Oxide phosphors for light upconversion; Yb³ and Tm³ co-doped Y₂BaZnO₅

The optical properties of Yb³ and Tm³ co-doped Y ₂BaZnO₅, synthesized by solid-state reaction, are investigated in detail. Three main emission bands centered around 479 nm (blue), 654 nm (red), and 796 nm (near-infrared) are observed under near-infrared laser excitation via an upconversion process. Detailed studies of the upconversion properties as a function of dopant concentrations are described and upconversion efficiencies quantified precisely. Maximum efficiencies of ∼ 1.53 in the 730-870 nm near-infrared emission range and of ∼ 0.09 in the 420-530 nm blue range are obtained. The results of power dependence studies and concentration dependent lifetime measurements are presented. This in-depth spectroscopic study allows us, for the first time, to identify the dominant processes involved in the upconversion mechanism of Yb³, Tm³ co-doped Y ₂BaZnO₅ oxides.