12020-58-5Relevant articles and documents
EuCN2 - The first, but not quite unexpected ternary rare earth metal cyanamide
Reckeweg, Olaf,DiSalvo, Francis J.
, p. 177 - 179 (2003)
Red-orange, transparent single crystals of EuCN2 (Pnma (62), a = 1232.41(9), b = 395.26(3) and c = 539.43(4) pm, Z = 4) are obtained by the reaction of EuN, C and NaN3 in arc-welded Ta ampoules at 1300 K. The first ternary rare earth metal cyanamide is isotypic to α-SrCN2 and shows the characteristic frequencies for the CN22- unit in the optical spectra (νs = 1244; νas = 1969 and 2087; δ = 655/666 cm-1).
Effects of full-range Eu concentration on Sr2-2xEu2xSi5N8 phosphors: A deep-red emission and luminescent thermal quenching
Liu, Xiaolang,Song, Zhen,Kong, Yuwei,Wang, Shuxin,Zhang, Shiyou,Xia, Zhiguo,Liu, Quanlin
, p. 1069 - 1077 (2019)
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 Sr2-2xEu2xSi5N8 (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.
Preparation of high performance CaAlSiN3:Eu2+ phosphors with the aid of BaF2 flux
Hu, Wei-Wei,Cai, Chao,Zhu, Qiang-Qiang,Xu, Xin,Hao, Lu-Yuan,Agathopoulos, Simeon
, p. 226 - 231 (2014)
A strong red-emitting Eu2+ activated CaAlSiN3 phosphor was successfully prepared by a pressureless low temperature solid-state reaction method with the aid of fluxes, namely BaF2, CaF 2, NH4F, and H3BO3. The experimental results showed that the addition of BaF2 flux effectively reduced the temperature of formation of CaAlSiN3:Eu2+ by about 100 K and suppressed the volatilization of the raw materials, suggesting that BaF2 flux modifies the mechanism of formation of CaAlSiN 3:Eu2+. The powder of the CaAlSiN3:Eu 2+ phosphor produced with 6 wt% BaF2 flux had an enhanced emission intensity, which was a result of the high crystallinity, the absence of secondary phases, the narrow particle-size distribution, and the clean surfaces of the particles in the final product.
Synthesis, structure, and luminescence properties of Eu2+ and Ce3+ activated BaYSi4N7
Li,De With,Hintzen
, p. 1 - 11 (2004)
BaYSi4N7 and its phosphors activated with Eu 2+ and Ce3+ were synthesized by solid-state reaction at 1400-1650 C under nitrogen mixed with hydrogen atmosphere. The crystal structure of BaYSi4N7 was solved by direct methods and refined by the Rietveld method from powder X-ray diffraction data. BaYSi4N 7 crystallizes in the hexagonal space group P63mc (No. 186), with a = 6.0550 (2) ?, c = 9.8567 (1)?, V = 312.96 (2) ?3, and Z = 2, which is isotypic with BaYbSi4N 7. The photoluminescence properties have been studied for the solid solutions of Ba1-xEuxYSi4N7 (x = 0-0.4)and BaY1-xCexSi4N7 (x = 0-0.1) at room temperature. Eu2+-doped BaYSi4N7 gives a broad green emission band centered between 503 and 527 nm depending on the Eu2+ concentration. The Eu2+ emission band shows a red-shift formulation with increasing Eu2+ concentration mainly caused by the change of the crystal field strength and Stokes shift. Concentration quenching of Eu2+ emission is observed for x = 0.05 due to energy transfer between Eu2+ ions by electric dipole-dipole interactions with a critical interaction distance of about 20 ?. Ce 3+-doped BaYSi4N7 exhibits a bright blue emission band with a maximum at about 417 nm, which is independent of Ce 3+ concentration. This is ascribed to a lower solubility of Ce 3+ ions in BaYSi4N7 lattice as shown by X-ray powder diffraction analysis.
Magnetic characteristics of some lanthanide nitrides
Schumacher, David P.,Wallace
, p. 1563 - 1567 (1966)
Magnetic susceptibilities (χ) of Y, La, Ce, Nd, Sm, Yb, Lu, and their nitrides were determined over a temperature range extending from 2 to 300°K. Y, La, and Lu and their nitrides are Pauli paramagnets. SmN orders antiferromagnetically below 13°K. NdN exhibits ferromagnetic ordering below 35°K. Its magnetic moment in the ferromagnetic state at 2°K is 2.15 μB, as contrasted with 3.3 μB for the free Nd3+ ion. The reduction is ascribed to crystal field quenching. From the measured moment an over-all splitting of the ground state Nd3+ ion multiplet is estimated to be 234°K. The effective moment of Nd in paramagnetic NdN is in good agreement with that expected for the free ion. YbN exhibits Curie-Weiss behavior at >100°K with a moment in fair agreement with that expected for the Yb3+ ion. However, the magnitude of χ for YbN and the low-temperature deviation from Curie-Weiss behavior are not understood. Results for Yb indicate 34% Yb3+ and 66% Yb2+. The CeN results indicate a mixture of Ce3+ and Ce4+ with the latter strongly predominating at low temperatures. In accordance with theoretical expectations no magnetic ordering is observed for CeN and YbN at temperatures down to 2°K.
