Phonon Effects On Zero-Phonon Transitions Between Stark Levels In Nabi(Wo4)(2):Yb3+

We report results from a modeling study of temperature-dependent line broadening and associated Debye-Waller factors (DWFs) for zero-phonon transitions between the F-2(J) (J=7/2,5/2) manifolds of Yb3+ in NaBi(WO4)(2). The Hamiltonian includes the electron-phonon interaction between the electronic states of the Yb3+ (4f(13)) ions and the lattice (Debye) phonon spectrum of the host crystal in a second quantization formulation. The temperature dependences of the linewidths, DWFs, and the intensities of the transitions are reported in terms of the ratio of temperature to Debye temperature (T/T-D). Of particular interest is the temperature dependence of the most intense transitions at emission wavelengths of 996.6 and 1010.2 nm. These transitions are the best candidates for low-threshold stimulated emission based on measured emission cross sections and lifetimes. We find that with a decrease in temperature, an abrupt increase in radiation intensity occurs for the 1010.2 nm emission transition, suggesting that an optimum temperature value for a maximum stimulated emission may be obtained for Yb3+ in this disordered structure.