Injecting Electrons into CeO2 via Photoexcitation of Embedded Au Nanoparticles

The electron injection efficiency and the steady state absorptance at different photon energies for a composite system made of Au NPs embedded in a cerium oxide matrix are reported. Cerium oxide can be coupled with plasmonic nanoparticles (NPs) to improve its catalytic properties by visible-light absorption. The present work is a study of the ultrafast dynamics of excited states induced by ultraviolet and visible-light excitation in Au NPs combined with cerium oxide, aimed at understanding the excitation pathways. The data, obtained by femtosecond transient absorption spectroscopy, show that the excitation of localized surface plasmon resonances (LSPRs) in the Au NPs leads to an ultrafast injection of electrons into the empty 4f states of the surrounding cerium oxide. Within the first few picoseconds, the injected electrons couple with the lattice distortion forming a polaronic excited state, with similar properties to that formed after direct band gap excitation of the oxide. At sub-picosecond delay times, we observed relevant differences in the energetics and the time dynamics as compared to the case of band gap excitation of the oxide. Using different pump energies across the LSPR-related absorption band, the efficiency of the electron injection from the NPs into the oxide was found to be rather high, with a maximum above 30%. The injection efficiency has a different trend in energy as compared to the LSPR-related static optical absorptance, showing a significant decrease in low energies. This behavior is explained considering different deexcitation pathways with variable weight across the LSPR band. The results are important for the design of materials with high overall solar catalytic efficiency

Fibre development in Hemp (Cannabis sativa L.) as affected by agrotechnique: preliminary results of a microscopic study.

This paper reports the preliminary results of a microscopic study carried out on stem cross sections of hemp. Stems were harvested from two field experiments carried out in 2001 and 2002 in the north of Italy to compare the monoecious genotype Futura 75 over four plant populations. Fibre characteristics such as cell shape, diameter, maturation and quantity of secondary fibre tended to vary with harvest time, plant density, and between and with internodes. After the end of internode elongation, fibre cells changed from oblong to round shaped in cross section and fibre maturation started and progressed to a maximum level. At various moments of the growing cycle, fibre maturity and presence of secondary fibre seemed higher at lower internodes and plant density

influence of agronomic factors on yield and quality of hemp (Cannabis sativa L.) fibre and implication for an innovative production system.

Research and development of an innovative production system for hemp (Cannabis sativa L.) fibre for textile use requires the integration of multidisciplinary knowledge from cultivation technique to realization of end products. Research was carried out to study the effect of the agronomic factors cultivation year (2003–2004), genotype (Futura 75 and Tiborszallasi), plant population (120, 240 and 360 plants m2) and harvesting time (beginning and full flowering) on fibre yield and quality in the whole hemp stem, and in the basal and apical stem portions separately. The study of separate stem portions was done to determine the effect on fibre quality of an innovative harvesting and processing system in which hemp stems are cut in two portions of approximately 1 m at harvest to enable processing on modern flax scutching lines. Stem and fibre yield were affected by most of the agronomic factors. The extreme drought experienced in the first year reduced stem and fibre yield, but stems had higher percentage of fibre (16.5%), that were finer (22.9 mm) and with a higher degree of maturity (73.6%) in 2003 than in 2004 (respectively 16.0%; 24.5 mm; 55.8%). Between the two genotypes under trial the monoecious Futura 75 largely out yielded the dioecious Tiborszallasi in both years. The latter however had finer primary fibres and less secondary ones. In both genotypes primary fibres maturity and quantity of secondary fibres increased at later harvest. Plant population affected stem biometrics and fibre characteristics, with finer fibres and less secondary growth at higher stands. It can be concluded that cultivation technique can be exploited in order to maximize the quality and yield of stems destined for the innovative harvesting and processing system herein described