Abstracts 1998

Abstract of Publication No. 304

Ralph P. Schenker, Thomas C. Brunold and Hans U. Güdel
Synthesis and Optical Spectroscopy of MnO42--Doped Crystals of Cs2CrO4, SrCrO4, CsBr and CsI
Inorg. Chem. 37, 918-927 (1998)      Full Text (PDF)      DOI-Link     

Abstract: The first low-temperature absorption and luminescence spectra of MnO42--doped crystals of Cs2CrO4, SrCrO4, CsBr, and CsI are reported. Single crystals of Cs2CrO4:MnO42-, which crystallize in the orthorhombic b-K2SO4 structure, were grown from basic aqueous solutions. An alkali-chloride flux composition was used to obtain single crystals of SrCrO4:MnO42- with the monoclinic monazite structure. Crystals of CsBr:MnO42- and CsI:MnO42- were prepared by slowly cooling the melt. The site symmetry in SrCrO4 is C1, but the deviations from D2 symmetry are small, and the spectra are analyzed in the approximate D2 symmetry. The 2E 2T2 ligand-field transitions are strongly c polarized, and in absorption only the transition to the lowest-energy component of the split 2T2 state is observed with its origin at 10303 cm1. Luminescence is exclusively observed to the lower-energy component of the 2E state. By a combination of absorption and luminescence data, it is shown that, in the cubic CsBr and CsI lattices, MnO42- is partly incorporated in the form of Cs2MnO4 crystallites. The observed nonexponential luminescence decay for these systems indicates the existence of several manganese(VI) species with different relaxation times. Within isomorphous host lattices, a correlation is established between the temperature-quenching behavior and the size of the M6+ host ion: the efficiency of multiphonon relaxation processes increases with increasing ionic radius of M6+.

Last modified: 13.12.11 by Gabriela Frei