RESUMO
Poly(vinylalcohol) (PVA)-stabilized silver nanoparticles were prepared by a seeding method. Nanoparticles of varying morphology were obtained by controlled variation of the reaction conditions, and this method allowed the tailoring of the position of the surface plasmon resonance. The samples show two bands in the visible absorption spectrum: one in the 410-440-nm region and a second peak between 500 and 600 nm. This tunable surface plasmon resonance serves to increase the third-order optical nonlinearity (chi 3) of the nanoparticles (measured at 532 nm) by a factor of 16.
Assuntos
Cristalização/métodos , Nanotecnologia/instrumentação , Nanotecnologia/métodos , Nanotubos/química , Nanotubos/ultraestrutura , Álcool de Polivinil/química , Prata/química , Ressonância de Plasmônio de Superfície/métodos , Teste de Materiais , Dinâmica não Linear , Tamanho da PartículaRESUMO
Van Hove singularities (VHS) in the density of states of multiwalled carbon nanotubes (MWNTs) have been observed by optical spectroscopy for the first time to the authors' knowledge. Additionally, unexpected visible luminescence has been observed on photoexcitation at 1064 nm. This luminescence is believed to arise from radiative transitions between energy states in the VHS. A mechanism describing the underlying processes, which involve multiphoton absorption followed by upconverted luminescence from VHS energy states, is presented. Our results show that the presence of VHS readily facilitates efficient optical transitions in
