Vibronic spectra and lattice dynamics of Cs2MnF6 and A12MIVF6:MnF2−6

Abstract

The 2Eg→4A2g luminescence spectra of Cs2MnF6 and A12MIVF6:MnF2−6(A1=K, Rb,MIV=Si; A1=Cs,MIV=Si,Ge) are reported, In each case the spectrum can be analyzed into (a) the magnetic dipole allowed pure electronic orgin, (b) a set of one phonon sidebands characteristic of the lattice, (c) several bands involving two lattice phonons, (d) three strong vibronic origins corresponding to the odd vibrational modes of the anion, (e) progressions in up to three quanta of the three even anion modes based on the strong vibronic origins, and (f) bands involving combinations of one internal mode and one or two lattice phonons. Apart from small differences in the vibrational frequencies, the only difference between the spectra of the pure and the diluted compounds is the observation of the transverse–longitudinal (TO–LO) splitting of the ν3 and ν4 internal modes and an additional small splitting of the ν4 TO mode in the pure compound. The spectra are compared with the predictions of a simple lattice dynamical model for Cs2MnF6. The spectrum of Cs2GeF6:MnF2−6 is complicated by interaction between the localized ν3 mode of MnF2−6 and the ν3 band of the host lattice. The intensity mechanisms for the features (a) – (f) are discussed.