Cathodoluminescence of CaWO4 and SrWO4 thin films prepared by spray pyrolysis

Thin films of CaWO₄ and SrWO₄ were prepared on glass substrates by spray pyrolysis. The effects of preparation conditions and monovalent, bivalent and trivalent cation doping on cathodoluminescence (CL) properties of the films were studied. Polycrystalline CaWO₄ and SrWO₄ films formed a scheelite structure after being annealed above 300°C. They exhibited analogous cathodoluminescence consisting of a blue emission band at 447 nm and a blue-green emission band at 487 nm. The blue and blue-green emission intensities increased with substrate and annealing temperature. Annealing atmosphere and doping with Ag⁺, Pb²⁺ and La³⁺ did not influence the characteristics of the blue and blue-green emissions, whereas Eu³⁺ did. The results indicated both the blue and blue-green emissions originated from the WO₄²⁻ molecular complex. The luminance and efficiency for CaWO₄ film were 150 cd/m² and 0.7 lm/W at 5 kV and 57 μA/cm².