Blue Upconversion Emission in Germanate Glass Co-Doped with Yb3+/Tm3+ Ions

In the paper, the upconversion luminescence of 70GeO(2)-30[Ga2O3-BaO-Na2O] glass system co-doped with Yb3+/Tm3+ ions was investigated. Strong blue emission at 478nm corresponding to the transition (1)G(4)(3)H(6) in thulium ions was measured under the excitation of 976-nm diode laser. The dependence of the upconversion emission upon the thulium ion concentration was studied to determine the optimal conditions of energy transfer between energy levels of active dopants. The most effective energy transfer Yb3+Tm3+ was obtained in glass co-doped with molar ratio of dopant 0.7 Yb2O3/0.07 Tm2O3. The increase in thulium concentration more than 0.07mol% results in the reverse energy transfer from Tm3+Yb3+, which leads to rapid quenching of the luminescence line at the wavelength 478nm. In germanate glass co-doped with 0.7Yb(2)O(3)/0.07Tm(2)O(3), the longest lifetime of (1)G(4) level equal 278s was achieved. The presented results indicate that elaborated germanate glass co-doped with Yb3+/Tm3+ ions is a promising material that can be used to produce fiber lasers and superluminescent fiber sources generating radiation in the visible spectrum.