Phosphor-converted White Light-Emitting Diodes (pc-WLEDs) have energy-saving, environmental protection and other excellent performance. At present, the commercial WLEDs are composed of blue LED chip combined with Y₃Al₅O₁₂:Ce³⁺ yellow phosphor. However, due to the lack of red components in the emission spectrum, the white light generated by this method has a low color rendering index (CRI<75) and a high correlation color temperature (CCT>4 500 K), which cannot satisfy the needs of indoor lighting. Researchers at home and abroad have proposed an improved method to generate white light by excitation of red, green and blue phosphors by a near-ultraviolet LED chip. Although this method can produce warm white light for indoor illumination, there is a significant cyan gap in the cyan region of the visible spectrum (480~520 nm), which makes it challenging to achieve full spectral illumination. Therefore, it is desirable to obtain a cyan luminescent material that can achieve full spectrum illumination by mixing phosphors. It is well known that rare-earths Eu²⁺ and Ce³⁺ have been widely used as activator ions in inorganic phosphors. However, Eu²⁺/Ce³⁺ activated phosphors have spectral overlap in the visible region, resulting in low luminescence efficiency and color drift of the synthesized devices. Compared with rare earth ions, Bi³⁺ hardly absorbs in the visible region, so Bi³⁺ activated phosphors can effectively avoid the spectral reabsorption problem encountered by rare earth Eu²⁺/Ce³⁺. At the same time, the outermost electrons 6s and 6p of Bi³⁺ are exposed and sensitive to the changes of crystal field environment, so Bi³⁺ is considered as an activator ion that can realize the color-tunable of phosphors luminescence. Therefore, the abundant optical properties of bismuth ions have attracted extensive attention. In this paper, a series of Cs₃Gd_1-xGe₃O₉:xBi³⁺ (0.02≤x≤0.1) blue phosphors were synthesized by the traditional high-temperature solid-state method. The local environment around Bi³⁺ is regulated by replacing Gd³⁺ in the matrix with Lu³⁺. A series of Cs₃Gd_0.96-yLu_yGe₃O₉:0.04Bi³⁺ (0.1≤y≤0.9) solid solution phosphors with color-tunable were prepared. The phase structure, luminescence properties, fluorescence lifetime, and thermal stability of the phosphors were characterized by X-ray diffraction, steady-state/transient fluorescence spectra and variable temperature spectra. The results showed that a series of pure phase Cs₃Gd_0.96-yLu_yGe₃O₉:0.04Bi³⁺ compounds were successfully synthesized. Under the excitation of the ultraviolet light wavelength of 330 nm, the emission peak of Cs₃Gd_1-xGe₃O₉:xBi³⁺ phosphor is located at 452 nm, showing blue emission. The broadband emission peak originates from the ³P₁ → ¹S₀ transition of Bi³⁺. When the Bi³⁺ doping concentration is 0.04 mol, the luminescence intensity of Cs₃Gd_1-xGe₃O₉:xBi³⁺ phosphor reaches the maximum value. Under the optimal Bi³⁺ doping concentration, by substituting Lu³⁺ for Gd³⁺, the emission peak of Cs₃Gd_0.96-yLu_yGe₃O₉:0.04Bi³⁺ gradually redshifted. With the gradual increase of Lu³⁺ doping concentration, the emission peak gradually redshifted from 453 nm at x=0.1 mol to 483 nm at x=0.9 mol, the corresponding half-peak width is widened from 88 nm to 116 nm, and the color coordinates transition from the blue region (0.168 5, 0.160 2) to the cyan region (0.217 9, 0.300 7). The change of spectral behavior is attributed to the increase of crystal field splitting degree and stokes shift displacement. The luminescence thermal stability of x=0.04 mol and y=0.5 mol samples was investigated,and the luminescence intensity of the samples remained 55% of the initial value when the temperature was raised to 423 K. A series of solid solution phosphors with adjustable luminescence color obtained have potential applications in the fields of full spectrum lighting and plant lighting.