphor be demonstrated in a prototype WLED device? By analyzing typical cases based on common sense, we hope to increase awareness of the issues with papers reporting the NTQ of specific phosphors based on spectral intensity, along with the importance of maintaining stable and consistent measurement conditions in temperature-dependent spectral intensity measurement, which is a prerequisite for the validity of the measurement results.

Genesis of temperature-driven red-shift of charge transfer band edge for Sm3+-doped vanadate self-activated phosphor

The temperature-driven redshift of the charge transfer band (CTB) exhibits promising potential for optical temperature sensing as well as for the design of anti-thermal quenching phosphors. Therefore, it is essential to investigate the displacement mechanism in detail. In this contribution, we created LiCa2.95MV3O12:5%Sm3+ (M = Mg/Zn) phosphors with considerably red-shifted CTB edges upon temperature stimulation and outstanding anti-thermal quenching behavior. To investigate this unusual behavior, gaussian fitting was performed on the excitation spectra and emission spectra at different temperatures to investigate the redshift mechanism. By averaging the peak energy of the lowest excitation and emission peaks, the zero phonon line (Ezp) indicating the electronic energy level location of the charge transfer state (CTS) shows a downward trend is obtained. As well as the energy reduction of the 1A2(1T1)-1B1(1T2) and 1E(1T1)-1B1(1T2) absorption bands in the [VO4]3- group is observed. Therefore, the drop in the CTS electronic energy level is the dominant factor in the temperature-driven CTB redshift. Based on the redshift phenomenon and anti-thermal quenching phenomenon of CTB, the phosphor exhibited exceptional optical temperature measurement performance in all three thermometry modes of excitation intensity ratio (EIR), International Committee on Illumination (CIE) color coordinates, and fluorescence intensity ratio (FIR), demonstrating its broad application prospects in the field of optical temperature sensing as well as guiding the design of anti-thermal quenching phosphors.

High-Quantum-Efficiency Blue Phosphors with Superior Thermal Stability Derived from Eu3+-Doped Faujasite Y Zeolite

Blue phosphors of high efficiency and superior thermal stability constitute the critical component for achieving high-quality white light-emitting diodes (WLEDs). Herein, we report a highly efficient blue-emitting phosphor with superior thermal stability by heating Eu3+-doped Faujasite Y zeolite under a reducing atmosphere. The intensity and peak value of the phosphor are highly dependent on calcination temperature, and the intensity of PLE and PL spectra reaches a maximum at 1100 °C. Under the excitation of 360 nm, the phosphor shows a high quantum efficiency (90%) and thermal stability (the emission intensity at 423 K is about 125% of that at room temperature). WLEDs fabricated using this blue phosphor, a yellow Eu2+-SOD phosphor, and a commercially available red Sr2Si5N8:Eu2+ phosphor exhibit an excellent optical performance with a correlated color temperature of 4359 K and a color rendering index of 97. This work provides a new strategy for the synthesis of phosphors with high thermal stability and luminous efficiency.

Emission color tuning and dual-mode luminescence thermometry design in Dy3+/Eu3+co-doped SrMoO4phosphors

The challenge of building a highly reliable contactless temperature probe with high sensitivity, good temperature-induced color discriminability, and economical synthesis has prompted the research community to work in the field of rare-earth-based luminescence thermometry. Moreover, the fast-growing market for optoelectronic devices has increased the demand for tunable color-emitting phosphors. In this study, Dy3+/Eu3+co-doped SrMoO4phosphors were developed as tunable color-emitting source and dual-mode luminescence thermometer. A facile and cost-effective auto-combustion method was used to synthesize the phosphors. Our work demonstrates a viable scheme for tailoring the emission of single-phase phosphors by precisely controlling the dopant concentrations and by modulating excitation wavelength. The overall emission is tuned from greenish-yellow to white and greenish-yellow to reddish-orange. A detailed energy transfer process from the host to the Ln3+ions and between the Ln3+ions is discussed. Further, anti-thermal quenching in the emission of Dy3+ion is observed when excited with 297 nm. The dual-mode luminescence thermometry has been studied by analyzing the fluorescence intensity ratio of Dy3+and Eu3+ions upon excitation at 297 nm. The maximum relative sensitivity value for 4% Eu3+co-doped SrMoO4:4%Dy3+phosphor is 1.46% K-1at 300 K. Furthermore, the configurational coordinate diagram is presented to elucidate the nature of temperature-dependent emission. Therefore, our research opens up new avenues for the development of color-tunable luminescent materials for various optoelectronic and temperature-sensing applications.

