Induced absorption and spontaneous emission due to biexciton in two-dimensional semiconductor (CH3C6H4CH2NH3)2PbBr4 single crystal

We examined the optical properties of two-dimensional semiconductor (CH3C6H4CH2NH3)2PbBr4 single crystals. Clear and sharp structures, originated in dipole allowed excitons and triplet excitons, were observed in both absorption and emission spectra. In the highly excited emission spectra, biexciton emission appeared with the increase of excitation intensity. An extremely large biexciton binding energy of 40 meV was estimated. We could observe both induced absorption and emission due to biexciton formation for the first time.