Electronic Structure of Luminescence Centers of ZnS Phosphors Activated with Impurity Ions of s2 Configuration (I) ZnS:Bi Phosphors

The excitation, reflection, and fluorescence spectra and glow curves of various ZnS:Bi phosphors were measured accurately. A, B, and C bands with peaks at 6200, 4350, and 4060 Å (room-temperature values), respectively, were found in the visible region of excitation or reflection spectra. These bands were analyzed by using Sugano's molecular orbital theory. The position of A, B, and C bands and the calculated ratio of the diple strength of C band to that of A band are consistent with each other. Thus, it is possible to conclude unambiguously that the resonance transitions between the ground (A1(1S0) and excited states (T2(1P1), T1(3P2), and T2(3P1)) of the localized Bi3+ center produce the A, B, and C bands or the observed red (7600 Å), orange (6200 Å), and green (5100 Å) emission bands. Furthermore, the excitation lines or bands in the uv region of spectrum were analyzed. The interpretation for the glow characteristics was also given.