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In order to obtain novel and more efficient red light‐emitting materials, a series of Sr2[Mg1−xLixAl5−xSixN7] : 0.01Eu2+ (SMAN‐xLS, 0≤x≤0.5) red phosphors were devised and successfully synthesized via the high temperature solid state reaction and the effects of the co‐substitution of [Mg−Al]5+ by [Li−Si]5+ on structural and luminescence properties is investigated in detail. A series of powder XRD data and Rietveld refinement indicate that [Li−Si]5+ co‐substitution can successfully enter the Sr2[MgAl5N7] : 0.01Eu2+ (SMAN) lattice. With the entry of [Li−Si]5+ into the lattice, the substitution of Al3+ by Si4+ leads to the weakening of the nephelauxetic effect of the 5d level of Eu2+, which shifts the emission peak from 657 nm to 647 nm and reduces the excitation in the green region, i.e., lowers the absorption of green light. When the amount of [Li−Si]5+ co‐substitution is x=0.1, the luminescence intensity and thermal stability of the sample are enhanced, in which the external quantum efficiency (EQE), reflecting the luminescence intensity, is elevated by 49.6 %. The increase in lattice rigidity gives rise to higher luminescence intensity, and the introduced trap levels for the compensation of luminescence enhances the thermal stability. Under blue laser excitation, the SMAN‐0.1LS can achieve an ultra‐high luminescence saturation threshold of 52.22 W/mm2, which is remarkably superior to other existing red phosphors, a breakthrough performance that has enormous potential for application in high‐power laser display light sources. Cathodoluminescence (CL) characterization and measurements attest to the favorable CL properties of SMAN‐0.1LS. By measuring the pressure‐dependent luminescence of SMAN‐0.1LS, the emission peak can be shifted from 650 nm to 702 nm with the increase of pressure, and the sensitivity dλ/dP is 5.07 nm/GPa, which is indicative of the potential application of this system as an optical pressure sensor. [ABSTRACT FROM AUTHOR]

The Eu2+‐activated nitride phosphors have been widely used in solid‐state lighting, but the applications in high‐power white‐light‐emitting diodes (wLEDs) field require higher thermal stability of luminescent materials. The oxidation of Eu2+ and the damage of nitride host in the Eu2+‐activated nitride phosphors are the two crucial reasons for the luminescence loss while operating. A superficial organic carbon modification is performed on the red‐emitting (Sr,Ca)AlSiN3:Eu2+ phosphor via the incorporation of organic carbon by solution mixing and thermal post‐treatment under the N2‐H2 atmosphere. After the superficial organic carbon modification, the oxidation of Eu2+ and the formation of impurity phases on the phosphor surface are effectively reduced. When the superficial organic carbon modified sample was treated in the 2 wt.% sucrose solutions, the relative brightness is strengthened by 2.15%, the thermal quenching characteristic is improved by 8.9% at 300℃, and the aging test results show an excellent thermal stability. All above indicate that the superficial organic carbon modification is a promising technique to enhance the thermal stability of analogous Eu2+‐activated nirtide phosphors. [ABSTRACT FROM AUTHOR]

To satisfy increasing stringent application requirements for high power wLEDs, we propose a superficial carbon modification method to enhance thermal stability of red‐emitting CaAlSiN3:Eu2+ phosphor via carbon coating by mechanical mixing and thermal post‐treatment at high temperature under N2‐H2 atmosphere. The modifications on the crystal surface include (a) elimination of amorphous phase, (b) introduction of carbon and (c) inhibition of the oxidation of Eu2+. During the whole processing, the route of carbon and its effects on the crystal structure and luminescence properties are investigated by XPS, TEM, SEM, Raman spectra and TG‐DSC analysis. After superficial carbon modification, the thermal quenching characteristic is improved by 5.7%, and the relative brightness decays more slowly during the aging test, which means that the superficial carbon modified samples still maintain good luminescence performance at high temperature and have superior performance for long‐term applications. All above indicate that the superficial carbon modification method is a promising application to enhance the thermal stability for analogous Eu2+‐activated nitride phosphors. [ABSTRACT FROM AUTHOR]

Broadband near‐infrared (NIR) phosphors have received increasing attention for fabricating phosphor‐converted light‐emitting diodes (pc‐LEDs) as NIR light source. Most of the reported broadband NIR phosphors originate from Cr3+ in weak crystal field environments. Herein, we report a luminescent material, MgAlSiN3:Mn2+ with CaAlSiN3‐type structure, demonstrating that broadband deep‐red‐to‐NIR emission can be achieved via doping Mn2+ into crystallographic sites with strong crystal field in inorganic solids. This phosphor is synthesized via easy‐handle solid‐state reaction, and the optimized sample, (Mg0.93Mn0.07) AlSiN3 shows an emission band with peak at ~754 nm, FWHM of 150 nm, and internal quantum efficiency of 70.1%. The photoluminescence intensity can further be enhanced by co‐doping Eu2+ as sensitizer. This work provides a new strategy for discovering new broadband NIR phosphors using Mn2+ in strong crystal field as luminescence center. [ABSTRACT FROM AUTHOR]

