Cooperative Down-Conversion Luminescence in Tb3+/Yb3+ Co-Doped LiYF4 Single Crystals

Cooperative down-conversion (DC) with emission of two near-infrared photons for each blue photon absorbed was achieved in Tb3+/Yb3+ co-doped yttrium lithium fluoride single crystals grown by an improved Bridgman method. The luminescent properties of the crystals were investigated through photoluminescence excitation, emission spectra, and decay curves. With the excitation of Tb3+ ion by a 486 nm light, emission between 980 and 1030 nm from the Yb3+ : F-2(5/2) -> F-2(7/2) transition was observed, and this emission originated from the DC between Tb3+ and Yb3+ ions. The energy transfer processes are studied based on the Inokuti-Hirayama's model, and the interaction between Tb3+ and Yb3+ is confirmed to be electric dipole-dipole. The large quantum cutting efficiency approaches up to 166.7% for 0.32 mol% of Tb3+ and 7.98 mol% of Yb3+ co-doped LiYF4, which is potentially used as a DC layer in silicon-based solar cells.