Increase of the 800 nm excited Tm3+ blue upconversion emission in fluoroindate glasses by codoping with Yb3+ ions

Intense Tm3+ blue upconversion emission has been observed in Tm3+-Yb3+ codoped fluoroindate glasses under direct excitation into Tm3+ ions with a diode laser at 796 nm. The dependence of the intensity of this upconversion emission on the Tm3+ and Yb3+ concentration has been studied in order to determine the optimum ion concentrations and the involved mechanisms. The blue upconversion emission is highly increased with the Yb3+ concentration. For fixed Yb3+ concentrations, the maximum upconversion efficiency was obtained with Tm3+ concentration of about 0.5 mol%. For this optimum Tm3+ concentration, the upconversion emission intensity is increased by a factor about 100 by codoping with 2.25 mol% of Yb3+. The results are well explained by a proposed rate equation model. (C) 2002 Elsevier Science B.V. All rights reserved.