Spectroscopic studies of radiative transitions and upconversion characteristics of Er^3+ ions in simple pseudoternary fluoride glasses MF_n–BaF_2–YF_3 (M: Zr, Hf, Al, Sc, Ga, In, or Zn)

Abstract

Optical properties of Er3+ -doped fluoride glasses in the pseudoternary systems MFn–BaF2–YF3, where M is Zr, Hf, Al, Sc, Ga, In, or Zn, were investigated, and the variation of the local structure was discussed. Of the three Judd–Ofelt Ωt parameters (t = 2, 4, 6) that dominate the f–f transition probabilities of Er3+ ions, Ω2 increased as the cationic field strength of network-forming Mn+ ions was increased. Ω6 showed a correlation with the Er—F bond length. The intensity of the 4S3/2→4I15/2 green upconversion luminescence at 0.55 μm induced by 0.80-μm laser pumping varied with the kind of MFn; the InF3-based glass showed the largest intensity, and the AlF3-based glass the lowest. The quantum efficiency and nonradiative decay rates of the 4S3/2 level changed with Mn+ and were not strongly dependent on the cutoff phonon energy of the host. The transition probability of the excitation process at 0.80-μm absorption and that of 0.55-μm emission can play a more important role in the upconversion intensity than the nonradiative loss in the present fluoride glasses with a low multiphonon decay rate.