Room temperature blue upconverted luminescence via photon avalanche pumping in Cs2NaGdCl6:Tm3+

Abstract

Experimental results are presented to show that the intense, blue upconverted luminescence observed from Cs2NaGdCl6 doped with 6,10 and 15 at.% Tm3+, when excited by a cw laser near 650 nm at room temperature, is due to a photon avalanche process. A slow rise of the upconverted blue-emission intensity, over several seconds, takes place near the threshold power level. Emission is not only observed from the1G4 term manifold, but also from1D2. The well-resolved upconversion excitation spectrum indicates clearly that excited-state absorption to1G4 takes place from the3F4 multiplet term of Tm3+.