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A SrLiAl3N4:Eu2+ (SLA) red phosphor prepared through a high-pressure solid-state reaction was coated with an organosilica layer with a thickness of 400-600 nm to improve its water resistance. The observed 4f65d→4f7 transition bands are thought to result from the existence of Eu2+ at two different Sr2+ sites. Luminescence spectra at 10 K revealed two zero-phonon lines at 15377 (for Eu(Sr1)) and 15780 cm−1 (for Eu(Sr2)). The phosphor exhibited stable red emission under high pressure up to 312 kbar. The configurational coordinate diagram gave a theoretical explanation for the Eu2+/3+ result. The coated samples showed excellent moisture resistance while retaining an external quantum efficiency (EQE) of 70 % of their initial EQE after aging for 5 days under harsh conditions. White-light-emitting diodes of the SLA red phosphor and a commercial Y3Al5O12:Ce3+ yellow phosphor on a blue InGaN chip showed high color rendition (CRI=89, R9=69) and a low correlated color temperature of 2406 K. [ABSTRACT FROM AUTHOR]

Abstract: Luminescent emission spectra and excitation spectra of Pr0.016Si5.9Al0.1O0.1N7.9 (β-SiAlON:Pr3+) were measured. Emission upon UV excitation consists of sharp lines peaked between 600 and 630nm, related to the 1D2→3H4 and 3P0→3H6 transitions in Pr3+ ion. Two other group of lines peaked between 500 and 530nm and between 640 and 680nm are related to the 3P0→3H4 and 3P0→3FJ transitions, respectively. Excitation spectrum of the β-SiAlON:Pr3+ luminescence (observed at 641nm and at 632nm) consists of sharp lines in the spectral region 450–500nm related to the 3H4→3P0, 3P1, 3P2 transitions and two broad bands peaked at 280 and 330nm attributed to ionization of Pr3+. Emission obtained upon excitation at 330nm band contains additional peaks besides earlier observed upon excitation at 280nm band and under excitation in the 3H4→3P2 absorption region. These additional lines were attributed to the second site of Pr3+ (Wyckoff letter 2a) where Pr3+ ions occupy the interstitial positions of nine-fold coordinated by nitrogen/oxygen ions. [Copyright &y& Elsevier]

Abstract: Luminescence kinetics and time-resolved luminescence spectra of SiO2, SiO2 doped with ZnS:Mn2+ nanocrystals and SiO2 doped with ZnS:Mn2+, and additionally co-doped with Tb3+, are presented. The purposes of the paper are the analysis of the kinetics of the Tb3+ and Mn2+ intra-shell luminescence and the elucidation of the energy-transfer mechanism between the ZnS:Mn2+ nanocrystals and the Tb3+ ions. We have found a blue luminescence related to defects in the ZnS nanocrystals and an intrinsic luminescence of the SiO2 lattice, which decays in few ns. A yellow luminescence related to the Mn2+ 4T1(G)→6A1 transition and yellow sharp lines related to the 5D4→7F6, 7F5, 7F4 and 7F3 transitions in Tb3+ are found to decay in ms. A very effective energy transfer between ZnS:Mn2+ nanoparticles and Tb3+ ions has been observed. [Copyright &y& Elsevier]

Abstract: A material consisting of Tb3+ ions and ZnS:Mn2+ nanocrystals was prepared by impregnation of silica gel. Comparison of its luminescence properties suggests energy transfer from excited ZnS nanocrystals to Tb3+ ions. Mn2+ ions as dopants in ZnS are inactive in the energy transfer process, since no further energy transfer to Tb3+ is possible when the ZnS:Mn2+ system relaxes to the Mn2+ excited state.. [Copyright &y& Elsevier]

This study presents the impact of temperature and pressure on AlN:Mn2+ luminescence kinetics. Unusual behavior of Mn2+ optical properties during UV excitation is observed, where a strong afterglow luminescence of Mn2+ occurs even at low temperatures. When the temperature increases, the contribution of the afterglow luminescence is further enhanced, causing a significant increase in the luminescence intensity. The observed phenomena may be explained by an energy diagram in which the ON–VAl complex in AlN:Mn2+ plays a key role. Hence the ON–VAl complex defect in AlN:Mn2+ plays a double role. When the ON–VAl defect is located close to Mn2+ ions, it is responsible for transferring excitation energy directly to Mn2+ ions. However, when the ON–VAl defect complex is located far from Mn2+ ions, its excited state level acts as an electron trap responsible for afterglow luminescence. Additionally, three models have been tested to explain the structure of the emission spectrum and the strong asymmetry between the excitation and emission spectra. From the most straightforward configuration coordinate diagram through the configuration coordinate diagram model assuming different elastic constants in the excited and ground-states ending by a model based on the Jahn–Teller effect. We proved that only the Jahn–Teller effect in the excited 4T1 electronic state with spin–orbit coupling could fully explain the observed phenomena. Finally, high-pressure spectroscopic results complemented by the calculations of Racah parameters and the Tanabe–Sugano diagram are presented. [ABSTRACT FROM AUTHOR]