Broadband near‐infrared (NIR) phosphors have received increasing attention for fabricating phosphor‐converted light‐emitting diodes (pc‐LEDs) as NIR light source. Most of the reported broadband NIR phosphors originate from Cr3+ in weak crystal field environments. Herein, we report a luminescent material, MgAlSiN3:Mn2+ with CaAlSiN3‐type structure, demonstrating that broadband deep‐red‐to‐NIR emission can be achieved via doping Mn2+ into crystallographic sites with strong crystal field in inorganic solids. This phosphor is synthesized via easy‐handle solid‐state reaction, and the optimized sample, (Mg0.93Mn0.07) AlSiN3 shows an emission band with peak at ~754 nm, FWHM of 150 nm, and internal quantum efficiency of 70.1%. The photoluminescence intensity can further be enhanced by co‐doping Eu2+ as sensitizer. This work provides a new strategy for discovering new broadband NIR phosphors using Mn2+ in strong crystal field as luminescence center. [ABSTRACT FROM AUTHOR]

In this study, the red-emitting phosphor-in-glass (PiG) using the CaAlSiN 3 : Eu2+ (CASN) phosphor is reported for the first time. The CASN: Eu2+ PiG samples with a maximum luminous flux of 25.1–29.4 for l minute at laser power of 1 W/mm2 was obtained using a low-temperature glass frit and GPS furnace. Despite the increase in the phosphor from 15 to 25 wt%, the PiG produced at low temperature of 380 °C showed robust properties. Finally, the red PiG module designed for rear lamp applications maintains over 90% lumens for a minute at 350 mA and achieves an intense red light having a color temperature of 4589 K. Image 1 • The composition of the low-temperature glass frit is mentioned in the experimental section. • The EDS analysis results have added to demonstrate the presence of phosphor particles in the glass. • To respond to the reviewer's comments, the photoluminescence and PLQY of the RPiG sample were analyzed again. [ABSTRACT FROM AUTHOR]

(La,Y)3Si6N11:Ce3+ (LSN) phosphor has been used for white LEDs in back light units (BLUs). We have succeeded in developing LSN phosphors with wide color variations, less thermal quenching and any other luminescence properties. We expect that LSN phosphors will be also used for lighting and laser devices. [ABSTRACT FROM AUTHOR]

Wavelength conversion materials with high thermal conductivity and heat resistance have been strongly desired for high power semiconductor lighting source. Glass has higher heat resistances at elevated temperatures than resin and dispersion of high thermal conductive particles should result in the improvement of thermal conductivity of the composites. In this study, the composites of phosphate glass dispersing nitride phosphor and high thermal conductive particles were fabricated instead of typical composites of resins and oxide phosphors. As a result of verification of reactivity of the nitride phosphor and the high thermal conductive particles with the phosphate glass, between the glass and fillers, the firing temperature was set to 500°C and h-BN particles were selected as high thermal conductive particles. Dense nitride phosphor particles dispersed h-BN/glass composites were successfully obtained by hotpressing. Thermal conductivity normal to hot-pressing direction was higher than that parallel to hot-pressing direction, and it increased with an increase in the hot-pressing pressure and the quantity of dispersed h-BN particles because of higher density and better orientation of the h-BN particles. Consequently, the nitride phosphor particle dispersed h-BN/glass composites with the thermal conductivity of 9.4 W/(m-1·K-1) were obtained. [ABSTRACT FROM AUTHOR]

Enhancing thermal quenching characteristic of phosphor for use in high power white‐light‐emitting diodes (wLEDs) is a significant materials challenge. To achieve this goal, a series of red‐emitting carbidonitride phosphors Ca0.992AlSiN3 − 4/3xCx:0.008Eu2+ have been synthesized by high‐temperature solid‐state reaction method. Crystal structure, luminescence properties, and thermal quenching process are investigated. The location of carbon in the lattice is proved by the Raman spectra. The preferential crystallographic site of carbon is validated by the first‐principles density functional theory calculations combining the Rietveld refinement. With carbon doping from x = 0 to x = 0.24, the emission spectra are blue‐shifted from 656.8 to 650.2 nm, and the fitted lifetime of Eu2+ decreases from 775.3 to 721.7 ns. Replacing nitrogen by carbon enhances thermal quenching characteristic by 8.9% at 300°C. Carbon doping enlarges the thermal ionization energy barriers (EdC) which is calculated at great length, and suppresses thermal ionization process. A wLED fabricated by the combination of a blue chip with the as‐synthesized red phosphor and LuAG: Ce3+ green phosphor shows a high color rendering indexes (Ra = 95.9 and R9 = 92). The promising application of Ca0.992AlSiN3 − 4/3xCx:0.008Eu2+ phosphor for wLEDs is proved by all results above. [ABSTRACT FROM AUTHOR]

