Doped CaS powder samples were prepared using two methods: (i) a metathesis reaction of carbonate with H2S at 1200°C; (ii) reaction with Na2Co3/S flux at 1000°C in nitrogen, followed by washing in an alkaline solution, drying and sieving to give 20–30 μm particles.
Powders produced from both reactions were strongly photoluminescent and singificant AC electroluminescence (ACEL) was observed when samples produced by the metathesis reactions were copper coated. Samples prepared using the flux technique on pre-copperdoped carbonate also showed ACEL.
The EL excitation process in the flux grown material differs from that in samples prepared using H2S; this stems from Cu2S microdeposits on the particle surfaces of the former. The formation of the needle-like deposit results from precipitation of copper from solid solution with decreasing temperature. The EL emission arises from observable point sources rather than the more uniform emission from copper-coated samples.