Spectral narrowing of self-trapped exciton emission in anatase thin films

Self-trapped excition (STE) emission of TiO2 (anatase) thin films grown by atomic layer deposition technique on single crystal alpha -Al2O3 (0 1 2) substrates were studied at temperatures 5-120 K. An in-plane preferential orientation of anatase crystallites was detected in the films by using the dependence of the emission polarisation on the observation angle. The STE emission recorded in the direction perpendicular to the film surface had a wide spectrum with the maximum at approximately 2.3 eV. The spectrum recorded from a cleaved edge in the direction nearly parallel to the film surface, showed two sharp peaks (spectral width as low as 0.03 eV) on the top of the broad STE emission band. The beam divergence determined at the wavelengths, of these peaks was 6-10 degrees. The effect was interpreted as a constructive interference of the emission leaving the Film at the angle that is close to the angle of total internal reflection. (C) 2001 Elsevier Science B.V. All rights reserved.