Optimization of processing parameters for designing an efficient AC driven powder electroluminescent device

This paper reports various critical processing parameters for the development of efficient ZnS doped with Cu, Al phosphors optimized to exhibit AC electroluminescence. Different firing atmospheres and temperatures were used for the synthesis of electroluminescent phosphor materials. As synthesized ZnS: Cu, Al phosphor powders were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Photoluminescence (PL) and Electroluminescence (EL) spectroscopy studies. Average crystallite size calculated from XRD lies in a range of 44-49 µm and average grain size as revealed by SEM lies in the range 3-5 µm. The results showed that the phosphor powders have hexagonal phase and exhibit near band edge luminescence in the blue region. This is one of very few reports that depict the observation of EL from hexagonal ZnS:Cu,Al phosphor system. Polycrystalline powders emit PL in a broad band with a maximum at 2.53-2.74 eV above the valence band. The PL spectrum of the ZnS:Cu,Al phosphor showed emission peaks at 453 nm, 467 nm, 485 nm and 490 nm that could be attributed to the generation of deep level energy traps. The prototype of an alternating current driven thick (40±2 µm) film EL device has been fabricated and the threshold voltage was observed to be around 95-120 V at a frequency of 1 kHz. The critical processing parameters for designing an efficient EL device have been highlighted and discussed thoroughly in the current paper.