Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were conducted on self-irradiated as well as gamma irradiated BaCO₃co-doped with²³⁷Np⁴⁺and NO₃⁻ ions. EPR studies of the irradiated sam-ples revealed that the electron transfer process between iso-electronic carbonate and nitrate groups is the dominant e ect of ionizing radiation, forming CO₃⁻ and NO₃² ions. This facilitated the radiation stability of the valence of N pin the tetravalent state. TSL spectral studies showed that Np⁴⁺ion acts as the luminescence centre. TSL–EPR correlation studies revealed the role of CO₃⁻ ion in the glow peak at 413 K.