KEu(MoO4)2: Polymorphism, Structures, and Luminescent Properties

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• 作者：Vladimir A. Morozov ; Alla V. Arakcheeva ; Philip Pattison ; Katrien W. Meert ; Philippe F. Smet ; Dirk Poelman ; Nicolas Gauquelin ; Johan Verbeeck ; Artem M. Abakumov ; Joke Hadermann
• 刊名：Chemistry of Materials
• 出版年：2015
• 出版时间：August 25, 2015
• 年：2015
• 卷：27
• 期：16
• 页码：5519-5530
• 全文大小：852K
• ISSN：1520-5002

文摘

In this paper, with the example of two different polymorphs of KEu(MoO₄)₂, the influence of the ordering of the A-cations on the luminescent properties in scheelite related compounds (A鈥?A鈥?_n[(B鈥?B鈥?O₄]_m is investigated. The polymorphs were synthesized using a solid state method. The study confirmed the existence of only two polymorphic forms at annealing temperature range 923鈥?203 K and ambient pressure: a low temperature anorthic 伪-phase and a monoclinic high temperature 尾-phase with an incommensurately modulated structure. The structures of both polymorphs were solved using transmission electron microscopy and refined from synchrotron powder X-ray diffraction data. The monoclinic 尾-KEu(MoO₄)₂ has a (3+1)-dimensional incommensurately modulated structure (superspace group I2/b(伪尾0)00, a = 5.52645(4) 脜, b = 5.28277(4) 脜, c = 11.73797(8) 脜, 纬 = 91.2189(4)^o, q = 0.56821(2)a*鈥?.12388(3)b*), whereas the anorthic 伪-phase is (3+1)-dimensional commensurately modulated (superspace group I1虆(伪尾纬)0, a = 5.58727(22) 脜, b = 5.29188(18)脜, c = 11.7120(4) 脜, 伪 = 90.485(3)^o, 尾 = 88.074(3)^o, 纬 = 91.0270(23)^o, q = 1/2a* + 1/2c*). In both cases the modulation arises due to Eu/K cation ordering at the A site: the formation of a 2-dimensional Eu³⁺ network is characteristic for the 伪-phase, while a 3-dimensional Eu³⁺-framework is observed for the 尾-phase structure. The luminescent properties of KEu(MoO₄)₂ samples prepared under different annealing conditions were measured, and the relation between their optical properties and their structures is discussed.