Low-temperature anomalies of two-photon absorption in In2O3 nanocrystals incorporated into PMMA matrixes

By using a method of two-photon absorption, it has been observed that monodisperse In2O3 nanocrystals (NCs) with sizes equal to approximately 14-24 nm show significant increase of two-photon absorption at low temperatures. When T = 40 K, the two-photon absorption coefficients for low-sized samples drastically increase, whereas such enhancement for the samples with averaged sizes above approximately 24 nm is not significant. The nondiagonal tensor components give one-order-less two-photon absorption values. A principal role in the observed dependences is played by interface nanolayers, demonstrating substantial contribution of nanoconfined effects. This phenomenon could only be observed in highly monodisperse NCs. Increase of the size distribution substantially suppresses the two-photon absorption observed. For the relatively large nanocrystals, the effects are comparable with those of the bulklike crystals. At the same time, the drastic increase at low temperatures may indicate a substantial role of the phonon subsystem.