Photoluminescence of the inorganic-organic layered semiconductor (C6H5C2H4NH3)2PbI4:: Observation of triexciton formation

By mean of subpicosecond pulsed excitation of excitons, we have measured the photoluminescence spectra of (C6H5C2H4NH3)(2)PbI4 under a high-excitation regime up to 4x10(14) photons/cm(2). At 10 K, two additional lines are observed below the exciton energy by 55 and 75 meV for excitation greater than 2x10(13) photons/cm(2). The former is assigned to the amplified spontaneous emission of the excitonic molecule. The latter is presumed to be the emission of a triexciton leaving two excitons behind, because the intensity is proportional to the 2.6 power of the excitation intensity. An elementary model of the triexciton is presented. The dissociation energy of a triexciton is estimated to be 14 meV from the temperature dependence.