The luminescence properties of Na 5 Lu 9 F 32 single crystals tridoped Tb 3+ , Yb 3+ , and Gd 3+ ions synthesized via a vertical Bridgman method were reported. Gd 3+ was codoped as a sensitizer in Na 5 Lu 9 F 32 :Tb 3+ , Yb 3+ , thus increasing the absorption line-width and the absorption cross sections in the ultraviolet− visible region. Effects of Gd 3+ concentration on the luminescence properties under ultraviolet and near-infrared were investigated. The energy transfer mechanism between the Gd 3+ and Tb 3+ ion was witnessed by the detailed analyses of the excited-state lifetimes, emission quantum yields, and emission and excitation spectra for the Na 5 Lu 9 F 32 :Tb 3+ , Yb 3+ single crystals codoping with various Gd 3+ concentrations ranging from 0 to 0.25 mol %. Following the excitation light in ultraviolet region, Na 5 Lu 9 F 32 single crystals tridoped Tb 3+ /Yb 3+ /Gd 3+ showed dominant green emissions in the visible region and at 980 nm which were attributed to 5 D 4 → 7 F 5 transition of Tb 3+ and 2 D 5/2 → 2 F 7/2 of Yb 3+ , respectively. Under the excitation of 980 nm, Na 5 Lu 9 F 32 single crystals tridoped Tb 3+ /Yb 3+ /Gd 3+ presented bright yellowish-green lights arising from the cooperative energy transfer between two Yb 3+ and one Tb 3+ . The practical up-conversion and down-conversion external quantum efficiency were measured by integrating spheres at ∼1.2% and ∼45%, respectively. The present results demonstrated successful Tb 3+ /Yb 3+ /Gd 3+ triply doping Na 5 Lu 9 F 32 single crystals with both up-and down-conversion luminescence properties that can be used as a potential spectrum converter in solar cells.

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