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With the development of solid-state lighting, full-spectrum lighting has gradually received extensive attention. Until now, Bi3+-doped narrow-band blue phosphors have been widely reported, but broadband green-yellow Bi3+-doped luminescent materials generated by metal-to-metal charge transfer have been rarely reported. In this study, a Bi3+ ion doped germanate luminescent material CsAlGe2O6:x%Bi3+ (1 ≤ x ≤ 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 Bi3+ ions are proved to be generated by the metal-to-metal charge transfer state and the 3P1 → 1S0 transition. By using theoretical research, luminescence kinetics, and Gaussian fitting, the luminescence mechanism of Bi3+ 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. [ABSTRACT FROM AUTHOR]