Chang-Dae Kim

Optical energy gaps of β-In2S3 thin films grown by spray pyrolysis

β‐In2S3 thin films for which x varied from 2.0 to 3.9 with the x composition of the spray solution (In2Sx) were grown on thoroughly cleaned glass slides by the spray pyrolysis method with the substrate temperature maintained at 350 °C and a rate of spray of 6 ml/min. The energy gap of the grown β‐In2S3 thin film was 2.20 eV, indicating an indirect transition, whereas that of In2S3.9 increased to 2.43 eV.

Influence of ligands on the photoluminescent properties of Eu3+ in europium β-diketonate/PMMA-doped systems

Abstract Three kinds of europium β-diketonates Eu(DBM) 3 , Eu(BA) 3 and Eu(TTA) 3 (DBM: Dibenzoylmethane; BA: 1-Benzoylacetone; TTA: Thenoyltrifluoroacetone) were doped in poly(methyl methacrylate) (PMMA) matrix. The doped systems were studied by using photoluminescent (PL) spectroscopy, emission decay experiments and X-ray diffractometry. Eu(III) ions in the doped Eu(DBM) 3 /PMMA systems have two distinct symmetric sites and the emission band changes greatly with the compositions. Eu(III) in the Eu(BA) 3 /PMMA systems gives only one symmetric site in the doped systems and the emission band changes slightly with the compositions. Although two distinct symmetric sites of Eu(III) can be distinguished in the doped systems of Eu(TTA) 3 /PMMA, the two sites have similar 5 D 0 lifetimes and the luminescent spectra almost do not change with the compositions. XRD reveals that crystallites were formed in the doped Eu(DBM) 3 /PMMA systems that have different crystalline structure from that of the chelate, and Eu(BA) 3 and Eu(TTA) 3 exist in amorphous state in the doped systems. The difference between the PL properties and structures of the doped systems for the three kinds of chelates should be attributed to different interactions between the chelate molecules and between the chelate and PMMA.

Structural and optical properties of CoxIn2S3+x thin films grown by spray pyrolysis method

CoxIn2S3+x thin films with various relative compositions were grown on thoroughly cleaned glass plates by the spray pyrolysis method. The substrate temperature during growth was maintained at 270 °C and the film then annealed in a vacuum chamber at 2×10−5 Torr at 500 °C for 30 min. The grown CoxIn2S3+x thin films, which had a composition of x=0.0–0.6, showed the tetragonal structure of In2S3, but above x=0.6 the films were amorphous. The energy gap for these films decreased with increasing x composition, and the impurity absorption spectra in near infrared region, ascribed to Co2+ ions, were observed at 13 333, 5970, and 4166 cm−1, which are the 4A2(F)−4T1(P), 4A2(F)−4T1(F), and 4A2(F)−4T2(F) transitions, respectively.

Isomeric Discrimination and Quantification of Thyroid Hormones, T3 and rT3, by the Single Ratio Kinetic Method Using Electrospray Ionization Mass Spectrometry

The single ratio kinetic method is applied to the discrimination and quantification of the thyroid hormone isomers, 3,5,3′-triiodothyronine and 3,3′,5′-triiodothyronine, in the gas phase, based on the kinetics of the competitive unimolecular dissociations of singly charged transition-metal ion-bound trimeric complexes [MII(A)(ref*)2-H]+ (MII = divalent transition-metal ion; A=T3 or rT3; ref* = reference ligand). The trimeric complex ions are generated using electrospray ionization mass spectrometry and the ions undergo collisional activation to realize isomeric discrimination from the branching ratio of the two fragment pathways that form the dimeric complexes [MII(A)(ref*)-H]+ and [MII(ref*)2-H]+. The ratio of the individual branching ratios for the two isomers Riso is found strongly dependent on the references and the metal ions. Various sets are tried by choosing the reference from amino acids, substituted amino acids, and dipeptides in combination with the central metal ion chosen from five transition-metal ions (CoII, CuII, MnII, NiII, and ZnII) for the complexes in this experiment. The results are compared in terms of the isomeric discrimination for the T3/rT3 pair. Calibration curves are constructed by relating the ratio of the branching ratios against the isomeric composition of their mixture to allow rapid quantitative isomer analysis of the sample pair. Furthermore, the instrument-dependence of this method is investigated by comparing the two sets of results, one obtained from a quadrupole ion trap mass spectrometer and the other from a quadrupole time-of-flight mass spectrometer.

