Ca AlSiN3 Research Articles

Revealing The Degradation Mechanism of (Sr,Ca)AlSiN3:Eu2+ Phosphor Aged Under Thermal‐Moisture‐Sulfur Conditions: A Combined Experimental and Ab Initio Study

AbstractMAlSiN3:Eu2+ (M = Ca, Sr) is commonly used in high‐power phosphor‐converted white‐light‐emitting diodes and laser diodes to promote their color‐rendering index. However, the wide application of this phosphor is limited by the degradation of its luminescent properties in high‐temperature, high‐humidity, and high‐sulfur‐content environment. Here, the degradation mechanism of the (Sr,Ca)AlSiN3:Eu2+ (SCASN) red phosphor under thermal‐moisture‐sulfur coupling conditions is investigated. Furthermore, by performing first‐principles calculations, the hydrolysis mechanism on an atomic scale is assessed. The adsorption energy (Eads) and charge transfer (ΔQ) results showed that H2O chemically adsorbed on the (0 1 0), (3 1 0), and (0 0 1) surfaces of the CaAlSiN3 (CASN) host lattice. The energy barrier for H2O dissociation is only 29.73 kJ mol−1 on the CASN (0 1 0) surface, indicating a high dissociation probability. The formation of NH3, Ca(OH)2, and CaAl2Si2O8 is confirmed by H+ tended to combine with surface N atoms, while OH− combined with the surface Al/Si or Ca atoms. Moreover, ab initio molecular dynamics simulations were performed to further understand the hydrolysis process. This work offers a guidance on the design and applications of luminescent materials in LED packages with higher reliability and stability requirements in harsh environment.

(M,Ca)AlSiN3:Eu2+ (M=Sr, Mg) long persistent phosphors prepared by combustion synthesis and applications in displays and optical information storage

Eu2+-doped CaAlSiN3‐type structure nitrides have been extensively studied as a red-emitting phosphors in white light emitting diodes (w-LEDs), but there are few reports of systematic research on the effect of solid solution substitution on their long persistent luminescent properties. In this work, a series of (M,Ca)AlSiN3:Eu2+ (M = Sr, Mg) phosphors have been successfully synthesized by efficient combustion synthesis. We investigated the effect of Sr and Mg solid solution on long persistent luminescent properties. Thermoluminescence (TL) measurements were performed in those persistent phosphors to obtain direct experimental results on the trap depth. The results show that the SrAlSiN3:0.2 at% Eu2+ phosphor exhibits the most intense red persistent luminescence with the persistent time of as long as 200 min at the threshold value of 0.32 mcd/m2 due to the presence of more trap levels with suitable depths of 0.71 eV. Compared with the solid solution of Sr, the solid solution of Mg ions can increase the depth of trap levels in CaAlSiN3. Among them, Mg0.2Ca0.8AlSiN3:0.2 at% Eu2+ phosphor achieved a maximum trap depth of 0.98 eV, making it a promising candidate for optical information storage applications.

Micro-ion beam-induced luminescence spectroscopy for evaluating SiAlON scintillators

Ion beam-induced luminescence (IBIL) spectroscopy was used for luminescent material characterization and analysis for the investigation of new scintillator families. Under continuous 3 MeV proton microbeam irradiation, the crystal structures of α-SiAlON:Eu, β-SiAlON:Eu, and CaAlSiN3 (CASN) emitted bright luminescence at peak wavelengths of 605, 540, and 670 nm, respectively. As the irradiation progressed, the IBIL intensity of the conventional ZnS:Ag scintillator decreased sharply, whereas that of the SiAlONs and CASN remained within the detection limit. IBIL spectroscopy was performed on individual grains of the SiAlON scintillators. IBIL imaging and spectroscopy of two grains of β-SiAlON:Eu showed that the main peak in the IBIL spectrum of β-SiAlON:Eu obtained from a large-area beam scan consisted of several small peaks, which were observed in spectra from individual grains. Our experimental results suggest that microscopic spectroscopy of IBIL is an effective tool for microscopic material characterization of luminescent targets.

Ammonothermal Synthesis of Novel Nitrides: Case Study on CaGaSiN3.

