Phonon density of states and the vibronic spectra of impurities in K2PtCl6-type single crystals

Abstract

Single crystals of the K₂PtCl₆ type at 4°K with impurities of Re⁺⁴, Os⁺⁴, and Ir⁺⁴ show optical absorption with extended phonon structure. To understand the details of this, a phonon density of states was calculated using the model of O'Leary and Wheeler for K₂ReCl₆ and the method of Gilat and Raubenheimer. The results are compared with the optical spectra of Re⁺⁴ and Os⁺⁴ in K₂PtCl₆ that provide strong evidence that the previously used k = 0 phonon analysis is incorrect and that all the lattice vibrations must be used. The implications in the calculation of phonon assisted transition selection rules are discussed.