EP1803123A1 - Photosensitive material - Google Patents

Photosensitive material

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Publication number
EP1803123A1
EP1803123A1 EP05798561A EP05798561A EP1803123A1 EP 1803123 A1 EP1803123 A1 EP 1803123A1 EP 05798561 A EP05798561 A EP 05798561A EP 05798561 A EP05798561 A EP 05798561A EP 1803123 A1 EP1803123 A1 EP 1803123A1
Authority
EP
European Patent Office
Prior art keywords
photosensitive material
shell portion
core portion
group
organic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05798561A
Other languages
German (de)
French (fr)
Inventor
Evgeny Kapinus
Marion Meir
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Matteris Ltd
Original Assignee
Matteris Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Matteris Ltd filed Critical Matteris Ltd
Publication of EP1803123A1 publication Critical patent/EP1803123A1/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers
    • G11B7/257—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of layers having properties involved in recording or reproduction, e.g. optical interference layers or sensitising layers or dielectric layers, which are protecting the recording layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/2403—Layers; Shape, structure or physical properties thereof
    • G11B7/24035—Recording layers
    • G11B7/24044—Recording layers for storing optical interference patterns, e.g. holograms; for storing data in three dimensions, e.g. volume storage
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/251—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials dispersed in an organic matrix
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24302—Metals or metalloids
    • G11B2007/24312—Metals or metalloids group 14 elements (e.g. Si, Ge, Sn)
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24302—Metals or metalloids
    • G11B2007/24314—Metals or metalloids group 15 elements (e.g. Sb, Bi)
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24302—Metals or metalloids
    • G11B2007/24316—Metals or metalloids group 16 elements (i.e. chalcogenides, Se, Te)
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0045—Recording
    • G11B7/00454—Recording involving phase-change effects
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0065—Recording, reproducing or erasing by using optical interference patterns, e.g. holograms
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/244—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only
    • G11B7/245—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing a polymeric component
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers
    • G11B7/253—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of substrates
    • G11B7/2531—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of substrates comprising glass

Definitions

  • This invention relates to materials for manufacturing of write-once-read many (WORM) recording media suitable for holographic data recording and storage.
  • the invention can be used for manufacturing of recording media including, but not limiting to CD write-once (CDR), DVD write-once (DVDR) discs, cards and tapes.
  • CD write-once (CDR) CD write-once
  • DVD write-once (DVDR) discs cards and tapes.
  • the invention can be used not only in holographic data recording and storage but also in other applications, like producing of holograms, sculpturing of artistic works, sculpturing of industrial articles, etc. Description of the prior art
  • Materials for writing permanent volume holograms generally involve irreversible photochemical or photo thermal reactions within a photo recording material.
  • the bright regions of the optical interference pattern trigger these reactions. Since these reactions are accompanied by change of refraction index the relevant recording materials are known in the art as photo refractive materials.
  • the material of the invention in its different embodiments will be referred-to as photo refractive material.
  • recording mediums employing photo refractive materials on ⁇ can mention for example holographic data memory described in US 2003/0161018. This memory has a polymer film, which is set up as a storage layer whose refractive index can be changed locally by heating.
  • Materials containing inorganic particles dispersed in a transparent media are of great interest for recoding because these materials show very high photochemical stability, very small shrinkage after recording and they do not need any treatment after recording since those areas of the media, which were not exposed to the recording radiation are not sensitive to light.
  • JP61053090 optical disc provided with recording layer that contains pulverous semiconductor particles of Ge, Te and InSb dispersed uniformly within bulk of chemically stable dielectric mate r ial.
  • the materials containing inorganic particles show excellent durability, they enable recording and erasing over a long period of time and enable obtaining a high signal level. Recording in these materials occurs due to the transition between a crystalline phase and an amorphous phase that is peculiar to dielectrics or due to the dissociation of nanoparticles as in the case of Gold particles dispersed in polymers under heating by a laser pulse.
  • the main object of the present invention is to provide a new and improved photo refractive material for manufacturing of recording media.
  • Another object of the invention is provide a new and improved photo refractive material and recording media, which is capable to record information upon pulse laser irradiation, while the photo refractive material contains nanoparticles of chalcogenide containing compounds dispersed within a matrix consisting of organic polymers or within a matrix consisting of inorganic glassy materials.
