Seung-Cheol Hyun

Optical properties of undoped and Ni-doped VA-VIA-VIIA single crystals

SbSl∶Cr, SbSel∶Cr, BiSl∶Cr, and BiSel∶Cr single crystals were grown by the vertical Bridgman technique using the ingots synthesized from the high-purity (99.9999%) elements antimony, bismuth, sulphur, selenium, iodine and chromium. The grown single crystals crystallized in the orthorhombic structure and had an indirect energy-band structure. The temperature dependence of the optical energy gap was well fitted by the Varshni equation. When chromium was doped into the single crystals, impurities in the optical absorption peaks appeared, and were attributed to the electron transitions between the energy levels of Cr2+ ions sited at the Td symmetry point in the host lattice.

Optical properties of undoped and Co-doped SbSBr and BiSBr single crystals

SbSBr, BiSBr, SbSBr:Co and BiSBr:Co single crystals were grown by the Bridgman technique. The grown single crystals crystallize in an orthorhombic structure and have an indirect band structure. The temperature dependence of the optical energy gap for the single crystals shows anomalies at the first and second-order phase transition points. Cobalt dopants are located at the Td symmetry point in the host single crystals as Co2+ and Co3+ ions. Impurity optical absorption peaks due to the electron transitions between the energy levels of the Co2+ and Co3+ ions are observed.

Optical Absorption of ZnGa2S4:Ni2+ and ZnGa2Mn2+ Single Crystals

Single crystals of ZnGa2S4:Mn2+ and ZnGa2S4:Ni2+ were grown by chemical vapor deposition technique. The absorption spectra of these crystals were measured in the wavelength region of 400–3000 nm at 298 K. The optical energy gap is found to be 3.25 eV for the ZnGa2S4, 3.21 eV for the ZnGa2S4:Mn2+ and 3.15 eV for the ZnGa2S4:Ni2+ crystals. Three absorption peaks were observed at 2.30 eV, 2.55 eV and 2.66 eV for the ZnGa2S4:Mn2+ and assigned as, 6A1→4E, 6A1→4T2 and 6A1→4T1 transitions of Mn2+ at Td crystal field. The absorption peaks of ZnGa2S4:Ni2+ were observed at 0.54 eV, 1.14 eV, 1.50 eV, 1.76 eV, 1.94 eV and 2.25 eV. These absorption transitions were assigned as, \varGamma1→\varGamma3+\varGamma4, \varGamma1→\varGamma5, \varGamma1→\varGamma3+\varGamma4, \varGamma1→\varGamma5, \varGamma1→\varGamma4 and \varGamma1→\varGamma3, respectively using Td crystal field along with the 1st order spin-orbit coupling effect.