High-pressure optical studies of doped alkali halides. II. Jahn-Teller effects

The emission spectra of heavy-metal-doped alkali halides exhibit a doublet in some temperature ranges at 1 atm. This splitting results from the Jahn-Teller effect which gives excited-state minima corresponding to a tetragonal (AT) and a rhombic (AX) distortion. The latter lies lower in energy. The effect of pressure has been studied on the shifts of the emission peaks and the relative occupations of the two states for various alkali halides in both the NaCl and CsCl structures doped with T1⁺, In⁺, and Ga⁺. In general, the effect of pressure is to increase the occupation of the higher-energy (AT) state at the expense of the AX state. This redistribution is explained in terms of the difference in the pressure shifts of the AT and AX peaks and the possible effect of this difference on the barrier to thermal transfer between the minima. A few remarks are included on pressure effects on the Jahn-Teller splitting in absorption spectra.