Synthesis and optical properties of Al2O3:Cr 3+ powders

Abstract

The Al2-xCrxO3 powders with dopant contents ranging from x = 0:005 to 0.35 have been prepared by sol-gel method. The powders were prepared from aluminium nitrate Al(NO3) 3·9H2O, chrome nitrate Cr(NO3) 3·9H2O, and citric acid and heat-treated at 650-1300°C for 5 h. The effect of dopant concentration and heat-treating temperature on the structural and optical properties of the synthesized samples has been studied. The results showed that the structure, the size and optical properties of Al2-xCrxO3 crystallites strongly depended on the mole fraction x and heating temperature. At low heating temperatures, the samples with the low mole fraction x exhibit γ-Al 2O3 phase and the emission spectra consist of a broad asymmetric peak with the maximum at 691 nm. With the high mole fraction x, the samples consist of α-Al2O3 and Cr2O 3 phases. By increasing the mole fraction x, the emission bands are broadened and shifted towards the long-wavelength side. At high heating temperatures, all the synthesized samples are α-Al2O 3 single phase and the emission spectra mainly consist of lines at 691.6 and 693.2 nm. © 2011 The Surface Science Society of Japan.