Femtosecond optical nonlinearities and ultrafast absorption dynamics of colloidal 2D organometal halide ((C12H25–NH3)2PbI4) nanoparticles and thin films

Abstract

Layered 2D Inorganic-Organic (IO) hybrid semiconductors of the type (R–NH3)2PbI4 have shown tremendous potential applications in various photonics and optoelectronic devices. In this work, femtosecond laser induced optical nonlinearities and excited state charge carrier dynamics of organometal halide (C12H25–NH3)2PbI4 (C12PI) 2D colloidal nanoparticles (NPs) and the thin film counterpart are investigated. These colloidal 2D NPs of sizes ∼9 nm, show third-order optical nonlinearity having two-photon absorption coefficient (2PA) (β∼26-23 cm/GW) and positive nonlinear refractive index (n2∼7.6 × 10−2 cm2/GW), while thin films show β∼78–134 cm/GW and n2∼0.003-0.2 × 10−2 cm2/GW. The origins of two-photon induced absorption and Kerr-type refractive nonlinearity are as a result of induced molecular polarization and charge transfer effects between organic cation (C12H25–NH3)+ and inorganic anion (PbI6 octahedra). The ultrafast transient absorption spectral studies demonstrate the room-temperature Mott-type exciton excited-state charge carrier dynamics and charge carrier recombination features. The laser pump intensity dependent transient absorption spectral (TAS) features reveal wide information about ground state bleaching (GSB∼510 nm, ΔA<0 with decay of 28.2–3.2 ps) along with a photo-induced absorption (PIA∼476 nm, ΔA>0, with decay of 22–6.3 ps) regions. The systematic studies of optical nonlinearities and ultrafast absorption dynamics of 2D IO hybrid semiconductor colloidal nanoparticles and thin film will provide a new platform for advanced photonics and ultrafast optical switching devices applications.