Study on photoelectric properties of a TiO₂ nanoparticle

Here we report a study of surface states in nanometer-sized TiO₂ particles (P1) prepared in our lab with the aid of surface photovoltage spectroscopy, electric field-induced photovoltage spectroscopy (EFISPS), and fluorescence spectrum. The diameter determined by x-ray diffraction is 3.5 nm. The EFISPS of P1 shows several subband gap absorption bands at 350, 375, and 460 nm, respectively. The fluorescence peaks of dry powder and an aqueous suspension of P1 at 361, 391, and 469 nm were detected. The above results are concluded to be relative with the located surface states within the band gap. The surface states were deduced to be oxygen vacancies, i.e., Ti³⁺, Ti²⁺, Ti⁺, whose maximum densities lie at 0.32, 0.50, and 1.02 eV below the maximum density of states in the conduction band, respectively.