Crystal Structure, Thermal Behavior, and Luminescence of BaZnCl_4-II: Sm~(2+) and Comparision to BaZnCl_4-I:Sm~(2+)

摘要

Slightly different reaction conditions lead to two modifications of single crystalline BaZnCl_4. The crystal structure of BaZnCl_4-II(orthorhombic, Pbcm(No.60),Z=4, a=6.5041(9),b=15.363(3),c=6.819(1)A, R_(all)=0.0608) consists of edge and corner sharing [BaCl_8] polyhedra with [ZnCl_4] tetrahedra filling the holes of the [BaCl_8] network.The polyhedra inBaZnCl_4-I are nearly equal but the linkage is dufferent .Both modifications can be obtained as single phases from BaCl_2/ZnCl_2 mixtures and show to phasde transitions down to 4K. Emission spectra of both modifications doped with Sm~(2+) reveal 4f~55d~1->~7F_J as well as ~5D_o->~7F_J transitions . In spite of the similar surrounding of Sm~(2+) in both modifications the shift of the maximum of the d->f emission is 450 cm~(-1) , showing that small changes in the coordination polyhedra of divalent rare earths cause large changes in luminescence properties