Branching ratio of uv and blue upconversions of Tm3+ ions in glasses

Tm3+ doped germanate, tellurite and heavy-metal fluoride glasses were prepared and their upconversion luminescence spectra were measured to investigate the effect of the host glass on the branching ratios, beta of D-1(2)-->H-3(6) at 0.36 mu m and D-1(2)-->F-3(4) at 0.45 mu m. Because the radiative emission probabilities of these electric dipole transitions are functions of Judd-Ofelt intensity parameters Omega(t) and the sets of reduced matrix elements (\U-(t)\)(t=2,4,6), it was possible to vary the beta of both transitions. The beta of 0.45 mu m luminescence increases slightly with increasing Omega(2) parameter, whereas beta of 0.36 mu m decreased. The ratio of beta 36/beta 45 was largest in a fluorozincate glass and lowest in a tellurite glass. The result could be well explained by the smaller Omega(2)/Omega(4) ratio in fluoride glasses than those in oxide glasses. The correlation between the luminescence intensity ratio and the Omega(t) parameters shows that we can control the branching ratio by the ligand field design for Tm3+ in glass matrices.