  We measure temperature-dependent one-photon and two-photon induced
photoluminescence from (CH3NH3)PbBr3 single crystals cleaved in ultrahigh
vacuum. An approach is presented to extract absorption spectra from a
comparison of both measurements. Cleaved crystals exhibit broad
photoluminescence spectra. We identify the direct optical band gap of 2.31 eV.
Below 200 K the band gap increases with temperature, and it decreases at
elevated temperature, as described by the Bose-Einstein model. An excitonic
transition is found 22 meV below the band gap at temperatures <200 K. Defect
emission occurs at photon energies <2.16 eV. In addition, we observe a
transition 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, and
the transition redshifts at higher temperature. The binding energy of the
exciton related to the direct band gap, in contrast, decreases in the cubic
phase. High-energy emission from free carriers is observed with higher
intensity than reported in earlier studies. It disappears after exposing the
crystals to air.
