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The sequence of amino acids in peptide chains consisting of proteins is the most fundamental information of living things. A direct and nondestructive method of reading is highly required as an alternative to the method based on the gene analysis. Luminescence detection is a very sensitive tool for investigating various materials. In order to find characteristic luminescence of each amino acid we study L-cysteine and L-tyrosine using UV laser of 3.36 eV with pulse duration of 1.5 ps. In addition to a common 2.66 eV band of the luminescence we have found 2.89 eV band for L-cysteine and 2.92 eV band for L-tyrosine. It can be interpreted that the side chain makes difference on the luminescence by affecting the peptide linkage or carbonyl group.

We have investigated the defect formation processes of BaF2 single crystals under vacuum ultraviolet radiation with the use of combination spectroscopy of synchrotron radiation (SR) and laser. The defect formation efficiency was measured as a function of excitation photon energy of SR by means of a laser-induced luminescence method. It was found that the efficiency depends significantly on the excitation photon energy. We show that the dependence can be explained in terms of the diffusive motion of hot conduction electrons generated by the photoexcitation. The relationship between the defect formation and the energy relaxation of core excitons is also discussed.

Metal–organic interfaces have been attracting continuous attention in many fields including basic biosciences. The surface of dental alloys could be one of such interfaces since they are used in a circumstance full of organic compounds such as proteins and bacteria. In this work, electronic structures of Au-dominant dental alloys, which have Ag and Cu besides Au, and those of l -cysteine on the dental alloys have been studied by photoelectron spectroscopy with synchrotron radiation. It was found that the density of states in the dental alloy originate from gold and copper as constituents, and the Cu-3d states contribute dominantly to the occupied states near the Fermi level. It was also found that the electronic structure of the l -cysteine thin film on the dental alloy is different from that of the l -cysteine thick film. The result indicates the formation of the orbital bonding between Cu-3d and S-3sp states in the thin film on the dental alloy.

The 2 P state energy of the valence exciton in SrF 2 has been obtained to be 11.1 v eV at 298 v K through two-photon absorption (TPA) spectroscopy. The luminescence of self-trapped excitons was monitored as the signal of TPA. The exciton binding energy is estimated to be 0.9 v eV. This value of binding energy is comparable not only to those obtained through TPA in other alkaline-earth fluorides of CaF 2 and BaF 2 , but also to those of alkali fluorides. The TPA coefficient of SrF 2 was about 5 ‐ 10 m 9 v cm/W for 5.55 v eV-photons. The value is in the same order of magnitude as those measured at 2 P state of the exciton in CaF 2 and BaF 2 crystals.

Production of radiation defects in a widely used scintillation material BaF 2 has been studied by means of a combination spectroscopy of synchrotron radiation (SR) and laser, in which defects produced by SR irradiation are sensitively detected by observing the luminescence stimulated by laser light. The photostimulated luminescence arises from the recombination of self-trapped holes (V K centers) with electrons released from trapped centers by laser light. The obtained result reveals that the production efficiency of radiation defects is drastically dependent on the excitation photon energy of valence or core excitons.

Biexciton luminescence of Nal is observed under excitation with intense laser light in the n = 1 exciton absorption region. The luminescence has two bands. The high-energy band is attributed to a biexciton state, which is a bound state of two free excitons, on the basis of the estimate of the binding energy. Measurement of luminescence spectra at various temperatures reveals that the low-energy band originates from a bound biexciton, which is a bound state of a free exciton and a bound exciton.

Exciton states in wide-gap materials CaF2 and BaF2 have been studied with the technique of two-photon spectroscopy using synchrotron radiation and laser. The two-photon excitation spectrum of CaF2, and that of BaF2 as well, exhibited a clear peak on the high-energy side of the 1 S exciton energy. The peaks are attributed to the 2 P states of the valence excitons. According to this assignment, the binding energies of the excitons have been determined to be 0.8 and 0.9 eV for CaF2 and BaF2, respectively. The signal intensities were larger than that in the case of one-beam excitation by a factor of about 500, which is attributed to a resonant effect on two-photon absorption. @S0163-1829~99!52836-1#

The migration of the core exciton in a mixed crystal of Rb 0.82 Cs 0.18 Cl is investigated through time-resolved measurement under excitation with synchrotron radiation (SR) and laser. The photon energy of SR is tuned to the absorption band due to the exciton composed of a conduction electron and the hole originated from the outermost core state of the Rb ion (Rb-core exciton). The time-integrated intensity of Auger-free luminescence (AFL) due to the outermost core state of the Cs ion is increased by the laser irradiation. The lifetime of the laser-induced AFL depends on the photon energy of SR. The experimental result suggests the difference between the migration length of the Rb-core exciton and that of the Cs-core hole.

