Preparation and luminescence of green-emitting ZnAl2O4:Mn2+ phosphor thin films

Nanocrystalline Mn2+-doped zinc spinel (ZnAl2O4:Mn2+) green-emitting phosphor films were deposited on silicon substrate by sol-gel spin coating and subsequent heat treatment up to 1000 degrees C. The effects of dopant concentration and heat treatment on the optical and structural properties were investigated. The variations in sol viscosity with time, film thickness with number of layers were also examined. Thin films were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray microscopy, atomic force microscopy, and photoluminescence spectrum. Single-phase ZnAl2O4 started to crystallize at around 600 degrees C, with a normal spinel structure. On annealing at 1000 degrees C, the films had smooth surfaces with a nanocrystalline structure. Under UV or visible light excitation, the phosphor films exhibited an intense green emission band peaking at around 512 nm, corresponding to the typical T-4(1) -> (6)A(1) transition of tetrahedral Mn2+ ions. The most intense green emission was obtained by exciting at 456 nm. The emission intensity of films was highly dependent upon the excitation wavelength, crystallinity, dopant content, and deposition conditions. The results show that the ZnAl2O4: Mn2+ films have good potential for use as a green phosphor for displays and/or white light-emitting diodes. (C) 2014 Elsevier B.V. All rights reserved.