Cooperative Energy Transfer Up-/Down-Conversion Luminescence in Tb3+/Yb3+ Co-Doped Cubic Na5Lu9F32 Single Crystals by Gd3+ Co-Doping

The luminescence properties of Na5Lu9F32 single crystals tridoped Tb3+, Yb3+, and Gd3+ ions synthesized via a vertical Bridgman method were reported. Gd3+ was codoped as a sensitizer in Na5Lu9F32:Tb3+, Yb3+, thus increasing the absorption-line-width and the absorption cross sections in the ultraviolet-visible region. Effects of Gd3+ concentration on the luminescence, properties under ultraviolet and near-infrared were investigated, The energy transfer mechanism between the Gd(3+)and Tb3+ ion Was. witnessed, by the detailed analyses of the excited-state lifetimes, emission quantum yields, and emission and excitation spectra for the Na5Lu9F32:Tb3+, Yb3+ single crystals codoping with various Gd3+ concentrations ranging from 0 to,0.25 mol %.Following the excitation light in ultraviolet region, Na5Lu9F32 single crystals tridoped Tb3+/Y3+/Gd3+ showed dominant green emissions in the visible region and at 980 nm which were attributed to D-5(4) -> F-7(5) transition of Tb3+ and D-2(5/2) -> F-2(7/2) of Yb3+, respectively. Under the excitation of 980 nm, Na5Lu9F32 single crystals tridoped Tb3+/Yb3+/Gd3+ presented bright yellowish-gteen lights-arising, from the cooperative energy transfer between two Yb3+ and one Tb3+. The practical up-conversion and down-conversioin external quantum efficiency were measured by integrating spheres at similar to 1.2% and similar to 45%, respectively. The present results demonstrated successful Tb3+/Yb3+/Gd3+ triply doping Na5Lu9F32 single crystals with both up- and down-conversion luminescence properties that can be used as a potential spectrum converter in solar cells.