The influence of metal aluminium on the reduction of the Sm3+ doped in aluminosilicate glass films

Sm3+-doped glass sol was prepared by a sol–gel method and coated on a bare Si substrate and an Al coated Si substrate (Al/Si). The coated glass films were heat treated in a hydrogen atmosphere or air to reduce the Sm3+ to Sm2+ and then the optical properties were examined through a photoluminescence (PL) experiment. While the glass films coated on a bare Si substrate or an Al/Si one were well reduced in hydrogen atmosphere, only the glass films coated on the Al/Si substrate were reduced in air. We thus suggest two possible reducing mechanisms related to hydrogen and the metal aluminium and we found that the metal aluminium coated on a Si substrate plays an important role in the reducing process.

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.

Impurity optical absorption of Cd1−xHgxGa2Se4:Co2+ single crystals

Structural and optical properties of Cd1−xHgxGa2Se4 and Cd1−xHgxGa2Se4:Co2+ single crystals grown by the chemical transport reaction method have been investigated. It has been found that these single crystals have a defect chalcopyrite structure and a direct optical energy gap. It has been seen that the optical energy gap decreases as a composition x increases and as a cobalt impurity is introduced. The temperature dependence of the optical energy gap is well presented by the Varshni equation. Impurity optical absorption peaks due to a cobalt atom were observed in the optical‐absorption measurements of Cd1−xHgxGa2Se4:Co2+ single crystals. It has been analyzed that the impurity optical‐absorption peaks are attributed to the electronic transition between the split energy levels of a Co2+ ion occupying a cubic Td symmetry site of the host lattice.

Influence of Sm3+-Ions on the Hole-Burning Efficiency of Sm2+-Ions Doped in Mg0.5Sr0.5FCl0.5Br0.5 Mixed Crystals

Sm-doped Mg0.5Sr0.5FCl0.5Br0.5 mixed crystals were prepared by three different methods and their optical properties were studied through emission spectroscopy and the hole-burning technique. While the sample prepared in air (MA) shows the transition lines due to Sm3+-ions, the sample prepared in hydrogen (MH) shows Sm2+ emission lines. We could also observe the reduction effects of Sm3+ in the X-ray irradiated sample (MX). The spectral holes were burnt within the 7F0–5D1 transition band and the hole-burning efficiencies in the MH and MX samples were measured at room temperature and 9 K, using the one color and two color hole-burning techniques. The hole-burning efficiency decreased with the lowering of the temperature, and almost no hole signal was found at 9 K in the MX sample. We thus performed a site selective excitation experiment to reveal the origin of the decrease of hole-burning efficiency with decreasing temperature. On the basis of these results, we found that the energy used to excite the Sm2+-ions in the hole-burning process is also simultaneously used to excite the residual (or unreduced) Sm3+-ions, and we also found that the excitation efficiency of the Sm3+, compared to that of Sm2+, increased with decreasing temperature. As a result, we consider that the residual Sm3+-ions strongly affect the hole-burning efficiency and the photoluminescence properties of the Sm2+ by depriving the Sm2+-ions of excitation energy.

Hybrid and Etch-Less Electrooptic Waveguide Modulator Based on Photo-Bleaching and Strain Induced Optical Waveguide Technique in Polymer

A hybrid and etchless electrooptic (EO) polymer waveguide modulator based on both a photo-bleaching-induced optical waveguide (PBOW) and a strain-induced optical waveguide (SIOW) is described. The SIOW is defined by a metal strip line stressor deposited on top of the upper cladding that introduces the refractive index change within the core region. The PBOW technique is used to form an optical waveguide which is based on a photo-bleaching process, known as a photo-oxidation that is an irreversible decomposition of EO material, resulting in a permanent decrease in index of refraction. It is shown that this proposed fabrication idea combining two etchless techniques can be applicable to a wide range of polymer photonic integrated circuits. Preliminary results obtained from fabricated devices reveal that their half-wave voltage are ranging from 8 V to 10 V, their extinction ratio exhibits more than 15 dB, and the fiber-to-waveguide-to-lens loss is estimated to be ~9.5 dB for TM polarization at 1.55/m wavelength in the active interaction of ~1.5 cm long.