Surface-enhanced Raman Scattering (SERS) of R6G has been observed in two different silver colloids in the presence of KBr. It was found in spherical nanoparticles with an average diameter of 10 ( 2 nm and in their photoinduced conversion products with sodium light irradiation, silver nanoprisms, with an average edge length of 70 ( 30 nm and thickness of about 10 ( 2 nm. The SERS intensity of R6G (4.5 × 10 -9 M) in the silver nanoprism colloid was 20× stronger than in the spherical nanoparticle colloid with the addition of KBr (0.05 M). Comparing the Raman signal intensity of water (55.5 M) and the SERS intensity of R6G (4.5 × 10 -9 M) in the same spectrum showed that the analytical enhancement factors (AEF) in the truncated silver nanoprism colloid and spherical nanoparticle colloid are about 1.6 × 10 5 and 8 × 10 3 , respectively. Monitoring the fluorescent intensity of R6G versus the concentration of R6G in two colloids in the absence of KBr displayed that the nanoprisms had better fluorescence quenching ability than the spherical nanoparticles by a factor of around 3. It implied that light irradiation not only converted the morphology of the spherical nanoparticles to nanoprisms, but also changed the surface character to have a higher affinity to the dye molecule. The surface enhancement factors (SEF) can also be calculated from AEF and the percentage of dye molecules adsorbed on the surface in the presence of KBr. The SEF of the nanoprism and spherical nanoparticle colloids are about 3.2 × 10 5 and 9 × 10 3 , respectively. The UV-vis-NIR spectra and TEM images show that the spherical nanoparticles remained dispersed, while the nanoprisms were sculptured by the bromide ions after the addition of KBr.

This article presents a mechanistic study of silver nanodecahedra prepared by the method of photoassisted sodium citrate reduction under irradiation of blue light-emitting diodes (LEDs). This synthesis of silver nanodecahedra can be easily reproduced in the absence of silver seeds and can be completed in one-pot. The data suggest a combination of two processes including gradual growth from multiple-twinned particles and subsequent plasmonmediated crystal growth. More than 85% of as-prepared silver nanoparticles are decahedra with edge lengths of 43.5 ± 5.2 nm. In addition, the as-prepared silver colloids exhibit a spectroscopic enhancement in comparison with spherical silver nanoparticle colloids and silver nanoprism colloids in the measurement of surface enhanced Raman spectroscopy (SERS) spectra of Rhodamin 6G, and with the decahedral silver colloids synthesized in the presence of PVP for detecting SERS signal of Rhodamin 6G. Overall, this photoassisted citrate reduction process is simple, and highly reproducible. As-prepared silver nanodecahedra are more stable and provide optimal SERS signal than those synthesized using commonly used plasmon-mediated photochemical methods.

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Plasmon-mediated shape conversion of spherical silver nanoparticles (NPs) to nanostructures with other shapes under the irradiation of green LEDs (520 ± 20 nm, 35 mw/cm2) at various temperatures (60, 40, 20, 10, 5, and 0 °C) was performed in this study. It was found that the bath temperature used in the reaction can influence the reaction rates, i.e., the times needed for the shape transformation process were 5, 11.5, 25, 45, 72, and 100 h at 60, 40, 20, 10, 5, and 0 °C, respectively. In addition, the bath temperature can also alter the morphologies of the final products. The major products are silver nanoplates at 60, 40 and 20 °C. However, they became decahedral silver NPs at 5 and 0 °C. The percentages of decahedral silver NPs synthesized at 60, 40, 20, 10, 5, and 0 °C are 0%, 1%, 5%, 45%, 73%, and 89%, respectively. Measuring the surface-enhanced Raman spectroscopy (SERS) spectra of the probe molecule R6G in the presence of KBr showed that both silver nanoplate colloids synthesized at 60 °C and decahedral silver NP colloids synthesized at 0 °C in the absence of PVP had good SERS activities.

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