Simultaneous Thermal Enhancement of Upconversion and Downshifting Luminescence by Negative Thermal Expansion in Nonhygroscopic ZrSc(WO4)2PO4:Yb/Er Phosphors

Thermal quenching (TQ) is still a critical challenge for lanthanide (Ln³⁺)-doped luminescent materials. Herein, we report the novel negative thermal expansion nonhygroscopic phosphor ZrSc(WO₄)₂PO₄:Yb³⁺/Er³⁺. Upon excitation with a 980 nm laser, a simultaneous thermal enhancement is realized on upconversion (UC) and downshifting (DS) emissions from room temperature to 573 K. In situ temperature-dependent X-ray diffraction and photoluminescence dynamics are used to reveal the luminescence mechanism in detail. The coexistence of the high energy transfer efficiency and the promoted radiative transition probability can be responsible for the thermally enhanced luminescence. On the basis of the luminescence intensity ratio of thermally coupled energy levels ²H_11/2 and ⁴S_3/2 at different temperatures, the relative and absolute sensitivities of the targeted samples reach 1.10% K^-1 and 1.21% K^-1, respectively, and the low-temperature uncertainty is approximately 0.1-0.4 K on the whole temperature with a high repeatability (98%). Our findings highlight a general approach for designing a hygro-stable, thermostable, and highly efficient Ln³⁺-doped phosphor with UC and DS luminescence.

Equivalent chemical substitution in double-double perovskite-type ALaLiTeO6:Mn4+ (A = Ba2+, Sr2+, Ca2+) phosphors enabling wide range crystal field strength regulation and efficient far-red emission

Mn⁴⁺-activated phosphors have shown wide prospective applications in phosphor-converted white light-emitting diodes (pc-WLEDs) and pc-LEDs used in illumination and indoor plant cultivation, respectively. Recently, double perovskites A₂B'B''O₆ with a tunable crystal structure and versatile octahedral sites have been extensively studied as good host matrixes for Mn⁴⁺-emitters to realize tunable far-red emissions. Herein, a series of double-double perovskite-type ALaLiTeO₆:Mn⁴⁺ (A = Ba, Ba_0.5Sr_0.5, Sr, Sr_0.5Ca_0.5, Ca) phosphors were synthesized and structurally characterized, and the correlations between their structure and luminescence were also studied systematically. With a decrease of the A-cation size, an increased distortion in the average structure and a structure symmetry lowering (I2/m → P2₁/_n) were observed for ALaLiTeO₆:Mn⁴⁺. In contrast, on the local scale, the degree of (Li/Te)O₆-octahedral distortion is positively correlated with the ΔIR value, which is the ionic radius difference between A²⁺ and La³⁺. The local structural changes were found to be irrelevant to the significant improvements in photoluminescence properties. In combination with careful spectroscopic analysis, we deciphered that a decreased A-cation is in fact helpful for the enhancements in crystal field strength (D_q/B = 2.12-2.82) and Mn-O covalent bonding, thereby resulting in an improved quantum efficiency, a suppressed nonradiative transition, and a redshift in photoluminescence spectra. Amongst the ALaLiTeO₆:Mn⁴⁺ phosphor series, CaLaLiTeO₆:Mn⁴⁺ exhibits the highest external quantum efficiency of 70.1% and internal quantum efficiency of 96.4% and superior thermal stability (93.3%@423 K), making CaLaLiTeO₆:Mn⁴⁺ very promising as far-red phosphors for pc-LEDs. The findings of this work will serve as a new guide for rational design of high-performance Mn⁴⁺-activated double-double perovskite-type far-red phosphors.

