Norio Murase

Frequency dependence of quantum efficiency for hole formation in photochemical hole-burning for dye-doped polymer systems

Abstract Marked frequency dependence of the quantum efficiency for hole formation was observed at 4 and 20 K for photochemical hole-burning of free-base tetraphenylporphin (TPP) and sulfonated TPP in poly(vinyl alcohol) (PVA) and other polymers as well as non-photochemical hole-burning of methylene blue in PVA. The quantum efficiency of hole formation at the lower-frequency foot of the lowest-energy absorption band is about 10 times larger than that at the higher-frequency foot, which could be due to the existence of several vibronic states in the lowest-energy absorption band with different molar extinction coefficients, hole formation efficiencies, and/or Debye—Waller factors.

Theoretical study of the recording density limit of photochemical hole-burning memory

To clarify the potential of photochemical hole-burning memory systems, we study the theoretical recording-density limit of such systems. Shot noise and material noise are considered the principal noises. Material noise originates in fluctuations in the chromophore concentration. The recording-density limit proves to be proportional to (multiplicity)1/2 × (chromophore concentration)1/2 × (hole depth), approximately. It becomes clear that the recording spot diameter can be optimized to maximize the recording density. A molar extinction coefficient for a chromophore can be also optimized, and its value is ∼105 L/(mol cm) under the conditions of a 0.2 hole depth, 1000 multiplicity, and 10−2 mol/L choromophore concentration. When the readout time is 10 ns/bit and the signal-to-noise ratio is 20, in addition to the above conditions, the recording-density limit is calculated to be 26 Gbits/cm2. For this readout time the optimal recording spot diameter is ∼2 μm. When the readout time is less than ∼10 ns/bit, shot noise becomes the dominant noise; when the readout time is more than ∼50 ns/bit, the recording-density limit increases, and the influence of material noise becomes prominent.

Apparent and real values of photochemical hole-burning parameters. Sulfonated tetraphenylporphin doped in polyvinyl alcohol

This paper presents real values of photochemical hole‐burning (PHB) parameters for dye‐doped polymer systems. The cross section for purely electronic zero‐phonon absorption σ*0, quantum efficiency of hole formation η and full‐width at half‐maximum of inhomogeneous broadening Δωi are determined by the least‐squares fitting method. Our sample is sulfonated tetraphenylporphin doped in polyvinyl alcohol at 20 K. The determined values are σ*0 = (2.3 ± 0.2)× 10−15 cm2, η=(1.6±0.6)×10−2, and Δωi=(223±7) cm−1. The errors are of the order of a standard deviation. The η is much greater than previously reported values. The apparent quantum efficiencies of hole formation are derived under the assumption that the lowest‐energy absorption band consists of transitions of one type. They exhibit a marked wavelength dependence, but their values are well explained quantitatively by the real values. There is no need to consider any wavelength dependence of σ*0 and η, at least at the initial stage of burning. The purely elect...

Mechanism of laser-induced hole filling in photochemical hole burning

Abstract A convincing mechanism of laser-induced hole filling (LIHF) in photochemical hole burning is presented. Extents of LIHF were precisely measured as a function of energy difference from the newly burned wavelength, of burning power, and of an originally burned hole depth. The sample measured is sulfonated tetraphenylporphin doped in poly(vinyl alcohol). Dyes doped into amorphous hosts can be excited non-site-selectively through other types of transitions than the purely electronic zero-phonon transition. The main mechanism of LIHF is found to be these non-site-selective excitations and reactions, which lead to smaller decrease in absorbance in the previously burned frequency region compared with the region that was not previously burned.

Quantitative analysis of wavelength and temperature dependence of laser-induced hole filling in photochemical hole-burning

Abstract This paper quantitatively analyzes laser-induced hole filling(LIHF)and discusses the site-selectivity in photochemical hole-burning (PHB). The dye is sulfonated tetraphenylporphin (TPPS) and the amorphous material is poly (vinyl alcohol) (PVA). Experimental temperatures are 4.2, 15, and 20 K. The observed LIHF data obtained at wavelengths shorter than the wavelength of a newly-burned hole closely follow the results calculated using the density of states derived from the following cage model: in PVA, the TPPS is confined to a square well potential ≈ 0.40 A long, over which its energy is thermally distributed. Site-selective excitation in PHB involves the excitation from the bottom level of this well. A monochromatic laser excites the dye both site-selectively and non-site-selectively owing to the thermal excitation at temperatures above absolute zero. The non-site-selective excitation leads to a smaller decrease in absorbance in the region of previously-burned wavelengths compared with unburned regions, resulting in the formation of LIHF.