Rare earth ions doped (oxy)nitride phosphors have been shown great potentials for the use as down-conversion luminescent materials in white light-emitting diodes (wLEDs). To realize super-high color rendering and high efficiency wLEDs driven by a 405 nm LED chip, a blue-green phosphor with high thermal stability and quantum efficiency is required. In this work, we reported an interesting blue-green emitting Li-α-sialon:Ce3+ (Li m Si 12-m-n Al m+n O n N 16-n :Ce3+) that has a high external quantum efficiency of 53.5% and a small luminescence intensity reduction of 6.1% at 423 K. A variety of analytic techniques, such as X-ray diffraction (XRD), photoluminescence (PL) spectra, X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and nuclear magnetic resonance (NMR) spectra, were used to clarify the relation between photoluminescent properties and local coordination environments. It showed that the emission color and luminescence intensity of Li-α-sialon:Ce3+ could be controlled by the microstructure tailoring. A warm wLED was demonstrated by pumping the phosphor with the blend of Li-α-sialon:Ce3+, β-sialon:Ce3+ and CaAlSiN 3 :Eu2+ by a 405 nm LED chip, which has the color temperature, color rendering index and luminous efficacy of 2390 K, 92.2 and 26.05 lm/W under a driven current of 20 mA. Our results indicate that Li-α-sialon:Ce3+ is a promising thermally robust blue-green phosphor for ultraviolet LED-driven wLEDs. Image 1 • Blue-green phosphor with external QE 53.5% and thermal quenching 6.1% was achieved. • The high QE was exploited by the modulation of ion distance and the ligand field. • The wLED shows the CT, CRI, and LE are 2390 K, 92.2 and 26.05 lm/W at 20 mA current. [ABSTRACT FROM AUTHOR]

Nitride phosphors of Ca0.99−xSrxAl1.01Si0.99N3:0.01Ce3+ (0 ≤ x ≤ 0.9) were synthesized by conventional solid‐state method. XRD data analysis shows that all samples are single phase with CaAlSiN3‐type structure. Under blue or near‐ultraviolet (~400 nm) light excitation, the emission peak can be tuned largely from 615 to 568 nm by increasing Sr content, and the emission intensity is maximal at x = 0.8. With the Sr content increase, the emission band blue‐shifts due to the decreased crystal field splitting and the reduced centroid shift; while the thermal luminescence quenching resistance is almost unchanged. The quenching temperature (T50) is well above 500 K for all samples, which satisfies the requirement of commercial application. The quenching process is mainly attributed to the radiationless transitions by thermally activated crossover from the 5d excited state to 4f ground state in the configurational coordinate diagram. The luminescence properties show that the (Ca,Sr)AlSiN3:Ce3+ phosphors are very promising for use in blue and near‐ultraviolet light excited white‐light‐emitting diodes. [ABSTRACT FROM AUTHOR]

Single crystals of a new nitrido-alumino-silicate containing both Sr and Ba, Sr 27.9 Ba 22.8 Al 61.4 Si 174.6 N 328.4 :Eu2+, were synthesized by heating a binary-nitride powder mixture at 2030 °C under a N 2 gas pressure of 0.85 MPa for 4 h. The fundamental X-ray diffraction spots were indexed using orthorhombic cell parameters (a = 19.0272(5) Å, b = 40.4608(10) Å, c = 9.8641(3) Å), and diffuse streaks were observed between these spots. The crystal structure was analyzed using a statistical average structure model with space group Amm 2. The (Al/Si)N 4 tetrahedra share vertex and edge N atoms to form a three-dimensional network structure. Sr, Ba, and Eu atoms are distributed in the spaces within the network. Single crystals of Sr 27.9 Ba 22.8 Al 61.4 Si 174.6 N 328.4 :Eu2+ excited by light with a wavelength of 400 nm emitted yellow–orange light and showed a broad emission spectrum with a peak at 684 nm and a peak full-width at half-maximum of 239 nm. The maximum emission intensity at 200 °C was 74% of that at 25 °C. [Display omitted] • Single crystals of a new nitride Sr 27.9 Ba 22.8 Al 61.4 Si 174.6 N 328.4 :Eu2+ were synthesized. • Fundamental X-ray diffraction spots were indexed with orthorhombic cell parameters. • Crystal structure was analyzed using a statistical average model with space group Amm 2. • Spaces in (Al/Si)N 4 framework are partially occupied by Sr and Ba. • Broad yellow–orange luminescence peak was observed under near-UV light excitation. [ABSTRACT FROM AUTHOR]

Abstract To fabricate white-light-emitting diodes (white LEDs) with high color-rendering index or full light spectrum emission, the discovery of more efficient deep-red emitting phosphor materials is essential. In this paper, we have synthesized a series of Sr 2-2x Eu 2x Si 5 N 8 (0 ≤ x ≤ 1) solid-solution compounds, and have systemically investigated effects of full-range Eu concentration on their luminescence. Their emission band maximum can be largely tuned from 610 to 725 nm by increasing Eu content. Reabsorption at low Eu2+ concentration while both the energy transfer and Stocks shift at high Eu2+ concentration account for this large spectral red-shift. Luminescent thermal quenching performance gets worse with Eu2+ concentration increasing. The compound with x = 0.15 possesses the best crystallinity and the highest luminescence intensity with the peak position around 660 nm, and still maintains 88.5% room-temperature intensity at 400 K, indicating that great potential for the application as a deep-red phosphor. Highlights • A full-range Sr 2-2x Eu 2x Si 5 N 8 (0 ≤ x ≤ 1) solid solution was synthesized. • Largely tunable red emission band from 610 to 725 nm by adjusting Eu content. • High quenching concentration and high thermal quenching temperature for Eu2+ emission. [ABSTRACT FROM AUTHOR]

