Search

Laser evaporation of an Al2O3 target by a continuous wave CO2 laser was used to obtain nanostructured Al2O3 condensates with a mean crystallite size of 6 nm, one nominally pure and another doped with chromium at a concentration of 0.2 wt%. Photoluminescence of Cr3+ was observed in all the samples of the Al2O3 condensate. In all the Al2O3 condensates the α-Al2O3 phase, undetectable by XRD and HRTEM, was revealed by Cr3+ probing. Photoluminescence studies with the use of Cr3+ as a probe also revealed the θ- and (γ + δ)-crystal phases of Al2O3; this finding was supported by XRD and HRTEM data.

The γ and γ* phases of alumina synthesized from crystalline boehmite and pseudoboehmite were shown to strongly differ in some physicochemical characteristics. Photoluminescence of Cr3+ and Fe3+ as luminescent probes with their natural impurity concentrations was detected in the tested alumina samples and the local structure of the samples was examined. The crystal field strength and Racah parameters in γ-Al2O3 phases were determined. The ratio of octahedral and tetrahedral cationic positions was equal to 1 for γ-Al2O3 synthesized from crystalline boehmite, and 0.3 for that obtained from pseudoboehmite. The effect of residual OH groups and weakly bound molecular water on the local structure of γ-Al2O3 phases was revealed. The luminescence of Cr3+ was detected in subsurface structures of each alumina; defects produced by nanocrystallites were shown to affect the luminescence.