Low-Temperature Anomalies of Two-Proton Absorption in In₂O₃ Nanocrystals Incorporated into PMMA Matrixes

Abstract

Pages 8219-8222: Several additional clarifications and extensions concerning the obtained nonlinear optical data and several measurement details in the article Kityk, I. V.; Liu, Q.; Sun, Z.; Fang, J. J. Phys. Chem. B 2006, 110, 8219 will be given.The obtained value of the TPA (about 90 cm/GW) is of the same order as for other semiconducting nanocomposites. For example, for the same PMMA matrices, TiO 2 embedded nanocrystals (NC) give 2260 cm/GW (at least two order larger). 1 For the ZnS NP, the enhancement achieves about 230 cm/GW. 2 For comparison in the bulk ZnS crystals, this coefficient is equal to only 0.02 cm/GW, which confirms its nanosized origin. Even for such nonpromising nonlinear crystals as GaAs without the polymer covering sheets, the value of the TPA is equal up to 40 cm/GW, which is larger than for many organic materials. 3 The optimal content of the chromophore (about 4.3%), which usually do not exceed 5.4% for typical semiconducting nanocrystallite-polymer composites (in weight), corresponds to maximal content at which the NC aggregation do not occur yet. Usually for larger NC contents, one can observe drastic enhancement of the scattered light. This aggregation diminishes the NLO output and this chromophore NC content is very close for many inorganic NC incorporated into the polymer matrices (see for example SiC/PMMA composites 4 ). In the case of the IR spectral wavelengths, additional favoring factor of the nonlinear optical susceptibility enhancement (up to 5 orders) for such nanosized structure is caused by polaronic effects (see for example ref 5). Physical mechanisms determining the observed effects were described elsewhere (see for instance ref 6 and reference there).Recently also it was established that the principal role for such kinds of the nanocomposites play the sheets with thickness from 0.5 up to 5 nm on the borders separating the nanocrystallites and the surrounding polymers. This fact was unambiguously established following the ab initio molecular dynamics and quantum chemical simulations in refs 7 and 8. So effectively we deal with a nanoporous composite material, principally different from amorphous. The influence of the nanosurfaces on the NLO susceptibilities was demonstrated many times experimentally and theoretically (see for example refs 9 and 10). For example for semiconducting CdTe nanocomposites, an enhancement of at least two order of the third-order susceptibilities was observed compared to the bulk one. 11 This origin of the nonlinear optical susceptibility is principally different with respect to the organic materials where local hyperpolarizabilities (both of the second as well as of the third order ones) possess a principal theoretical limit. 12 Moreover, in several types of metallic nanoparticles, enhancement of the third-order susceptibilities may achieve even 5-6 orders, 13 and the role of the nanoconfined effects on the interfaces is crucial.The technology of preparaing optically homogeneous nanocomposites always includes several field alignments causing ...