Effect of Temperature on Upconversion Luminescence in Yb3+/Tb3+ Co-Doped Germanate Glass

In the article effect of temperature on the cooperative energy transfer in germanate glass co-doped with Yb3+/Tb3+ under 976 nm laser diode pumping was investigated. The optimization of Tb3+ concentration on the upconversion luminescence was determined. Strong luminescence at 489, 543, 586, 621 nm corresponding to D-5(4) -> F-7(J) (J = 6, 4, 3) transitions and luminescence at 381, 415, 435 nm resulting from D-5(3), (5)G(6) -> F-7(J) (J = 6, 5, 4) transitions were presented. The highest upconversion emission intensity was obtained in glass co-doped with 0.7 Yb2O3/0.7 Tb2O3 (mol%). The effect of temperature on the luminescent properties of germanate glass in the range of 5-250 degrees C indicates the presence of competing phenomena: an increase in the effective absorption cross-section of Yb3+ ions donor as a function of temperature and migration of energy between pairs of ions Yb3+-Yb3+ and of multiphonon excitation levels F-7(J).