Drastic increase in the second-order optical susceptibilities for monodisperse In₂O₃ nanocrystals incorporated into PMMA matrices

Using photoinduced second-order non-linear optical methods, we have determined that monodisperse In₂O₃ nanocrystals of size ∼11-24 nm incorporated into poly(methyl methacrylate) (PMMA) matrices possess significant second-order optical susceptibilities up to 17 pm V ^-1 at λ ≤ 1.76 νm; this is almost one order higher than that of traditional nanolayers of In₂O₃. A substantial increase in the corresponding susceptibilities is dependent on a relatively high monodispersion of the nanocrystals. Calculations such as quantum chemical, molecular dynamics and band structure simulations of interfaces indicate that the principal role in the observed non-linear optical effects is played by interfaces on the borders separating the nanocrystals and the surrounding host polymer matrix. In order to clarify a role of the monodispersion and that of the surfaces, additional experiments were carried out using samples with a larger size-distribution of nanocrystals and highly polarized photopolymers of oligoethercrylates as the host matrix. A drastic decrease in the effective optical nonlinearity in these two cases further supports the crucial role of the nanointerfaces.