  • the further object of the invention is to provide a new and improved material and recording media, which is defined by the following properties:
  • Still further object of the invention is to provide a new photo refractive material employing nanoparticles, which exhibit fast and irreversible transformation from amorphous or metastable crystalline state to a stable crystalline state upon exposure to pulsed laser radiation with energy ⁇ 3 mJ/mm and duration of the pulse from 1 up to 50 ns.
  • Yet another object of the invention is to provide a new and improved photo refractive material employing nanoparticles, distributed within a hosting matrix, while the particles are defined by a core portion, which substantially remains in a stable crystalline state during recording and by a shell portion, which covers the core portion and which is substantially either in an amorphous or in a metastable crystalline state, wherein this shell portion is capable to undergo irreversible transformation into stable crystalline state upon exposure to pulsed laser radiation.
  • the present invention can be implemented in its various embodiments, which comprise the photo refractive material as such, method of preparation of the photo refractive material and various recording media manufactured from the new photo refractive material. This media comprises but is not limited to optical CD and DVD disks including multilayer disks.
  • Fig. Ia shows schematically the structure of the photo refractive material of the present invention.
  • Fig. Ib shows enlarged shell layer Of Bi 2 S 3 formed on core portion consisting Of Sb 2 S 3 .
  • the shell layer has the same structure as the initial core portion and it is obtained by substitution of Sb 3+ ions by Bi 3+ ions.
  • Fig. Ic shows schematically shell layer Of Bi 2 S 3 formed upon laser pulse irradiation of a core portion consisting of mixed sulfide Bi 2 S 3 / Sb 2 S 3 .
  • Fig. 2 is an example of threshold dependence of diffraction efficiency on recording energy for nanoparticles consisting of Sb 2 S 3 core portion covered by Bi 2 S 3 shell portion.
  • Concentration of the particles in polyvinyl alcohol is 3.75x10 "3 M.
  • Fig. 3 shows how diffraction efficiency depends on concentration of nanoparticles composed of core portion consisting of sulfide of antimony and shell portion consisting of sulfide of bismuth.
  • a photo refractive material 10 of the invention which comprises a polymeric or inorganic glasslike matrix 12 and nanoparticles 14, distributed within the bulk of the matrix.
  • the nanoparticles absorb recording pulsed laser radiation and upon heating undergo phase transition accompanied by change of their structure, which, in its turn, results in essential change in refraction index.
  • Temperature of nanoparticle increases with increasing of the laser pulse energy and with decreasing of the laser pulse duration.
  • the phase transition occurs when temperature of nanoparticle is equal or exceeds the temperature of the phase transition.
  • Temperature of nanoparticles depends on the heating rate, which is inversely proportional to the laser pulse duration and to the heat diffusion rate.
  • temperature of nanoparticles decreases due to some other processes like dissociation of nanoparticles and of the surrounding matrix. These processes are associated with absorption of energy and loss of heat and therefore with retardation of the phase transition.
  • the phase transition induced by the pulse laser radiation is associated with producing of heat assisting to maintain the phase transition in spite of the above mentioned heat losses. Since this heat partially compensates for the heat losses the photo refractive material has improved holographic sensitivity, because it requires less energy to initiate and sustain the phase transition.
  • the structural change namely the transition from metastable crystalline phase into stable crystalline phase or the transition from amorphous phase into stable crystalline phase. Both structural changes are employed in the photo refractive material of the present invention.
  • the nanoparticles can be synthesized in such a manner that they are defined by a crystalline nucleous, which is covered by a non ⁇ crystalline amorphous or metastable shell.
  • the nucleous is referred to as core portion and the shell as shell portion.
  • FIG. Ib An example of the shell portion is schematically depicted in Fig. Ib, which shows very enlarged outer layer (shell portion) obtained on a nucleus (core portion) consisting of Sb 2 S 3 .
  • the shell portion is comprised Of Bi 2 S 3 that is obtained by partial substitution of Sb 3+ ions by Bi 3+ in Sb 2 S 3 .
  • Fig. Ic demonstrates the stable structure Of Bi 2 S 3 formed upon laser pulse radiation of Sb 2 S 3 /Bi 2 S 3 mixed sulfide.
  • diameter of the nanoparticles varies from 5 to 50 nm.
