Energy transfer and 2.0 μm emission in Tm3+/Ho3+ co-doped α-NaYF4 single crystals

Abstract

Cubic NaYF4 single crystals co-doped with ∼1.90mol% Tm3+ and various Ho3+ concentrations were grown by Bridgman method. The energy transfer from Tm3+ to Ho3+ and the optimum fluorescence emission around 2.04μm of Ho3+ ion were investigated based on the measured absorption spectra, emission spectra, emission cross section and decay curves under excitation of 800nm LD. The emission intensity at 2.04μm increased with the increase of Ho3+ concentration from 0.96mol% to 3.89mol% when the concentration of Tm3+ was held constantly at ∼1.90mol%. Moreover, the maximum emission cross section reached 1.06×10−20cm2 and the maximum fluorescence lifetime was 23.23ms for Tm3+(1.90mol%)/Ho3+(3.89mol%) co-doped one. According to the measured lifetime of Tm3+ single-doped and Tm3+/Ho3+ co-doped samples, the maximum energy transfer efficiency of Tm3+:3F4 level was 95.0%. Analysis on the fluorescence dynamics indicated that electric dipole–dipole is dominant for the energy transfer from Tm3+ to Ho3+.