Cathodoluminescent characteristics of green-emitting ZnAl₂O₄:Mn thin film phosphors

Green electroluminescence was obtained from thin films of ZnAl₂O₄:Mn prepared by rf magnetron sputtering onto thick insulating ceramic sheets. Photoluminescence and stress-stimulated luminescence was obtained for Mn-doped ZnAl₂O₄ powder synthesized by the solid phase reaction. Since it is extremely stable chemically and thermally, ZnAl₂O₄ may emerge as an alternative choice to sulphide-based phosphors. In the present paper, thin films of ZnAl₂O₄:Mn were grown on aluminosilicate ceramic plates using spray pyrolysis of aqueous solutions. The cathodoluminescence (CL) properties of the films under low to medium excitation voltage (< 5 kV) were investigated. The films exhibited green CL after being annealed at temperatures above 550°C, which corresponds to the transition between ⁴T₁ and ⁶A₁ of Mn²⁺ ions located in the tetra coordination of the Zn²⁺ site in the spinel structure. The chromaticity coordinates were x=0.150 and y=0.734 with a dominant wavelength of 525 nm and an 82% color purity. The CL luminance and efficiency depended on the excitation voltage and current density. Saturation effects were observed as the current density increased. A luminance of 540 cd·m^-2 and an efficiency of 4.5 lm·W^-1 were obtained at an excitation voltage of 4 kV with a current density of 38 μA·cm^-2.