Highlights: [•] Pressure induced of the 5D3 luminescence. [•] Kinetics of the 5D0, 5D1 and 5D2 emission under pressure. [•] Configurational diagram of the Y2O2S:Eu3+ system. [Copyright &y& Elsevier]

Highlights: [•] Luminescence properties of β-Ca2SiO4 doped with Eu2+ and Eu3+ are studied. [•] Short distance compensation model of the Eu3+ replacing Ca2+ is discussed. [•] The existence of stable Eu2+ and Eu3+ was discussed in relation to the Fermi level. [ABSTRACT FROM AUTHOR]

Abstract: Three-component luminescent material consisting of silica xerogel as a support with immobilized ZnS:Mn2+ nanocrystals and Tb3+ ions was compared with such two-component materials as the silica support with ZnS:Mn2+ as well as the support with Tb3+. In each case the nanocrystals and the lanthanide ions were immobilized at silica surface by impregnation procedure. Size of the ZnS quantum dots doped with Mn2+ were estimated by Scherrer method from the X-ray diffraction (XRD) pattern. The materials have been characterized by EPR and optical spectroscopy techniques. EPR spectra allow to distinguish two different Mn2+ sites: the first is assigned to isolated Mn2+ substitutionally and incorporated into cubic ZnS lattice and the second is ascribed to the Mn2+ situated near the nanocrystal surface. From the optical spectra we have found that in the three-component material, energy transfer from excited ZnS:Mn2+ nanocrystals to Tb3+ ions takes place. The different mechanisms of such transfer are discussed. [Copyright &y& Elsevier]

Distinct types of luminescence that are activated by various stimuli in a single material offer exciting developmental opportunities for functional materials. A versatile sensing platform that exhibits photoluminescence (PL), persistent luminescence (PersL), and mechanoluminescence (ML) is introduced, which enables the sensitive detection of temperature, pressure, and force/stress. The developed Sr 2 MgSi 2 O 7 :Eu 2+ /Dy 3+ material exhibits a linear relationship between ML intensity and force and can be used as an ML stress sensor. Additionally, the bandwidth of the PL emission band and the PL lifetime of this material are remarkably sensitive to temperature, with values of ≈0.05 nm K -1 and 1.29%/K, respectively. This study demonstrates PersL pressure sensing for the first time, using long-lasting (seconds) lifetime as a manometric parameter. The developed material functions as an exceptionally sensitive triple-mode visual pressure sensor; specifically, it exhibits: i) a sensitivity of ≈-297.4 cm GPa -1 (8.11 nm GPa -1 ) in bandshift mode, ii) a sensitivity of ≈272.7 cm -1 /GPa (14.8 nm GPa -1 ) in bandwidth mode, and iii) a sensitivity of 42%GPa -1 in PL-lifetime mode, which is the highest value reported to date. Notably, anti-counterfeiting, night-vision safety-sign, 8-bit optical-coding, and QR-code applications that exhibit intense PersL are demonstrated by 3D-printing the studied material in combination with a polymer., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Microplastics (MPs) are plastic particles between 0.1 and 5,000 µm in size that can contaminate food. Unfortunately, to date, little attention has been paid to analyzing the presence of such particles in baby foods. The present study aimed to determine the degree of contamination of infant formula with MPs. A total of thirty products were subjected to analysis. The research methodology used included the isolation of plastic particles, identification and characterization of MPs using advanced microscopic and spectroscopic techniques. Microplastics were detected in all tested samples. The most frequently identified polymers were polyamide, polyethylene, polypropylene, and poly(ethylene terephthalate). The particles exhibited diverse forms, including fibers, fragments, and films, displaying a range of colors such as colorless, black, and brown particles. Furthermore, the daily intake of MPs by children fed exclusively infant formula was estimated to be approximately 49 ± 32 MPs. This poses a potential health risk for the youngest., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