The first gallium-containing nitridosilicate CaGaSiN3 was synthesized in newly developed high-pressure autoclaves using supercritical ammonia as solvent and nitriding agent. The reaction was conducted in an ammonobasic environment starting from intermetallic CaGaSi with NaN3 as a mineralizer. At 770 K, intermediate compounds were obtained, which were subsequently converted to the crystalline nitride at temperatures up to 1070 K (70-150 MPa). The impact of other mineralizers (e.g., LiN3 , KN3 , and CsN3 ) on the product formation was investigated as well. The crystal structure of CaGaSiN3 was analyzed by powder X-ray diffraction and refined by the Rietveld method. The structural results were further corroborated by transmission electron microscopy, 29 Si MAS-NMR, and first-principle DFT calculations. CaGaSiN3 crystallizes in the orthorhombic space group Cmc21 (no. 36) with lattice parameters a=9.8855(11), b=5.6595(1), c=5.0810(1) Å, (Z=4, Rwp =0.0326), and is isostructural with CaAlSiN3 (CASN). Eu2+ doped samples exhibit red luminescence with an emission maximum of 620 nm and FWHM of 90 nm. Thus, CaGaSiN3 :Eu2+ also represents an interesting candidate as a red-emitting material in phosphor-converted light-emitting diodes (pc-LEDs). In addition to the already known substitution of alkaline-earth metals in (Ca,Sr)AlSiN3 :Eu2+ , inclusion of Ga is a further and promising perspective for luminescence tuning of widely used red-emitting CASN type materials.

Synthesis, structure and photoluminescence properties of (Sr,Ca)AlSiN3:Eu2+ phosphor for white light emitting diodes with controllable optical performance

A series of SryCa1−x−yAlSiN3:xEu2+ (x = 0–0.01, y = 0–0.8) phosphors have been successfully prepared by solid state reaction under atmospheric pressure. All the phosphors exhibit orthorhombic crystal structure similar with CaAlSiN3 structure. It is found that the emission bands for all Ca1−xAlSiN3:xEu2+ phosphors are centered at ~650 nm and fluorescence quenching has been observed along with the increase of Eu2+ concentration in host materials. Through substitution of Ca2+ by Sr2+, an expected red emission peak (625 nm) and enhanced luminescent intensity can be achieved. The obtained Sr0.8Ca0.192AlSiN3:0.008Eu2+ phosphor was further used as efficient red component to fabricate white light emitting diodes (LEDs). Under the optimized condition of LED packaging, the white LEDs own the excellent optical properties with luminous efficiency of 90.6 lm/W and an ideal color rendering index (Ra = 82). Furthermore, the color correlated temperature of white LEDs can be simply adjusted through changing the red phosphor concentration and dispensing package saves time.

New Green and Red Phosphors for White LEDs

High-luminous green phosphors and a red phosphor have been newly developed for white LEDs. The developed green phosphors are Ca3(Sc,Mg)2Si3O12:Ce made by replacing with Mg a part of Sc of green phosphor Ca3Sc2Si3O12:Ce, a new green phosphor CaSc2O4:Ce, and a new host material doped with a rare-earth element, Ba3Si6O12N12:Eu. The new red phosphor is (Sr,Ca)AlSiN3:Eu made by replacing a part of Ca of CaAlSiN3:Eu with Sr.

Nitridoaluminosilicate CaAlSiN3 and its Derivatives - Theory and Experiment

AbstractNitridoaluminosilicate MAlSiN3(M: alkaline-earth element) and its derivatives have attracted more and more attention owing to the fact that the material doped with rare-earth element has intense body color and exhibit efficient luminescence under InGaN diode irradiation. In particular, red phosphor, Eu-doped CaAlSiN3 (CASN), has good thermal property of luminescence and sufficient chemical durability for white LED use. Still, for the lineup of various kinds of white color, it is hoped to tune the red luminescence with other physical/chemical properties kept as possible. Thus the derivatives with different chemical compositions have been intensively explored so far. For the feasibility of such chemical composition change, it is necessary to understand its atomic/electronic structure of the unique crystal, which is a distorted AlN-based wurtzite superstructure (Cmc21, No.36) with Al and Si disordered on 8b site and Ca occupying 4a site. Recently, we have performed first-principles band calculation of CASN and clarified the origin of the Al/Si disorder configuration as well as the feasibility of the virtual crystal approximation of heterovalent cations (Al/Si) for the reproducibility of atomic/electronic structure of CASN.[1] As a natural extension of this study, we have investigated some CASN-derivatives to confirm/predict the crystal structure. The VCA allows us to model the superstructure with various chemical compositions quite easily. In this work, we will present two examples of solid-solution, (Ca,Sr)AlSiN3 and CaAlSiN3-Si2N2O. The agreement between experiment and theory appears quite satisfactory. It is emphasized that the crystal structure of SrAlSiN3 has been successfully predicted by first-principles calculation prior to experimental result. The collaboration of experiment and theory promises us ‘gcrystal-engineering’ to develop new nitrides/oxynitrides effectively and efficiently.