Abstract A new narrowband red phosphor, Ba 0.8 Sr 0.2 Mg 3 SiN 4 :Eu, suitable for use in LED lighting, has been identified as the optimal composition from the series of Ba (1-x) Sr x Mg 3 SiN 4 :Eu including x = 0, 0.2, 0.5, 0.8, and 1. Experimental X-ray diffraction measurements and structures calculated via density functional theory reveal that Ba (1-x) Sr x Mg 3 SiN 4 :Eu stabilizes in a tetragonal crystal structure, changing to the triclinic structure for Ba >0.8. Narrow band Eu2+ emission is observed in the tetragonal phase, but as a function of Ba substitution onto the Sr site, several properties change in concert: the emission maximum shifts to longer wavelengths, room temperature quantum efficiency improves, Eu2+ decay time increases and thermal stability of emission improves. Concomitant with the structure change to triclinic, the narrow Eu2+ emission band becomes broadened, the bandgap increases, and decay time slows to a typical Eu2+ decay of ∼1 μs. Although significantly moisture-sensitive, the strong absorption of Ba 0.8 Sr 0.2 Mg 3 SiN 4 :Eu at 450 nm, its emission peak at 635 nm and width of 51 nm FWHM provide efficient color rendering in the red, potentially achieving CRI and R9 values in excess of 95, along with good efficacy, in combination with other phosphors. Excitation intensity droop is comparable to other similar Eu-doped nitrides, but while thermally induced quenching is reduced with Ba substitution, it is still significant. The measured photoluminescence decay for Ba 0.8 Sr 0.2 Mg 3 SiN 4 :Eu of ∼200 ns is faster than of related Eu-doped nitrides, and together with a Q.E. of only ∼40% suggests the presence of competing non-radiative decay routes, thought to be due to thermal ionization of the Eu2+ excited state to the conduction band. Improved Q.E. for SrMg 3 SiN 4 :Eu partially substituted with Ba is likely due to the cation disorder this introduces, suppressing nonradiative processes correlated with lattice vibrations and increasing the population of shallow traps that release electrons on the emission lifetime timescale, consistent with the emission decay time lengthening and Q.E. improvement as a function of Ba content. Graphical abstract A new narrowband red phosphor, Ba 0.8 Sr 0.2 Mg 3 SiN 4 :Eu, suitable for use in LED lighting, has been identified as the optimal composition from the series of Ba (1-x) Sr x Mg 3 SiN 4 :Eu including x = 0, 0.2, 0.5, 0.8 and 1. Experimental X-ray diffraction measurements and structures calculated via density functional theory reveal that for x = 0–0.8, Ba (1-x) Sr x Mg 3 SiN 4 :Eu stabilizes in a tetragonal crystal structure, changing to the triclinic structure for Ba >0.8. Narrow band Eu2+ emission is observed in the tetragonal phase, but as a function of Ba substitution onto the Sr site, several properties change in concert: the emission maximum shifts to longer wavelengths, room temperature quantum efficiency improves, Eu2+ decay time increases and thermal stability of emission improves. Concomitant with the structure change to triclinic, the narrow Eu2+ emission band becomes broadened, the bandgap increases, and decay time slows to a typical Eu2+ decay of 1 μs. Although significantly moisture-sensitive, the strong absorption of Ba 0.8 Sr 0.2 Mg 3 SiN 4 :Eu at 450 nm, its emission peak at 635 nm and width of 51 nm FWHM provide efficient color rendering in the red, potentially achieving CRI and R9 values in excess of 95, along with good efficacy, in combination with other phosphors. Excitation intensity droop is comparable to other similar Eu-doped nitrides, but while thermally induced quenching is reduced with Ba substitution, it is still significant. The measured photoluminescence decay for Ba 0.8 Sr 0.2 Mg 3 SiN 4 :Eu of 200 ns is faster than of related Eu-doped nitrides, and together with a Q.E. of only 40% suggests the presence of competing non-radiative decay routes, thought to be due to thermal ionization of the Eu2+ excited state to the conduction band. Improved Q.E. for SrMg 3 SiN 4 :Eu partially substituted with Ba is likely due to the cation disorder this introduces, suppressing nonradiative processes correlated with lattice vibrations and increasing the population of shallow traps that release electrons on the emission lifetime timescale, consistent with the emission decay time lengthening and Q.E. improvement as a function of Ba content. Image 1 Highlights • In combination with other phosphors, both CRI and R9 values in excess of 95 might be obtained. • The series ­Ba (1-x) Sr x Mg 3 SiN 4 :Eu for x = 0, 0.2, 0.5, 0.8, and 1 reveal a structural change from triclinic to tetragonal at x > 0.2. • Significant moisture sensitivity limits utilization of the family of nitridomagnesosilicate phosphors. [ABSTRACT FROM AUTHOR]

Energy of 5d -levels of Ce 3+ in numerous nitrides has become available due to the development of nitride phosphors recently. In this work, we have collected data on 5d -levels of Ce 3+ and reconsidered the 5d centroid shift of Ce 3+ in nitrides. The uniform standard, derived from the bond valence theory and the requirement for the high stability of the coordination polyhedron, has been proposed to determine the coordination number. The relationship between the 5d centroid shift of Ce 3+ , the polarizability of the anions and the electronegativity of the cations is revealed. The anion polarizability is linearly related to the inverse square of the average electronegativity of the cations; and the 5d centroid shift of Ce 3+ can be well predicted by virtue of crystallographic data. This paper provides a feasibility to predict luminescence properties of Ce 3+ -doped nitrides. [ABSTRACT FROM AUTHOR]

