Shin-ichiro Tamura

A Blue Organic Light Emitting Diode

A blue organic light emitting diode (OLED) which has a structure like an SH-B type diode has been developed. The blue OLED consists of a hole-injection layer (m-MTDATA), a hole-transporting emissive layer, a hole-blocking layer and an electron-injection layer (Alq3) formed on an ITO anode by vacuum vapor deposition. α-NPD was used for the hole-transporting emissive layer, which has an emission peak at around 455 nm. For the hole-blocking layer, we found that 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (Bathocuproine) is a very effective material. As Bathocuproine has a good hole-blocking ability, the recombination area is in the α-NPD layer. The electroluminescence peak from the new blue OLED is at around 455 nm. The color coordinate in CIE chromaticity is (0.15, 0.16). The blue OLED has a potential of over 10,000 cd/m2 at 9.5 V under DC operation with an AlLi cathode. When this OLED is driven under a 1/100 duty ratio, the peak luminance is over 54,000 cd/m2. The luminous efficiency was 1.1 lm/W at 150 cd/m2. The blue OLED device is also a good green device without the Bathocuproine layer. The green OLED shows electroluminescence from the Alq3 layer with luminance of 40,000 cd/m2 at 10 V under DC operation, and the color coordinate in CIE chromaticity is (0.33, 0.55).

RGB luminescence from passive-matrix organic LED'S

We fabricated an 8/spl times/9 (3RGB) passive matrix of organic light-emitting diodes (OLEDs) and operated it at a video-rate to simulate NTSC signals. The color purity of red emission was improved by controlling the depth distribution of DCM in the Alq/sub 3/ layer. A newly synthesized binuclear metal complex compound was incorporated for blue emission and provided good chromaticity. We found that the rectification property of the OLED is important to drive a passive matrix and about 10/sup 5/ OLED pixels can be driven when aluminum is used as the cathode material.

Macrocyclic functional dyes: Applications to optical disk media, photochemical hole burning and non-linear optics

Our recent research activities on macrocyclic functional dyes such as phthalocyanines and porphyrins are reviewed. For optical data storage, we have established tetrabenzoporphme derivatives are suitable for shorter wavelength recording. we have proposed new photon-mode superresolution. The playback of double density EFM signals was achieved using a naphthalocyanine derivative. For future ultrahigh density optical recording, tetraphenylporphine derivatives are found to be a promising class of photochemical hole burning materials. The potential recording density is expected to be enhanced by two or three orders of magnitude compared to conventional optical-data storage. Fundamental computational research is going on to develop new materials with high nonlinear optical properties. We have predicted the hyperpolarizabilities of a series of metallo-porphyrins. These theoretical calculations enabled us to quantitatively design materials.

Light stability of a β-cyclodextrin inclusion complex of a cyanine dye

The stability to light of 1,3,3,1′,3′,3′-hexamethyl-2,2′-indotricarbocyanine iodide (HITC) included in β-cyclodextrin (β-CyDx) has been examined. The quantum yield of the photodegradation of HITC was found to decrease with increasing formation of the inclusion complex, showing that the photostability of the dye can be improved by the formation of the complex. Emission from singlet oxygen (1Δg→3Σ–g, 1268 nm and 1580 nm) for systems of HITC with or without β-CyDx in aqueous solution was also measured. It was found that the amount of singlet oxygen generated by flash irradiation is reduced by the inclusion complex formation, and that the lifetime of singlet oxygen increased with increasing concentration of β-CyDx, suggesting that the photodegradation of HITC for the system of HITC/β-CyDx is reduced by two factors; first, the inhibited formation of singlet oxygen, and secondly, the inhibited attack of singlet oxygen on the dye.

Focusing Effects of Surface Acoustic Waves in Crystalline Solids

Focusing of surface acoustic waves (SAW) due to elastic anisotropy of substrate crystals is investigated theoretically. For propagation on the (001) plane of GaAs, we find strong focusing effects of the SAW along certain directions. We also find that the number of independent pure-mode axes lying in the focusing directions is just one on the (001) surface.

Transmission of sub-THz acoustic phonons in a Kronig-Penny system for phonons

Based on the transfer matrix method, we study the transmission characteristics of sub-THz acoustic phonons in multiple barrier systems for phonons consisting of alternate stacking of bulk layers and periodic superlattices. Specifically, we consider a frequency window within a frequency gap of the periodic superlattice and examine the behavior of phonon transmission as the number of the barriers increases. The systems we consider are analogous to the Kronig-Penny potential structure for electrons.

Multiple Photochemical Hole Burning of Tetraphenylporphine Derivatives

We have studied multiple photochemical hole burning of tetraphenylporphine derivatives in the frequency domain. More than 100 holes were produced in an inhomogeneously broadened absorption band at liquid helium temperature. High resolution monitoring of photochemical holes by scanning the wavelength of a single-mode dye laser proves that the potential area density of recording reaches up to 1000 holes/laser spot. We also carried out multiple photochemical hole burning in a focused laser spot, and produced more than 10 holes. These experiments indicate that tetraphenylporphine derivatives are suitable materials in practical applications of photochemical hole burning.

Multiple-Barrier Systems for Phonons: Transmission Characteristics

Transmission characteristics of acoustic phonons in multiple-barrier systems are theoretically studied. These systems consist of an alternate stacking of bulk layers and periodic superlattices. The phonon transmission rates are derived analytically based on the transfer matrix method. We consider phonons within a frequency gap of the superlattices and find the resonant transmission of these phonons. The systems considered is analogous to the Kronig-Penny potential structure for electrons.

Multiple Photochemical Hole Burning in Tetraphenylporphine Derivatives Using a Focused Laser Beam

The recording properties of photochemical hole burning (PHB) in tetraphenylporphine (TPP) derivatives with a focused laser beam were studied. We demonstrated the possibility of more than 200-multiplicity recording in the frequency domain in tetrakis(pentafluorophenyl)porphine (TFP) in a 10-µm-diameter laser spot at 4 K. The effect of the laser irradiation time on the depth was also investigated using tetrakis(4-methoxyphenyl)porphine (TMP). Although the hole depth decreased with decreasing laser irradiation time down to the ms order due to the bottleneck effect (because of long triplet lifetime), a detectable hole is formed with irradiation by a 8 ms pulse using TMP.

Optical Recording Characteristics of Dye/Polymer Systems

The influence of the molten polymer properties on the optical recording sensitivity was examined for cyanine dye/polymer systems. We obtained a linear relationship between the recording sensitivity and the surface entropy of the binder polymers and found that the non-Newtonian flow induced by the surface entropy is responsible for pit formation by laser marking.