Ultrafine particles of TiO
2 were prepared by the hydrolysis of titanium tetrachloride (TiCl
4) in a highly concentrated hydrochloric acid aqueous solution at a low temperature, in which the surfacing modifier did not coexist. The absorption spectrum of the prepared TiO
2 ultrafine particle showed a blue shift, which was more remarkable than that of a bulk sample. The fluorescence of the prepared TiO
2 fine particles confirmed being within the ultraviolet wavelength range with a peak at 370 nm by changing the excitation wavelength from 220 nm to 300 nm. The bulk TiO
2 of Rutile and Anatase type showed light absorption in proportion to the transition of inter-bands at 413 nm (3.0 eV) and 388 nm (3.2 eV), respectively. Because the excitation wavelength of 230 nm corresponds to 5.4 eV, it is converted into the band energy. The size of TiO
2 identified from a laser scatter measurement was 3.5±1.0 nm, which was confirmed to be the size at which a quantum size effect appears. From the XRD measurement, secondary fine particles (aggregate) of TiO
2 after separation by a membrane filter was identified to be of the Rutile type. The size of the (110), (101) and (211) crystal planes were estimated to be 5.3, 8.0 and 5.1 nm by an evaluation using the Scherrer equation for the half-value width of the diffraction peak of each crystal plane. The shape of the aggregate observed from the SEM image was tabular, of μm size. It was concluded that TiO
2 fine particles with a hierarchy of sizes from nm to mm were possible by the low-temperature hydrolysis of TiCl
4 in a high concentration of hydrochloric acid aqueous solution. Application to an ultraviolet ray protective agent for UVC, UVB and UVA is expected in the future.
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