Efficiently Cooperative Energy Transfer Up‐Conversion Luminescence in Tb 3+ /Yb 3+ Co‐Doped Cubic Na 5 Lu 9 F 32 Single Crystals by Vertical Bridgman Method

Tb 3+ /Yb 3+ co‐doped Na 5 Lu 9 F 32 single crystals with ≈1.0 mol% Tb 3+ concentrations and various Yb 3+ are prepared by Bridgman method. Several visible up‐conversion (UC) luminescence are observed following the excitation of 980 nm laser diode (LD) as well as its pump power dependence on UC emission of the crystals. The quadratic dependence of pump power on UC emission reveals that two‐photon UC processes are mainly responsible for the 486 nm and 543 nm emissions of Tb 3+ /Yb 3+ co‐doped system in Na 5 Lu 9 F 32 single crystals. It is proposed that cooperative energy transfer (CET) from two excited Yb 3+ ions to the ground state of Tb 3+ ions is in charge of the ≈486 nm, ≈543 nm and ≈620 nm, which are attributing to 5 D 4 → 7 F 6 , 5 D 4 → 7 F 4 and 5 D 4 → 7 F 3 , respectively, are obtained in Tb 3+ /Yb 3+ doped Na 5 Lu 9 F 32 single crystals. Furthermore, a favorable yellowish green light performance can be achieved with certain Yb 3+ concentrations and 1.0 mol% Tb 3+ co‐doped samples, and its external quantum efficiency approached to 1.25% under 5.5 W cm −2 980 nm excitation which makes further research valuable in developing processable UC materials for electro‐optical devices.