Site selective excitation, upconversion and laser operation in Er 3+:LiKYF 5

Abstract

The energy level structures of Er 3+ ions occupying two, almost identical, low symmetry Y 3+ sites in LiKYF 5 have been determined using site selective laser excitation and luminescence. The positions of the (2 J+1)/2 Stark levels of 10 of the lowest energy multiplets were obtained. Upconversion fluorescence in the green, blue and violet while exciting the 4 I 15/2→ 4 F 9/2 transition was observed and modelled via excited state absorption and energy transfer processes populating the energy levels of the 4S 3/2, 2H 9/2 and 2P 3/2 multiplets. Room temperature upconversion laser operation in the green at 550 nm has also been achieved by pumping the 1% Er 3+:LiKYF 5 gain medium with laser diodes at 651 and 800 nm.