LUMINESCENCE PROPERTIES OF MN-2+ IN KMGF3 AND KZNF3 PEROVSKITE CRYSTALS - EVIDENCE OF A DYNAMIC JAHN-TELLER EFFECT

The luminescence spectra of KZnF3: Mn2+ and KMgF3: Mn2+ are presented and analysed. At T = 5 K, both spectra consist of one zero phonon line from which a phonon sideband centered at about 600 nm is formed. The existence of the dynamical Jahn-Teller (JT) effect in the first 4T1g excited state is evidenced through a reduction of the spin-orbit splitting displayed by the zero phonon lines. JT energies of 530 and 450 cm-1 associated with electron-phonon couplings carrying e(g) type distortions around Mn2+ are estimated for KZnF3: Mn2+ and KMgF3: Mn2+, respectively. Vibronic sidebands are interpreted in terms of lattice modes rather than local vibrations of the MnF6(4-) complex. The magnetic and electric dipole character of the 4T1g --> 6A1g transition is analysed by the temperature dependence of the luminescence spectra and their lifetimes.