Intense 2.0 µm emission from Ho3+/Yb3+ co-doped Na5Lu9F32 single crystal excited by 980 nm

This paper reported on optical spectra of Na5Lu9F32 single crystals co-doped with ~ 0.91 mol% Ho3+ and various Yb3+ concentrations by using an improved Bridgman method. The emission spectra and fluorescence decay curves were measured to investigate the luminescent properties of the Ho3+/Yb3+ co-doped Na5Lu9F32 and the energy transfer process from Yb3+ to Ho3+ ion. Compared with the Ho3+ singly doped Na5Lu9F32 crystal, the Ho3+/Yb3+ co-doped crystal had an obviously enhanced emission at 2.0 µm via the 980 nm laser diode excitation because of the efficient energy transfer from Yb3+ to Ho3+ ion. The maximum emission intensity at 2.0 µm was obtained at about 6.99 mol% Yb3+ concentration when the concentration of Ho3+ ions is fixed at ~ 0.91 mol% in the current research. The maximum emission cross section of the above sample at 2.0 µm was calculated to be 1.23 × 10−20 cm2 according to the measured emission spectrum. The energy transfer efficiency from Yb3+:2F5/2 to Ho3+:5I6 for the crystal was estimated up to 90.8% indicating that Yb3+ ions can efficiently sensitize the Ho3+ ions.