Recently a lot of Ce 3+ /Eu 2+ -activated nitride and oxonitride phosphors have been explored due to potential or practical application for white-light LEDs. In this paper, data of crystal field splitting of the 4f n−1 5d -levels of Ce 3+ and Eu 2+ in nitride compounds is collected and analyzed. The relationship between the crystal field splitting and the coordination polyhedron around the Ce 3+ and Eu 2+ is revealed, showing that crystal field splitting is related to coordination number, polyhedron shape and size, while being irrelevant of the anion types. In addition, the crystal field splitting of Ce 3+ and Eu 2+ in the nitride compounds is correlated by a multiplication factor 0.76, which is in consistent with those in halides, sulfides and oxides. This paper makes it possible to predict luminescence properties of Ce 3+ - or Eu 2+ - doped nitride compounds. [ABSTRACT FROM AUTHOR]

The thermal degradation is considered as one the most common limitations of Sr 2−x Eu x Si 5 N 8 nitride phosphors due to the elevated working temperatures in LED. In order to examine the origin of the thermal degradation, Sr 2−x Eu x Si 5 N 8 was synthesized using high-temperature solid-state reaction. The nitride with activators and the nitride host lattice were studied separately. The diffuse reflectance spectra, the internal quantum efficiency, and optical absorption rate, as well as the element binding energy and element content before and after annealing at high temperature, were investigated. Also, the morphology and surface layers were observed using high-resolution transmission electron microscopy (HRTEM). The results suggested the formation of an amorphous layer on the grain surface, which decreased luminescence efficiency after the heat treatment. It was found that oxidation of both the europium and Sr 2 Si 5 N 8 host lattice caused the formation of the amorphous layer. [ABSTRACT FROM AUTHOR]

Eu 2+ , Dy 3+ co-doped Sr 2 Si 5 N 8 red phosphors were prepared using a sol–gel-nitridation method at a lower temperature comparing with traditional solid state reaction. Effects of synthesis process, Eu 2+ and Dy 3+ doping concentration on the crystal structure and luminescence property of as-prepared phosphors were investigated. X-ray diffraction patterns indicated that all Sr 2 Si 5 N 8 :Eu 2+ , Dy 3+ phosphors have the standard phase of Sr 2 Si 5 N 8 structure. With a broad excitation from UV to blue light, a strong emission of Sr 2 Si 5 N 8 :Eu 2+ , Dy 3+ with 4f 6 5d 1 →4f 7 transition of Eu 2+ ions was obtained at red region in photoluminescence spectra. Emission peaks in spectra were red-shifted from 611 to 632 nm for all Sr 2 Si 5 N 8 :xEu 2+ as Eu 2+ ion concentrations increased, which due to Eu 2+ ions occupying from the tenfold coordinated site (Sr1) to the eightfold coordinated site (Sr2). These Sr 2 Si 5 N 8 :Eu 2+ phosphors with Dy 3+ co-doping showed excellent luminescence properties, included emission intensity and luminescence quenching. It is potential that Sr 2 Si 5 N 8 :Eu 2+ , Dy 3+ phosphors can be applied in white LEDs combining with blue InGaN LEDs. [ABSTRACT FROM AUTHOR]

In order to improve photoluminescence properties of the Sr 2 Si 5 N 8 :Eu 2 + phosphor, Li 3 N flux was added into the phosphors and the effect of the Li 3 N flux on the properties was investigated. The results show that, the amount of Li 3 N flux had a significantly positive effect on the phosphor properties, such as the particle size, activator occupy site in the crystal lattice and luminescent properties. The emitting integrated intensity of Sr 2 Si 5 N 8 :Eu 2 + phosphor was increased by 40%, by selecting the appropriate initial compositions and combustion parameters. Moreover, the phosphor with Li 3 N flux additions, showed improved heat stability. The improved luminescent properties were attributed to the proper grain size and the increasing N 3 − concentration during firing. [ABSTRACT FROM AUTHOR]

We report high efficiency luminescence with a manganese-doped aluminum nitride red-emitting phosphor under 254 nm excitation, as well as its excellent lumen maintenance in fluorescent lamp conditions, making it a candidate replacement for the widely deployed europium-doped yttria red phosphor. Solid-state reaction of aluminum nitride powders with manganese metal at 1900 °C, 10 atm N 2 in a reducing environment results in nitrogen deficiency, as revealed diffuse reflectance spectra. When these powders are subsequently annealed in flowing nitrogen at 1650 °C, higher nitrogen content is recovered, resulting in white powders. Silicon was added to samples as an oxygen getter to improve emission efficiency. NEXAFS spectra and DFT calculations indicate that the Mn dopant is divalent. From DFT calculations, the UV absorption band is proposed to be due to an aluminum vacancy coupled with oxygen impurity dopants, and Mn 2+ is assumed to be closely associated with this site. In contrast with some previous reports, we find that the highest quantum efficiency with 254 nm excitation (Q.E. = 0.86 ± 0.14) is obtained in aluminum nitride with a low manganese doping level of 0.06 mol.%. The principal Mn 2+ decay of 1.25 ms is assigned to non-interacting Mn sites, while additional components in the microsecond range appear with higher Mn doping, consistent with Mn clustering and resultant exchange coupling. Slower components are present in samples with low Mn doping, as well as strong afterglow, assigned to trapping on shallow traps followed by detrapping and subsequent trapping on Mn. [ABSTRACT FROM AUTHOR]

