Nonlinear optical behaviour of indium-phthalocyanine tethered to magnetite or silica nanoparticles

Nonlinear absorption and optical limiting properties of indium phthalocyanine (complex 1) tethered to magnetite (SiMNP-1) or silica (SiNP-1) nanoparticles have been investigated using 10 ns pulses at 532 nm laser excitation. The optical limiting behaviours of the nanocomposites and the bare phthalocyanine are compared. Investigation of the triplet state dynamics revealed highly efficient triplet state absorption in the SiMNP-1 dyad. A large nonlinear absorption (beta(eff)) that increased with decrease in the peak input fluence was observed for SiMNP-1. The SiNP-1 composite showed a slight increase in beta(eff) with decreasing peak input fluence. The nonlinear optical data obtained for the SiNP-1 are within the same range of those of the indium phthalocyanine alone. The nanosecond nonlinear absorption and the optical limiting of the nanocomposites are shown to be dominated by a strong excited state absorption from a two-photon pumped state. Nonlinear scattering effects and strong excited state absorption from a two-photon pumped state account for the enhanced optical limiting behaviour of SiMNP-1 relative to the phthalocyanine alone.