Radiophotoluminescence (RPL) is an emission phenomenon induced by the photoexcitation of luminescent centers (RPL centers) formed by ionizing radiation. Ag-doped phosphate glasses exhibiting RPL are applied in dosimeters. In this paper, we discuss the RPL behavior of Ag-doped phosphate glasses and their properties along with RPL center formation and disappearance mechanisms. When Ag-doped phosphate glasses are exposed to ionizing radiation, Ag0, Ag2+, and Agm
n+, such as Ag2
+, clusters are formed because Ag+ acts as an electron and hole trap. Ag2+ is formed by the transfer of holes from PO4
3- tetrahedra. On the other hand, electrons are trapped by Ag+ to form Ag0. Subsequently, Ag2
+ is formed by the association between Ag0 and Ag+ owing to the diffusion of Ag+. Ag0 is attributed to blue RPL center, while Ag2+ and Ag2
+ are attributed to orange RPL centers. Moreover, Ag2
+ and Ag2+ disappear upon heating at 500 and 673 K, respectively.