The temperature-dependent luminescence of Sm 2 + ions in MBPO 5 (M=Ca 2 + ,Sr 2 + ,Ba 2 + ) was studied. At low temperature, Sm 2 + in this series shows 4f 6 ->4f 6 luminescence with only a single emission line observed for the 5 D 0 -> 7 F 0 transition, revealing that only one crystallographic cationic site is available for Sm 2 + in all the hosts. With increasing temperature, the emission intensity of the 5 D 0 -> 7 F 0 transition increases whereas that of the 5 D 0 -> 7 F 1 transitions decreases. The 5 D 1 -> 7 F 0 transitions of Sm 2 + were observed in BaBPO 5 and its intensity increases with increasing temperature. At 450K, a broad band of the 4f 5 5d->4f 6 luminescent transition of Sm 2 + in SrBPO 5 and BaBPO 5 with maximum at ~600nm appears due to the thermal population. The lifetime of the 5 D 0 -> 7 F 0 transition was recorded at different temperatures, showing a single exponential decay for Sm 2 + in SrBPO 5 and BaBPO 5 but a non-single-exponential decay in CaBPO 5 .