The effects of Er3+ ion concentration on 2.0-μm emission performance in Ho3+/Tm3+ co-doped Na5Y9F32 single crystal under 800-nm excitation* *Project supported by the National Natural Science Foundation of China (Grant No. 51772159), the Natural Science Foundation of Zhejiang Province, China (Grant No. LZ17E020001), the Natural Science Foundation of Ningbo City (Grant No. 202003N4099), and K C Wong Magna Fund in

Abstract

Na5Y9F32 single crystals doped with ∼ 0.8-mol% Ho3+, ∼ 1-mol% Tm3+, and various Er3+ ion concentrations were prepared by a modified Bridgman method. The effects of Er3+ ion concentration on 2.0-μm emission excited by an 800-nm laser diode were investigated with the help of their spectroscopic properties. The intensity of 2.0-μm emission reached to maximum when the Er3+ ion concentration was ∼ 1 mol%. The energy transfer mechanisms between Er3+, Ho3+, and Tm3+ ions were identified from the change of the absorption spectra, the emission spectra, and the measured decay curves. The maximum 2.0-μm emission cross section of the Er3+/Ho3+/Tm3+ tri-doped Na5Y9F32 single crystal reached 5.26 × 10−21 cm2. The gain cross section spectra were calculated according to the absorption and emission cross section spectra. The cross section for ∼ 2.0-μm emission became a positive gain once the inversion level of population was reached 30%. The energy transfer efficiency was further increased by 11.81% through the incorporation of Er3+ ion into Ho3+/Tm3+ system estimated from the measured lifetimes of Ho3+/Tm3+- and Er3+/Ho3+/Tm3+-doped Na5Y9F32 single crystals. The present results illustrated that the Er3+/Ho3+/Tm3+ tri-doped Na5Y9F32 single crystals can be used as promising candidate for 2.0-μm laser.