Quadratic Jahn-Teller Effect in the Line Shapes of the A-Emission and A-Absorption Bands in KBr: Tl+-Type Phosphors

Abstract

The adiabatic potential energy surfaces (APES's) of Tl + -type impurities in alkali halides, \(^{3}T_{1u}(\varGamma_{4}^{-})\) and \(^{3}A_{1u}(\varGamma_{1}^{-})\) have been calculated taking account of the spin-orbit interaction and both the linear and quadratic Jahn-Teller effect with the α 1 g and ε g vibrational modes. It has been found that the 3 T 1 u APES's have one kind of minima or the two kinds of minima, depending on whether we assume the linear or both the linear and quadratic Jahn-Teller interactions. A trap level 3 A 1 u lies just below both the minima. The line shapes of the A -emission and A -absorption bands in KBr: Tl + are calculated by using the Franck-Condon and Condon approximations. It has been found that the theoretical line shape of the A -emission band has the asymmetric doublet structure and reproduces the experimental emission bands A T and A X . This shows that the large energy differnce between the A X and A T bands is caused by the quadratic Jahn-Teller terms involving Q 1 (α 1 g ).