Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
1999-06-30
2002-01-08
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064400, C428S147000, C428S148000, C428S690000, C428S913000, C430S495100, C430S945000
Reexamination Certificate
active
06337117
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical memory device, and more particularly, to an optical memory device operating according to a Time-Dependent Luminescence and Memory (TDLM) phenomenon which is actually a combination of two phenomena: a phenomenon that photoluminescence intensity is increased by exposure of the optical memory to excitation light; and another phenomenon that the photoluminescence intensity of the optical memory device before storage of the optical memory device is regained when the optical memory device is exposed to light after having been stored for a long period of time in a dark place without being exposed to light; namely, a retentive phenomenon.
Since the optical memory device can be subjected to rewriting and erasure a plurality of times, the optical memory device can be applied to fields such as information recording mediums, displays, image pick-up devices, image processing devices, retentive duplication, integration optical sensors, and multi-channel processors.
2. Description of the Related Art
Emission characteristics which do not change with time have been utilized for conventional light-emitting devices. The physical reason for such invariable characteristics is a very quick transition between energy levels.
The transition process is defined by Quantum mechanics and reflects interaction between carriers (electrons and holes) or excitons and photons. If the interaction (i.e., photo-(to-)electric or electric-(to-)photo conversion) is effected at very high speed within a considerably small space (on the order of atoms or molecules), luminous intensity also fluctuates at very high speed. Accordingly, in this case, the luminous intensity seems to remain unchanged on an ordinary time scale.
In most applications of light-emitting devices, from a practical viewpoint attention has conventionally been paid to materials other than nanoparticles(nano-size of particles); for example, a matrix (the continuous phase), such as polymers (Herron et al., and Buetje et al.), glass (Naoe et al.), and fluids, in which nanoparticles are embedded. Of these light-emitting devices, fluids are commonly used for measuring photoluminescence/spectrum of nanoparticles or visualization of color of the emitted light [see, for example, Dabbousi B. O., et al., J. Physic. Chem. 101, 9463 (1997)].
Light-emitting devices/mediums and optical processing devices/mediums, both using nanoparticles, are also disclosed. However, these employ light-emission characteristics which do not change with time. In all of these devices and mediums, nanoparticles (and their clusters) are spaced far apart from one another. Upon exposure to excitation light, each of the nanoparticles acts as a isolated single light-emitting substance. Such a structure of the light-emitting device is widely used for mediums such as light-emitting mediums or photoelectric materials (e.g., a photoelectric material disclosed by Herron et al.) used for producing an X-ray image.
High-density integration of nanoparticles, such as a nanoparticle film formed on a solid substrate or deposition of a nanoparticle layer, is of importance to application of nanoparticles to devices. A thin film of semiconductor nanoparticles is applied to a light-emitting diode (LED) (Alivisatos et al.), a photoelectric converting device [Greenham, N. C., et al., Phys. Rev. B, 54, 17628(1996)], an ultra high speed detector (Bhargave), an electroluminescence display and panel (Bhargave, Alivisatos et al.), a memory device of a nanostructure (Chen et al.) , and a multicolor device consisting of an arrangement of nanoparticles (Dushkin et al.) In most of these applications, nanoparticles are spaced in close proximity to one another within the thin film. Under certain conditions, nanoparticles exhibit a new photophysical property which is not observed in a single particle). The arrangement of particles [nanoparticle crystal (Murray et al.)] and the shift of the wavelength of emission (the red shift of the emission peak) of a patterned nanoparticle film (Dushkin et al.) are mentioned as examples of the photophysical property. The shift of the emission wavelength stems from long-distance resonance transportation of excitation among nanoparticles (kagan et al.).
However, for the functions of the devices and mediums the conventional art has not actively utilized the photophysical property that stems from the interaction among the particles. One conceivable reason for this is that the nanoparticle film does not have any definite (microscopic) structure and/or the structure is not uniform. Another conceivable reason is that basic interaction among the particles is cancelled by considerable interaction of electric fields (i.e., electroluminescence) (Alivisatos et al.).
The object of the present invention is to provide an optical memory device capable of increasing and storing luminous intensity.
SUMMARY OF THE INVENTION
To achieve the foregoing object, the present inventors actively utilized a collective function of a thin film for the first time, in which nanoparticles are arranged and integrated at high density. The collective function corresponds to the foregoing TDLM function of the nanoparticle film. By means of active utilization of such a function, formation of an image on the nanoparticle film can be achieved by utilization of an intensity ratio (contrast) between an exposed region and an unexposed region. The subject of the present invention is a unique photophysical property of a group of nanoparticles spatially arranged. This photophysical property differs from the physical properties of atoms and molecules, the physical properties of bulks, and the physical property of a single nanoparticle. The luminous intensity becomes greater by several orders of magnitude with time (typically with lapse of tens of minutes). At present, definite physical grounds for the process of shift in the arrangement of nanoparticles over a very long period of time still remain uncertain. Image pick-up and processing operations are examples of evident application of the foregoing phenomenon.
There will be given an explanation of a difference between the conventional technology and the TDLM phenomenon applied to the present invention.
All the conventional applications are directed toward generation of photons through recombination of carriers; namely, generation of carriers (electrons and holes) through interaction between photons and an external electric field, or vice versa. In contrast, the present invention employs the TDLM phenomenon, which is similar to optical pumping used for oscillating a laser (Sze, S. M., “Physics of Semiconductor Devices,” Wiley, N.Y., 1981). The TDLM phenomenon corresponds to photo-to-photo conversion by means of generation and transportation of excitons or electron-hole pairs. Generation and transportation of electron-hole pairs is observed in a photo-refractive device/medium such as an electro-optical crystal (Valley et al.) or a polymer (Sutter et al.). A photo-refractive device/medium records an image on the basis of the principle that carriers (electrons and holes) are spatially separated by exposure of the photo-refractive device/medium to spatially-periodic photo and an external field, which involves a change in refraction factor. This principle is generally called dynamic holography (Peyghambarian et al., Nature, vol. 383, Oct. 10, 1996, pg. 481). Transportation of excitons or carriers in the TDLM phenomenon leads to emission of light of different wavelengths (i.e., colors) from an image and differs from the photo-refractive phenomenon.
A hole-burning effect (Naoe et al.) observed in a semiconductor nanocrystal differs from the TDLM phenomenon, as will be described below. The hole-burning effect is usually observed in a matrix (continuous phase); for example, glass, in which nanoparticles of a certain particle size distribution are dispersed in an isolated manner. Upon exposure to a monochrome laser beam (i.e., a laser having a single wavelength), o
Asami Harumi
Dushkin Ceco
Maenosono Shinya
Saita Soichiro
Yamaguchi Yukio
Evans Elizabeth
Mitsubishi Chemical Corporation
LandOfFree
Optical memory device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical memory device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical memory device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2839786