The effect of temperature treatment on structural and optical properties of cr3+doped alumina nanocrystals

Abstract

Cr3+doped alumina nanocrystals have been successfully prepared using combustion method. The chemicals used in this preparation are aluminium nitrate, chromium nitrate, urea and glucose. All these chemicals were thoroughly mixed then heated in a furnace. The mixture was heated at 600 °C for 1 hour then heated at 700, 800 and 900 °C for 30 minutes. At the final stage the mixture was heated at the temperature of 1000 °C for 30, 60, and 120 minutes. At every different temperature and heating time, some of the sample was taken for analysis. The samples were analysed in terms of their structure and optical properties by using X-ray diffraction (XRD) and spectrofluorometer, respectively. From the analysis, it is found that the structure and optical properties were strongly affected with the temperature and heating time. The sample heated at 1000 °C for 30 minutes contains gamma and alpha phases structures. The structure fully transformed to alpha phase after 1 hour of heating at 1000 °C. From the X-ray diffractogram, crystallite size was estimated using Scherrer equation, which shows increasing trend from 21 nm to 33 nm as the heating time prolonged from 30 minutes to 120 minutes at 1000 °C. The fluorescence spectra at 694 nm observed for the samples annealed at 1000 °C. The intensity of fluorescence increases with longer heating time. Based on the result, it shows that the temperature and heating time significantly influence the structure and fluorescence intensity.