RESUMO
Coated silver (Ag) colloids synthesized with D-glucose permit the observation of surface-enhanced fluorescence (SEF) and surface-enhanced resonance Raman scattering (SERRS) of the rhodamine B (RhB) molecule. The organic coating formed during the synthesis of the Ag nanostructures was identified by its surface-enhanced Raman scattering (SERS) spectrum as D-gluconic acid. The RhB molecule is used to exemplify the distance dependence of SEF and SERRS on the coated Ag nanostructures. The fluorescence enhancement factor for RhB on D-gluconic acid coated silver nanoparticles was determined experimentally and estimated using a simple model. Further support for the plasmon enhancement is obtained from the fact that the measured fluorescence lifetime of RhB on the silver coated with D-gluconic acid is shorter than that found on a glass surface. A very modest enhancement factor is obtained, as expected for very short distance between RhB and the metal surface. Given the very thin metal-fluorophore separation, estimated from the size of the D-gluconic acid, the energy transfer or fluorescence quenching is still efficient and the SEF enhancement is just overcoming the energy transfer. Therefore, both SEF and SERRS are observed. Notably, the aggregation of coated nanoparticles also increases the enhancement factor for SEF.
Assuntos
Gluconatos/química , Nanopartículas Metálicas/química , Prata/química , Análise Espectral Raman/métodos , Coloides , Nanopartículas Metálicas/ultraestrutura , Microscopia de Força Atômica , Tamanho da Partícula , Espectrometria de Fluorescência , Ressonância de Plasmônio de SuperfícieRESUMO
The vibrational spectra and surface-enhanced Raman scattering (SERS) of 1,6-diphenyl-1,3,5-hexatriene (DPH) are discussed. The fundamental vibrational frequencies, overtones, and combinations observed in the infrared and Raman spectra of DPH are reported. The interpretation of the observed vibrational spectra was supported by a complete geometry optimization, followed by vibrational frequency and intensity computations for the cis- and trans- isomers of the DPH using density functional theory at the B3LYP/6-31G(d,p) level of theory. Because the molecule is photo-chemically active on Ag metal surfaces, the best SERS results for silver islands were obtained at low temperature and low energy density of the exciting laser line. DPH SERS on Au films was obtained at room temperature.