Radiation effects on Co²⁺ and Ni²⁺ doped NH<inf>4</inf>Cl crystals

Unirradiated Co2+:NH4Cl and Ni2+:NH4Cl crystals have shown the characteristic absorption bands associated with these impurities. These absorption bands are interpreted in terms of electronic transitions within the crystal field levels determined mainly by the ligands of octahedral coordination. On X-irradiation at room temperature Co2+:NH4Cl crystals are found to absorb at 270, 345, 585, 900 and 1000 nm. These absorption bands have been attributed to the charge transfer transitions between the radiation induced hydrazine-like defect, N2H+4, and the ligand H2O or NH3 which are available in the crystal along with the divalent impurity. Some of the absorption bands observed in Co2+:NH4Cl are also found in Ni2+ doped NH4Cl crystals after X-irradiation. ESR studies of X-rayed Ni2+ doped NH4Cl crystals revealed the formation of Ni+ and Ni3+. Spin-Hamiltonian parameters for these centers are given. Effects of impurities on the stabilisation of various intrinsic defects are also discussed. © 1984.