DETERMINATION OF MICROSCOPIC PARAMETERS FOR NONRESONANT ENERGY-TRANSFER PROCESSES IN RARE-EARTH-DOPED CRYSTALS

A method for estimating the microscopic probability rate of phonon-ass isted energy transfer between rare-earth (3+) ions in solids was devel oped based on Dexter's theory for phonon-assisted energy transfer. The proposed method in this paper enables one to calculate the overlap in tegral from fundamental cross-section spectra of nonresonant energy tr ansfer involving a multiphonon generation in both donor and acceptor s ites. A translation of the donor emission spectrum towards the accepto r absorption scaled with the N-phonon emission probability represents the m-phonon emission band which performs the energy transfer to the a cceptor. A nonvanishing overlap integral 10(-2)-10(-3) limes smaller t han for the resonant case is found. A multiphonon generation probabili ty assisting the energy transfer was considered due to a combined mech anism of creation and annihilation of phonons. The participation of ea ch phonon in the process was determined. This method was used to inves tigate the (7)),Er3+(I-4(13/2))-->[Ho3+(I-5(7)),Tm3+(F-3(4))] direct e nergy transfers in LiYF4 crystals, as well the back transfers.