Thermodynamics and Kinetics Accounting for Antithermal Quenching of Luminescence in Sc2(MoO4)3: Yb/Er: Perspective beyond Negative Thermal Expansion

Defects are common in inorganic materials and not static upon annealing of the heat effect. Antithermal quenching of luminescence in phosphors may be ascribed to the migration of defects and/or ions, which has not been well-studied. Herein, we investigate the antithermal quenching mechanism of upconversion luminescence in Sc₂(MoO₄)₃: 9%Yb1%Er with negative thermal expansion via a fresh perspective on thermodynamics and kinetics, concerning the thermally activated movement of defects and/or ions. Our results reveal a second-order phase transition taking place at ∼573 K induced by oxide-ion migration. The resulting variation of the thermodynamics and kinetics of the host lattice owing to the thermally induced oxide-ion movement contributes to a more suppressed nonradiative decay rate. The dynamic defects no longer act as quenching centers with regard to the time scale during which they stay nearby the Yb³⁺/Er³⁺ site in our proposed model. This research opens an avenue for understanding the antithermal quenching mechanism of luminescence via thermodynamics and kinetics.

Tuning of the thermal quenching performance of Bi3+-doped scheelite Ca(Mo/W)O4 solid solution phosphors

The utilization of phosphor materials has always been a significant challenge in terms of improving thermal quenching performance. In this work, the thermal quenching performance tuning mechanism which establishes the band gap and thermal quenching correlation patterns is proposed. The crystal field splitting energy D_q was decreased by changing the surrounding crystal lattice environment of Bi³⁺ through a solid solution replacement, and the thermal quenching activation energy ΔE of Bi³⁺ was tuned from 0.117 eV to 0.182 eV accordingly. At 423 K, the luminous intensity increases from 0.101 to 0.396 of the preliminary intensity at 303 K with increasing substitution. In addition, the band gap value of Bi³⁺ calculated by diffuse reflectance spectroscopy increased from 4.40 eV to 4.72 eV, which corresponds to a linear positive correlation between the band gap and the thermal quenching properties. Furthermore, a monophase white-emitting phosphor with good thermal stability was prepared by constructing a Bi³⁺-Eu³⁺ co-doping system. In particular, the relative sensitivity of S_r for temperature measurement applications reached 3.17% K^-1 based on the double-luminescence fluorescence intensity ratio. Thus, this modulation scheme can be used as a reference for the design of various phosphor materials with tunable thermal quenching properties in the future.

Thermally boosted upconversion and downshifting luminescence in Sc2(MoO4)3:Yb/Er with two-dimensional negative thermal expansion

Rare earth (RE³⁺)-doped phosphors generally suffer from thermal quenching, in which their photoluminescence (PL) intensities decrease at high temperatures. Herein, we report a class of unique two-dimensional negative-thermal-expansion phosphor of Sc₂(MoO₄)₃:Yb/Er. By virtue of the reduced distances between sensitizers and emitters as well as confined energy migration with increasing the temperature, a 45-fold enhancement of green upconversion (UC) luminescence and a 450-fold enhancement of near-infrared downshifting (DS) luminescence of Er³⁺ are achieved upon raising the temperature from 298 to 773 K. The thermally boosted UC and DS luminescence mechanism is systematically investigated through in situ temperature-dependent Raman spectroscopy, synchrotron X-ray diffraction and PL dynamics. Moreover, the luminescence lifetime of ⁴I_13/2 of Er³⁺ in Sc₂(MoO₄)₃:Yb/Er displays a strong temperature dependence, enabling luminescence thermometry with the highest relative sensitivity of 12.3%/K at 298 K and low temperature uncertainty of 0.11 K at 623 K. These findings may gain a vital insight into the design of negative-thermal-expansion RE³⁺-doped phosphors for versatile applications.

Rare-earth doped phosphors with negative thermal expansion (NTE) may display thermally-enhanced emission, but their performance is generally limited. Here the authors report thermally-boosted green upconversion luminescence and near-infrared downshifting luminescence in Sc₂(MoO₄)₃:Yb/Er phosphors with two-dimensional NTE, and their application in temperature sensing.

