Cathodoluminescent Characteristics of Green-Emitting ZnAl2O4∶Mn Thin Film Phosphors
LOU Zhi-dong,XU Zheng,YI Lan-jie,YANG Sheng-yi
Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronics Technology, Beijing Jiaotong University, Beijing 100044，China
Abstract：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 ℃, 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.
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