Gadolinium gallium aluminum garnet (GGAG) is a very promising host for the highly efficient luminescence of Ce3+ and shows potential in radiation detection applications. However, the thermodynamically metastable structure would be slanted against it from getting high transparency. To stabilize the crystal structure of GGAG, Yb3+ ions were codoped at the Gd3+ site. It is found that the decomposition of garnet was suppressed and the transparency of GGAG ceramic was evidently improved. Moreover, the photoluminescence of GGAG:Ce3+,xYb(3+) with different Yb3+ contents has been investigated. When the Ce3+ ions were excited under 475 nm, a typical near-infrared region emission of Yb3+ ions can be observed, where silicon solar cells have the strongest absorption. Basing on the lifetimes of Ce3+ ions in the GGAG:Ce3+,xYb(3+) sample, the transfer efficiency from Ce3+ to Yb3+ and the theoretical internal quantum efficiency can be calculated and reach up to 86% and 186%, respectively. This would make GGAG:Ce3+,Yb3+ a potential attractive downconversion candidate for improving the energy conversion efficiency of crystalline silicon (c-Si) solar cells.