Separation of extremely small indium oxide quantum dots and their highly luminescent properties by dispersing agent

Acquiring extremely small quantum dots (QDs) absorbing and emitting light in the ultraviolet region is challenging because of the difficulty in size control via chemical synthesis. Here, we report that extremely small In2O3 QDs with high crystallinity can be earned from a pristine In2O3 powder of which the average size exceeds the range of QDs. Interestingly, we extracted the extremely small In2O3 QDs by a series of filtration processes of an In2O3 suspension. Transmission electron microscopy images confirmed In2O3 nanoparticles falling within the range of QDs. The tiny In2O3 QDs absorbed light at a wavelength of 220 and 280 nm and exhibited the maximum photoluminescence spectra in the ultraviolet region under the excitation of the wavelengths. Furthermore, we investigated the effect of a surfactant on the optical properties of In2O3 QDs separated from the powder. As a result, the luminescent intensity of In2O3 QDs enhanced drastically with the addition of sodium dodecylbenzene sulfonate. Our findings pave the way to acquiring highly luminescent tiny QDs from other semiconducting powders.