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 ⁵D₄ → ⁷F₅ 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 ²F_5/2 → ²F_7/2 transition of Yb³⁺. Emission decay measurements of the ⁵D₄ → ⁷F₅ 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 (∼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.