RELATIONSHIP BETWEEN MOLECULAR STRUCTURE OF A DOPED DYE AND THE EXTENT OF LASER-INDUCED HOLE FILLING IN PHOTOCHEMICAL HOLE-BURNING

This paper reports that the extent of laser-induced hole filling (LIHF) in photochemical hole burning (PHB) is related to the molecular structure of a doped dye. We measured the extent of LIHF for disodium mesoporphyrin (MPS) doped into poly(vinyl alcohol) (PVA) at 20 K, and found it to be smaller than for sulfonated tetraphenylporphine (TPPS) doped into PVA at 20 K. The MPS molecule is flatter, lighter, and more rigid than the TPPS molecule. These features decrease the number of energy levels in the ground state S0 and in the electronically excited state S1 of the dye, resulting in an increase in the site-selectivity in PHB. This causes the smaller extent of LIHF for the MPS system.

Excitation Processes of a Dye Doped into an Amorphous Material Investigated by Photochemical Hole-Burning

This paper discusses the excitation processes of a dye doped into an amorphous material as studied by using the photochemical hole-burning (PHB) technique. Our system is sulfonated tetraphenylporphin doped into poly(vinyl alcohol). The observed data were the extents of laser-induced hole filling (LIHF) in PHB at 20 K for wavelengths longer than the wavelength of the newly burned hole. Quantitative analysis using the least-squares method showed that the measured extents of LIHF can be explained by system parameters expressing non-site-selective excitations: the Debye-Waller factor, the energy of lattice vibrational excitation accompanied by the purely electronic excitation, and other parameters related to two kinds of vibronic excitations.

Thermal Excitation of Dyes Doped in Amorphous Material Investigated by Laser-Induced Hole Filling in Photochemical Hole-Burning

This letter reports the detection of thermal excitation of dyes doped in an amorphous material by photochemical hole-burning. Our sample is sulfonated tetraphenylporphin (TPPS) doped in poly (vinyl alcohol) (PVA) at 4.2 K, 15 K and 20 K. We measured the extent of laser-induced hole filling (LIHF) for holes, using the irradiation of longer-wavelength light as a function of wavelength difference between the filled holes and irradiation light. Our results for wavelength difference and temperature dependence of the extent of LIHF can be explained by a cage model: the TPPS dye in PVA is confined to a rigid square well potential ≈0.40 A long. The energy of the TPPS in the electronic ground state is thermally distributed in the well. The validity of the cage model and the possibilities of more appropriate models are also discussed.

Non-Site-Selective Excitation of a Doped Dye and Laser-Induced Hole Filling in Photochemical Hole-Burning

Abstract The mechanism of laser-induced hole filling (LIHF) in photochemical hole-burning is discussed qualitatively and quantitatively based on non-site-selective excitation of a doped dye. The dye molecules used were sulfonated tetraphenylporphine and disodium mesoporphyrin, both embedded in poly(vinyl alcohol). Experimental temperatures were in the range 4–20 K. The extent of LIHF at wavelengths shorter than the wavelength of a newly irradiating laser has a monotonically decreasing dependence on the increase in wavelength difference and reflects the degree of thermal excitation in the S0 state. On the other hand, the wavelength dependence of the extent of LIHF at wavelengths longer than the wavelength of a newly irradiating laser exhibits two peaks, reflecting the energy levels in the S1 state. It also depends on the experimental temperature. Besides these dependences, the extent of LIHF also depends on the molecular structure of the doped dye.

Photochemical hole-burning in fluorine-containing polymers

Abstract This paper reports photochemical hole-burning (PHB) properties at 20 K in three kinds of host matrices of fluorine-containing polymers (two of which exhibit ferroelectricity). The guest dye molecule is tetra-(pentafluorophenyl)porphin, which easily disperses molecularly in the polymers. The quantum efficiency of hole formation at the absorption peak wavelength is 2 X 10 -4 at most. Hole widths are ∼ 1.6 cm -1 at 20 K. Frequencies of the low-energy excitation mode, E s , are in the range of 10–13 cm -1 . The electric field (∼ 50 kV/cm) does not affect any of the PHB properties, such as thermal durability, E s , or hole width, for a ferroelectric polymer system, within our experimental resolution (0.7 cm -1 ). This suggests that the guest molecules are confined to amorphous domains in the polymer, which are known to occupy ∼20% of the polymer volume and to exhibit no ferroelectricity.