Ken-ichi Kan'no

Efficient Immobilization of Enzymes on Microchannel Surface Through His-Tag and Application for Microreactor

We developed a simple immobilisation method for His-tagged enzymes on a microchannel surface. It facilitates immobilisation of protein molecule on microchannel surface through Ni-complex, using crude or purified protein solutions. By this method, we could immobilize proteins on microcapillary constantly. This method might be useful for further development of microreactor with reversibly immobilized enzymes.

Decay time measurements of intrinsic luminescence in alkali halides using single-bunched light pulses from UVSOR

The combination of single-bunched light pulses (duration: 0.5 ns, interval: 177.6 ns) from UVSOR (Okazaki, Japan) with a method of time-correlated single-photon counting was applied to study decay behaviors of intrinsic luminescence in nine typical alkali halide crystals (Na, K, Rb) × (Cl, Br, I). Under excitation into the band-to-band transition, two emission bands, so far called σ emission (fluorescence with a short lifetime) and π emission (phosphorescence with a much longer lifetime), were observed in general at LHeT. The decay behaviors observed were essentially the same as those reported in previous studies where pulsed particles were used as an excitation source. A novel situation has, however, been recognized in the π emission in both NaBr and NaI: A fluorescent component was found clearly to coexist with the long-lived phosphorescent component. This suggests that the initial state of the π emission in NaBr and NaI is a singlet-triplet pair slightly split by the exchange interaction.

Time-Resolved Spectroscopic Study on the Type I Self-Trapped Excitons in Alkali Halide Crystals. I. Emission Spectra and Decay Behavior

Decay behaviors of Self-Trapped Exciton (STE) luminescence categorized into type I in seven alkali halides, i.e., the σ bands in NaCl, KBr, RbBr, KI and RbI, and the π bands in NaBr and NaI, are studied by using synchrotron radiation pulses from UVSOR under single-bunch operation. Counting photons over four orders of magnitude reveals that every σ band involves a phosphorescent component with a lifetime longer than 100 ns, in addition to the main fluorescent component. This evidences that the σ band originates from the lowest orbital state of the STE. Simultaneous detection through two different time windows discloses a split in the peak energy of the fluorescent and phosphorescent components. From this result, a slight difference in the location of the minima is suggested in the adiabatic energy surfaces for a nearly degenerate singlet-triplet STE pair with the on-center configuration.

Luminescence from KCl: I at Low Temperatures

In addition to the well-known three impurity emission bands (BG-, B-, and UV-emission), a new emission band is found at 5.88 eV in a KCl: I system under excitation with UV-light, X-rays, or N 2 laser light. Its intensity and lifetime (0.52 µs at 9 K) fall off rapidly above 12 K with an activation energy of Δ E =21 meV. The intensities of the new emission and the BG emission are anti-correlated with varying temperature. Measurements of the excitation spectrum confirm that the 5.88 eV emission arises from de-excitation of localized excitons at I - monomer ion sites. Based on the small Stokes shift (0.82 eV) and small halfwidth (0.23 eV) of this emission band, and the results obtained in an experiment of recombination luminescence of X-rayed crystal, one-center model for relaxed excitons is suggested as the origin of a relaxed excited state responsible for the 5.88 eV emission band.

Optical absorption of Cu-centers in CdCl2 and CdBr2 single crystals

Abstract The absorption spectra of CdCl 2 and CdBr 2 single crystals doped with cuprous or cupric halides were measured. Optical bleaching of the absorption bands due to Cu + gives rise to new absorption bands which suggest the conversion of Cu + →Cu 2+ . This was confirmed also by detecting the growth in ESR signals characteristic of Cu 2+ centers.

Luminescence from C60 single crystals in glassy phase under site-selective excitation

Abstract Luminescence from C 60 single crystals has been investigated at liquid He temperature under selective excitation into the tail part below the fundamental absorption edge. Luminescence line narrowing is observed for resonant excitation, in which a characteristic vibrational quantum is found ∼420 cm −1 in the excited state. It is revealed that the spectrum which has been known as photo-luminescence from C 60 single crystals is an superposition of site-selective luminescence from several localized states. Such inhomogeneity is most likely to arise from fluctuation of the intermolecular orientational correlation in a pair of C 60 molecules over which the excitation is delocalized.

Time-Resolved Spectroscopic Study on the Type I Self-Trapped Excitons in Alkali Halide Crystals: II. Excitation Spectra and Relaxation Processes

Excitation spectra for the fluorescent and phosphorescent components of type I bands in seven alkali halides, NaCl, NaBr, KBr, RbBr, NaI, KI and RbI, are measured in both energy ranges of the free exciton absorption and the band-to-band transition. Using SR pulses as the excitation light source, the two components are resolved by the method of simultaneous photon-counting through two independent time-windows. Excitation spectra for the phosphorescent bands of type II or III are also measured for comparison. From these spectra, total luminescence yield and the fraction of the type I band are determined as a function of excitation energy. On the basis of these results, the relaxation processes of free electron-hole pairs and free excitons, especially on the difference between them, are discussed.

Luminescence of Localized Excitons in KCl: I at Low Temperatures

Temperature dependence of the intensities of 5.88 eV ( Near-Edge ) and 2.64 eV ( Blue-Green ) emission bands in KCl:I has been investigated in crystals containing various amount of iodine impurities under excitation into each of three absorption bands due to isolated I - ions. Localized excitons created on the I - monomer sites have two relaxed states, NE-state ( one-center type ) and BG-state ( two-center type ). It is confirmed that there is a thermal activation process from the NE-state to the BG-state. Fraction of the relaxation rate into the BG-states, γ BG , is found to increase with increasing iodine contents. This means that the relaxation mechanism of the localized exciton is influenced markedly if another iodine ion is present in the vicinity of the localized exciton.

Self-Trapped Exciton Luminescence in KBr1-xIx and RbBr1-xIx Solid Solutions

Emission spectra and decay characteristics of luminescence in KBr 1- x I x and RbBr 1- x I x solid solutions have been investigated in the whole range of composition x . The emission band due to localized excitons at I - dimer centers in bromides, which consists of singlet and triplet components, is found to connect continuously with intrinsic σ band in pure iodides. The triplet component of the band is transformed into another emission with larger Stokes-shift in the intermediate region of x . Time-resolved studies on this emission in KBr 1- x I x have clarified that it consists of two triplet emission bands differing by ∼ 0.2 eV in their peak energies. The lower energy one corresponds to π band in KI. We demonstrate that the relaxed exciton configurations of different types are selectively realized depending on the local environment surrounding the I 2 - molecular core of the exciton. Discussion is given on the dynamical relaxation process of free excitons in iodides.

Lifetimes of Singlet and Triplet Excitons in β-ZnP 2

Temporal behaviors of the radiative recombination of excitons have been studied in β-ZnP 2 by using picosecond laser pulses at 2 K. Under interband excitation with E // c , the singlet exciton lumi...