The growing interest in the use of near-infrared (NIR) radiation for spectroscopy, optical communication, and medical applications spanning both NIR-I (700-900 nm) and NIR-II (900-1700 nm) has driven the need for new NIR light sources. NIR phosphor-converted light-emitting diodes (pc-LEDs) are expected to replace traditional lamps mainly due to their high efficiency and compact design. Broadband NIR phosphors activated by Cr 3+ and Cr 4+ have attracted significant research interest, offering emission across a wide range from 700 to 1700 nm. In this work, we synthesized a series of Sc 2(1- x ) Ga 2 x O 3 :Cr 3+/4+ materials ( x = 0-0.2) with broadband NIR-I (Cr 3+ ) and NIR-II (Cr 4+ ) emission. We observed a substantial increase in the intensity of Cr 3+ (approximately 77 times) by incorporating Ga 3+ ions. Additionally, our investigation revealed that energy transfer occurred between Cr 3+ and Cr 4+ ions. Configuration diagrams are presented to elucidate the behavior of Cr 3+ and Cr 4+ ions within the Sc 2 O 3 matrix. We also observed a phase transition at a pressure of 20.2 GPa, resulting in a new unknown phase where Cr 3+ luminescence exhibited a high-symmetry environment. Notably, this study presents the pressure-induced shift of NIR Cr 4+ luminescence in Sc 2(1- x ) Ga 2 x O 3 :Cr 3+/4+ . The linear shifts were estimated at 83 ± 3 and 61 ± 6 cm -1 /GPa before and after the phase transition. Overall, our findings shed light on the synthesis, luminescent properties, temperature, and high-pressure behavior within the Sc 2(1- x ) Ga 2 x O 3 :Cr 3+/4+ materials. This research contributes to the understanding and potential applications of these materials in the development of efficient NIR light sources and other optical devices., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Cr-doped inorganic materials are pivotal in developing near-infrared optical materials; however, multivalent Cr ions and their respective distribution in the materials remain ambiguous. Herein, a series of Li(Sc 1- x In x )O 2 :Cr phosphors containing both Cr 3+ /Cr 6+ ions are prepared. High-resolution synchrotron X-ray diffraction (XRD) reveals two similar phases in Li(Sc 1 -x In x )O 2 . Raman spectra further confirm distinct scattering patterns for the two end-member compositions, corroborating the findings from the synchrotron XRD analysis. Cr K -edge X-ray absorption near-edge structure and extended X-ray absorption fine structure demonstrate that most Cr ions in the as-prepared samples are Cr 6+ , while Cr 3+ becomes dominant after washing with water. Moreover, the source and distribution of Cr 3+ and Cr 6+ ions in the as-prepared and washed samples are revealed through X-ray fluorescence and X-ray excited optical luminescence techniques, which indicate that Cr 6+ ions aggregate within the sample, while Cr 3+ ions are evenly distributed. Photoluminescence, decay curves, and line shape analyses are implemented to resolve the electron-lattice interactions, and the corresponding mechanisms are provided to explain the asymmetry between photoluminescence and photoluminescence excitation spectra. Overall, this study provides valuable insights into the distribution of low-concentration multivalence ions in solid-state materials and offers a deeper understanding of the approaches to precisely resolve the subtle changes in the crystal structure.

Endowing a single material with various types of luminescence, that is, exhibiting a simultaneous optical response to different stimuli, is vital in various fields. A photoluminescence (PL)- and mechanoluminescence (ML)-based multifunctional sensing platform is built by combining heterojunctioned ZnS/CaZnOS:Mn 2+ mechano-photonic materials using a 3D-printing technique and fiber spinning. ML-active particles are embedded in micrometer-sized cellulose fibers for flexible optical devices capable of emitting light driven by mechanical force. Individually modified 3D-printed hard units that exhibit intense ML in response to mechanical deformation, such as impact and friction, are also fabricated. Importantly, they also allow low-pressure sensing up to ≈100 bar, a range previously inaccessible by any other optical sensing technique. Moreover, the developed optical manometer based on the PL of the materials demonstrates a superior high-pressure sensitivity of ≈6.20 nm GPa -1 . Using this sensing platform, four modes of temperature detection can be achieved: excitation-band spectral shifts, emission-band spectral shifts, bandwidth broadening, and lifetime shortening. This work supports the possibility of mass production of ML-active mechanical and optoelectronic parts integrated with scientific and industrial tools and apparatus., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

CuLaO 2 is a rare-earth and dopant-free inorganic compound able to emit green light upon blue excitation. Its absorption amounts to 90% but its internal quantum efficiency is poor (<17%). The origin of this deleterious radiationless behavior is addressed by investigating the spectroscopic properties of this compound under the action of temperature and hydrostatic pressure in the 15-400 K and 1 bar-40 kbar intervals, and by combining the spectroscopic data with earlier results of DFT calculations. A two-step radiationless process is demonstrated, involving radiative re-absorption and cross-over to excitonic states.

