The photoluminescence (PL) and radioluminescence (RL) of Sn 2+ centers in alkaline earth oxide (RO)-substituted ZnO-P 2 O 5 glasses, which were prepared under Ar, were examined. We confirm that the network structure of the host glass was changed by the substitution of RO for ZnO. Although it seems that the optical absorption is independent of the kind of substituted RO, the PL intensities and the PL decay constants suggest that the local coordination state of the Sn 2+ center is affected by the substitution. From the results of RO-substituted SnO-ZnO-P 2 O 5 (SZP) glasses, it is expected that an aggregation of Sn 2+ centers occurs preferentially in a more highly substituted system. The thermally stimulated luminescence of the RO-substituted glasses suggests that structural rearrangement during the quenching process induces both aggregation of Sn 2+ centers and decrease in the number density of traps in the SZP glasses.