We have carried out nonlinear spectroscopy by making use of tunable VUV light from synchrotron radiation (SR) together with intense light from a laser. The valence excitons of BaF 2 with a large band gap of ∼11 eV were chosen as our target. A single crystal of BaF 2 was irradiated at 15 K by the two light pulses from the SR (6–9 eV) and an Nd : YAG laser (2.33 eV). Self-trapped exciton luminescence induced by two-photon excitation was detected with a time-gated photon-counting system developed for the present study. This zero-method technique is expected to be sensitive compared to early experiments by an Italian group monitoring transmittance changes. The obtained two-photon spectrum shows a distinct band below the band gap energy. This band includes two contributions, a two-step cascade process and a two-photon absorption process. The energy of the 2 P exciton is estimated to be 10.6 eV at 15 K.

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.

Energy-transfer and self-trapping processes of orthoexcitons and paraexcitons in alkali iodides are studied. Intensities of emission bands caused by Tl+ impurities and the self-trapped excitons are measured with varying temperature and excitation photon-energy. It is clarified that free excitons participating in the energy transfer to Tl+ in KI and RbI are mainly paraexcitons. The intensity of the σ band increases gradually with elevating temperature in KI. The increase of the intensity will be attributed to a thermally activated process over a potential barrier.

Luminescence of free excitons (FEs) and self-trapped excitons (STEs) in alkali iodide crystals are investigated under excitation in the n =1 exciton absorption region using a narrow-band UV laser. Experimental results support the identification that the prominent peaks of the FE luminescence spectra of KI and RbI are triplet emission and that of NaI is singlet emission. It is clarified that most singlet FEs in KI and RbI are scattered to the triplet state during the relaxation in the n =1 exciton band. The accumulation of FEs on the triplet state induces the decrease in the intensity of singlet STE luminescence. On the other hand, the scattering rate of the singlet FE to the triplet FE state in NaI is found to be small. The relation between scattering rate of FE and the magnitude of the exchange energy relative to the LO phonon energy is discussed.

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.

A new TAC-MCA detection system has been developed for combined laser–SR spectroscopy such as two-photon excitation or pump-probe experiments in the VUV region. In order to improve the signal to noise ratio, the time structure under partial-filling operation of UVSOR is utilized together with this detection system. In our experiment, where the two-photon excitation efficiency of laser and SR is more important than the time resolution, a pulse stretching technique using optical fiber is applied to the output pulse of a CW mode-locked Ti : sapphire laser. The usefulness of the present system is successfully demonstrated by observing luminescence signals from the two-photon-excited core state in BaF 2 crystals.

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.

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.

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 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.

We have conducted two-photon spectroscopy of core excitons in BaF2. Synchrotron radiation and laser light were used for 5p core-electron excitation and Auger-free luminescence was detected as the signal. Two-photon excitation enables access to f and p orbitals that cannot be reached by one-photon excitation of electrons in p orbitals. It has been found that the spin-orbit splittings of 4f and 6p states of the Ba ion in BaF2 are 0.7 +/- 0.1 and 1.4 +/- 0.1 eV, respectively.

A decay time of 1.2ns was observed ar 15K in resonant luminescence of the free exciton in RbI. It decreases with increasing temperature due to the enhancement of the self-trapping rate. Accumulation of free excitons in the triplet state through LO phonon scattering is discussed.

The valence electronic structures of the dental alloys, type 1, type 3, K14, and MC12 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 electronic states of the MC12 dental alloy 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 4d states. The peak shift and the change in shape due to alloying are observed in all the dental alloys. For the L-cysteine thin films, new peak or structure observed around 2 eV on all the dental alloys is suggested to be due to the bonding of S 3sp orbitals with the dental alloy surfaces. 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 type 1, type 3 and K14. For MC12, the interaction with L-cysteine may be dominantly due to the Pd-S, Cu-S, and Ag-O bonds, while the contribution of the Ag-S bond is small.

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...

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.

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.

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.