Shallow hole traps in ZnS: Cu,Al phosphors

Localized shallow trapping levels for minority carries, i.e., holes, in ZnS: Cu, Al phosphors are studied by the Dishman method, i.e. by measuring the temperature dependence of the ratio of the quantum efficiency for the green luminescence by the host excitation to that by the direct copper acceptor excitation over the temperature range from 4.2 K to room temperature. The ratio shows increases in three temperature ranges of 20–53 K, 58–100 K and 180–260 K. These increases are attributed to the release of holes to the valence band from three kinds of traps. Analyzing results, the depths of these traps are determined as 35, 68 and 306 mev.