Low Inhomogeneous Broadening of Excitonic Resonance in MAPbBr Single Crystals.

We present an optical study of MAPbBr single crystal grown from solution. The crystal Pm3m symmetry was confirmed by electron backscatter diffraction. Our major attention was focused on optical effects related to the excitonic states in MAPbBr. Photoluminescence temperature dependence of narrow exciton resonance showed encouragingly low inhomogeneous broadening Γ ≈ 0.5 meV that allows one to distinguish the signals from free excitons and those arising from recombination of excitons localized on defects. Excitonic origin of the resonance was proved by its superlinear pump intensity dependence, in contrast to the linear behavior of the defect-assisted recombination bands. For the first time, the phonon replicas originating from free exciton recombination accompanied by partial energy transfer to the phonons were observed in high-resolution PL spectra and confirmed by independent low-temperature Raman scattering experiments. In turn, low-temperature, low-frequency Raman scattering studies let us resolve the structure of the low-frequency phonon spectrum.