This research focuses on LPE growth, and the examination of the optical and photovoltaic properties of single crystalline film (SCF) phosphors based on Ce 3+ -doped Y 3 Mg x Si y Al 5-x-y O 12 garnets with Mg and Si contents in x = 0-0.345 and y = 0-0.31 ranges. The absorbance, luminescence, scintillation, and photocurrent properties of Y 3 Mg x Si y Al 5-x-y O 12 :Ce SCFs were examined in comparison with Y 3 Al 5 O 12 :Ce (YAG:Ce) counterpart. Especially prepared YAG:Ce SCFs with a low (x, y < 0.1) concentration of Mg 2+ and Mg 2+ -Si 4+ codopants also showed a photocurrent that increased with rising Mg 2+ and Si 4+ concentrations. Mg 2+ excess was systematically present in as-grown Y 3 Mg x Si y Al 5-x-y O 12 :Ce SCFs. The as-grown SCFs of these garnets under the excitation of α-particles had a low light yield (LY) and a fast scintillation response with a decay time in the ns range due to producing the Ce 4+ ions as compensators for the Mg 2+ excess. The Ce 4+ dopant recharged to the Ce 3+ state after SCF annealing at T > 1000 °C in a reducing atmosphere (95%N 2 + 5%H 2 ). Annealed SCF samples exhibited an LY of around 42% and similar scintillation decay kinetics to those of the YAG:Ce SCF counterpart. The photoluminescence studies of Y 3 Mg x Si y Al 5-x-y O 12 :Ce SCFs provide evidence for Ce 3+ multicenter formation and the presence of an energy transfer between various Ce 3+ multicenters. The Ce 3+ multicenters possessed variable crystal field strengths in the nonequivalent dodecahedral sites of the garnet host due to the substitution of the octahedral positions by Mg 2+ and the tetrahedral positions by Si 4+ . In comparison with YAG:Ce SCF, the Ce 3+ luminescence spectra of Y 3 Mg x Si y Al 5-x-y O 12 :Ce SCFs greatly expanded in the red region. Using these beneficial trends of changes in the optical and photocurrent properties of Y 3 Mg x Si y Al 5-x-y O 12 :Ce garnets as a result of Mg 2+ and Si 4+ alloying, a new generation of SCF converters for white LEDs, photovoltaics, and scintillators could be developed.

Erbium (Er) complexes are used as optical gain materials for signal generation in the telecom C-band at 1540 nm, but they need a sensitizer to enhance absorption. Na + substitution for Ag + and Bi 3+ doping at the In 3+ site is a possible strategy to enhance the broadband emission of Cs 2 AgInCl 6 , which could be used as a sensitizer for energy transfer to rare-earth elements. Herein, self-trapped exciton (STE) energy transfer to Er 3+ at 1540 nm in double perovskite is reported. An acid precipitation method was used to synthesize Cs 2 AgInCl 6 and its derivatives with Er 3+ , Bi 3+ , and Na + . Bare Cs 2 AgInCl 6 :Er emission signals were found to be weak at 1540 nm, but Bi 3+ doping increased them by 12 times, and Bi 3+ and Na + doping increased signal intensity by up to 25 times. Electron paramagnetic resonance spectroscopy characterized a decrease in axial symmetry over the Er 3+ ions after the substitutions of Na + and Bi 3+ in Cs 2 AgInCl 6 at low temperatures (<7 K) for the first time. Moreover, an increase in pressure compressed the structure, which tuned the STE transition for free exciton emission, and a further increase in pressure distorted the cubic phase above 70 kbar.

