Atusi Kurita

Room-temperature persistent spectral hole burning in Sm 2+ -doped fluoride glasses

Persistent spectral hole burning is observed in Sm(2+)-doped glasses at room temperature. The holes are burned in the (7)F(0) ? (5)D(0), (5)D(1) lines of the Sm(2+) ions in three kinds of fluoride glass. The dependence of the burning efficiency on the sample and on the burning intensity is measured. The intensity dependence is approximately linear, and no antihole is observed around the burned hole. The hole-burning mechanism is discussed. The temperature dependence of the homogeneous width is also measured.

Optical properties of Sm-doped ZnS nanocrystals

In order to understand the spectral characteristics of ZnS: Sm nanocrystals, in which a novel optical memory effect has been observed, optical properties have been studied between 2 and 300 K for the samples prepared by a solution method. The broad fluorescence and excitation bands observed in the visible region are tentatively assigned to the transitions between the 4f 6 and 4f 5 5d states of Sm 2 + and also to the transitions of excitons bound to Sm 2+ . Temperature dependence of the intensity of the lowest-energy emission band and the dependence of its peak position on the excitation wavelength have been explained well by these assignments.

High temperature persistent spectral hole burning of Sm2+ in fluorohafnate glasses

Abstract Persistent spectral hole burning of Sm2+ in a fluorohafnate glass was observed. The hole was burned even at 180 K. In this system, the photochemical process is likely to be dominant because of the absence of an anti-hole adjacent to the hole.

Real-time observation of conformational fluctuations in Zn-substituted myoglobin by time-resolved transient hole-burning spectroscopy.

Equilibrium fluctuations of the protein conformation have been studied in myoglobin by a novel method of time-resolved transient hole-burning spectroscopy over a temperature range of 180-300 K and a time range of 10 ns to 10 ms. The temporal shift of the hole spectrum has been observed in a wide temperature region of 200-300 K. It has been found that the time behavior of the peak position of the hole is highly nonexponential and can be expressed by a stretched exponential function with a beta value of 0.22. As compared with the results for a dye solution sample, the time scale of the fluctuation of the protein conformation is much more weakly dependent on temperature. The time scale of the observed conformational dynamics shows a temperature dependence similar to that associated with the ligand escape process of myoglobin.

Non-photochemical hole-burning in Zn-substituted myoglobin

Abstract Persistent holes were burned in the inhomogeneously broadened 595 nm absorption band of Zn-substituted myoglobin (ZnMb) at 2 K. A prominent laser-induced hole-filling effect was observed, which suggests that the burning mechanism is non-photochemical. Zn-substituted protoporphyrin IX and the surrounding polypeptide chain in this material are considered to correspond to a localized center and a glassy host in ordinary hole-burning materials. The phonon sideband hole showed a maximum around 25 cm-1 from the zero-phonon hole, and the shape of the sideband was almost the same for the freeze-dried ZnMb and for ZnMb dissolved in a glycerol-water (3:1) mixture. This result indicates that the phonon sideband represents the low frequency vibrational modes in the protein molecule. The time evolution of the hole depth during the burning process was found to obey a logarithmic law, which can be explained by assuming a large dispersion of the burning rate. The distribution of the conformational barriers between nearly-degenerate ground states was also determined by using a heat cycle method. The distribution obtained obeys a power law which has no characteristic value of energy. All of the above results suggest the glass-like character of protein molecules.

Structural relaxations in H2‐substituted myoglobin observed by temperature‐cycling hole burning

A spectral hole‐burning experiment has been carried out on H2‐protoporphyrin‐substituted myoglobin by cycling temperature from 4 K up to 70 K. When the excursion temperature Tc is below 30 K, the spectral diffusion kernel (SDK) has been found to show a Lorentzian shape. A steep increase in the hole width has been observed around 20 K, which is attributed to a narrow distribution of the barrier height of two‐level systems (TLS’s) in myoglobin. When Tc is raised to ∼50 K, on the other hand, the major broadening has occurred in the tail of the hole, and the SDK has deviated significantly from a Lorentzian line shape. The hole profiles after the temperature cycling have been analyzed by the stochastic model which assumes that the spectral diffusion is induced by random flips of TLS’s. Both the non‐Lorentzian SDK for Tc around 50 K and the Lorentzian SDK around 20 K have been found to be reproduced well by this model, if the finite size of the protein is taken into account. The details of the fitting procedure...

5D0-7F0 TRANSITION MECHANISM OF EU3+ IN CA(PO3)2 GLASS, Y2O2S CRYSTAL AND POLYVINYL ALCOHOL

Abstract Luminescence properties have been studied for the Eu3+ ion in glass, crystal powder and a polymer film under monochromatic laser-light excitation. In the case of Eu3+ in Ca(PO3)2 glass, it has been found that the transition strength of the site-selected 5D0-7F0 line is proportional to the square of the second-order crystal-field parameter B20. This suggests that the 5D0−7F0 transition in this material is partially allowed by the crystal-field mixing of the MJ = 0 component of the 7F2 manifold into 7F0. The analysis of the intensity ratio between the 5D0−7F0 and the 5D0− 7F2 lines gives support to this interpretation. For Y2O2S:Eu3+, on the other hand, a fluorescence measurement under hydrostatic pressure has revealed that the transition probability of the 5D0−7F0 line is rather insensitive to the value of B20. The same result has also been obtained for Eu3+-doped polyvinyl alcohol from a fluorescence line-narrowing experiment. Therefore, it is concluded that there exist at least two kinds of mechanisms in the 5D0−7F0 transition of Eu3+. Probable mechanisms are discussed.

Optical Memory Effect by Interference of Multiple-Scattered Light in a Fluorescent Fulgide Derivative

Abstract We report an observation of a new wavelength- and angle-selective optical memory effect caused by interference of multiple-scattered light in polystyrene powder doped with a fluorescent fulgide derivative. This effect is applicable to three-dimensional optical data storage.

Glass transition of deoxymyoglobin probed by optical absorption spectroscopy

We have measured the absorption spectrum of horse deoxymyoglobin in glycerol-water mixture around 430 nm in the 130 - 320 K temperature range. The observed asymmetric spectral shape of the Soret band was analyzed using a configuration-coordinate model. The results support the idea that myoglobin is liquid-like at physiological temperatures, but is glass-like below about 250 K. The equilibrium position of the iron atom in the heme group in the electronic excited state was estimated from the determined parameter values.

Wavelength- and angle-selective properties of optical memory effect by interference of multiple-scattered light in Sm-doped ZnS nanocrystals

Abstract Our recent experiments have shown that both the wavelength and the angle of incident light are memorized in Sm-doped ZnS nanocrystals by photobleaching coupled with interference of the multiple-scattered light. We have measured the angle-selective properties by scanning the incident angle, as well as the wavelength-selective properties, and we discuss the density of data storage that can be derived from this effect.