Two-Dimensional Excitons and Photoluminescence Properties of the Organic/Inorganic (4-FC6H4C2H4NH3)2[PbI4] Nanomaterial

Abstract

Single crystals of a hybrid organic/inorganic material with the formula (4-FC6H4C2H4NH3)2[PbI4] were synthesized and studied by X-ray diffraction, ellipsometry, and photoluminescence. The crystals consist of a self-assembled multilayer structure with a P21/a space group. The inorganic semiconductor sublattice is built up from corner-sharing PbI6 octahedra forming infinite two-dimensional quantum wells. The organic (4-FC6H4C2H4NH3)+ chains form the insulator barriers. A strong room temperature photoluminescence emission, due to excitons confined in the PbI quantum wells, is found around 2.34 eV. The exciton binding energy 540 meV is determined from the temperature dependence of the photoluminescence intensity and using a modified Arrhenius model, which accounts for the two-dimensional electronic structure. Calculations of the exciton binding energy based on a variational method indicate that the dielectric confinement effect is enhanced by the low value of the organic barrier dielectric constant. Moreover, it is shown that the temperature variation of the photoluminescence peak energy is well described by Varshni’s model, thus indicating the free character of the two-dimensional excitons. The temperature dependence of the photoluminescence line width is also analyzed and interpreted in terms of homogeneous broadening due to exciton−phonons interaction.