LiEuMo₂O₈ - crystal growth, structure, and optical properties

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• 作者：Sebastian Schwung ; Daniel Rytz ; Andreas Gross ; Ute Ch. Rodewald ; Rolf-Dieter Hoffmann ; Birgit Gerke ; Birgit Heying ; Christian Schwickert ; Rainer P枚ttgen ; Thomas J眉stel
• 关键词：Molybdate ; Crystal growth ; Optical properties ; Magnetism ; Mö ; ssbauer spectroscopy ; ESR
• 刊名：Optical Materials
• 出版年：January, 2014
• 年：2014
• 卷：36
• 期：3
• 页码：585-590
• 全文大小：1065 K

文摘

Centimeter size LiEu(MoO₄)₂ bulk single crystals have been grown by top-seeded solution growth using Li₂MoO₄ as a flux. The resulting crystals exhibited different coloration shades from dark to bright violet. Small single crystal fragments were studied by X-ray diffraction: CaWO₄ type, space group I4₁/a, a = 519.74(4), c = 1132.56(11) pm, wR2 = 0.0143, 270 Fp>2p> values at 300 K and a = 518.70(4), c = 1130.25(11) pm, wR2 = 0.0197, 268 Fp>2p> values at 90 K. The Lip>+p> and Eup>3+p> cations statistically occupy the 4b site. Down to 90 K, the single crystal X-ray data give no hint for cation ordering. Some of the grown crystals show dark violet color. This is due to defects in the oxygen substructure accompanied by partial reduction of Mop>6+p> (dp>0p>) to Mop>5+p> (dp>1p>) which was detected by electron spin resonance. p>151p>Eu M枚ssbauer spectra of the bright and also of the dark violet LiEuMo₂O₈ samples show the presence of trivalent europium solely. Temperature dependent magnetic susceptibility data exhibit weak van Vleck type paramagnetism as a consequence of trivalent europium ([Xe]4fp>6p>). The dark violet samples show slightly higher susceptibility due to the contribution of Mop>5+p>. These data point to a formula LiEuMo₂O_8-x for the violet samples. p>7p>Li solid state NMR spectra underline the single lithium sites in both samples. Both colored crystals show identical emission spectra, which indicate the same chemical surrounding of the trivalent europium ions. However, excitation spectra and thermal quenching and decay curves points to a higher defect density in the violet sample.