Upconversion fluorescence in LiKGdF 5 single crystal co-doped with Er3+, Tb3+

Abstract

The upconversion fluorescence was recorded at room temperature and investigated in LiKGdF5: 2%Er 3+ , 0.4%Tb 3+ single crystal grown by the hydrothermal synthesis technique under 514.5 nm and 785 nm laser excitation, respectively. Under 514.5 nm laser excitation, four strong upconverted emission bands with peaks at 410 nm (violet), 470 nm, 486 nm and 492 nm (blue) were obtained. The former two emission bands were assigned to be corresponding to 2 H 9/2 -> 4 I 15/2 and 2 P 3/2 -> 4 I 11/2 transitions of Er 3+ ions, and the latter two are possibly corresponding to 5 D 4 -> 7 F 6 of Tb 3+ and 4 F 7/2 -> 4 I 15/2 of Er 3+ . The power dependence for 410 nm and 470 nm indicates that they arose from two-photon upconversion processes. While for 486 nm and 492 nm emission, the logarithmic slope is 0.98, which was explained by mutiphonon assisted upconversion process and energy transfer from 4 F 7/2 (Er 3+ ) to 5 D 4 (Tb 3+ ). Under 785 nm laser excitation, besides four weak upconverted emissions mentioned above, three strong emissions with peaks at 523 nm ( 2 H 11/2 -> 4 I 15/2 ), 550 nm ( 4 S 3/2 -> 4 I 15/2 ) and 660 nm ( 4 F 9/2 -> 4 I 15/2 ) were also observed. The possible upconversion mechanism for these seven emissions was all given with the help of the power dependence of upconversion emission intensity and the energy level diagram of Er 3+ ions.