The origin of photon absorption below and above surface plasmon resonance of gold colloids confined in dielectric media

Experimental and theoretical investigation of gold implanted in silica and gold colloids in solution has been conducted. It is shown that the effective medium theories can be successfully used to predict surface plasmon absorption (SPA) energy. However, the model calculation failed to explain the relatively stronger absorption below and above the gold SPA regions. It is argued that the lower energy photon absorption of SP resonance can be attributed to the change of the real part of the dielectric constant resulting from the ion implantation damage. The strong optical absorption above the SPA energy may be due to the physical and quantum confinement effects on both conduction and valence bands thereby changing the oscillator strength of the interband transitions.