Influence of annealing on structure and optical properties of Mn-substituted ZnO nanoparticles

The influence of annealing on crystal growth and the micro- and mesoscopic structures of Mn-substituted nanocrystalline zinc oxide (ZnO) has been investigated using X-ray diffraction, high-resolution transmission electron microscopy and small-angle neutron scattering (SANS). Average particle sizes and their distributions have been estimated from scattering experiments as well as a microscopy study, and found to be in the nanometre range. The SANS study indicates that the fractal dimension, which describes the nature of the agglomerate, is almost unchanged up to an annealing temperature of 1023 K. However, at 1223 K, the fractal dimension increases to 3. An attempt has also been made to understand the influence of the annealing temperature on the growth of the structural morphology of the aggregates by performing a simulation based on a diffusion-limited aggregate model. By showing the variation of the band gap estimated from UV-visible absorption spectra with particle size, an attempt has been made to establish a structure-property correlation.