Infrared, blue and ultraviolet upconversion emissions in Yb 3+–Tm 3+-doped fluoroindate glasses

Abstract

Intense ultraviolet (362.5 nm), blue (479 nm) and IR (800 nm) upconversion emissions were obtained in fluoroindate glasses co-doped with Yb 3+ and Tm 3+ 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 Tm 3+ ions excited by successive energy transfers from Yb 3+ 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 Yb 3+, 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 Tm 3+ to Yb 3+ ions.