  • the thickness of the shell portion lies between 10 and 30 % of the nanoparticle diameter.
  • the concentration of the nanoparticles in the polymer matrix lies between 5xlO '3 and 5xlO '2 M being preferably 1x10 "2 M.
  • the nanoparticles are substantially homogeneously distributed within the matrix and center-to-center distance between adjacent particles lies between 20 and 100 nm.
  • the nanoparticles have round shape or slightly elliptical shape.
  • either the core portion or the shell portion consists of a compound, which is capable to produce heat upon exposure to pulsed laser radiation and to undergo phase transformation.
  • a compound which is capable to produce heat upon exposure to pulsed laser radiation and to undergo phase transformation.
  • Such compounds are for example chalcogene- containing compounds.
  • the particular chemical composition of the core portion and the shell portion usually is dissimilar, but might be also identical.
  • the structure of the shell portion is similar to the structure of the core portion. Under laser heating the metastable crystalline phase and amorphous phase changes its structure and refraction index. This change is accompanied by producing of heat and therefore the nanoparticles temperature depends less on the heating rate and the rate of heat diffusion.
  • the photo refractive material of the invention exhibits threshold properties, namely recording occurs when the energy of the laser pulse exceeds some value. Due to the heat, which accompanies the phase transition, this threshold value is significantly lowered. It can be readily appreciated that by virtue of this provision lasers with less power would be required for recording. On the other hand, light beams with smaller energy could be used for reading of the recorded information, which means that photo refractive material of the invention would be not sensitive to prolonged exposure to daylight and therefore the media manufactured from this material would not need any treatment after recording. Concentration of nanoparticles within the matrix, their chemical composition and size are chosen to obtain recording medium with the necessary resolution, the highest number of pages in the hologram, and with the high photosensitivity.
  • the nanoparticles are composed from chemical compounds, which produce heat upon pulsed laser irradiation. It has been found that it is especially advantageous for this purpose if the nanoparticles are composed of sulfides, selenides or tellurides as well of chemical compounds containing two or more metallic chalcogene, e.g. sulfur and selenium, sulfur and tellurium, selenium and tellurium. It should be born in mind, however, that the nanoparticles could be composed also from other compounds if these compounds are capable to produce heat upon laser irradiation and undergo phase transformation from metastable form to stable crystalline form accompanied by the change of refraction index.
  • the nanoparticles may contain the core portion comprised of azides, like Cu(N 3 ) 2 or Cd(N 3 ) 2 covered by the shell portion composed of sulfide. Under laser heating the azide decomposes while producing energy that maintains phase transformation of sulfide in the shell portion.
  • the nanoparticles with required chemical composition are produced by virtue of chemical reaction between soluble salts of transition or non-transition metals and chalcogene containing compounds, i.e. compounds containing sulfur, selenium and tellurium. This reaction is carried out in a solution containing a stabilizer, polymer or a hardening compound. The reaction can be conducted at ambient temperature, however it is advantageous if this reaction is conducted at elevated temperature.
  • photorefractive materials of the invention can be used for holographic data recording and storage. It has been found that photo refractive materials of the invention exhibit very small shrinkage, which is about 0.01%. This can be explained by the fact that the phase transition cannot essentially change the small size of nanoparticles in the matrix.
  • suitable chalcogene containing compounds comprises hydrides of sulfur, selenium, and tellurium, soluble sulfides of alkaline metals, selenosulfites, tellurides etc.
  • the chemical reaction can be conducted in the presence of stabilizers like sodium polyphosphate, trioctyl phosphine oxide or mercaptoacetic acid, which prevent the produced nanoparticles from aggregation during precipitation.
  • Polymers like polyvinyl alcohol or gelatin can also be used as stabilizers.
  • the chemical reaction can be conducted in such a manner that the produced nanoparticles consist of compounds containing a single chalcogene element or more than one chalcogene element. This is achieved by precipitation or by substitution reactions.
  • a source of sulfur, selenium or tellurium is added to the solution containing salts of two or more metals.
  • An example of _ • ⁇ itable reaction can be . interaction of sodium sulfide with acidic solution of bismuth and antimony chlorides.
  • ions capable to form insoluble chalcogene containing compounds on the surface of the core portion are added to dispersion of nanoparticles in water and in the presence of a stabilizer.
