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 F2J (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+ (4f13) 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/TD). 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 optim...