Effects of Ca content (in the reactant mixture) on the formation and the photoluminescence properties of CaAlSiN3:Eu2+ phosphor (CASIN) were investigated by a combustion synthesis method. Ca, Al, Si, Eu2O3, NaN3, NH4Cl and Si3N4 powders were used as the starting materials and they were mixed and pressed into a compact which was then wrapped up with an igniting agent (i.e., Mg + Fe3O4). The compact was ignited by electrical heating under a N2 pressure of ≤1.0 MPa. By keeping the molar ratios of Al and Si (including the Si powder and the Si in Si3N4 powder) both at 1.00 and that of Eu2O3 at 0.02, XRD (X-ray diffraction) coupled with TEM-EDS (transmission electron microscope equipped with an energy-dispersive X-ray spectroscope) and SAED (selected area electron diffraction) measurements show that AlN:Eu2+ and Ca-α-SiAlON:Eu2+ are formed as the major phosphor products when the Ca molar ratio (denoted by Y) is equal to 0.25 and AlN:Eu2+ and Ca-α-SiAlON:Eu2+ could not be detected at Y ≥ 0.75 and ≥1.00, respectively. CASIN (i.e., CaAlSiN3:Eu2+) becomes the only phosphor product as Y is increased to 1.00 and higher. The extent of formation of CASIN increases with increasing Y up to 1.50 and begins to decrease as Y is further increased to 1.68. While the excitation wavelength regions are similar at various Y, the emission wavelength regions vary significantly as Y is increased from 0.25 to 1.00 due to different combinations of phosphor phases formed at different Y. The emission intensity of CASIN was found to vary with Y in a similar trend to its extent of formation. The Ca and Eu contents (expressed as molar ratios) in the synthesized products were found to increase roughly with increasing Y but were both lower than the respective Ca and Eu contents in the reactant mixtures. [ABSTRACT FROM AUTHOR]

Nitride phosphor, CaAlSiN 3 :Eu 2+ , was efficiently synthesized without any impurity phase by the direct-nitriding method using metal hydride fine powders of (Ca 0.97 Eu 0.03 )AlSiH x and/or CaH 2 in a particle size range below 20 μm as starting materials under atmospheric pressure heating conditions in a stream of N 2 gas. High-quality powders of CaAlSiN 3 :Eu 2+ (3 at%) phosphor were obtained from such metal hydride powder mixed with a large excess amount of CaH 2 powder (>30 wt%) as a flux and gave an intense red emission band peaking at 650 nm under the excitation of 450 nm, of which the relative integrated emission intensity was about 110% versus that of a commercially-available YAG:Ce 3+ (P46-Y3) standard phosphor. Also, the thermal quenching effect was as low as the CaAlSiN 3 :Eu 2+ phosphors prepared by the other methods (−6% at 150 °C), so that this direct-nitriding method was noted as one of excellent procedures to produce the high-quality nitride phosphors for white-LED illumination lamps. [ABSTRACT FROM AUTHOR]

Two types of reddish-orange afterglow emitting nitride phosphors Ca 2 Si 5 N 8 :Eu 2+ , Tm 3+ (CSN:E, T) and Ca 2 Si 5 N 8 :Eu 2+ , Tm 3+ , Dy 3+ (CSN:E, T, D) were synthesized via a solid-state reaction route and were comparatively investigated. Comparing with the di-doped CSN:E, T phosphor, the tri-doped CSN:E, T, D samples show higher afterglow intensity and longer duration time which can be attributed to the balanced defect micro-environment caused by the presence of Dy 3+ . [ABSTRACT FROM AUTHOR]

Abstract: Bluish-green phosphors were synthesized by precursor and solid-state reaction methods, and their photoluminescence (PL) properties were investigated. A single phase of Ba3Si6O9N4 was formed in the precursor method whereas a mixture of Ba3Si6O9N4 and Ba3Si6O12N2 phases was obtained in the solid-state reaction method. The as-synthesized phosphor exhibited a single band emission centered at 487nm under the excitation of λ ex =400nm, and the emission intensity increased by ∼20 times when the temperature was reduced from 298 to 10K. The effects of starting material composition, calcination temperature, and Eu2+ doping concentration on the phase formation and PL characteristics were examined. The peak intensity of was about 10% of at 298K, but its thermal stability was comparable to that of in the range of 298–473K. [Copyright &y& Elsevier]

Abstract: This study was carried out to characterize the crystal structure and luminescence properties of Eu2+ doped red-emitting Ba2Si5N8 phosphor. In this research, Ba2Si5N8 phosphors with various Eu compositions were prepared by normal pressure sintering (NPS). Ba3N2, Si3N4 and Eu2O3 were sintered at a high temperature in a mixture of N2 and H2. The crystal structure was analyzed by X-ray diffraction(XRD), and the photoluminescence(PL) properties of the Eu2+ - activated Ba2Si5N8 phosphors were evaluated as a function of the Eu2+ activator concentration. The red-emitting Ba2Si5N8 phosphors showed a broad excitation band range as well as high quantum output. [Copyright &y& Elsevier]

