Local atomic environment of Yb 3+ in alkaline-earth fluorohalide nanocrystals
Local atomic environment of Yb 3+ in alkaline-earth fluorohalide nanocrystals
复制标题
碱土氟卤化物纳米晶中Yb 3 的局域原子环境
DOI：
10.1039/d2ce00636g
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发表时间：
2022
期刊：
影响因子：
3.1
通讯作者：
Rabuffetti, Federico A.
中科院分区：
文献类型：
--
作者：
Amarasinghe, Dinesh K.;Dissanayake, K. Tauni;Dhanapala, B. Dulani;Rabuffetti, Federico A.
利用Yb L2边EXAFS谱研究了Yb：Er：SrFCl、Yb：Er：SrFBr和Yb：Er：BaFCl纳米晶中Yb 3+离子的局域原子环境。由Yb 3+取代氟卤化物晶格中的Sr 2+或Ba 2+得到的结构模型未能提供Yb 3+的第一配位壳层的晶体化学有意义的描述。在此基础上，排除了Yb ~（3+）配位为YbF_4Cl_5或YbF_4 Br_5的C_4v对称正方反棱柱的可能性。评价了两种备选模型。第一个模型的灵感来自于YbF 9覆盖的正方形反棱镜，它构成了正交YbF 3的晶体结构。第二个模型是基于YbO 4F 3盖帽三角棱镜遇到单斜YbOF。这两种模型都正确地再现了径向结构函数，并产生了化学上有意义的镱-氟和镱-氧距离。EXAFS研究结果表明，Yb 3+异价掺杂后，氟卤化物晶格中出现了成分和结构的不均匀性。从组成的角度来看，额外的氟阴离子和/或氧化物阴离子似乎被纳入附近的Yb 3+掺杂剂。从结构的角度来看，在Yb 3+（Cs或C1）周围的局部对称性低于碱土金属阳离子所占据的晶体学位置。这些结论适用于三种不同的氟卤化物主体组合物和稀土掺杂水平跨越一个数量级。
The local atomic environment of Yb3+ ions doped into Yb:Er:SrFCl, Yb:Er:SrFBr, and Yb:Er:BaFCl nanocrystals was probed using Yb L2 edge EXAFS spectroscopy. A structural model derived from substitution of Yb3+ for Sr2+ or Ba2+ in the fluorohalide lattice failed to provide a crystallochemically meaningful description of the first coordination shell of Yb3+. On this basis, the presence of Yb3+ coordinated as YbF4Cl5 or YbF4Br5 capped square antiprisms of C4v symmetry was ruled out. Two alternative models were evaluated. The first model was inspired by YbF9 capped square antiprisms that make up the crystal structure of orthorhombic YbF3. The second model was based on YbO4F3 capped trigonal prisms encountered in monoclinic YbOF. Both models correctly reproduced radial structure functions and yielded chemically meaningful ytterbium–fluorine and ytterbium–oxygen distances. Results from EXAFS studies indicate that compositional and structural heterogeneities appear in the fluorohalide lattice upon aliovalent doping with Yb3+. From a compositional standpoint, extra fluoride anions and/or oxide anions appear to be incorporated in the vicinity of Yb3+ dopants. From a structural standpoint, the local symmetry around Yb3+ (Cs or C1) is lower than that of the crystallographic sites occupied by alkaline-earth cations. These conclusions hold for three different fluorohalide host compositions and rare-earth doping levels spanning one order of magnitude.