Energy Transfer and 1.8 µm Emission in Tm³⁺/Yb³⁺ Co-Doped LiYF₄Crystal.

LiYF4 single crystals co-doped with various Tm3+/Yb3+ concentrations were grown using the Bridgman method. The luminescent properties of the crystals were investigated through emission spectra, emission cross section, and decay curves under excitation by 980 nm. Compared with the Tm3+ single-doped LiYF4 crystal, an enhanced emission band from 1600 to 2150 nm was observed upon excitation of a 980 nm laser diode. The energy transfer from Yb3+ to Tm3+ and the optimum fluorescence emission around 1.80 mu m of Tm3+ ion were investigated. The maximum emission cross section at 1.8 mu m was calculated to be 1.48 x 10(-20) cm(2) according to the measured absorption spectrum. The high energy transfer efficiency of 86.5% from Yb3+ to Tm3+ ion demonstrate that the Yb3+ ions can efficiently sensitize the Tm3+ ions.