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We measure temperature-dependent one-photon and two-photon inducedphotoluminescence from (CH3NH3)PbBr3 single crystals cleaved in ultrahighvacuum. An approach is presented to extract absorption spectra from acomparison of both measurements. Cleaved crystals exhibit broadphotoluminescence spectra. We identify the direct optical band gap of 2.31 eV.Below 200 K the band gap increases with temperature, and it decreases atelevated temperature, as described by the Bose-Einstein model. An excitonictransition is found 22 meV below the band gap at temperatures <200 K. Defectemission occurs at photon energies <2.16 eV. In addition, we observe atransition at 2.25 eV (2.22 eV) in the orthorhombic (tetragonal and cubic)phase. Below 200 K, the associated exciton binding energy is also 22 meV, andthe transition redshifts at higher temperature. The binding energy of theexciton related to the direct band gap, in contrast, decreases in the cubicphase. High-energy emission from free carriers is observed with higherintensity than reported in earlier studies. It disappears after exposing thecrystals to air.

Temperature-dependent optical spectra of single-crystal (CH$_3$NH$_3$)PbBr$_3$ cleaved in ultrahigh vacuum