Photon-induced luminescence degradation of Ce, Yb co-doped yttrium aluminum garnet phosphors with different Yb concentrations under 457 nm irradiation is studied for the first time, to the best of our knowledge. The degradation behavior is more significant in nano-phosphors prepared via the solgel method, compared with bulkier samples prepared via solid-state reaction. Photoluminescence intensity of Ce3+ ions experiences a drop after initial illumination, due to photoionization of Ce3+ ions, whereas the down-converted luminescence of Yb3+ ions remains relatively stable. Co-doping Yb3 contributes to the luminescence drop of Ce3+ with the excessive Yb3+ ions serving as additional electron traps. The results are in support of a charge transfer process.