Energy transfer in LaAlO 3:Cr 3+

Abstract

The transfer of optical excitation energy from the Cr 3+ single ions to the first nearest Cr 3+ pairs in LaAlO 3:Cr 3+ was investigated by means of time-resolved laser spectroscopy. The fluorescence responses of the single ions and pairs after flash and switched-off cw-excitation at different concentrations and temperatures was analysed by our “discrete shell model” assuming incoherent transition probabilities for energy migration and direct transfer. All fluorescence responses were fitted to the same set of parameters to test the consistency of the model. The energy migration between the single ions turned out to be negligible (diffusion constant D<1.4 nm 2 sec -1). For the direct transfer from the single ions to the pairs superexchange interaction was found to be responsible. The weak temperature dependence of the energy transfer leads to the assumption that the direct transfer is due to a one-phonon assisted non radiative process. Using a theory of Orbach the electronic matrix element responsible for the energy transfer could be estimated from experimental data.