Seok-Kyun Oh

Optical properties of β-In2S3 and β-In2S3:Co2+ single crystals

β-In2S3 and β-In2S3:Co2+ single crystals were grown by the chemical transport reaction method using In2S3, S, and ZnS as starting materials and (ZnCl2 + I2) as a transport agent. The single crystals crystallized into a tetragonal structure. The indirect optical energy band gaps of the single crystals at 298 K were found to be 2.240 eV and 1.814 eV for β-In2S3 and β-In2S3:Co2+, respectively. The direct optical energy band gaps were found to be 2.639 eV and 2.175 eV for β-In2S3 and β-In2S3:Co2+, respectively. Impurity optical absorption peaks were observed for the β-In2S3:Co2+ single crystal. These impurity absorption peaks were assigned, based on the crystal field theory, to the electron transitions between the energy levels of the Co2+ ion sited in Td symmetry.

Brain Activation in Response to Visually Evoked Sexual Arousal in Male-to-Female Transsexuals: 3.0 Tesla Functional Magnetic Resonance Imaging

Objective This study used functional magnetic resonance imaging (fMRI) to contrast the differential brain activation patterns in response to visual stimulation with both male and female erotic nude pictures in male-to-female (MTF) transsexuals who underwent a sex reassignment surgery. Materials and Methods A total of nine healthy MTF transsexuals after a sex reassignment surgery underwent fMRI on a 3.0 Tesla MR Scanner. The brain activation patterns were induced by visual stimulation with both male and female erotic nude pictures. Results The sex hormone levels of the postoperative MTF transsexuals were in the normal range of healthy heterosexual females. The brain areas, which were activated by viewing male nude pictures when compared with viewing female nude pictures, included predominantly the cerebellum, hippocampus, putamen, anterior cingulate gyrus, head of caudate nucleus, amygdala, midbrain, thalamus, insula, and body of caudate nucleus. On the other hand, brain activation induced by viewing female nude pictures was predominantly observed in the hypothalamus and the septal area. Conclusion Our findings suggest that distinct brain activation patterns associated with visual sexual arousal in postoperative MTF transsexuals reflect their sexual orientation to males.

Optical properties of ZnAl2Se4, ZnAl2Se4:Co2+, and ZnAl2Se4:Er3+ single crystals

Single crystals of ZnAl2Se4, ZnAl2Se4:Co2+, and ZnAl2Se4:Er3+ were grown by the chemical transport reaction method using iodine as a transporting material. It has been shown that these single crystals have a defect chalcopyrite structure and a direct band gap. The direct band gap at 13 K has been found to be 3.525 eV for ZnAl2Se4, 2.952 eV for ZnAl2Se4:Co2+, and 3.283 eV for ZnAl2Se4:Er3+, respectively. Impurity optical absorption spectra of ZnAl2Se4:Co2+ showed absorption characteristics of Co2+ ions due to electron transitions between their split energy levels under a Td symmetry crystal field. Photoluminescence spectra at 13 K of ZnAl2Se4 showed two emission bands centered at 470 and 799 nm. For ZnAl2Se4:Er3+, we observed sharp photoluminescence peaks due to emission transitions between the energy levels of Er3+ ions with S4 symmetry sites.

Absorption spectra of Co 2+ in AgInS 2 orthorhombic single crystals

The optical absorption spectra of AgInS 2 :Co 2+ single crystals grown by chemical transport reaction using iodine as a transporting medium have been studied at 6 K. The peaks can be explained by the transitions of Co 2+ in the T d symmetry with the spin-orbit coupling, which means that the deviations of the atomic sites from those of the ideal wurtzite structure can be considered negligibly small. The consideration of both the crystal field parameters and the electronegativity difference between atoms may indicate that Co atoms substitute In atoms.

Photoluminescence spectra of Er3+-doped MgAl2S4 and CaAl2S4 single crystals

MgAl2S4, CaAl2S4, MgAl2S4:Er3+ and CaAl2S4:Er3+ single crystals were grown by the chemical transport reaction method. The single crystals crystallized in an orthorhombic structure. The single crystals had the direct energy band structure and their optical energy gaps were 4.334 eV, 4.213 eV, 4.835 eV and 4.716 eV for the MgAl2S4, MgAl2S4:Er3+, CaAl2S4, and CaAl2S4:Er3+ single crystals, respectively, at 13 K. Sharp emission peaks appeared in the MgAl2S4:Er3+ and CaAl2S4:Er3+ single crystals, and they were interpreted to originate from the Er3+ ion substituted Mg2+ and Ca2+ ions in the MgAl2S4:Er3+ and CaAl2S4:Er3+ single crystals.