  • This reaction results in the nanoparticles having the core portion and the shell portion, which differ in chemical composition.
  • bismuth chloride is added to dispersion of Sb 2 S 3 nanoparticles, bismuth replaces antimony in the surface layer of the partciles and mixed sulfide is formed.
  • the core portion of the nanoparticles is composed Of Sb 2 S 3 and the shell portion is composed Of Bi 2 S 3 .
  • solid holographic films can be produced by evaporation of the solvent from the dispersion with nanoparticles distributed within a vehicle, which is a polymer or a polymerizable compound.
  • a vehicle which is a polymer or a polymerizable compound.
  • the solid film is hardened photochemically or thermally. Hardening of polymerizable compound can be carried out with the aim of a photoinitiator upon irradiation by the UV light or by visible light or with the aim of a proper thermoinitiator.
  • Non-limiting list of polymers suitable for manufacturing of the present photo refractive material and the holographic media of the invention comprises acrylic and vinyl polymers, alkyd, coumarone-indene, epoxy and phenolic resins, fluoropolymers, aminoplasts, polyacetals, polyacrylics, polyalkylenes, polyalkenyles, polyalkynyles, polyamicacids, polyamides, polyanhydrides, polyarylenealkenyles, polyarylenealkylenes, polyarylenes, polyazomethynes, polybenzimidazoles, polybenzothiazoles, polybenzoxazinones, polybenzoxazoles, polybenzyls, polycarbodiimides, polycarbonates, polycarboranes, polycarbosilanes, polycyaurates, polydienes, polyesters, polyurethanes, polyethereketones, polyethers, polyuretanes, polyhydrazides, polyimidazoles, polyimides, poly
  • Non-limiting limiting list of suitable polymerizable compounds comprises acrylates, metacrylates or epoxides.
  • suitable commercially available products are polyether or polyester urethane acrylates like BR-200, BR- 300, BR- 400 manufactured by Aldrich Inc. or bifunctional polyester or polyether urethane acrylates or metacrylates manufactured by Bomar Specialties Inc
  • plasticizers can be introduced in the photo refractive material.
  • suitable plasticizers comprises alkyl phthalates, phosphates, adipates and sebacates, polyethers, epoxides, etc.
  • suitable substrate one can use transparent inorganic glasses, polycarbonate, polymethylmethacrylate, polymethylacrylate, and polystyrene etc. The non-limiting examples below illustrate preparation of the photo refractive material of the present invention.
  • Example 1 illustrate preparation of the photo refractive material of the present invention.
  • Fig.2 is shown dependence of diffraction effrciency ⁇ of the holograms on the energy of laser pulse.
  • Diffraction efficiency is the ratio of the power in the diffracted beam to the power in the incident beam. It is clearly seen that this dependence has a threshold, i.e. the recording is achieved after the laser pulse energy reaches certain minimum value and this efficiency increases until some maximum value.
  • maximum value of diffraction efficiency ⁇ can range up to 80%.
  • the maximum value of diffraction efficiency corresponds to change of the refraction index by about 0.005.
  • M- number M#
  • d thickness of photosensitive layer
  • ⁇ angle between reference and object beams ⁇ - wavelength of recording light ⁇ , - diffraction efficiency of each hologram.
  • the photo sensitivity S was calculated according to the following formula:
  • Photosensitivity of the present photo refractive materials is not worse than photosensitivity of the known in the art photo polymerizable materials.
  • photo refractive material developed by Aprilis Ventrures demonstrates photosensitivity between 2.5 and 4.5 cm/mJ.
  • the present photo refractive materials have significant advantage over the known in the art materials since they do not shrink and have much shorter recording time.
  • Non-limiting Table 2 displays how photosensitivity of the present photo refractive material depends on the temperature of the synthesis.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Nanotechnology (AREA)
  • Physics & Mathematics (AREA)
  • Inorganic Chemistry (AREA)
  • Mathematical Physics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Dispersion Chemistry (AREA)
  • Composite Materials (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Biophysics (AREA)
  • Optics & Photonics (AREA)
  • Theoretical Computer Science (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Materials Engineering (AREA)
  • Holo Graphy (AREA)
  • Thermal Transfer Or Thermal Recording In General (AREA)
  • Optical Record Carriers And Manufacture Thereof (AREA)

Abstract

Photosensitive material for holographic recording and storage is disclosed. The material comprises a hosting matrix with distributed hosted discrete particles. The particles comprise a core portion and a shell portion surrounding the core portion, wherein the shell portion is capable to undergo a phase transformation from an amorphous or a metastable crystalline state to a stable crystalline state in response to laser beam irradiation. The phase transformation is accompanied by change of refractive index.

