Direct Evidences of Shallow Donor Level Enhanced Green Emission in ZnO Quantum Dots.

ZnO Quantum dots with particle sizes about 5 nm were prepared by sol-gel method, the research about the photo luminescence(PL)/photoluminescence excitation(PLE) spectrum and the fluorescence lifetime indicated that the green emissions can be divided into two parts which were attributed to different transit mechanisms. The higher energy green emission was due to the electrons transit from conduction band to oxygen vacancies while the lower energy green emission was assigned to the electrons transit from the shallow donor levels which enhanced the green emission to the oxygen vacancies and the shallow donor levels was also the reason why the green emission reach strongest intensity when the excitation energy was a little lower than the band gap energy. While the blue emission can be explained by the electrons transiting from Zinc intervals to the valence band. The two mechanisms of green emission are first highlighted and should be considered in the optical application.

Conformal Microfluidic-Blow-Spun 3D Photothermal Catalytic Spherical Evaporator for Omnidirectional Enhanced Solar Steam Generation and CO2 Reduction.

Solar-driven water evaporation and valuable fuel generation is an environmentally friendly and sustainable way for clean water and energy production. However, a few bottlenecks for practical applications are high-cost, low productivity, and severe sunlight angle dependence. Herein, solar evaporation with enhanced photocatalytic capacity that is light direction insensitive and of efficiency breakthrough by virtue of a three-dimensional (3D) photothermal catalytic spherical isotopic evaporator is demonstrated. A homogeneous layer of microfluidic blow spun polyamide nanofibers loaded with efficient light absorber of polypyrrole nanoparticles conformally wraps onto a lightweight, thermal insulating plastic sphere, featuring favorable interfacial solar heating and efficient water transportation. The 3D spherical geometry not only guarantees the omnidirectional solar absorbance by the light-facing hemisphere, but also keeps the other hemisphere under shadow to harvest energy from the warmer environment. As a result, the light-to-vapor efficiency exceeds the theoretical limit, reaching 217% and 156% under 1 and 2 sun, respectively. Simultaneously, CO2 photoreduction with generated steam reveals a favorable clean fuels production rate using photocatalytic spherical evaporator by secondary growth of Cu2 O nanoparticles. Finally, an outdoor demonstration manifests a high evaporation rate and easy-to-perform construction on-site, providing a promising opportunity for efficient and decentralized water and clean fuel production.