Infrared, blue and ultraviolet upconversion emissions in Yb3+-Tm3+-doped fluoroindate glasses

Intense ultraviolet (362.5 nm), blue (479 nm) and IR (800 nm) upconversion emissions were obtained in fluoroindate glasses co-doped with Yb3+ and Tm3 ions pumped at 975 nm. The dependence of these upconversion emissions on e xcitation intensity has been studied and it is concluded that emissions com e from Tm3+ ions excited by successive energy transfers from Yb3+ ions. The temporal evolution of the 800 nm upconversion emission obtained under flas h excitation at 975 nm cannot be described using the energy migration model . This indicates that at this concentration of Yb3+, the rapid migration re gime among these ions has not been reached. A model is proposed in order to explain the temporal evolution of this emission, taking into account back- transfer processes from Tm3+ to Yb3+ ions. (C) 1999 Elsevier Science B.V. A ll rights reserved.