LUMINESCENCE AND THE FORMATION OF ELECTRON-HOLE TRAPPING CENTERS IN CaSO4–Bi PHOSPHOR

The mechanisms of creation of a new combined electron-emissive state at 2.95 eV, 3.1 eV, 2.6–2.7 eV and 2.25–2.4 eV, which is a pre-decay state for energy transfer from the matrix to the emitters, were investigated in the CaSO 4 − Bi phosphor. Combined electron-emissive states are formed from intrinsic SO 4 3 − − SO 4 − and impurity Bi 2 + − SO 4 − electronhole trapping centers according to studying via spectroscopic and thermal activation methods. In turn, the intrinsic and impurity electron-hole trapping centers are created during excitation of the anionic complex SO 4 2 − as a result of charge transfer from the matrix to impurities ( О 2 − − Bi 3 + ) and neighboring anions ( О 2 − − SO 4 2 − ). It is shown that the energy accumulated in the intrinsic matrix during external irradiation in the form of a combined electron radiative state of SO 4 3 − and Bi 2 + decays as a result of the recombination process and is transferred to impurities.