Violet-blue photoluminescence in aluminium oxide films prepared by ultrasonic spray pyrolysis

Violet-blue photoluminescent emission has been observed in aluminium oxide films deposited by the ultrasonic spray pyrolysis process at atmospheric pressure, using solutions of 0.05 M aluminium acetylacetonate in a mixture of two parts of deionised water and two parts of methanol and aluminium chloride in the same solvent mixture. The films were deposited at substrate temperatures in the range from 240 to 440 degrees C. The refractive index has values lower than those associated with crystalline phases of Al2O3. These values are due to the amorphous nature of the deposited films and the incorporation of organic or chlorine related radicals. The photoluminescence excitation spectra show two peaks located at 281 and 371 nm, the latter being with higher intensity. The photoluminescent emission spectra are constituted by a broad band with a peak located at 405 nm and, it has a maximum intensity for the sample prepared at 380 degrees C. It is suggested that this emission is associated with radiative recombination from an excited level of the aluminum ions. The photoluminescence emission spectra can be formed by several contributors, for all the samples, which suggests that these emissions are associated with aluminium ions incorporated in excess in aluminium oxide host on different sites, as it has been observed in several glasses. From an Arrhenius plot of the intensity of the peak located around 405 mm, as a function of substrate temperature an activation energy of 1.16 eV has been calculated. (C) 1999 Elsevier Science B.V. All rights reserved.