Excitons in a single two-dimensional semiconductor crystal of H3N(CH2)6NH3PbI4

We have measured the reflection and luminescence spectra of synthetic two-dimensional semiconductor crystals of H3N(CH2)6NH3PbI4 for E∥〈010〉 and E∥〈100〉 polarizations at low temperatures. There appear two absorption bands related to excitons with polarization vectors parallel and oblique to the inorganic layer. From the temperature dependence of the free exciton luminescence intensity, the exciton binding energy is obtained as 0.33 eV, the value of which is consistent with the energy distance between the n=1 and n=2 exciton absorption bands. This very large binding energy is characteristic of layered perovskite crystals.