Optical properties of undoped and Co‐doped CuAlGeSe4 and CuAlSnSe4 single crystals

CuAlGeSe4, CuAlSnSe4, CuAlGeSe4:Co2+, and CuAlSnSe4:Co2+ single crystals were grown by the chemical transport reaction method. These single crystals had a defect chalcopyrite structure and a direct band structure. Optical energy gaps at 286 K were found to be 2.394, 1.874, 2.302, and 1.794 eV for CuAlGeSe4, CuAlSnSe4, CuAlGeSe4:Co2+, and CuAlSnSe4:Co2+ single crystals, respectively. Impurity optical‐absorption peaks due to cobalt dopants were observed at 12 243, 7002, and 3890 cm−1 in CuAlGeSe4:Co2+ single crystal and 11 949, 7056, and 3920 cm−1 in CuAlSnSe4:Co2+ single crystal at 286 K. Each of these peaks split into four peaks due to the second‐order spin‐orbit coupling effect at 30 K. The peaks are assigned to the electron transition between the energy levels of a Co2+ ion sited at the cubic Td symmetry point in the host lattice. Then, for CuAlGeSe4:Co2+ and CuAlSnSe4:Co2+ single crystals, the crystal‐field parameter Dq is found to be 389 and 392 cm−1, respectively, the first‐order spin‐orbit coupling ...

Impurity optical absorption of Co2+-doped MgAl2Se4 and CaAl2Se4 single crystals

MgAl2Se4, MgAl2Se4:Co2+, CaAl2Se4 and CaAl2Se4:Co2+ single crystals were grown by the chemical transport reaction method in a closed system using iodine as a transport agent. The MgAl2Se4 and MgAl2Se4:Co2+ single crystals crystallized into a hexagonal (rhombohedral) structure, and the CaAl2Se4 and CaAl2Se4:Co2+ single crystals crystallized into an orthorhombic structure. The optical energy gaps of the MgAl2Se4, MgAl2Se4:Co2+, CaAl2Se4 and CaAl2Se4:Co2+ single crystals at 10 K were found to be 3.286 eV, 2.596 eV, 3.823 eV and 3.082 eV, respectively. The impurity optical absorption peaks were observed in the MgAl2Se4:Co2+ and CaAl2Se4:Co2+ single crystals and analysed to appear as a result of the electron transitions between energy levels of the Co2+ ion in sites of Td symmetry.

Photoluminescence spectra of ZnAl2Se4-4xS4x single crystals

Single crystals of ZnAl2Se4-4xS4x quaternary solid solution were grown by the chemical transport reaction method. The ZnAl2Se4-4xS4x single crystals were found to have a defect chalcopyrite structure in the region of 0.0≤x≤0.2 and a cubic spinel in the region of 0.8≤x≤1.0. It was also shown in these regions that the lattice constants and optical energy gaps depend on a composition x. A miscibility region existed in the region of 0.2<x<0.8. The photoluminescence spectra for the crystals with 0.0≤x≤0.2 and 0.8≤x≤1.0 showed a strong blue emission band and a weak broad emission band due to donor-acceptor pair recombination at low temperatures. A simple energy band scheme for the radiative mechanism in the ZnAl2Se4-4xS4x was proposed on the basis of our experimental results along with the measurements of thermoluminescence and photo-induced current transient spectroscopy.

Photoluminescence spectra of undoped and Er3+-doped MgAl2Se4 and CaAl2Se4 single crystals

MgAl2Se4, MgAl2Se4:Er3+, CaAl2Se4, and CaAl2Se4:Er3+ single crystals were grown by the chemical transport reaction method. The single crystals had the direct energy band gap and their optical energy gaps were 3.286, 2.855, 3.823, and 3.525 eV for the MgAl2Se4, MgAl2Se4:Er3+, CaAl2Se4, and CaAl2Se4:Er3+ single crystals, respectively, at 13 K. Broad photoluminescence spectra peaked at 477 and 672 nm for the MgAl2Se4 single crystal and at 459 and 633 nm for the CaAl2Se4 single crystal were obtained. Sharp emission peaks due to the Er3+ ion in the MgAl2Se4:Er3+ and CaAl2Se4:Er3+ single crystals were observed.

Optical Properties of α-In 2 S 3 :Co 2+ Single Crystal

The single crystal with a good quality and stabilized property were gained successfully by the CTR(Chemical Transport Reaction)method. XRD analysis showed that the grown single crystals were cubic structure. The optical absorption spectra of single crystal showed impurity absorption peaks due to cobalt impurity. These impurity absorption pesks were assigned to the ligand transition between the split energy levels of ions sited in symmetry of these semiconductor host lattice.