Description

PHOTOSENSITIVE MATERIAL
BACKGROUND OF THE INVENTION Field of the invention
This invention relates to materials for manufacturing of write-once-read many (WORM) recording media suitable for holographic data recording and storage. The invention can be used for manufacturing of recording media including, but not limiting to CD write-once (CDR), DVD write-once (DVDR) discs, cards and tapes. The invention can be used not only in holographic data recording and storage but also in other applications, like producing of holograms, sculpturing of artistic works, sculpturing of industrial articles, etc. Description of the prior art
Materials for writing permanent volume holograms generally involve irreversible photochemical or photo thermal reactions within a photo recording material. The bright regions of the optical interference pattern trigger these reactions. Since these reactions are accompanied by change of refraction index the relevant recording materials are known in the art as photo refractive materials. In the future disclosure the material of the invention in its different embodiments will be referred-to as photo refractive material. Among recording mediums employing photo refractive materials on<.; can mention for example holographic data memory described in US 2003/0161018. This memory has a polymer film, which is set up as a storage layer whose refractive index can be changed locally by heating.
Materials containing inorganic particles dispersed in a transparent media are of great interest for recoding because these materials show very high photochemical stability, very small shrinkage after recording and they do not need any treatment after recording since those areas of the media, which were not exposed to the recording radiation are not sensitive to light.
Recently materials based on inorganic particles dispersed in a transparent dielectric material like organic polymers, oxides B2O3, Sb2O3, Bi2O3, PbO etc. were proposed for holographic date storage. For example, in JP61053090 is described optical disc provided with recording layer that contains pulverous semiconductor particles of Ge, Te and InSb dispersed uniformly within bulk of chemically stable dielectric material. The materials containing inorganic particles show excellent durability, they enable recording and erasing over a long period of time and enable obtaining a high signal level. Recording in these materials occurs due to the transition between a crystalline phase and an amorphous phase that is peculiar to dielectrics or due to the dissociation of nanoparticles as in the case of Gold particles dispersed in polymers under heating by a laser pulse.
Materials for manufacturing of recording medium containing nanoparticles have particular advantage since these materials do not scatter light and this property is a precondition for the volume hologram recording. Properties of material provided with nanoparticles incorporated in a glassy matrix or in polymers also attract attention of researchers. These properties are discussed for example in the following publications: K.V.Yumashev, N.N.Posnov, I.A.Denisov, P.V.Prokoshin, V.P.Mikhailov, V.S.Gurin, V.B.Prokopenko, A.A.Alexeenko. Nonlinear optical properties of sol-gel-derived glasses doped with copper selenide nanoparticles. J.Opt.Soc.Am.B, 17, 572 (2000); F. M. Pavel and R. A. Mackay, Reverse Micellar Synthesis of a Nanoparticle/Polymer Composite, Langmuir, 16, 8568 (2000); S. W Lu, U. Sohling, M. . : Mennig and H. Schmidt, Nonlinear optical properties of lead sulfide nanocrystals in polymeric coatings, Nanotechnology 13, 669 (2002).
However, these publications are of purely scientific character and do not relate to the . . described materials as potential candidates for optical data storage in general, or for holographic data storage in particular.
Recently, it has been found that amorphous solid chalcogenide systems can undergo photoinduced crystallization. This phenomenon is discussed in the following publication K.Tanaka, Photoinduced structural changes in amorphous semiconductors, Physics and Technics of Semiconductors. 32, 964 (1998). It is also mentioned in the literature that thermal process can be utilized in phase-change based memories, see for example T.Ohta, N.Akahira, S.Ohara, l.Satoh. Optoelectronics, 10, 361 (1995)].
However, these publications deal with phase transformation, which is induced in bulk of a solid, continuous material and not within a photo refractive material consisting of discrete nanoparticles. SUMMARY OF THE INVENTION
The main object of the present invention is to provide a new and improved photo refractive material for manufacturing of recording media.
