The effect of the atmosphere on the optical properties of as-synthesized colloidal indium tinoxide

Abstract

The optical properties of indium tin oxide (ITO) have often been explored when it is in theform of deposited thin films. In this study, a colloidal chemistry approach is taken toinvestigate the influence of the atmosphere on the optical properties of ITO nanoparticles.X-ray diffraction (XRD), transmission electron microscopy (TEM), absorption spectroscopyand photoluminescence (PL) were used to characterize colloidal ITO samples, synthesizedunder aerated and inert conditions, with the same composition. In both cases, theITO can be completely dispersed in a non-polar solvent without any evidenceof agglomeration. For the ITO made in air, the nanoparticle–solvent solutionexhibits a pale green color, and XRD and TEM indicate an average particle size of∼7 nm and small shrinkage in the lattice structure. When the ITO is synthesized under inertconditions, the solution turns blue, and XRD and TEM indicate an average particle size of∼8 nm and even less strain in the lattice than for the ITO synthesized under aeratedconditions. The change in color and lattice strain is attributed to the difference in oxygenvacancy concentration for the ITO nanoparticles synthesized under aerated and inertconditions, which exhibit different optical band gap values of 3.89 eV and 4.05 eV,respectively. Our work here shows that thin film deposition or sintering steps may not berequired for studying the optical properties of as-synthesized ITO nanoparticles.