Energy transfer based NIR to visible upconversion: Enhanced red luminescence from Yb3+/Ho3+ co-doped tellurite glass

Yb3+-Ho3+: co-doped and Yb3+: singly doped tellurite glasses prepared by conventional melt quenching technique were studied for their sensitised NIR to vis-upconversion performance. The oscillator strength of an absorption transition of the sensitizer (Yb3+) ions was calculated by using the smakula equation from the base glass corrected absorption spectra of Yb3+ singly doped glass. A bright green upconversion emission of Ho3+ ions from the co-doped glass upon exciting Yb3+ ions with 980 nm laser diode and a simultaneous 12 fold decrease in 1.008 mu m emission intensity of Yb3+ ions has been attributed to the energy transfer from sensitizer (Yb3+) to the acceptor (Ho3+) ions. Donor. Yb3+ ion decay kinetics has been analysed by considering Inokuti-Hirayama and Burshtein theoretical models and confirmed the donor-donor hopping migration assisted energy transfer among Yb3+-Ho3+. The energy transfer efficiency estimated from the experimental lifetimes of the singly doped and co-doped system was found to be 85.8%. Further, the upconversion spectra recorded by varying the pump laser power revealed a two photon contribution for the green and red upconversion emission process with the prevalence of saturation. The phenomena of upconversion emissions in the co-doped system were explained with the partial energy level diagram. This glass has been found to be a promising material for the development of solid state upconversion green emitting laser. (C) 2012 Published by Elsevier B.V.