Optical processes and apparent increase of optical band gap in Y2O3:Eu2+ nanoparticles synthesised by a gradually-heated solution combustion method

Abstract

We report optical absorption and emission features of Eu doped Y2O3 nanoparticles synthesised by a gradually-heated solution combustion method. An X-ray diffraction analysis reveals that the samples exhibit body centred cubic structure. The crystallite size of an undoped Y2O3 sample was estimated to be ~19.87 nm but it is found to increase up to 46.38 nm in a sample doped with 4% Eu. The samples have spherical structure of diameter ~23–57 nm. Analysis of optical absorption spectra indicates an apparent increase of optical band gap from 5.00 eV to 5.24 eV after the doping. This apparent widening of band gap is explained with reference to the Burstein-Moss effect. The Eu doped samples produce a primary emission band at 447 ± 1 nm and a secondary band between 480 and 630 nm. Analysis reveals that the primary band is composed of two overlapping components with peak maxima at 446 ± 1 nm and 455 ± 3 nm. These emission bands are attributed to the transition from degenerate 5d → 4f level of Eu2+ ion. The absorption and emission features have been discussed with reference to an energy band model.