Optical thermometry based on europium doped self-activated dual-emitting LiCa3ZnV3O12 phosphor

In this study, rare-earth-doped self-activated LiCa₃ZnV₃O₁₂ (LCZV) vanadate phosphors were preparation by a high-temperature solid-state reaction. Their crystal structure, non-contact temperature sensing, and luminescence properties were studied deeply. Excited by ultraviolet light at 340 nm, the emission of [VO₄]^3- group and the Eu³⁺ ions were monitored. The highest strength emission peaks at 470 nm and 610 nm for [VO₄]^3- and Eu³⁺, respectively, provide favorable signal identification for estimating temperature. Due to thermal quenching behavior and energy transfer, the FIR (Fluorescence Intensity Ratio) from Eu³⁺ to [VO₄]^3- exhibits excellent sensitivity performance at 303 K - 523 K. In the meantime, the maximum absolute and relative sensitivities of the obtained phosphors are 0.0068 K^-1 and 1.18 % K^-1, which are overtopped to those reported previously. Furthermore, for the luminescent color of the CIE diagram with a strong temperature effect, the color coordinate could be verified from (0.2871, 0.3416) to (0.4121, 0.3420), which was matched well with the linear equation. Consequently, the Eu³⁺ doped LCZV phosphor not only can be used for high-temperature environmental safety signals but also is an extraordinary viable material in the field of optical sensing.

Multiobjective Machine Learning-Assisted Discovery of a Novel Cyan-Green Garnet: Ce Phosphors with Excellent Thermal Stability

Ce-doped garnet phosphors play an important role in the white light-emitting diode (LED) family. In the past years, a lot of trial-and-error experiments guided by experience to discover phosphors suitable for white LEDs have been presented. The working temperature of phosphors may reach 200 °C in white LEDs, and so, the exploration of phosphors with excellent thermal stability at the desired wavelength continues to be a challenge. In the present study, to discover novel cyan-green garnet:Ce phosphors, wavelength and thermal stability machine learning models were built by constructing reasonable features. Among the 171,636 compounds with garnet structures predicted by our models, 25 samples were selected for preparation and characterization by multiobjective optimization based on active learning. Lu_1.5Sr_1.5Al_3.5Si_1.5O₁₂:Ce performed the best with excellent thermal stability (≥60% emission intensity was retained at 640 K) and exhibited emission peaks of about 505 nm, and it is a very promising phosphor for future applications, especially in high-temperature operating environments.

Synergistic luminescent thermometer using co-doped Ca2GdSbO6:Mn4+/(Eu3+ or Sm3+) phosphors

Luminescent thermometers provide a non-contact method of probing temperature with high sensitivity and response speed at the nanoscale. Synergistic photoluminescence from different activators can realize high sensitivity for luminescent thermometers by finely selecting ions with specific crystallographic sites. Herein, the more temperature-sensitive Mn⁴⁺ and the less-sensitive Eu³⁺ (or Sm³⁺) activators are co-doped into a Ca₂GdSbO₆ matrix to form an effective thermometer, where Mn⁴⁺ and Eu³⁺ (or Sm³⁺) ions occupy the Sb⁵⁺ and Gd³⁺ sites, respectively. The co-doping of Eu³⁺ ions or Sm³⁺ ions leads to lattice expansion of Ca₂GdSbO₆ matrix and a tuned narrow emission from deep-red to orangish-red. According to the ratio of luminescence intensity, the maximal S_a and S_r values are 0.19 K^-0 (347 K) and 1.38% K^-( (420 K) for Ca₂GdSbO₆:Mn⁴⁺/Eu³⁺ probe and 0.26 K^-p (363 K) and 1.55% K^-( (430 K) for Ca₂GdSbO₆:Mn⁴⁺/Sm³⁺ probe thermometers, respectively. In addition, thermometers based on Mn⁴⁺ emission lifetimes can provide the highest relative sensitivity of 1.47% K^-s at 425 K. Thus, the highly-temperature-sensitive Ca₂GdSbO₆:Mn⁴⁺/(Eu³⁺ or Sm³⁺) phosphor is a promising candidate for practical luminescence thermometers.