This study presents the impact of temperature and pressure on AlN:Mn 2+ luminescence kinetics. Unusual behavior of Mn 2+ optical properties during UV excitation is observed, where a strong afterglow luminescence of Mn 2+ occurs even at low temperatures. When the temperature increases, the contribution of the afterglow luminescence is further enhanced, causing a significant increase in the luminescence intensity. The observed phenomena may be explained by an energy diagram in which the O N -V Al complex in AlN:Mn 2+ plays a key role. Hence the O N -V Al complex defect in AlN:Mn 2+ plays a double role. When the O N -V Al defect is located close to Mn 2+ ions, it is responsible for transferring excitation energy directly to Mn 2+ ions. However, when the O N -V Al defect complex is located far from Mn 2+ ions, its excited state level acts as an electron trap responsible for afterglow luminescence. Additionally, three models have been tested to explain the structure of the emission spectrum and the strong asymmetry between the excitation and emission spectra. From the most straightforward configuration coordinate diagram through the configuration coordinate diagram model assuming different elastic constants in the excited and ground-states ending by a model based on the Jahn-Teller effect. We proved that only the Jahn-Teller effect in the excited 4 T 1 electronic state with spin-orbit coupling could fully explain the observed phenomena. Finally, high-pressure spectroscopic results complemented by the calculations of Racah parameters and the Tanabe-Sugano diagram are presented.

Organic-inorganic hybrid metal halides have recently attracted attention in the global research field for their bright light emission, tunable photoluminescence wavelength, and convenient synthesis method. This study reports the detailed properties of (C 10 H 16 N) 2 MnBr 4 , which emits bright green light with a high photoluminescence quantum yield. Results of powder X-ray diffraction, photoluminescence, thermogravimetric analysis, and Raman spectra show the phase transition of (C 10 H 16 N) 2 MnBr 4 at 430 K. This phase transition was identified as the solid to liquid state of (C 10 H 16 N) 2 MnBr 4 . Moreover, the pressure- and temperature-induced relationship between structural and optical properties in (C 10 H 16 N) 2 MnBr 4 can be identified. This investigation provides deep insights into the luminescent properties of metal halide crystals and promotes further research.

Here, we report a halide precursor acid precipitation method to synthesize Cs 2 AgIn 1- x Bi x Cl 6 ( x = 0, 0.02, 0.04, 0.08, 0.16, 0.32, 0.64, and 1) microcrystals. Cs 2 AgInCl 6 and Bi derivative double perovskites show broadband white light emission via self-trapped excitons (STEs) and have achieved the highest internal quantum efficiency of up to 52.4% at x = 0.08. Synchrotron X-ray diffraction confirmed the linear increase of lattice parameters and cell volume with Bi 3+ substitution at In 3+ sites. Absorbance, photocurrent excitation, and photoluminescence excitation spectra are used to observe possible transitions from the valence to the conduction band or free exciton (FE) states as well as transitions within local Bi 3+ states. The broadband photoluminescence is quenched via a single nonradiative process with an activation energy Δ E = 1490 cm -1 for Cs 2 AgIn 0.92 Bi 0.08 Cl 6 . Under normal conditions, we observed STE emission, but applying external pressure alters the electronic structure such that at elevated pressure, the only emission via the FE state is observed. We anticipate that structure, temperature and pressure-dependent photoluminescence studies will help the future use of a single-source lead-free double perovskite for white light-emitting diode applications.

Portable near-infrared (NIR) light sources are in high demand for applications in spectroscopy, night vision, bioimaging, and many others. Typical phosphor designs feature isolated Cr 3+ ion centers, and it is challenging to design broadband NIR phosphors based on Cr 3+ -Cr 3+ pairs. Here, we explore the solid-solution series SrAl 11.88- x Ga x O 19 :0.12Cr 3+ ( x = 0, 2, 4, 6, 8, 10, and 12) as phosphors featuring Cr 3+ -Cr 3+ pairs and evaluate structure-property relations within the series. We establish the incorporation of Ga within the magentoplumbite-type structure at five distinct crystallographic sites and evaluate the effect of this incorporation on the Cr 3+ -Cr 3+ ion pair proximity. Electron paramagnetic measurements reveal the presence of both isolated Cr 3+ and Cr 3+ -Cr 3+ pairs, resulting in NIR luminescence at approximately 650-1050 nm. Unexpectedly, the origin of broadband NIR luminescence with a peak within the range 740-820 nm is related to the Cr 3+ -Cr 3+ ion pair. We demonstrate the application of the SrAl 5.88 Ga 6 O 19 :0.12Cr 3+ phosphor, which possesses an internal quantum efficiency of ∼85%, a radiant flux of ∼95 mW, and zero thermal quenching up to 500 K. This work provides a further understanding of spectral shifts in phosphor solid solutions and in particular the application of the magentoplumbites as promising next-generation NIR phosphor host systems.

