Spectroscopic characterization and systematic crystal-field modeling of optically active rare earth R3+ ions in the bismuth germanate BiY1-xRxGeO5 host

The synthesis conditions and structural characteristics of polycrystalline R-doped BiY1-xRxGeO5 or stoichiometric BiRGeO5 (R = trivalent rare earth Pr3+, Nd3+, Sm3+, Eu3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, or Yb3+) germanate compounds are presented. The energy levels of each R3+ up to the absorption edge of the germanate matrix have been established from 10 K optical absorption and photoluminescence spectra measurements. Detailed single-electron C-2(C-s) Hamiltonians combining free-ion and crystal-field interactions have been used to model the above 4f(N) configurations. Very satisfactory correlations were obtained between observed and the calculated energy levels, and corresponding tabulated data are reported. Systematic trends in the evolution of crystal-field parameters have been identified. The proper estimation of phenomenological crystal-field parameters and crystal-field strengths at the R3+ site for the whole Pr-Yb series is the first step in prospecting the possibilities of this germanate structure as a new solid-state laser host. The observed medium-high (similar to 660 cm(-1)) splitting for the F-2(7/2) ground state of Yb3+ in BiYbGeO5 fulfills a prerequisite for an efficient Yb quasi-three-level laser operation. The possibility of accepting large amounts of optically active R3+ ions and the intense Raman shifts observed at high frequencies are other advantageous characteristics of the title host.