Upconversion of infrared radiation into visible light has been investigated for applications in photovoltaics and biological imaging. However, low conversion efficiency due to small absorption cross-section for infrared light (Yb(3+)), and slow rate of energy transfer (to Er(3+) states) has prevented application of upconversion photoluminescence (UPL) for diffuse sunlight or imaging tissue samples. Here, we utilize resonant surface plasmon polaritons (SPP) waves to enhance UPL in doped-lanthanide nanocrystals. Our analysis indicates that SPP waves not only enhance the electromagnetic field, and hence weak Purcell effect, but also increase the rate of resonant energy transfer from Yb(3+) to Er(3+) ions by 6 fold. While we do observe strong metal mediated quenching (14-fold) of green fluorescence on flat metal surfaces, the nanostructured metal is resonant in the infrared and hence enhances the nanocrystal UPL. This strong Coulombic effect on energy transfer can have important implications for other fluorescent and excitonic systems too.
A rapid increase in anthropogenic emission of greenhouse gases, mainly carbon dioxide, has been a growing cause for concern. While photocatalytic reduction of carbon dioxide (CO2) into solar fuels can provide a solution, lack of insight into energetic pathways governing photocatalysis has impeded study. Here, we utilize measurements of electronic density of states (DOS), using scanning tunneling microscopy/spectroscopy (STM/STS), to identify energy levels responsible for photocatalytic reduction of CO2-water in an artificial photosynthetic process. We introduce desired states in titanium dioxide (TiO2) nanoparticles, using metal dopants or semiconductor nanocrystals, and the designed catalysts were used for selective reduction of CO2 into hydrocarbons, alcohols, and aldehydes. Using a simple model, we provide insights into the photophysics governing this multielectron reduction and design a new composite photocatalyst based on overlapping energy states of TiO2 and copper indium sulfide (CIS) nanocrystals. These nanoparticles demonstrate the highest selectivity for ethane (>70%) and a higher efficiency of converting ultraviolet radiation into fuels (4.3%) using concentrated sunlight (>4 Sun illumination), compared with platinum-doped TiO2 nanoparticles (2.1%), and utilize hot electrons to tune the solar fuel from alkanes to aldehydes. These results can have important implications for the development of new inexpensive photocatalysts with tuned activity and selectivity.
The gelation of the amphiphilic quaternary ammonium oligoether-based ionic liquid (AMMOENG100) with water is addressed. This approach allows the preparation of thermoreversible ionogels with high ionic conductivity (up to 60 mS cm(-1)), remarkable mechanical properties (storage moduli above 10(5) Pa a value comparable to the mechanical properties of some rubbers), and melting points in the range from -20 to 53 degrees C. These properties can be easily tuned in a broad range by varying the water (and/or inorganic salts) concentration in the ionogels. The described method is a very convenient way to prepare ionogels because it is based on simple and inexpensive materials, namely AMMOENG100 and water (no volatile organic solvents involved). Infrared measurements suggested that the observed gelation phenomenon might occur via the formation of a hydrogen bonded network between water and the AMMOENG100 ionic liquid
The aqueous gelation of a quaternary ammonium oligo(propylene oxide)-based ionic liquid yields ion gels with a reverse thermoresponsive behavior (i.e., mechanical moduli and viscosity increase with temperature) and enhanced ionic conductivities.
The aqueous gelation of an amphiphilic ammonium oligoether-based ionic liquid (AMMOENG 102) is addressed and compared to the gelation of a similar compound (AMMOENG 100) recently reported (J. Casamada Ribot, C. Guerrero-Sanchez, R. Hoogenboom and U. S. Schubert, J. Mater. Chem., 2010, 20, 8279.).(1) The comparison is based on proton nuclear magnetic resonance spectroscopy, rheological, ionic conductivity, water uptake, differential scanning calorimetry, surface tension and small angle X-ray scattering investigations. The results demonstrate that slight changes in the chemical structure of these ionic liquids can have an important effect on the properties of their corresponding ion gels. Hence, this contribution provides an insight into the stability and formation mechanism of these new ion gels solely consisting of ionic liquid and water and expands the range of amphiphilic ionic liquids which can be utilized for the straightforward and inexpensive preparation of thermoresponsive materials with tunable properties (i.e., ionic conductivity and melting point) and high mechanical moduli
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.