Conventional optical anti-counterfeiting strategies are based on the single-color emission, which are easily deciphered and thus greatly limited in the application of information security. Herein, a multimodal dynamic optical information coding with red, green, and blue (RGB) tricolors has been developed by photoluminescence (PL), persistent luminescence (PersL), thermally stimulated luminescence (TSL), and thermally stimulated persistent luminescence (TSPL). The BaSi 2 O 2 N 2 :Eu 2+ phosphors with a blue emission peak at 494 nm were used as the crucial blue optical information coding material and exhibited the distinctive response properties to light, heat, and force stimuli with intrinsic trap depths of 0.674 and 0.82 eV. More importantly, by combining the red Sr 2 Si 5 N 8 :Eu 2+ ,Dy 3+ and green SrSi 2 O 2 N 2 :Eu 2+ ,Dy 3+ nitride phosphors, a RGB tricolor and multimodal strategy has been successfully developed for anti-counterfeiting applications. The "RGB tricolor flower" with RGB emissions is given as a typical example to achieve the dynamic display of optical information encryption and decoding through the various PL, PersL, TSL, and TSPL modes. Finally, the traditional quick response (QR) code mechanism has been integrated into the design of multi-information encrypted RGB tricolor anti-counterfeiting devices with different identifiabilities of the encrypted information in natural light, PL, PersL, TSL, and TSPL modes. The laminated layers of RGB QR code patterns containing different specific information, such as "DLPU" and "116034", can be effectively recognized in the corresponding modes. The design strategy of RGB tricolor and multimodal optical information encryption and decoding devices in this work greatly improves the security level of advanced optical information technologies and extends the potential applications in dynamic anti-counterfeiting fields.

Abstract: In order to enhance luminescence properties of Eu2+-doped ternary nitride phosphor for white light-emitting diodes (LEDs), Sr2Si5N8:Eu2+ phosphors with different Eu2+ concentrations were synthesized using a multi-step heat treatment. Impurities and luminescence properties of prepared Sr2Si5N8:Eu2+ phosphors were investigated using X-ray diffraction (XRD) and photoluminescence spectroscopy. Excitation spectra of Sr2Si5N8:Eu2+ phosphor showed broad excitation bands by both UV and blue light. Emission peak positions in spectra were red-shifted from 613 to 671nm as Eu2+ ion concentrations increased. Phosphors following a multi-step heat treatment showed excellent luminescence properties. These included high emission intensity and very low thermal quenching compared to measurements using a commercially available YAG:Ce3+ phosphor. [Copyright &y& Elsevier]

Abstract: A novel synthesis method was developed for the efficient red phosphor, Eu2+-activated Sr2Si5N8, by employing the strontium acetate as both the reducing agent and strontium source. The phase purity of final product was strongly dependent on the heating rate of the precursors. Sr2Si5N8:Eu2+ (2at%) phosphor presented a broadband excitation spectrum in the range 300–500nm, matching well with the blue emission (400/460nm) of current InGaN light-emitting diodes (LEDs). The red emission peaking at 619nm gave the relatively high (about 155%) intensity compared with the Y3Al5O12 (YAG) (P46-Y3) standard phosphor. In addition, the saturated chromatic coordinates (0.638, 0.359) allowed it a promising candidate as a red phosphor in white LEDs application for illumination or display. [Copyright &y& Elsevier]

Abstract: Strontium europium aluminum silicon nitride, Sr0.99Eu0.01AlSiN3, was synthesized by heating a mixture of binary nitrides at 2173K and a N2 gas pressure of 190MPa. Single crystals of Sr0.99Eu0.01AlSiN3 approximately 30μm were obtained. The structure was confirmed to be an isotypic structure of CaAlSiN3 in the orthorhombic space group Cmc21, analyzed by single-crystal X-ray diffraction. The lattice parameters are a=9.843(3), b=5.7603(16), c=5.177(2)Å, cell volume=293.53(17)Å3. It shows an orange-red photoluminescence by 5d→4f transition of Eu2+ at around 610nm under excitation ranging from ultraviolet to 525nm. The photoluminescence intensity, temperature characteristics, and oxidative stability were comparable or superior to those of CaAlSiN3:Eu2+ phosphor. [Copyright &y& Elsevier]

Exploring efficient and stable phosphors have already attract highly public attentions and always been considered as a crucial issue in the development of field emission displays (FEDs). In order to discover the potential application for FEDs, the red phosphor, SrLiAl 3 N 4 :Eu2+, was synthesized by a simple preparation method at low temperature and the photoluminescence(PL) as well as cathodoluminescence (CL) performances were studied in our work. The SrLiAl 3 N 4 : Eu2+ phosphor exhibits irregular spherical morphology with a soft agglomeration and the mean particle size is 4.52 µm. When excited by a low-voltage electron beam, it shows a narrow band red emission in the 600–700 nm range with the 51 nm of full width at half maximum (FWHM) and the strongest emission peak is located at 647 nm, which is attributed to the 4f65d → 4f7 electron transition of Eu2+. The effects of different Eu2+ doping concentration and probe current, accelerating voltage, as well as electron bombardment time on the CL performance of SrLiAl 3 N 4 :Eu2+ were studied in detail and found that the optimal sample, SrLiAl 3 N 4 :0.5%Eu2+, exhibits no saturation effect and excellent degradation property compared with the commercial Y 2 O 3 :Eu3+ phosphor. In view of the prominent CL performance of SrLiAl 3 N 4 :Eu2+, it can be considered as candidate phosphor in full color FEDs. • SrLiAl3N4:Eu2+ red phosphor was designed by N2 gas pressure sintering method . • The phosphor had a narrow-band and bright red emission under low-pressure electron beam excitation and there is no saturation effect was observed with increasing current. • Moreover, the phosphor exhibited excellent thermal stability and degradation resistance performance due to the highly condensed and firm lattice structure . • The CIE coordinates of SrLiAl3N4:Eu2+ is almost unchanged and the color gamut of the trichromatic FEDs phosphors increased significantly after the addition of the phosphor. • All the results indicate that SrLiAl3N4:Eu2+ phosphors have great potential in full-color FEDs applications. [ABSTRACT FROM AUTHOR]

