Study of Surface Plasmon Resonance (SPR) In a Nano-Structured Material

In the present analysis, absorption spectrum of gold nanorod is modeled by Gans theory with the introduction of interband transition contribution to the dielectric function of the gold material. A linear relationship is found between the absorption maxima of longitudinal plasmon resonance and aspect ratio. Since the absorption maxima of the longitudinal plasmon resonance also depend on the refractive index value of the surrounding medium therefore, the surrounding medium in present analysis was taken as water with its refractive index value of 1.33. It is observed that with the increase in aspect ratio of gold nanorod the absorption intensity increases and the resonance wavelength shifts towards red regime of visible spectrum and further increase in the aspect ratio (~4) results a resonance wavelength in the near infrared regime. Further, a comparison with the results obtained for gold nanorods by the different theoretical models, like LC circuit model, discrete dipole approximation (DDA), experimental data, as well as the linear fit equation of experimental data was done to authenticate the parametric effect in present analysis on plasmon resonance in nano-structured materials (nanorod here). Our analytical results show a close agreement with linear curve fit equation of experimental data in comparison to the other models.