Cs 4 PbI 6 , as a rarely investigated member of the Cs 4 PbX 6 (X is a halogen element) family, has been successfully synthesized at low temperatures, and the synthetic conditions have been optimized. Metal iodides such as LiI, KI, NiI 2 , CoI 2 , and ZnI 2 , as additives, play an important role in enhancing the formation of the Cs 4 PbI 6 microcrystals. ZnI 2 with the lowest dissociation energy is the most efficient additive to supply iodide ions, and its amount of addition has also been optimized. Strong red to near-infrared (NIR) emission properties have been detected, and its optical emission centers have been identified to be numerous embedded perovskite-type α-CsPbI 3 nanocrystallites (∼5 nm in diameter) based on investigations of temperature- and pressure-dependent photoluminescent properties. High-resolution transmission electron microscopy was used to detect these hidden nanoparticles, although the material was highly beam-sensitive and confirmed a "raisin bread"-like structure of the Cs 4 PbI 6 crystals. A NIR mini-LED for the biological application has been successfully fabricated using as-synthesized Cs 4 PbI 6 crystals. This work provides information for the future development of infrared fluorescent nanoscale perovskite materials.

Cs 4 PbBr 6 is regarded as an outstanding luminescent material with good thermal stability and optical performance. However, the mechanism of green emission from Cs 4 PbBr 6 has been controversial. Here we show that isolated CsPbBr 3 nanoparticles embedded within a Cs 4 PbBr 6 matrix give rise to a "normal" green luminescence while superfluorescence at longer wavelengths is suppressed. High-resolution transmission electron microscopy shows that the embedded CsPbBr 3 nanoparticles are around 3.8 nm in diameter and are well-separated from each other, perhaps by a strain-driven mechanism. This mechanism may enable other efficient luminescent composites to be developed by embedding optically active nanoparticles epitaxially within inert host lattices.

Phosphors with a rigid and symmetrical structure are urgently needed. The alkali lithosilicate family (A[Li 3 SiO 4 ]) has been extensively studied with a narrow emission band due to its unique cuboid-coordinated environment and rigid structure. However, here we demonstrate for the first time Ce-doped NaK 2 Li[Li 3 SiO 4 ] 4 phosphors with a broad emission band, a high internal quantum efficiency (85.6%), and excellent thermal stability. Photoluminescence indicates the Ce's preference to occupy the Na + site, leading to a strong blue color emission with peak maxima at 417 and 450 nm. Temperature- and pressure-dependent photoluminescence reveals thermal stability and a phase transition. Moreover, the X-ray absorption near-edge structure reveals the mixing of Ce 3+ and Ce 4+ in the materials; this result differs from that of Eu 2+ -doped A[Li 3 SiO 4 ] phosphors. The charge compensation process is then proposed to explain this difference. This study not only provides insights into Ce-doped UCr 4 C 4 -type phosphors but also explains the charge compensation mechanism of the aliovalent doping process.

The process of persistent luminescence or glow-in-the-dark, the delayed emission of light of irradiated substances, has long fascinated researchers, who have made efforts to explain the underlying physical phenomenon as well as put it to practical use. However, persistent luminescence is an elusive and difficult process, both in terms of controlling or altering its properties, as well as providing a quantitative description. In this paper, we used SrSi 2 N 2 O 2 :Eu 2+ as a model persistent phosphor, characterized by the broad distribution of structural defects and exhibiting long-lasting Eu 2+ luminescence that is visible for a few minutes after switching off UV light. We investigated the persistent luminescence process by two complementary methods, namely, thermoluminescence and temperature-dependent persistent luminescence decay measurements. Analysis of experimental data allowed us to determine the depth distribution of traps, and allowed us to distinguish two different mechanisms by which the emission is delayed. The first, the temperature-dependent mechanism, is related to trap activation, while the second, temperature-independent mechanism is related to carrier migration. Finally, we employed the strategy of the co-doping of the phosphor SrSi 2 N 2 O 2 :Eu 2+ ,M 3+ (M = Ce, Nd, Dy) to modify the persistent luminescence properties.

