Abstract Samarium doped SrBPO5 phosphor was synthesized by a high temperature solid state reaction route and its luminescence properties were investigated before and after gamma irradiation. A photo-acoustic spectroscopic technique was used to record the excitation/absorption spectrum of the sample. Photoluminescence studies on the sample prior to gamma irradiation confirmed the presence of Sm3+ at an asymmetric site. After 2kGy of gamma irradiation, the sample showed strong afterglow without any external source that lasted for several minutes. Thermoluminescence (TSL) studies revealed the presence of glow peak at 323K for the system. Electron spin resonance (ESR) studies suggested the formation of borate and oxygen based radical centers in the gamma irradiated system. Detailed ESR–TSL correlation study confirmed the destruction of the oxygen radical to be responsible for the observed glow peak. Based on the findings, a probable mechanism was proposed for the glow peak and observed afterglow.