Enhanced luminescence performances of BaLaMgTaO6:Mn4+ red phosphor by Bi3+, Ca2+ doping for indoor plant lighting supplementary LED

A new perovskite BaLaMgTaO₆:Mn⁴⁺ (BLMTO:Mn⁴⁺) red phosphor was synthesized for the first time via the high-temperature solid-state method. The emission band of the phosphor ranges from 650 to 750 nm, which matches well with the absorption band of P_FR and P_R. By doping of Bi³⁺ and Ca²⁺ ions in the BLMTO:Mn⁴⁺ phosphor, a 4.76-fold enhancement in the luminescence emission intensity was achieved. The optimized BLMTO:0.5%Mn⁴⁺, 1.5%Bi³⁺, 2%Ca²⁺ phosphor exhibited a high quantum efficiency of 65% and a high color purity of 98.1% with the chromaticity coordinate (CIE) at (0.733, 0.267). Finally, a LED device was fabricated with the BLMTO:0.5%Mn⁴⁺, 1.5%Bi³⁺, 2%Ca²⁺ phosphor for further agricultural lighting, which emits warm white light with a low color temperature of 3549 K. The result indicates that the BLMTO:Mn⁴⁺, Bi³⁺, Ca²⁺ phosphors have a potential for applications in agricultural cultivations.

Elaborate Size-Tuning of Silica Aerogel Building Blocks Enables Laser-Driven Lighting

Silica aerogels with accurate building-block control are realized by adjusting the surfactant concentration during the synthesis process. The resulting silica-aerogel monolith with spherical building blocks of ≈24-40 nm, together with a deliberately created hole along the incident light direction, shows an incredibly promising application in monochromatic laser-driven lighting. The resulting coefficient of illuminance variation is as low as 8.1%, significantly outperforming commercially available ground-glass diffusers (139.0%) and polymer diffusers (249.1%); the speckle contrast is lower, as well as better, than that can be recognized by the human eye (4%), and the illuminance uniformity in the range of 0.770-0.862 is much better (higher) than that indoor workplace lighting required by the International Organization for Standardization. Lighting with any color in the visible spectrum, including white, can be obtained by using three primary color lasers (450, 532, and 638 nm) with different powers simultaneously as the light source. The resulting silica aerogel, which has excellent thermal stability, high laser-damage threshold, outstanding mechanical performance, and superhydrophobicity, can be further applied to long-distance and noncontact laser-driven lighting in rain or underwater without any additional encapsulation components.

Enhancement in the water resistance and thermal stability of Na3HTiF8:Mn4+ by co-doping with organic amine cations

Organic amine ions change the structural rigidity and improve the thermal stability and water resistance of phosphors.

Achieving highly thermostable red emission in singly Mn2+-doped BaXP2O7 (X = Mg/Zn) via self-reduction

The non-rare earth doped red phosphors are attracting wide attention for warm-white lighting and indoor plant cultivation applications. The Mn2+-doped phosphors have well spectral tunability and great potential to generate...

Thermal stability and self-reduction of a new red phosphor NaMg(PO3)3:Mn2+

For Mn-activated phosphors, the luminescent performance is strongly dependent on the oxidation state of Mn. In this paper, a series of red phosphors NaMg(PO3)3:xMn2+ (NMP:xMn2+) were synthesized by high temperature...

Microstructural origin of peculiar spectra and excellent luminescence properties of Y10Ta4O25:Eu3+ with a fluorite-related structure

Y10Ta4O25:Eu3+ presents peculiar spectra and excellent red luminescence properties due to its special fluorite-related structure. The microstructure was characterized by the site-selective luminescence of Eu3+ activators.

