Exciton luminescence from Cu2SnS3 bulk crystals

The optical properties of Cu2SnS3 (CTS) bulk crystals grown by chemical vapor transport were studied by photoluminescence (PL) spectroscopy. The PL spectra from the CTS bulk crystals were analyzed as a function of excitation power and temperature. The main phase of the as-grown samples was determined to be monoclinic CTS by Raman spectroscopy. The observed PL spectra from the CTS bulk crystals were composed of peaks corresponding to free-exciton, two bound-excitons, and donor-acceptor pair recombination luminescence. The peak energies for the free-exciton and two bound-exciton emissions were 0.9317, 0.9291, and 0.9260 eV, respectively, at temperature of 4.2 K. The bound-exciton luminescence was not observed above 30 K. The thermal activation energies for the free-exciton and two bound-exciton emissions were 6.5, 4.8, and 5.2 meV, respectively. The fundamental band gap in the CTS bulk crystals was expected to be ca. 0.94 eV.