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 pr essure, using solutions of 0.05 M aluminium acetylacetonate in a mixture of two parts of deionised water and two parts of methanol and aluminium chlor ide in the same solvent mixture. The films were deposited at substrate temp eratures in the range from 240 to 440 degrees C. The refractive index has v alues lower than those associated with crystalline phases of Al2O3. These v alues are due to the amorphous nature of the deposited films and the incorp oration of organic or chlorine related radicals. The photoluminescence exci tation spectra show two peaks located at 281 and 371 nm, the latter being w ith higher intensity. The photoluminescent emission spectra are constituted by a broad band with a peak located at 405 nm and, it has a maximum intens ity for the sample prepared at 380 degrees C. It is suggested that this emi ssion is associated with radiative recombination from an excited level of t he aluminum ions. The photoluminescence emission spectra can be formed by s everal contributors, for all the samples, which suggests that these emissio ns are associated with aluminium ions incorporated in excess in aluminium o xide host on different sites, as it has been observed in several glasses. F rom an Arrhenius plot of the intensity of the peak located around 405 mm, a s a function of substrate temperature an activation energy of 1.16 eV has b een calculated. (C) 1999 Elsevier Science B.V. All rights reserved.