Yttrium silicates Y2SiO5upconversion nanomaterials with different doping concentrations of praseodymium ion Pr are prepared by using a sol-gel method. X-ray diffractometer, SEM, Fourier transform infrared spectrometer, and fluorescence spectrometer have been employed to test the crystal structure and upconversion luminescence performances. The results indicate that samples calcined higher than 950°C present fine crystal structures, of which Si-O-Si band at 757–1048 cm−1splits into three fine peaks. The crystal size of the samples calcined at 950°C and 1000°C is 29.1 nm and 66.7 nm, respectively. The luminescence intensities of the samples are increasing at first and then decreasing, with the increasing of the doping concentrations of 0.47%, 0.77%, 0.96%, 2.95%, and 4.93%. Nanomaterial sample doped 0.96% Pr emits the highest upconversion luminescence intensity of 6.43 × 106 cps and shows the best photodegradation performance for nitrobenzene wastewater. It demonstrates that too much of Pr doping concentration would result in quenching of the fluorescence. Nevertheless, as the degradation time expands, sample doped 0.96% Pr shows much faster increasing of photodegradation rate than samples of other doping concentrations and reaches to a high photodegradation rate of 97.14% in 6 hours for 10 mg/L nitrobenzene wastewater.

Based on the substrate of Pr:Y 2 SiO 5 upconversion nanomaterials, lithium ion Li(I) doped Pr:Y 2 SiO 5 and TiO 2 nanofilm coated Li,Pr:Y 2 SiO 5 composites were prepared by using a sol-gel method. X-ray diffractometer, SEM, and fluorescence spectrometer have been employed to test the crystal structure, microimages, and upconversion luminescence performances. The doping of Li(I) affects highly the crystal transition of Pr:Y 2 SiO 5 and X2-Y 2 SiO 5 phase was well formed by doping 8% Li(I). Furthermore, the doping of Li(I) also brings high luminance intensity of Pr:Y 2 SiO 5 and contributes to a maximum intensity of 9.76 × 10 6 cps doped 8%. Too much of Li(I) doping would result in big crystal size and fluorescence quenching of Pr:Y 2 SiO 5 material. However, the coating of TiO 2 nanofilm is not helping in increasing the upconversion fluorescence of Li,Pr:Y 2 SiO 5 but is promoting the full use of the fluorescence. The luminescence intensities of TiO 2 /Li,Pr:Y 2 SiO 5 composites are getting down sharply with the coating amount since the luminescence emitted by Li,Pr:Y 2 SiO 5 is quickly adsorbed in situ by the TiO 2 coating film. With the optimum coating concentration of 1%, the TiO 2 /Li,Pr:Y 2 SiO 5 composite shows excellent photodegradation performances on nitrobenzene wastewater, though it shows a low luminescence intensity. For 5 mg/L nitrobenzene wastewater, the composite presents a photodegradation rate of 97.08% in 4 hours.

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Titanium dioxide (TiO2) has been widely used as photoanodes in photoelectrochemical (PEC) water splitting. However, the typically high density of bandgap trap states results in fast charge carrier recombination and poor electrical conductivity, and thereby weak PEC performance. Rational creation of oxygen vacancy (Vo) in TiO2 has been demonstrated as an effective method to modify the electronic and optical properties, as well as improved PEC performance. Different strategies have been developed to fabricate oxygen deficient TiO2 photoanodes, such as hydrogen treatment, thermal annealing, electrochemical reduction, flame reduction, and chemical reduction. In conjunction with oxygen vacancy creation, doping of TiO2 with elements further enhances the PEC activity by introducing other bandgap states. Various techniques, including ultrafast laser spectroscopy, have been employed to probe the chemical nature and associated charge carrier dynamics of the bandgap states.