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 Bridg- man 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 fluo- rescence emission around 1.80 µm of Tm³⁺ ion were investigated. The maximum emission cross section at 1.8 µm was calculated to be 1.48 x 10⁻²⁰ cm² 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.