SrS-based phosphors have been the most successful materials for blue-emitting thin film electroluminescent devices. Contrary to the widely used ZnS:Mn phosphor, the light generation mechanism in SrS is mainly due to the ionization of dopant centers and the subsequent recombination of electrons with ionized centers. Recently a setup for low-noise measurements has been developed which makes it possible to determine the time-dependency of conduction current and luminance during AC operation with triangular voltage pulses. Right after the voltage has reached its highest amplitude, the emission from the cell is relatively bright, while the measured current is small. The observed time-dependency of current and brightness will be used to estimate the quantum efficiency and the distribution of the space charge in a SrS:Ce phosphor layer.
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