Effect of crystal structure and dopant the luminescence of Cr3+ in Al2O3 concentration on nanocrystals

The sol-emulsion-gel method is used for the preparation of Cr3+-doped Al2O3 nanocrystals. The luminescence spectra of Cr3+ ions in Al2O3 nanocrystals are found to be sensitive to the crystal structure and dopant concentration. It is found that a broad band emission in the range of 680-720 nm and the R-lines (R-2, 692.9 and R-1, 694.3 nm) are obtained at 900 degrees C (theta-Al2O3) and 1025 degrees C (alpha-Al2O3) heat-treated 0.2 mol% Cr-doped Al2O3 samples respectively. However, for higher concentrations of chromium (2 mol%) R-lines are obtained at 900 degrees C annealed samples and these lines are broadened and red shifted at 1025 degrees C annealed sample which is due to Cr-pair (and/or cluster) formation. The analysis suggests that luminescence properties of Cr3+ ions are strongly dependent on concentration and crystal phase of the Al2O3 nanocrystals. (c) 2004 Elsevier B.V. All rights reserved.