Probing multimodal light emission from Tb3+/Yb3+-doped garnet nanophosphors for lighting applications

Herein we report the solution-combustion-method-synthesized Tb3+- and Tb3+/Yb3+-doped Gd3Ga5O12 nanophosphors, which possess luminescent and magnetic properties. The phase formation/crystal structure, and morphology of the prepared nanophosphors are studied using X-ray diffraction (XRD)/Raman spectroscopy and a field emission scanning electron microscope (FE-SEM), respectively. Tb3+/Yb3+-doped phosphor samples exhibit green emission with an intense band around 544 nm through downshifting (DS) and upconversion (UC) processes because of the D-5(4) -> F-7(5) transition of Tb3+. In addition to this visible emission, these samples also show a NIR emission band around 1024 nm via the quantum cutting (QC) process due to the F-2(5/2) -> F-2(7/2) transition of Yb3+. Emission decay measurements of the D-5(4) -> F-7(5) transition of Tb3+ are performed to obtain the rate of energy transfer from Tb3+ to nearby Yb3+. Furthermore, using this energy transfer, the quantum cutting efficiencies were estimated. For their practical application, a selected sample was used to fabricate a LED device by combining the sample with a UV-C LED (274 nm). The obtained results, such as the activation energy (similar to 0.20 eV) and the high CRI value (78), suggest that the prepared sample can be utilized as a green-light-emitting agent in phosphor-coated (pc) WLEDs.