Octaammine EuIIand YbIIAzides and Their Thermal Decompositions to the Nitrides
Müller, Thomas G.,Mogk, Jochen,Conrad, Matthias,Kraus, Florian
, p. 4162 - 4169 (2016)
The common preparation for many nitrides is the synthesis from the corresponding metals and nitrogen at quite high temperatures and/or high pressures. Here we present a route to metal nitrides by the use of ammine metal azides under relatively mild conditions. Europium(II) and ytterbium(II) azides are prepared in liquid ammonia at –36 °C in form of their temperature-sensitive octaammine complexes. These were investigated by single-crystal X-ray diffraction at low temperatures, and their structures seem to be the first evidence for the existence of homoleptic ammine EuIIand YbIIcomplexes, as well as that the coordination number of these divalent cations can go beyond six with NH3ligands. In one of the cases presented here the observed coordination polyhedron is better described as a bicapped trigonal prism (C2v), in one case better as square-antiprismatic (D4d). Warming of these compounds to room temperature leads to the lanthanoid metal azides still containing approximately 1 equiv. of ammonia. The behaviour of these azides towards further heating was investigated: By very careful and slow decomposition, the nitrides of europium(III) and ytterbium(III) are obtained at only 230 °C at ambient pressure. This method may be suitable to obtain other metal nitrides at remarkably low temperatures and pressures.
Preparation, structure and photoluminescence properties of Eu2+ and Ce3+-doped SrYSi4N7
Li,Fang,De With,Hintzen
, p. 4687 - 4694 (2004)
Undoped and Eu2+ or Ce3+-doped SrYSi 4N7 were synthesized by solid-state reaction method at 1400-1660 °C under nitrogen/hydrogen atmosphere. The crystal structure was refined from the X-ray powder diffraction data by the Rietveld method. SrYSi4N7 and EuYSi4N7, being isotypic with the family of compounds MYbSi4N7 (M=Sr, Eu, Ba) and BaYSi4N7, crystallize with the hexagonal symmetry: space group P63mc (No. 186), Z=2, a=6.0160 (1) A, c=9.7894 (1) A, V=306.83(3) A3; and a=6.0123 (1) A, c=9.7869 (1) A, V=306.37(1) A3, respectively. Photoluminescence properties have been studied for Sr1-xEu xYSi4N7 (x=0-1) and SrY1- xCexSi4N7 (x=0-0.03) at room temperature. Eu2+-doped SrYSi4N7 shows a broad yellow emission band peaking around 548-570 nm, while Ce3+-doped SrYSi4N7 exhibits a blue emission band with a maximum at about 450 nm. SrYSi4N7:Eu2+ can be very well excited by 390 nm radiation, which makes this material attractive as conversion phosphor for LED lighting applications. Emission spectra of Sr1- xEuxSi4N7 as function of Eu 2+ concentration (λexc=390nm). With increasing Eu2+ concentration the emission band shows a red-shift from 548 to 570 nm.
Evolution of Structure and Photoluminescence by Cation Cosubstitution in Eu2+-Doped (Ca1-xLix)(Al1-xSi1+x)N3 Solid Solutions
Wang, Ting,Xiang, Qianchuan,Xia, Zhiguo,Chen, Jun,Liu, Quanlin
, p. 2929 - 2933 (2016)
Red-emitting nitride phosphors excited with blue light have great potential for the fabrication of warm white light-emitting diodes (WLEDs). Chemical composition and structural modification are generally adopted to optimize the photoluminescence behaviors of the targeted phosphors. Herein, on the basis of the famous CaAlSiN3 phosphors, Eu2+-doped (Ca1-xLix)(Al1-xSi1+x)N3 solid solutions via the cations' cosubstitution of (CaAl)5+ pair by (LiSi)5+ pair are successfully synthesized by a solid state reaction, and the lattice parameters show a linear decrease with chemical compositions suggesting the formation of the isostructural phase relationship. Four types of coordinated structure models, corresponding to different coordination environments of Eu2+, are proposed over the course of structural evolution, which induces different structural rigidity and stability, and then they are responsible for three-stage changes of emission spectra of Eu2+ in (Ca1-xLix)(Al1-xSi1+x)N3 solid solution.
Magnesium nitride chemistry
Reckeweg, Olaf,Molstad, Jay C.,Disalvo, Francis J.
, p. 134 - 142 (2001)
Experiments in the system RE-Mg-N (RE = La, Ce, Gd) have been done to explore the possible synthesis of nitrides using Mg as reactive melt and to extend the number of known nitride compounds containing Mg. Since these experiments produce only binary nitrides, we explored the use of mixed Na/Mg melts and discovered the quarternary nitrides BaMg3.33Nb0.67N4 (1), BaMg3.33Ta0.67N4 (2) and Eu4TaMgN5 (3), which were characterized by single crystal structure analysis. The BaMg3.33M0.67N4 compounds are isotypic to UCr4C4 (filled MoNi4 type) and crystallize in the space group I4/m (#87) with the lattice parameters a = 856.40(12) and c = 353.90(7) pm for (1), and a = 859.61(8) and c = 354.21(5) for (2). (3) crystallizes in a new structure type in the acentric orthorhombic space group Pna21 (#33) with the lattice parameters a = 1265.5(3), b = 1015.9(2) and c = 692.5(1) pm.
The effect of replacement of Sr by Ca on the structural and luminescence properties of the red-emitting Sr2Si5N8:Eu2+ LED conversion phosphor
Li,de With,Hintzen
, p. 515 - 524 (2008)
The influence of the replacement of Sr by Ca on structural and luminescence properties of Eu2+-doped Sr2Si5N8 is reported. The Rietveld refinement of the powder X-ray diffraction data shows that the Ca2+ ion preferentially occupies the larger Sr site in Sr2Si5N8:Eu2+. Although the excitation spectrum is hardly modified, the position of the emission band of Eu2+ can be tailored through partial replacement of Sr by Ca in Sr2Si5N8:Eu2+, resulting in red-emission shifting from 620 to 643 nm. Furthermore, (Sr, Ca)2Si5N8:Eu2+ shows high potential as a conversion phosphor for white-light LED applications due to similar absorption, conversion efficiency and thermal quenching behaviour for 465 nm excitation after the introduction of the Ca ion.
