Origin of visible photoluminescence in combustion synthesized α-Al2O3: Photoluminescence and EPR spectroscopy

Abstract

The present work explores the synthesis of Al2O3 by self-assisted gel combustion synthesis followed by annealing at different temperatures. Excitation spectrum depicted the presence of various kinds of F-center in alumina samples. The differential temperature treatment is expected to give differences in the defect structure which has been investigated. The samples were characterized by powder XRD which confirmed them as α-Al2O3. The alumina samples heated at different temperatures exhibited qualitatively similar broad luminescence spectra which on deconvolution yielded different emissions with a systematic trend in intensity as the function of annealing temperature. The various emissions could be assigned to defect centers such as F, F2 and F22+ centers. The time resolved emission studies could delineate the lifetimes of various emissions. Electron paramagnetic resonance (EPR) study has been resorted to assign the emission bands to respective defect centers. The study highlights the nature of defects generated due to synthesis and annealing and their characterization using photoluminescence and EPR spectroscopy in a technologically important material like Al2O3. The motivation behind this work is to design a simple material which exhibit temperature dependent tunable luminescence without doping any expensive rare earth ion. Such work is important from the prospect of replacing rare earth based phosphor material by holds undoped luminescent materials.