Ab initio study of the stokes shift of the ns-np transition of Tl+ and In+in KCl, Jahn-Teller effect in the nsnp configuration

Detailed lattice relaxation studies of the excited nsnp states of TI+ and I n+ in KCl have shown that the calculated Stokes shift of the 6s-6p transiti on of TI+ is most sensitive to the accuracy of the lattice relaxation aroun d the substituted ion. This is a result of the strong cancellation between the influence of the spin-orbit interaction and the lattice relaxation on t he 6s6p level positions. The results were calculated with a HF-LCAO embedde d cluster method as well as with a DFT based supercell approach. Unexpected ly the supercell method completely fails for thallium in predicting the Sto kes shift. Using the embedded cluster method, a value of 0.706 eV was found for the shift for thallium and 1.24 eV for indium. The experimental values are 0.88 and 1.44 eV respectively. It was also clearly established that th e temperature dependence of the decay time of the main emission line of tha llium is directly related to the Jahn-Teller distortion by which the trappi ng (3)A(1u) level approaches the emitting T-3(1u) level. For indium this do es not play a role because of the much smaller spin-orbit interaction.