Cancellation of photoinduced absorption in metal nanoparticle composites through a counterintuitive consequence of local field effects

By applying the Maxwell Garnett model to gold nanoparticles in water we deduce a Value of fm chi(i)((3)) = 1.1 x 10(-7) esu for the imaginary part of the cubic susceptibility for gold corresponding to a Fermi smearing mechanism. We also demonstrate a sign reversal in the nonlinear absorption for gold particles in 1, 1', 3, 3, 3', 3'-hexamethylindotricarbocyanine iodide. Although the imaginary part of chi((3)) is positive for each component by itself, remarkably the imaginary part of chi((3)) is negative for the colloid as a whole. We show that the nonlinearity of the host must be considered and that the sign reversal in chi((3)) is a result of the fact that at the surface plasmon resonance the local field factor has an imaginary component that arises from a phase shift between the applied field and the local field inside the particle. (C) 1997 Optical Society of America.