Choudhury Amitava, Dorhout Peter K
Department of Chemistry, Colorado State University, Fort Collins, CO 80523, USA.
Inorg Chem. 2008 May 5;47(9):3603-9. doi: 10.1021/ic701986j. Epub 2008 Mar 15.
Three new quaternary seleno-gallates containing rare-earth metals and sodium cations, have been synthesized by a solid-state route in evacuated quartz ampoules: Na LnGa 4Se 8 ( Ln = La( I), Ce ( II) and Nd ( III)). The synthesis involved the stoichiometric combination of sodium polyselenides, rare-earth metal, Ga 2Se 3, and Se or elemental Ga in place of Ga 2Se 3. Single-crystal structure analysis indicated that the compounds are isostructural to the thio-analogue, NaNdGa 4S 8. The structures of I- III are described in terms of layers of GaSe 4 tetrahedra joined by corner- and edge-sharing; the alkali-metal cations and the trivalent rare-earth metal cations occupy square antiprismatic sites between the layers. The optical properties of the compounds have been investigated and compared with the isostructural thio-gallate. The band gap of I was located around 2.65 eV. The band gaps of II and III were 2.66 and 2.73 eV, respectively, considerably narrower than their thio-analogues ( approximately 3.4 eV). The contraction of the band gap was attributed to the shift of the valence band to higher energy due to the involvement of higher energy (4p) Se orbitals. The 4f --> 5d gap of II is found to be located around 2.32 eV, which is 0.26 eV narrower than the thio-analogue is due to a greater dispersion of the Ln-(5d) band caused by more covalent Ce-Se bonds as well as rising of the f level energy.
Na LnGa₄Se₈（Ln = La(I)、Ce(II)和Nd(III)）。合成过程涉及多硒化钠、稀土金属、Ga₂Se₃以及用硒或元素镓代替Ga₂Se₃的化学计量组合。单晶结构分析表明这些化合物与硫代类似物NaNdGa₄S₈同构。I - III的结构是根据通过角共享和边共享连接的GaSe₄四面体层来描述的；碱金属阳离子和三价稀土金属阳离子占据层间的方形反棱柱位置。对这些化合物的光学性质进行了研究，并与同构硫代镓酸盐进行了比较。I的带隙约为2.65 eV。II和III的带隙分别为2.66和2.73 eV，比它们的硫代类似物（约3.4 eV）窄得多。带隙的缩小归因于由于更高能量（4p）的硒轨道的参与，价带向更高能量的移动。发现II的4f→5d能隙约为2.32 eV，比硫代类似物窄0.26 eV，这是由于更多共价的Ce - Se键以及f能级能量的升高导致Ln-(5d)能带的更大色散。