• Ternary solid solution phosphors CALSON:Ce were developed for high-power lighting. • The title phosphor exhibits an excellent thermal stability (91% at 200 °C). • The structure–property relations were revealed. • The title phosphor has a high external quantum efficiency of 41.5%. • A high-brightness pc- w LD (781 lm mm−2) was created using the CALSON:Ce-PiG film. The discovery of thermally robust phosphors is essential to achieve efficient and stable luminescence in solid-state lighting devices, especial in high-power devices. Here, a novel ternary solid solution phosphor enabling to address this challenge is designed by introducing isostructural LiSi 2 N 3 and Si 2 N 2 O into CaAlSiN 3 lattice. The compound, Ca 1- x - y Li x Al 1- x - y Si 1+ x + y N 3- y O y :Ce3+ (CALSON:Ce), exhibits an excellent thermal stability with an integrated emission loss of only 9% at 200 °C, far smaller than that of the parent CaAlSiN 3 :Ce3+ (25%). The enhanced thermal stability is assigned to the broadened band gap (5.21 → 5.50 eV) upon the formation of solid solutions. Moreover, the new phosphor presents a broadband (full width at half maximum of 135 nm) yellow-orange emission peaking at 580 nm and shows a high external quantum efficiency of 41.5%. The excellent photoluminescence properties and thermal stability of CALSON:Ce thus enable it to be used under high-power laser excitation, and to produce high-brightness white light having a luminous flux of 392 lm (luminous emittance of 781 lm mm−2), a low correlated color temperature of 4349 K, and a high color rendering index of 70. This work suggests that creating multi-component solid solutions would be a general strategy for designing novel phosphors. [ABSTRACT FROM AUTHOR]

Colorless transparent single crystals of a new aluminum silicon nitride, (Sr 0.98 Eu 0.02)(Al 0.05 Si 0.95) 6 N 8 , were obtained from a sample prepared by heating a mixture of binary Sr, Eu, Al, Si, and Mg nitrides at 2080 °C under a N 2 gas pressure of 0.85 MPa. The X-ray diffraction spots from a single crystal of (Sr 0.98 Eu 0.02)(Al 0.05 Si 0.95) 6 N 8 were indexed with orthorhombic cell parameters (a = 7.8803(2) Å, b = 9.3044(2) Å, c = 4.8413(1) Å). The crystal structure that could be analyzed with the space group Pmnn was related to that of SrSi 6 N 8 :Eu2+ (space group: Imm 2). The framework is constructed by sharing the vertex N atoms of Si/Al-centered nitrogen tetrahedra. (Si/Al)–(Si/Al) dumbbells are bonded to N atoms of the small cages in the framework. Tunnels in which Sr/Eu atoms are located extend in the framework in the a -axis direction. An emission spectrum of blue light with a peak wavelength of 448 nm and a full width at half maximum (FWHM) of 33 nm was observed from the single crystals under 400 nm light irradiation at room temperature. The emission intensity at 200 °C was 54% of that at 25 °C. Image 1 • Single crystals of a new nitride, (Sr 0.98 Eu 0.02)(Al 0.05 Si 0.95) 6 N 8 , were prepared. • The crystal structure was primitive orthorhombic and the space group was Pmnn. • The stacking sequence of tetrahedral layers different from that of SrSi 6 N 8 was clarified. • The single crystals emitted blue light (peak top: 448 nm) by near-UV light excitation. • The luminescence intensity at 200 °C was reduced to 54% that at room temperature. [ABSTRACT FROM AUTHOR]

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.

The degradation and failure mechanisms of nitride phosphor in GaN‐based white LEDs are studied using an in situ multi‐functional accelerated life test and different analytical technologies. The electroluminescence results show that both the intensities of the blue emission (BL) from the LED chips and the yellow emission (YL) from the phosphors decrease with the stress time increasing. However, the YL/BL intensity ratio increases with a yellow shift for the chromaticity coordinates. The reason is not only due to the degradation of the LED chip but the nitride phosphors. The generated microcracks and delamination of phosphor layer lead to the increase of blue light absorption. Except for that, we find that the reason for the decrease of the phosphor conversion efficiency is related to the oxidization of the phosphor's luminescence center Eu2+ ions instead of phosphor thermal quenching. These findings help further understand failure mechanism of phosphors during the operation, and improve the long‐term color quality for the white LEDs. In this article, the degradation and failure mechanisms of nitride phosphor in GaN‐based white LEDs are studied. The generated micro‐cracks of phosphor layer coated on the LED chip causes an increase of blue light absorption and the oxidization of the phosphor's luminescence center Eu2+ ions results in the decrease of the phosphor conversion efficiency. Both degradation modes lead to a color yellow shift of white LEDs. [ABSTRACT FROM AUTHOR]