Abstract
Three different phases, namely anatase, mixed and rutile phases of TiO2 nanoparticles (NPs) were developed with varying temperatures from 400 to 900 °C and confirmed using various characterization techniques. The XRD analysis of TiO2 NPs in temperature range of 290 to 77 K with no significant changes predict the thermally stable NPs. Photoinduced carrier dynamics of TiO2 NPs were investigated by the temperature dependence (TD) photoluminescence (PL) and TD time-resolved PL (TRPL) decays. With varying temperatures from 290 to 77 K, the anatase phase exhibits an additional and dominant 530 nm PL band. However, the mixed and rutile phases show three well-resolved PL bands, including 420 nm, 530 nm and near-infrared (NIR) bands at 820 nm at a lower temperature. Again, 530 nm band dominated for mixed-phase.In contrast, for the rutile phase, the 820 nm band dominated at <100 K. The PL lifetime of the 420 nm band is nearly a single exponential for all the phases. And is also true for the 530 and 820 nm PL bands, but bi-exponential for ≤100 K. Both the PL and TRPL results predict the presence of trap states in TiO2 NPs for anatase and rutile phases. The PL is originated due to donor-acceptor recombination, whereas oxygen vacancies served as donor and hydroxyl groups serve as accepter sites. The NIR band is attributed to the trapped electrons in rutile TiO2, which recombine with free holes and intrinsic defects. Also, the trapped electrons were generated in one of two ways: direct trapping or trap-to-trap hopping. The carrier dynamic in NPs depends on the trap states as the photoexcited carriers transfer into surface sites which competes with non-radiative and radiative recombinations during the relaxation process. Thus, the findings show that the trap states in TiO2 can significantly influence TiO2 photocatalytic activity when exposed to appropriate light.
Published Version
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