Electrical properties of SrS:Ce EL devices

Luminance, transferred charge, photo-induced transferred charge, and efficiency are analyzed for SrS:Ce, Cl EL devices with different phosphor layer thicknesses. At a constant Ce doping concentration of 0.05 at.%, the width of the phosphor layer is varied from 380 to 890 nm. It is found that the increase of luminance with higher phosphor thickness is mainly attributed to an increasing emission at the leading edge of the voltage pulse, whereas the trailing-edge response is comparable in all samples. The decrease of the EL efficiency at higher peak voltage is due to a strong space-charge formation in the phosphor layer. Highest EL efficiency is obtained at a phosphor thickness of around 700 nm. The photo-induced charge (PQ) response due to the direct excitation ( lambda exc=430 nm) of Ce3+ in high electric fields is investigated as a function of peak voltage. As a result, the PQ response behaves like a sense parameter for the mean electric field of the phosphor layer.