Theoretical study of the effects of F to Cl chemical substitution on the electronic structure and the luminescence properties of Cs2GeF6 : Os4+ and Cs2ZrCl6 : Os4+ materials

摘要

It has been experimentally determined that Cs2ZrCl6:Os4+ shows luminescence and up-converted luminescence from the highest t(2g)(4) excited level 2 A(1g)((1)A(1g)), whereas Cs2GeF6:Os4+ 2 A(1g)((1)A(1g)) does not luminescence at all. Ab initio quantum chemical calculations on these materials are presented here and show that the variation of the energy gap between the t(2g)(4) and t(2g)(3) e(g)(1) manifolds with F to Cl chemical substitution is a key factor to interpret the experimental findings. This energy gap is calculated to be some 1500 cm(-1) (similar or equal to 2 (v) over bar (a1g)) in the fluoride host, whereas it is about 3300 cm(-1) (similar or equal to 9 (v) over bar (a1g)) in the chloride host. The calculated values for the ground state totally symmetric vibrational frequency (v) over bar (a1g) are 626 cm(-1) (Cs2GeF6:Os4+) and 355 cm(-1) (Cs2ZrCl6:Os4+), in good agreement with the available experimental data. Geometrical structure of (OsX6)(2-) clusters (X=F,Cl) embedded in Cs2GeF6 and Cs2ZrCl6 lattices is calculated as well. New assignments for some spectral features based in the results of our calculations are proposed.