Excitonic feature in CsAg2I3 crystals prepared by Bridgman method

This study investigated the optical spectra of the CsAg 2 I 3 crystals at low temperatures. In the reflection spectrum, remarkable reflection peaks owing to band-edge exciton transitions were observed at approximately 3.8 eV above the fundamental absorption edge at 3.6 eV. Under excitation in the energy region of exciton transitions, an intense luminescence band attributed to a self-trapped exciton (STE) was observed at 3.37 eV. In addition to STE luminescence, a weak luminescence line was observed at 3.77 eV. Because the value of 3.77 eV is practically equal to the lowest exciton transition energy estimated from the reflection spectrum, the luminescence line at 3.77 eV comes from a free exciton (FE). The intensities of the FE and STE luminescence peaks decrease with increasing temperature. The activation energies of the FE and STE were estimated from the quenching of luminescence intensities. The features of the exciton states in the CsAg 2 I 3 crystals are presented.