The systematic substitution of Ba in the Sr site of Sr[Mg 2 Al 2 N 4 ]:Eu 2+ generates a deep-red-emitting phosphor with enhanced thermal luminescence properties. Gas pressure sintering (GPS) of all-nitride starting materials in Molybdenum (Mo) crucibles yields pure-phase red-orange-colored phosphors. Peaks in the synchrotron X-ray diffraction (SXRD) data show a systematic shift toward smaller angles due to the introduction of the larger Ba cation in the same crystal structure. The photoluminescence property reveals that Ba substitution shifts the original emission wavelength of Sr[Mg 2 Al 2 N 4 ]:Eu 2+ (625 nm) toward ∼690 nm for Ba[Mg 2 Al 2 N 4 ]:Eu 2+ . Thermal stability measurement of Sr 1- x Ba x [Mg 2 Al 2 N 4 ] indicates a systematic increase in stability from x = 0 to x = 1. X-ray absorption near-edge spectroscopy (XANES) results demonstrate the coexistence of Eu 2+ and Eu 3+ . The red-shift and the enhanced thermal stability reveals that the distance of the emitting 5 d level to the conduction band of Ba[Mg 2 Al 2 N 4 ]:Eu 2+ is large. The ionic size mismatch of Eu occupying a Ba site reduces the symmetry, thereby further splitting the degenerate emitting 5 d level and lowering the energy of the emitting center. The development of deep-red phosphors emitting at 670-690 nm ( x = 0.8-1.0) offers possible candidates for plant lighting applications.

In this study, a series of Sr(LiAl 3 ) 1-x (SiMg 3 ) x N 4 :Eu 2+ (SLA-SSM) phosphors were synthesized by a solid-solution process. The emission peak maxima of SLA-SSM range from 615 nm to 680 nm, which indicates structural differences in these materials. 7 Li solid-state NMR spectroscopy was utilized to distinguish between the Li(1)N 4 and Li(2)N 4 tetrahedra in SLA-SSM. Differences in the coordination environments of the two Sr sites were found which explain the unexpected luminescent properties. Three discernible morphologies were detected by scanning electron microscopy. Temperature-dependent photoluminescence and decay times were used to understand the diverse environments of europium ions in the two strontium sites Sr1 and Sr2, which also support the NMR analysis. Moreover, X-ray absorption near-edge structure studies reveal that the Eu 2+ concentration in SLA-SSM is much higher than that in in SrLiAl 3 N 4 :Eu 2+ and SrSiMg 3 N 4 :Eu 2+ phosphors. Finally, an overall mechanism was proposed to explain the how the change in photoluminescence is controlled by the size of the coordinated cation., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

New results presented by Wang et al. showing the temperature dependence of the Y3Ga5O12:Ce3+ energy bandgap have been taken into account in the calculations of the changes of the energy distance between the lowest 5d state of Ce3+ and the edge of the conduction band. Our calculations show that the diminishing of the band gap energy with temperature has a negligible effect on the difference between the energy of the conduction band and the localized states of the 5d configuration of Ce3+, which means that the new experimental results do not undermine the validity of the conclusions of our previous paper.

In this work we present the results of photocurrent excitation spectroscopy (PCE) of Gd3Al2Ga3O12:Ce3+ (GAGG:Ce3+) and Gd3Ga5O12:Ce3+ (GGG:Ce3+) performed at temperatures ranging from 100 to 500 K supplemented by spectroscopic measurements (steady state and time resolved photoluminescence spectroscopy) performed at temperatures ranging from 10 to 500 K and at high pressure up to 300 kbar. The PCE spectra contain bands related to transitions from the ground state 2F5/2 of the 4f1 electronic configuration to the crystal field split states related to the 5d1 electronic configuration of Ce3+. This implicates the presence of the autoionization process - transfer of electrons from the localized, excited states of Ce3+ to the conduction band (CB), directly linked to luminescence quenching of Ce3+. The mechanism of autoionization of GAGG:Ce3+ and GGG:Ce3+ was determined to be different on the grounds of differences in temperature dependence of photocurrent intensity. The latter system exhibits autoionization, which occurs when all of the 5d excited states are degenerated with the CB, whereas in the former system, the autoionization process is thermally assisted with an activation energy barrier (distance to the edge of the CB) of approximately 1600 cm-1. In GGG:Ce3+ the degeneracy of 5d1 states of Ce3+ was lifted by application of high pressure, shifting the edge of the CB up and exposing Ce3+ luminescence at 20 kbar. Further spectroscopic analyses of the pressure-temperature dependence of the luminescence decay time as well as the temperature dependence of photocurrent intensity of GGG:Ce3+ have independently shown existence of a luminescence quenching state located approximately 600 cm-1 below the CB, attributed to the impurity trapped exciton.

Luminescence properties of SrS:Ce pellets sintered at 1700 °C were investigated under high pressure. Two different Ce3+-related emissions were confirmed to appear in the blue-green and red parts of the spectrum and were shown to shift significantly and linearly to longer wavelengths with increasing pressure. Changes in decay times of both emissions were also thoroughly analyzed. The results confirmed that Ce3+ ion pairing/clustering occurring due to their enhanced mobility at high temperatures is responsible for the appearance of the recently reported red Ce3+ emission in sintered SrS:Ce pellets.