Photoluminescence and optical temperature measurement of Mn4+/Er3+ co-activated double perovskite phosphor through site-advantageous occupation

Because traditional methods based on thermal coupling energy level temperature measurement have large errors, a new temperature sensing strategy is proposed to attain strong sensitivity and excellent signal resolution ability. The rare-earth and also transition metal ions with poles apart thermal quenching channels are used as dual emission centers to find a suitable host to achieve high-efficiency dual-mode emission. In this work, a string of phosphors with NaLaMgWO₆ (NLMW) as the host, the single-doped and double-doped Mn⁴⁺ and Er³⁺ phosphors were adopted by the traditional high temperature solid-state reaction method. The crystallographic structure of the phosphor was analyzed by X-ray power diffraction and Rietveld refinement methods, and the results showed that a pure double perovskite phosphor with a monoclinic structure was successfully prepared. The photoluminescence excitation and emission spectrum properties, CIE chromaticity coordinates and photoluminescence spectra at different temperatures are detailed studied. Excited by ultraviolet light (300 nm), corresponding to the ⁴A₂→⁴T₁ transition of Mn⁴⁺ and the charge transfer from O^2- to W⁶⁺ of Er³⁺. There is no energy transfer between Mn⁴⁺ and Er³⁺. NLMW:Mn⁴⁺/Er³⁺ phosphors were especially sensitive to temperature changes within the scope of 303 K to 523 K. As the temperature increases, the fluorescence intensity of Mn⁴⁺ is thermally quenched faster than Er³⁺. The luminescent intensity ratio of Er³⁺ thermal coupling level and the FIR of Er³⁺/Mn⁴⁺ are used to study the temperature performance. The results show that the maximum relative sensitivity of FIR up to 1.31% K^-1, which is higher than the maximum temperature sensitivity based on the thermal coupling energy level, and which is beyond most of the non-contact temperature measurement materials previously reported, confirming that NLMW:Mn⁴⁺/Er³⁺ phosphors have application potential in non-contact temperature measurement.

Research on the quantum confinement effect and enhanced luminescence of red-emitting P5+-doped CaAl12O19:Mn4+,Mg2+ phosphors

Mn⁴⁺-activated oxide red phosphors are always a hot topic in the luminescent material field to solve the lack of red light components in white-light-emitting diodes (WLEDs). Herein, a series of novel deep red-emitting CaAl_12-mP_mO_19+m:0.01Mn⁴⁺,0.2Mg²⁺ (m = 0-0.15) phosphors were synthesized and their crystal structure, luminescence properties and thermal stability were investigated in detail. The high-valence P⁵⁺ is used to replace low-valence Al³⁺ in the luminescent host CaAl₁₂O₁₉ to improve the photoluminescence quantum yield (PLQY) of phosphors. The doping of P⁵⁺ does not change the crystal phase structure of phosphors, and the luminescence intensity and PLQY are significantly enhanced. The analysis of the photocurrent and fluorescence lifetime shows that an electron trap with a quantum-confinement structure is formed in the phosphor host, which plays a key role in buffering photogenerated electrons. Therefore, the PLQY of the P⁵⁺-doped CaAl_11.90P_0.1O_19.10:0.01Mn⁴⁺,0.2Mg²⁺ phosphor increased from 9.8% (P⁵⁺-undoped) to 70.2%, and the mechanism of PLQY enhancement is proposed based on the analysis of the crystal structure. Furthermore, the phosphor has superior thermal stability and color purity (96.8%). Overall, this work provides new insights and ideas on quantum confinement effects for improving the quantum yield of Mn⁴⁺-activated luminescent materials.

A colorimetric optical thermometry of host-sensitized Pr3+-doped niobate phosphors based on electronic-rich-site strategy

Most praseodymium-doped red-emitting phosphors need high-temperature synthesis conditions with a reducing atmosphere. The niobate matrix selected in this work provides a sufficient electron-rich-site environment for praseodymium through charge migration, and praseodymium can be self-reduced in air atmosphere, which is safe and environmentally friendly. By building the [NbO₆] group → Pr³⁺ energy transfer and finely modifying the doping concentration of Pr³⁺ ions, we constructed a dual-luminescence-system of the [NbO₆] group and Pr³⁺. Thereby, optical temperature measurement based on fluorescence intensity ratio (FIR) technology of Pr³⁺ ions and [NbO₆] groups was carried out using non-thermal coupling pairs, through the Boltzmann fitting and integral calculation, the maximum S_r and S_a values were 2.25% K^-1 and 0.0049 K^-1 at 403 K and 443 K, respectively, the S_r value is four times that obtained from the thermal coupling of Pr³⁺ ions, which exceeded most values previously reported for the fluorescence powder. Accordingly, we also studied the thermal sensitivity of Er³⁺ ions and Eu³⁺ ions mono-doped CaNb₂O₆ substrates. Results reveal that CaNb₂O₆:Pr³⁺/Er³⁺/Eu³⁺ phosphors have splendid temperature sensitivity and have far-reaching application prospects in the field of temperature measurements.

