Stabilization of Silver Colloids by Various Types of Anions and Their Effect on the Surface-Enhanced Raman Spectra of Organic Dyes

Using a recently published procedure, silver colloids with uniform particle size were prepared and stabilized by nine different anions. Although the UV–visible extinction spectra of the colloids showed only small variations with the nature of the stabilizing ions, dramatic differences were observed in the SERS spectra of seven dyes studied. It was demonstrated that each family of dyes experiences a large enhancement factor only with certain stabilizing ions. The adsorption geometry of oxazine dyes changes with the nature of the stabilizing anion and with the concentration of the dye. By comparison of observed and calculated normal modes, conclusions about the adsorption geometry are drawn. The results are discussed in the framework of the ‘adatom model’.