On the luminescence of Te4+ in A2ZrCl6 (A = Cs, Rb) and A2ZrCl6 (A = Cs, Rb, K)

The luminescence spectra and decay curves of Te4+-doped A2ZrCl6 (A = Cs, Rb) and A2ZrCl6 (A = Cs, Rb, K) are reported. In these lattices the Te4+ ion is octahedrally coordinated by the chloride ions. The emission consists of one band. For the compositions Cs2ZrCl6:Te4+, Cs2SnCl6Te4+ and Rb2SnCl6:Te4+ vibrational structure is observed in the emission band at low temperatures. The excitation spectra can be interpreted by assuming a dynamical Jahn-Teller effect in the excited state of the Te4+ ion. The vibrational frequency derived from the temperature dependence of the A band splitting is equal to the one obtained from the vibrational progression in the emission band and corresponds to the frequency of the eg mode of the TeCl26− octahedron. Vibrational structure is also observed in the B excitation band of Cs2SnCl6: Te4+ at low temperatures. Finally, a comparison is made with the luminescence of Sn2+ in perovskite lattices and the luminescence of Sb3+ in elpasolite lattices. The Stokes shift decreases in the sequence Sn2+−Sb3+−Te4+ which can be explained by a decreasing contribution of the Jahn-Teller effect to the Stokes shift due to an increasing spin-orbit coupling.