α- Ga 2 S 3 and α-Ga2S3:Fe2+ single crystals were grown by the two-zone sublimation method. The optical energy gaps of α-Ga2S3 and α-Ga2S3:Fe2+ at 10 K were found to be 3.440 and 3.392 eV, respectively. From the absorption spectra of α-Ga2S3:Fe2+, the crystal field parameter Dq of 345 cm−1 and Racah parameters B of 700 and C of 3365 cm−1 were obtained for tetrahedral Fe2+ ions. From the photoluminescence spectra at 10 K, the blue and red emissions at 424 and 643 nm, respectively, for α-Ga2S3 and the violet and yellow emissions at 400 and 580 nm, respectively, for α-Ga2S3:Fe2+ were observed. All the emission lines observed in the photoluminescence spectra were identified.

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Optical absorption and dielectric properties have been investigated for TlGaSe2 and TlGaSe2: Co single crystals grown by Bridgman method. The temperature dependence of the exciton peak position in TlGaSe2 showed the anomalies at 50 K, 90 K, 107 K and 120 K. The dielectric anomalies of TlGaSe2 are found which exhibit structural phase transitions (PT) at T 2=107 K and T 1=120 K corresponding to first-order and second-order PT, respectively. It is found that an increase in concentration of Co impurity leads to shift of two phase transition points (T 1 and T 2) towards the lower temperature and changes the dielectric properties for TlGaSe2: Co. The impurity absorption bands observed in TlGaSe2: Co are attributed to the electronic transitions between the split energy levels of Co2+ ions with tetrahedral (T d) symmetry in TlGaSe2 host lattice.

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