Fig. 5. (A) Configuration coordinate diagram for the (SnBi˙–SnBi/) to (SnBi×–SnBi×) IVCT transition, showing the calculated optical excitation (Eabsorption), vibrational relaxation (Erelaxation) and thermodynamic transition (E0) energies. The solid lines are harmonic fits to the DFT energies, represented by filled circles. X-Axis given in units of mass-weighted displacement. (B) Difference absorption spectrum of Sn doped and undoped Cs3Bi2Br9, fitted with three components corresponding to the IVCT absorption and two ‘band to band gap state’ transitions at energies calculated from DFT.
