Biuret-assisted formation of nanostructured In2O3 architectures and their photoluminescence properties

Nanostructured indium oxide (In2O3) microcrystals were prepared by calcining hydrothermally synthesized indium hydroxide (In(OH)3) samples. A cubic structure and small crystallite sizes of the In2O3 microcrystals are determined from the X-ray diffraction (XRD) analysis. Observation of the scanning electron microscopy (SEM) shows that the crystalline morphology could be changed from micocubes, microrods to microspheres with appropriately control of the mole ratios of In3+ to biuret. Based on the SEM and FTIR analysis, a possible formation mechanism of In2O3 microcrystals with different morphologies is also proposed. The photoluminescence (PL) spectra show that the energy separation of the blue peaks at 2.85 eV and 2.78 eV corresponds to a phonon in sub band-gap energy levels of oxygen vacancies; and an ultraviolet peak near 3.22 eV is observed, possibly originating from the longitudinal optical-phonon replica of the donor-acceptor pair transition.