Wei Xie

We proposed a differential fiber-optic refractive index sensor based on coupled plasmon waveguide resonance (CPWR) in the C-band. The sensor head is a BK7 prism coated with ITO/Au/ITO/TiO₂ film. CPWR is excited on the film by the S-polarized components of an incident light. The narrow absorption peak of CPWR makes it possible to realize dual-wavelength differential intensity (DI) interrogation by using only one incident point. To implement DI interrogation, we used a DWDM component to sample the lights with central wavelengths of 1529.55 and 1561.42 nm from the lights reflected back by the sensor head. The intensities of the dual-wavelength lights varied oppositely within the measurement range of refractive index, thus, a steep slope was produced as the refractive index of the sample increased. The experimental results show that the sensitivity is 32.15/RIUs within the measurement range from 1.3584 to 1.3689 and the resolution reaches 9.3 × 10⁻⁶ RIUs. Benefiting from the single incident point scheme, the proposed sensor would be easier to calibrate in bio-chemical sensing applications. Moreover, this sensing method is expected to be applied to retro-reflecting SPR sensors with tapered fiber tip to achieve better resolution than wavelength interrogation.

Modification of the surface properties of SrTiO₃ crystals by regulating the reaction environment in order to improve the photocatalytic activity has been widely studied. However, the development of a facile, effective, and universal method to improve the photocatalytic activity of these crystals remains an enormous challenge. We have developed a simple method to modify the surface environment of SrTiO₃ by ethanol quenching, which results in enhanced UV, visible and infrared light absorption and photocatalytic performance. The SrTiO₃ nanocrystals were preheated to 800 °C and immediately quenched by submersion in ethanol. X-ray diffraction patterns, electron paramagnetic resonance spectra, and X-ray photoelectron spectra indicated that upon rapid ethanol quenching, the interaction between hot SrTiO₃ and ethanol led to the introduction of a high concentration of oxygen vacancies on the surface of the SrTiO₃ lattice. Consequently, to maintain the regional charge balance of SrTiO₃, Sr²⁺ could be substituted for Ti⁴⁺. Moreover, oxygen vacancies induced localized states into the band gap of the modified SrTiO₃ and acted as photoinduced charge traps, thus promoting the photocatalytic activity. The improved photocatalytic performance of the modified SrTiO₃ was demonstrated by using it for the decomposition of rhodamine B and production of H₂ from water under visible or solar light.

Fiber-optic surface plasmon resonance (SPR) sensors possess the advantages of small size, flexible, allowing for a smaller sample volume, easy to be integrated, and high sensitivity. They have been intensively developed in recent decades. However, the polarizing nature of the surface plasmon waves (SPWs) always hinders the acquisition of SPR spectrum with high signal-noise ratio in wavelength modulation unless a polarizer is employed. The addition of polarizer complicates the system and reduces the degree of compactness. In this work, we propose and demonstrate a novel, polarization-independent fiber-optic SPR sensor based on a BK7 bi-prism with two incident planes orthogonal to each other. In the bi-prism, TM-polarized components of non-polarized incident lights excite SPWs on the first sensing channel, meanwhile the TE components and the remaining TM components are reflected, then the reflected TE components serve as TM components of incident lights for the second sensing channel to excite SPWs. Simulations show the proposed SPR structure permit us to completely eliminate the polarization dependence of the plasmon excitation. Experimental results agree well with the simulations. This kind of devices can be considered an excellent option for development of simple and compact SPR chemical sensors.

Oxygen vacancy defects play an important role in improving the light-capturing and photocatalytic activity of tungsten trioxide (WO₃). However, the hydrogen treatment method that is commonly used to introduce oxygen vacancies is expensive and dangerous. Therefore, the introduction and control of oxygen vacancy defects in WO₃ remains a challenge. Here, we demonstrated that oxygen vacancies could be successfully introduced into WO_3−x while using a facile method through low temperature annealing in alcohol. The obtained WO_3−x samples with optimal oxygen vacancies showed strong absorption of light, extending from the ultraviolet to the visible and near-infrared regions, and exhibits strong plasmon resonance from 400–1200 nm peaking at approximately 800 nm. When compared to pristine WO₃, the photocatalytic activity of WO_3−x was greatly improved in the ultraviolet and visible regions. This study provides a simple and efficient method to generate oxygen vacancies in WO₃ for photocatalysis, which may be applied in the photoelectrochemical, electrochromic, and photochromic fields. Because oxygen vacancy is a common characteristic of metal oxides, the findings that are presented herein may be extended to other metal oxides.

Black TiO₂ has triggered worldwide research interest due to its excellent photocatalytic properties. However, the understanding of its structure–property relationships and a more effective, facile and versatile method to produce it remain great challenges. We have developed a facile approach to synthesize black TiO₂ nanoparticles with significantly improved light absorption in the visible and infrared regions. The experimental results show that oxygen vacancies are the major factors responsible for black coloration. More importantly, our black TiO₂ nanoparticles have no Ti³⁺ ions. These oxygen vacancies could introduce localized states in the bandgap and act as trap centers, significantly decreasing the electron–hole recombination. The photocatalytic decomposition of both rhodamine B and methylene blue demonstrated that, under ultraviolet light irradiation, better photocatalytic performance is achieved with our black TiO₂ nanoparticles than with commercial TiO₂ nanoparticles.