Preparation,characterization And Property Study Of W₁₈O₄₉-based Optoelectronic Nanomaterials

Transition metal oxides are the key ingredients for the development of many advanced materials and photoelectric devices.It has been widely studied in the field of photocatalysis that W₁₈O₄₉ nanowires exhibit the strong localized surface plasmon resonance?LSPR?in the visible and near-infrared region owing to the abundant oxygen vacancies.Plasmonic mental nanostructures have been integrated with the upconversion luminescence nanoparticles?UCL NPs?to enhance the conversion efficiency of NIR photon energy into visible region due to the LSPR.However,so far,it is still a great challenge to make the direct utilization of the low-cost non-metal semiconductors to concentrate and transfer the NIR-plasmonic energy in the UCL system.In this paper,we synthesized a variety of W₁₈O₄₉ based multifunctional nanocomposites by using a simple experimental method,and carried out a series of investigations into the structure,morphology and properties.Our work provides a new perspective for the development of non-metal plasmon-sensitized optical materials that can be potentially applied in photocatalysis,optoelectronics and photovoltaics devices.The main contents are as follows:W₁₈O₄₉ nanowires were successfully synthesized through a simple surfactant-free solvothermal method.These nanowires exhibit strong plasmonic absorption in the visible and near-infrared region owing to the abundant oxygen vacancies.The plasmon excitation of W₁₈O₄₉ nanowires can make ammonia borane accelerate hydrolysis to produce hydrogen.We demonstrate a novel NIR-plasmonic energy UC process in the Ln³⁺-NaYF4/W₁₈O₄₉nanowires?NWs?heterostructure,which can lead to a selectively enhanced UCL by almost one order of magnitude.We propose that the NIR-excited LSPR effect of W₁₈O₄₉ NWs is primarily responsible for the enhancement of UCL that can be partly absorbed by the W₁₈O₄₉ NWs to re-excite its higher-energy LSPR,leading to a selective enhancement of UCL for the Ln³⁺-doped NaYF4 NPs.We designed and synthesized a NIR-driven catalyst of Na YF4:Yb³⁺,Er³⁺@W₁₈O₄₉ NWs quasi-core/shell heterostructure,which exhibited a³5-flod increase in the catalytic H2evolution from ammonia borane by 980 nm excitation in 1h.It is indicated that the catalytic performance of NaYF₄:Yb³⁺,Er³⁺@W₁₈O₄₉ NWs quasi-core/shell heterostructure is optimal.Ag-W₁₈O₄₉ heterostructure nanowires were synthesized by photocatalytic reduction method,and their NLO properties were investigated using Z-scan technique with 532 nm nanosecond pulse laser.It was found that,the addition of Ag nanoparticles on W₁₈O₄₉ nanowires can switch the nonlinear absorption of W₁₈O₄₉ NWs from RSA to SA,the nonlinear refraction from self-defocusing to self-focusing.Moreover,with increasing Ag nanoparticles,the optical nonlinear properties of W₁₈O₄₉ nanowires increase obviously.The experimental results were explained in terms of ground state plasmon bleaching,thermal effect and free carrier.