Mn 4+ -doped fluoride phosphors have been widely used in wide-gamut backlighting devices because of their extremely narrow emission band. Solid solutions of Na 2 (Si x Ge 1-x )F 6 :Mn 4+ and Na 2 (Ge y Ti 1-y )F 6 :Mn 4+ were successfully synthesized to elucidate the behavior of the zero-phonon line (ZPL) in different structures. The ratio between ZPL and the highest emission intensity υ 6 phonon sideband exhibits a strong relationship with luminescent decay rate. First-principles calculations are conducted to model the variation in the structural and electronic properties of the prepared solid solutions as a function of the composition. To compensate for the limitations of the Rietveld refinement, electron paramagnetic resonance and high-resolution steady-state emission spectra are used to confirm the diverse local environment for Mn 4+ in the structure. Finally, the spectral luminous efficacy of radiation (LER) is used to reveal the important role of ZPL in practical applications., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Temperature dependence of the luminescence shape and decay time of narrow band Mn 4+ fluoride phosphors: Rb 2 GeF 6 :Mn 4+ and KNaSiF 6 :Mn 4+ was investigated. The temperature changes in the relative intensity between the zero-phonon line and both phonon sidebands were observed in both samples. The sideband spectra consist of three lines related to interaction with three different phonon modes labeled ν 3 , ν 4 and ν 6 . We present a comprehensive quantum theory which allows calculation of the luminescence intensity and the luminescence lifetime by simultaneously taking into account odd parity crystal fields, odd parity phonon modes and spin-orbit coupling. Since we include all modes, for which the respective interaction strengths and energies of the phonons are known, our approach does not involve any free parameters. We also discuss our results in relation to the temperature dependence of the lifetime of the 2 E g → 4 A 2g transition, taking into account the quantum efficiency of the system and the migration of the excitation energy. The presented model is applicable to all materials doped with Mn 4+ ions and also to any narrow line emitting phosphor, where a zero-phonon line and phonon structure is simultaneously observed in the emission spectrum.

A SrLiAl3 N4 :Eu(2+) (SLA) red phosphor prepared through a high-pressure solid-state reaction was coated with an organosilica layer with a thickness of 400-600 nm to improve its water resistance. The observed 4f(6) 5d→4f(7) transition bands are thought to result from the existence of Eu(2+) at two different Sr(2+) sites. Luminescence spectra at 10 K revealed two zero-phonon lines at 15377 (for Eu(Sr1)) and 15780 cm(-1) (for Eu(Sr2)). The phosphor exhibited stable red emission under high pressure up to 312 kbar. The configurational coordinate diagram gave a theoretical explanation for the Eu(2+/3+) result. The coated samples showed excellent moisture resistance while retaining an external quantum efficiency (EQE) of 70 % of their initial EQE after aging for 5 days under harsh conditions. White-light-emitting diodes of the SLA red phosphor and a commercial Y3 Al5 O12 :Ce(3+) yellow phosphor on a blue InGaN chip showed high color rendition (CRI=89, R9=69) and a low correlated color temperature of 2406 K., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Red phosphors AMF6:Mn(4+) (A = Na, K, Cs, Ba, Rb; M = Si, Ti, Ge) have been widely studied due to the narrow red emission bands around 630 nm. The different emission of the zero-phonon line (ZPL) may affect the color rendering index of white light-emitting diodes (WLED). The primary reason behind the emergence and intensity of ZPL, taking KNaSiF6:Mn(4+) as an example, was investigated here. The effects of pressure on crystal structure and luminescence were determined experimentally and theoretically. The increase of band gap, red shift of emission spectrum and blue shift of excitation spectrum were observed with higher applied pressure. The angles of ∠FMnF and ∠FMF(M = Si, Ti, Ge) were found clearly distorted from 180° in MF6(2-) octahedron with strong ZPL intensity. The larger distorted SiF6(2-) octahedron, the stronger ZPL intensity. This research provides a new perspective to address the ZPL intensity problem of the hexafluorosilicate phosphors caused by crystal distortion and pressure-dependence of the luminescence. The efficacy of the device featuring from Y3Al5O12:Ce(3+) (YAG) and KNaSiF6:Mn(4+) phosphor was 118 lm/W with the color temperature of 3455 K. These results reveal that KNaSiF6:Mn(4+) presents good luminescent properties and could be a potential candidate material for application in back-lighting systems.