Anisotropic excitonic absorption in SbI3 films: Theory and experiment

•Optical properties of monoclinic SbI3 are investigated using DFT calculations and experiment.•The calculated absorption spectra of six (hkl) planes show highly anisotropic nature.•2.66 eV or 2.7 eV are possible indirect band gaps from band structure compared to measured 2.8 eV.•One exciton appears at 3.56 eV for (hkl) oriented film and two excitons at 2.95 eV and 3.30 eV for (130)•The experimental and theoretical optical properties match reasonably well. Structurally characterized antimony triiodide films grown by vacuum thermal evaporation exhibit anisotropic exciton formation at room temperature for different (hkl) oriented growth. Band structure of monoclinic SbI3 was calculated using Density functional Theory with appropriate functional along with the absorption spectra of different (hkl) planes for comparing with the experimental results. The indirect band gap of 2.8 eV determined by measured absorption spectra matches closely with the calculated 2.66 eV. All (hkl) oriented films show one exciton at 3.56 eV which can be interpreted as direct type along D symmetry from the band structure. Similarly, the two excitons at 2.95 eV and 3.30 eV appearing for (130) oriented films can also be direct either at D or B symmetry. All three excitonic transitions are found to be from Iodine p states to Antimony p states.