Blue-upconversion in thulium and ytterbium codoped tellurite-gallium glasses pumped by laser diodes

This paper reports on upconversion properties of Tm 3+ /Yb 3+ co-doped TeO 2 -Ga 2 O 3 - R 2 O ( R =Li, Na, K) glasses pumped by 808 and 977 nm laser diodes (LD). An intense upconversion emission centered at 476-nm (blue) along with a weak emission at 650 nm (red) has been observed when pumped by 977 nm LD, assigned to the transitions of 1 G 4 → 3 H 6 and 1 G 4 → 3 H 4 and/or 3 F 2，3 → 3 H 6 of Tm 3+ , respectively. The 476-nm upconversion intensity has a nearly cubic dependence on incident pump laser power, indicating a three-photon process. However, a quadratic dependence of the 476-nm upconversion intensity on the incident pump laser power has been observed when pumped by 808 nm LD, due to two-photon absorption process. It is noticed that the intensity of the blue-upconversion emission increases signifieantly with increasing radius of alkali metal of samples when pumped by 977 nm LD, while no obvious change has been observed when pumped by 808 nm LD.