Jahn-Teller and A_(1g) Vibrations for Mn~(2+) Doped Fluoroperovskites: Stokes Shift

摘要

The totally symmetric and Jahn-Teller vibrations due to a Mn~(2+) impurity in cubic fluoroperovskites are explored by means of Density Functional calculations on 21 atom clusters. In addition to reproduce the experimental Mn~(2+)-F~- distances at zero pressure, R_e, the present calculations indicate that on passing from KMgF_3:Mn~(2+) (R_o=2.06A) to CsCdF_3:Mn~(2+) (R_o=2.15A) both ω_E and ω_A are reduced by about 45%. As salient feature this huge reduction is found to be practically twice that calculated for a system like KMgF_3:Mn~(2+) when the equilibrium distance is forced to change 9 pm due to an applied hydrostatic pressure. Therefore this result stresses that though chemical and hydrostatic pressures produce the same effects on the electronic properties of a localized center in an insulating material, this conclusion is not necessarily true when local vibrations are considered. The relevance of this result with regard to the Stokes shift is discussed.