Jahn-Teller and A{sub}(1g) vibrations for Mn{sup}(2+) doped fluoroperovskites: stokes shift

摘要

The totally symmetric and Jahn-Teller vibrations due to a Mn{sup}(2+) impurity in cubic fluoroperovskites are explored by means of Density Functional calculations on 21 atom clusters. In addition to reproduce the experimental Mn{sup}(2+)-F distances at zero pressure, Re, the present calculations indicate that on passing from KMgF{sub}3:Mn{sup}(2+) (R{sub}0=2.06A) to CsCdF{sub}3:Mn{sup}(2+) (R{sub}0=2.15A) both WE and 0)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{sub}3:Mn{sup}(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.