Toru Tsujibayashi

Spectral profile of the two-photon absorption coefficients in CaF2 and BaF2

Two-photon absorption spectra due to the valence excitons in CaF2 and BaF2 have been measured using the second harmonic of the output of a XeCl-excimer-laser pumped dye laser as a light source. The band gap energies of CaF2 and BaF2 are obtained as 11.8 and 10.6 eV at 298 K, respectively. The two-photon absorption coefficient β in the spectral region below the 2P exciton is expressed by an exponential function of the photon energy in both crystals. The values of β at the 2P exciton peak are about 2×10−9 cm/W for CaF2 and 3×10−9 cm/W for BaF2.

Photoelectron spectroscopic study on the electronic structures of the dental gold alloys and their interaction with L-cysteine

The valence electronic structures of the dental gold alloys, type 1, type 3, and K14, and their interaction with L-cysteine have been studied by ultraviolet photoelectron spectroscopy with synchrotron radiation. It was found that the electronic structures of the type-1 and type-3 dental alloys are similar to that of polycrystalline Au, while that of the K14 dental alloy is much affected by Cu. The peak shift and the change in shape due to alloying are observed in all the dental alloys. It is suggested that the new peak observed around 2 eV for the L-cysteine thin films on all the dental alloys may be due to the bonding of S 3sp orbitals with the dental alloy surfaces, and the Cu–S bond, as well as the Au–S and Au–O bonds, may cause the change in the electronic structure of the L-cysteine on the alloys.

Time-gated photon counting method for two-photon spectroscopy using synchrotron radiation and laser

A new measurement system has been developed for two-photon spectroscopy in solids with a combination of synchrotron radiation and laser. This system is based on a time-gated photon counting technique to observe luminescence signals induced by two-photon excitation. It is demonstrated that this technique enables us to achieve a high sensitivity and a good signal-to-noise ratio because it is a kind of zero method.

Two-photon excitation spectra of exciton luminescence in CaF2 obtained by using synchrotron radiation and laser

Abstract Excitonic states in CaF2 are studied with luminescence-detected two-photon spectroscopy using synchrotron radiation and laser. The two-photon excitation spectrum for the luminescence due to self-trapped excitons (STEs) exhibits a clear peak on the high-energy side of the 1S exciton band. The peak is assigned to the 2P exciton state. The two-photon excitation spectrum for perturbed-STE luminescence is different from that for the STE luminescence, suggesting that localized excitons generated by SR are re-excited by the laser irradiation.

Photoelectron spectroscopic study on the interaction of l-cysteine with the silver-based dental alloy

The electronic structure of the silver-based dental alloy MC12 and its constituent metals and their interaction with l-cysteine have been investigated by ultraviolet photoelectron spectroscopy (UPS) using synchrotron radiation. The UPS spectra of l-cysteine on polycrystalline Ag, Cu, Pd, and Au substrates have been measured to understand the interaction of l-cysteine with the dental alloy surface. It was found that the electronic states of MC12 originate dominantly from Cu 3d states and Pd 4d states around the top of the valence bands, while the 4–7-eV electronic structure of MC12 originates from the Ag 4 d5/2 and Ag 4 d3/2 states. For l-cysteine, it was found that a new peak at 2 eV is observed for the thin films on Ag, Cu, and Au, while the structure around 2 eV on MC12 is similar to that on Pd. The shift of the 5-eV peak is observed for the thin films on Cu, Pd, and Au, but not on Ag and MC12. These results indicate that the interaction of l-cysteine with MC12 may be dominantly due to the Pd-S, Cu-S, a...

Photo-induced valence change of the sulfur atom in an L-cysteine thin film grown on a silver metal substrate in a saliva-emulated aqueous solution

A thin film of L-cysteine (HSCH2CH(NH2)COOH) is grown on a silver substrate in saliva-emulated aqueous solution. X-ray photoemission spectroscopic measurements have revealed that the sulfur atom shows valence change under IR laser irradiation at 825 nm. The valence change maintains for about a minute at room temperature and more than an hour between 110 and 250 K after stopping the laser irradiation. It is not observed at all at temperatures lower than 110 K. This temperature-dependent behavior indicates that the photo-excited electronic change should be accompanied by a conformational change in the L-cysteine molecule. It is strongly suggested that the reversible valence change of the sulfur atom is applicable to a memory used around room temperature.

Time-resolved study of free exciton luminescence in KI and RbI

Temporal behaviours of free exciton luminescence in KI and RbI have been studied with picosecond light pulses under excitation in the n = 1 exciton absorption region. The decay curves are explained by one-dimensional diffusion and self-trapping of free excitons, which are represented by t−12 and an exponential function, respectively. The exponential decay constant is 0.35 ns for KI and 1.7 ns for RbI at around 10 K.

Combined system of synchrotron radiation and laser for solid-state research.

Two combined systems of synchrotron radiation and laser have been constructed for solid-state research. One is a laser-induced fluorescence system to observe synchrotron radiation-induced desorption of alkali atoms from ionic crystals, which consists of a laser diode with a high repetition rate and synchrotron radiation under a single-bunch operation. The other is a system of two-photon spectroscopy, which is based on the combination of synchrotron radiation pulses with a low intensity and high repetition rate and Nd:YAG laser pulses with a high intensity and low repetition rate. The experimental systems and the preliminary results are presented in this report.

Molecular-Chain Formation Induced by Infrared-Laser Light Observed in L-Cysteine and Potassium Dihydrogenphosphate

Each of amino acids and phosphate group is capable of forming a chain through repeating dehydration condensation reaction. We have observed Raman scattering spectra of L-cysteine (HSCH2CH(NH2)COOH) and potassium dihydrogenphosphate (KH2PO4 or KDP) before and after irradiation of one pulse of an erbium-doped yttrium aluminum garnet (Er:YAG) laser with its wavelength of 2.94 µm, duration of 0.2 ms, and peak power density of 0.4 MW/cm2. Extra peaks are observed in the spectra after the irradiation, which are not seen in the spectra before the laser irradiation. Comparison of the experimentally obtained spectra with the calculated ones of the chain compounds suggests that the laser light does induce such reactions.

Biexciton luminescence in alkali iodides

Abstract We have observed a luminescence band at about 50 meV lower than the energy of the main peak of free exciton luminescence (FEL) in KI and RbI under dense excitation with a UV-laser. The intensity of the band increases with increase in the excitation intensity depending quadratically on the FEL intensity. The band is assigned to luminescence of a biexciton leaving an exciton behind. A spectral change of the luminescence of self-trapped excitons is observed with the appearance of the biexciton luminescence.