A series of near-infrared (NIR) down-conversion phosphors of La₃Ga₅SiO₁₄ (LGS):Ce³⁺/Yb³⁺ were synthesized via high-temperature solid-state reaction. Under excitation at 345 nm, the phosphors show strong NIR emission around 978 nm, which matches well with the optimal spectral response of crystalline silicon (c-Si) solar cells. The emission spectra and decay curves were used to demonstrate the energy transfer from Ce³⁺ to Yb³⁺. The energy transfer mechanism was discussed in detail, indicating that the energy transfer from Ce³⁺ to Yb³⁺ is dominated by a single photon process, and the energy transfer efficiency is up to 51%. In addition, La₃Ga_5-zAl_zSiO₁₄ (z = 0, 1, 2, 3):Ce³⁺/Yb³⁺ were also synthesized. The NIR emission intensity of La₃Ga₂Al₃SiO₁₄:1%Ce³⁺/5%Yb³⁺ is 4.6 times that of LGS:1%Ce³⁺/5%Yb³⁺, and the thermal relaxation was used to explain this phenomenon. The results show that La₃Ga_5-zAl_zSiO₁₄ (z = 0, 1, 2, 3):1%Ce³⁺/5%Yb³⁺ phosphors have the potential to increase the conversion efficiency of c-Si solar cells.