Ba3YB3O9 based phosphor ceramic plates with excellent thermal stability for wLED applications

A series of Eu3+ and Tb3+ singly doped Ba3YB3O9 phosphors were synthesized by a solution combustion approach. The most luminescent phosphors were selected as the starting materials to fabricate phosphor ceramic plates (PCPs). More intense red and green emission is observed from the PCPs than the corresponding phosphors. The emission colour can be effectively tuned by varying the mass ratio of the red and green phosphors and the excitation wavelength. White light emission was obtained by incorporating the blue-emitting Eu2+ doped BaMgAl10O17 phosphor into the PCP component. The synthesized phosphors and PCPs show robust thermal stability, maintaining more than 80% of emission intensity at 423 K of that at 298 K after a long time operation. The results indicate that the prepared red and green PCPs are promising candidates for high-power wLED applications.

Thermally stable and highly efficient red-emitting Eu3+-doped Cs3GdGe3O9 phosphors for WLEDs: non-concentration quenching and negative thermal expansion

Red phosphor materials play a key role in improving the lighting and backlit display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). However, the development of a red phosphor with simultaneous high efficiency, excellent thermal stability and high colour purity is still a challenge. In this work, unique non-concentration quenching in solid-solution Cs₃Gd_1 - xGe₃O₉:xEu³⁺ (CGGO:xEu³⁺) (x = 0.1-1.0) phosphors is successfully developed to achieve a highly efficient red-emitting Cs₃EuGe₃O₉ (CEGO) phosphor. Under the optimal 464 nm blue light excitation, CEGO shows a strong red emission at 611 nm with a high colour purity of 95.07% and a high internal quantum efficiency of 94%. Impressively, this red-emitting CEGO phosphor exhibits a better thermal stability at higher temperatures (175-250 °C, >90%) than typical red K₂SiF₆:Mn⁴⁺ and Y₂O₃:Eu³⁺ phosphors, and has a remarkable volumetric negative thermal expansion (coefficient of thermal expansion, α = -5.06 × 10^-5/°C, 25-250 °C). By employing this red CEGO phosphor, a fabricated pc-WLED emits warm white light with colour coordinates (0.364, 0.383), a high colour rendering index (CRI = 89.7), and a low colour coordinate temperature (CCT = 4508 K). These results indicate that this highly efficient red-emitting phosphor has great potential as a red component for pc-WLEDs, opening a new perspective for developing new phosphor materials.

Preparation of zero-thermal-quenching tunable emission bismuth-containing phosphors through the topochemical design of ligand configuration

We report a high performance bismuth-containing phosphor with zero-thermal-quenching, which can be used for white light illumination and non-contact temperature sensing.

Red-tunable LuAG garnet phosphors via Eu3+→Mn4+ energy transfer for optical thermometry sensor application

The Eu³⁺→Mn⁴⁺ energy transfer strategy is designed in the Lu₃Al₅O₁₂ garnet structure to achieve color-adjustable narrow emission from orangish-red to deep-red light and remarkable thermal quenching improvement for optical thermometry sensors.

Complex crystal structure and photoluminescence of Bi3+-doped and Bi3+/Eu3+ co-doped Ca7Mg2Ga6O18

The multiple and site-selective occupancies of Bi³⁺ activators in Ca₇Mg₂Ga₆O₁₈:xBi³⁺ lead to a continuous red-shift of the broad emission band upon increasing the Bi³⁺-content.