A metal-to-metal charge transfer induced green-yellow phosphor CsAlGeO:Bi for full-spectrum LED devices.

With the development of solid-state lighting, full-spectrum lighting has gradually received extensive attention. Until now, Bi-doped narrow-band blue phosphors have been widely reported, but broadband green-yellow Bi-doped luminescent materials generated by metal-to-metal charge transfer have been rarely reported. In this study, a Bi ion doped germanate luminescent material CsAlGeO:%Bi (1 ≤ ≤ 11) is synthesized by a high-temperature sintering method. The phosphor can generate a broad green-yellow band peaking at 535 nm with a full width at half maximum of 165 nm under ultraviolet radiation. Through the analysis of the coordination environment, photoluminescence spectra and decay curves, the broadband emission spectra of Bi ions are proved to be generated by the metal-to-metal charge transfer state and the P → S transition. By using theoretical research, luminescence kinetics, and Gaussian fitting, the luminescence mechanism of Bi is examined. Meanwhile, the high quantum efficiency and superior thermal stability prove that the phosphor can be used as an efficient luminescent material in the field of full-spectrum LED devices.