Synthesis, Structural, Linear, and Nonlinear Optical Studies of Inorganic–Organic Hybrid Semiconductors (R–C6H4CHCH3NH3)2PbI4, (R = CH3, Cl)

Abstract

Synthesis, crystal structure, and optical properties of two-dimensional (2D) layered structurally slightly different inorganic–organic (IO) hybrid semiconductors (R–C6H4C2H4NH3)2PbI4 (R = CH3, Cl) are presented. They are naturally self-assembled systems where two (RNH3)+ moieties are sandwiched between two infinitely extended 2D layers of the [PbI6]4– octahedral network and treated as natural IO multiple quantum wells. While the former compound crystallizes into an orthorhombic system in the Cmc21 space group, the latter crystallizes into a monoclinic system in the space group P21/c. As a thin film, they are well-oriented along the (l00) direction. Both single crystals and thin films show strong room-temperature Mott type exciton features that are highly sensitive to the self-assembly and crystal packing. Linear (one-photon) and nonlinear (two-photon) optical probing of single crystals for exciton photoluminescence imaging and spectral spatial mapping provide deep insight into the layered re-arrangement and structural crumpling due to organic conformation. The strongly confined excitons, within the lowest band gap of inorganic, show distinctly different one- and two-photon excited photoluminescence peaks: free excitons from perfectly aligned 2D self-assembly and energy down-shifted excitons originated from the locally crumpled layered arrangement. Their structural aspects are successfully presented with proper correlation that emphasize various differences in physical and optical properties associated between these novel IO hybrids.