The Zn_1+xGa_2-0.01-yGe_xO_3x+4∶0.01Cr,_{yBi (x=1－4; y=0.00－0.04) persistent luminescence nanoparticles (PLNPs) are synthesised via hydrothermal synthesis followed by calcinations. The persistent luminescence properties are improved by optimising the reaction conditions, composition of Zn and Ge, and Cr/Bi co-doping ratio. In this study, the effects of calcination temperature and Cr/Bi co-doping ratio on the persistent luminescence properties and phase of PLNPs are investigated. The PLNPs prepared at hydrothermal temperature of 180 ℃ and hydrothermal reaction time of 24 h have the best afterflow luminescence properties when x and y are 2 and 1.02, respectively. The optimal composition of the prepared PLNPs is Zn3Ga1.97Ge2O10∶0.01Cr, 0.02Bi, which has a spinel structure and persistent luminescence time over 15 d, demonstrating good persistent luminescence performance.}