Temperature dependent two-photon photoluminescence of CH₃NH₃PbBr₃: structural phase and exciton to free carrier transition

The intrinsic photoluminescence emission properties of high-quality bulk crystals of CH3NH3PbBr3 under excitation by two-photon absorption at 810 nm are presented. A strongly non-monotonous wavelength shift of the two-photon photoluminescence with increasing temperature is observed, which can be associated with discrete transitions between several stable crystalline phases. Experimentally, both temperature (5 – 300 K) and excitation density are varied. At room temperature, a scaling of the photoluminescence with the 4th power of the excitation density is observed, in contrast to a quadratic behavior at cryogenic temperatures. We attribute this due to a transition from exciton gas to free charge carriers with a temperature increase.