Effect of ligand field on branching ratio of ultraviolet and blue upconversions of Tm3+ ions in halide and oxide glasses

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Abstract
Tm3+ doped zirconium barium lanthanum chloro‐fluoride, germanate, and tellurite glasses were prepared and their upconversion luminescence and excitation spectra were measured to investigate the effect of the host matrix glass on the branching ratio of 0.36 and 0.45 μm luminescences. Since the radiative emission probabilities of electric‐dipole transitions are functions of Judd–Ofelt intensity parameters, Ωt(t=2,4,6), absorption spectra were also measured to obtain Ωt parameters. The branching ratio β of 0.45 μm luminescence in zirconium barium lanthanum chloro‐fluoride glasses increases slightly with increasing Cl− doping, but the ratios were much smaller than those in tellurite and germanate glasses. The result could be explained by the smaller Ω2/Ω4 ratio in zirconium barium lanthanum chloro‐fluoride glasses than those in oxide glasses. The correlation between the luminescence intensity ratio and the Ωt parameters suggests that the branching ratio can be controlled by the ligand field for Tm3+ in glass matrix.