Resonant Higher Order Scattering in Double Perovskites

Resonant and non-resonant higher order Raman scattering in the double perovskites La$_{2-x}$Sr$_{x}$FeCrO$_{6-}$ (x = 0, 0.33, 0.66,1) and Ba$_{2}$(Sr$_{2})$FeWO$_{6}$ is investigated. The B-site disordered compound La$_{2}$FeCrO$_{6}$ displays an exceptional series of resonant higher order excitations for =514 nm (2.42 eV). This feature is attributed to defects, in the form of oxygen vacancies, resulting in a localized resonant electron-phonon coupling effect similar to the Franck-Condon effect predicted in the perovskite structured manganites. The resonant state is critically sensitive to Sr doping and . Higher energy excitations in the compounds Ba$_{2}$(Sr$_{2})$FeWO$_{6 }$are shown to be of non-resonant multiphonon character.