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 excitation intensity has been studied and it is concluded that emissions come from Tm3+ ions excited by successive energy transfers from Yb3+ ions. The temporal evolution of the 800 nm upconversion emission obtained under flash excitation at 975 nm cannot be described using the energy migration model. This indicates that at this concentration of Yb3+, the rapid migration regime 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. All rights reserved.