Manganese-activated zinc selenide phosphors show three main luminescence emission bands, one at 1.95 ev (0.635 μm) characteristic of 3d shell transitions in the Mn²⁺ ions, another at 1.24 ev (1 μm) and the last at 0.5-0.7 ev (1.8-2.4 μm); both the last two are independent of the manganese concentration. Both photoconduction and emission can be excited by absorption of radiation characteristic of 3d shell transitions which helps in locating the Mn²⁺ ions levels, relative to the energy bands of zinc selenide, within the forbidden energy gap. A photovoltaic effect is also observed, the spectral response being affected by simultaneous infra-red irradiation. Characteristic thermoluminescence curves are obtained which are also influenced by infra-red irradiation. An energy-band model for emission centres and trapping states is proposed and a quantitative treatment of the kinetics of luminescence photoconduction processes is given. The trapping states have relatively small capture cross sections and are of near-neutral character. The excited states of the Mn²⁺ ion centres are shown to lie near to the bottom of the crystal conduction band.