Another object of the invention is provide a new and improved photo refractive material and recording media, which is capable to record information upon pulse laser irradiation, while the photo refractive material contains nanoparticles of chalcogenide containing compounds dispersed within a matrix consisting of organic polymers or within a matrix consisting of inorganic glassy materials.
The further object of the invention is to provide a new and improved material and recording media, which is defined by the following properties:
- High photosensitivity;
- Threshold dependence of recording parameters like diffraction efficiency on the energy of recording light, while the threshold energy is low so as to provide high photosensitivity and fast recording; - Insensibility of the material to continuous light radiation;
- Long shelf life (>15 years) for the initial media for recorded information;
- Convenience and simplicity in material preparation;
- Very small shrinkage (< 0.01%) after recording.
Still further object of the invention is to provide a new photo refractive material employing nanoparticles, which exhibit fast and irreversible transformation from amorphous or metastable crystalline state to a stable crystalline state upon exposure to pulsed laser radiation with energy < 3 mJ/mm and duration of the pulse from 1 up to 50 ns. Yet another object of the invention is to provide a new and improved photo refractive material employing nanoparticles, distributed within a hosting matrix, while the particles are defined by a core portion, which substantially remains in a stable crystalline state during recording and by a shell portion, which covers the core portion and which is substantially either in an amorphous or in a metastable crystalline state, wherein this shell portion is capable to undergo irreversible transformation into stable crystalline state upon exposure to pulsed laser radiation. The present invention can be implemented in its various embodiments, which comprise the photo refractive material as such, method of preparation of the photo refractive material and various recording media manufactured from the new photo refractive material. This media comprises but is not limited to optical CD and DVD disks including multilayer disks.
The present invention has only been summarized briefly.
For better understanding of the present invention as well of its advantages, reference will now be made to the following description of its various embodiments with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. Ia shows schematically the structure of the photo refractive material of the present invention.
Fig. Ib shows enlarged shell layer Of Bi2S3 formed on core portion consisting Of Sb2S3.
The shell layer has the same structure as the initial core portion and it is obtained by substitution of Sb3+ ions by Bi3+ ions.
Fig. Ic shows schematically shell layer Of Bi2S3 formed upon laser pulse irradiation of a core portion consisting of mixed sulfide Bi2S3/ Sb2S3.
Fig. 2 is an example of threshold dependence of diffraction efficiency on recording energy for nanoparticles consisting of Sb2S3 core portion covered by Bi2S3 shell portion.
Concentration of the particles in polyvinyl alcohol is 3.75x10"3 M.
Fig. 3 shows how diffraction efficiency depends on concentration of nanoparticles composed of core portion consisting of sulfide of antimony and shell portion consisting of sulfide of bismuth.
DESCRIPTION OF THE PREFERED EMBODIMENTS Referring to Fig. I a it shown a photo refractive material 10 of the invention, which comprises a polymeric or inorganic glasslike matrix 12 and nanoparticles 14, distributed within the bulk of the matrix. The nanoparticles absorb recording pulsed laser radiation and upon heating undergo phase transition accompanied by change of their structure, which, in its turn, results in essential change in refraction index. Temperature of nanoparticle increases with increasing of the laser pulse energy and with decreasing of the laser pulse duration. The phase transition occurs when temperature of nanoparticle is equal or exceeds the temperature of the phase transition. Temperature of nanoparticles depends on the heating rate, which is inversely proportional to the laser pulse duration and to the heat diffusion rate. Besides, temperature of nanoparticles decreases due to some other processes like dissociation of nanoparticles and of the surrounding matrix. These processes are associated with absorption of energy and loss of heat and therefore with retardation of the phase transition.
It has been unexpectedly revealed that in the photo refractive material of the invention the phase transition induced by the pulse laser radiation is associated with producing of heat assisting to maintain the phase transition in spite of the above mentioned heat losses. Since this heat partially compensates for the heat losses the photo refractive material has improved holographic sensitivity, because it requires less energy to initiate and sustain the phase transition. There are two principal types of the structural change, namely the transition from metastable crystalline phase into stable crystalline phase or the transition from amorphous phase into stable crystalline phase. Both structural changes are employed in the photo refractive material of the present invention. In accordance with the present invention the nanoparticles can be synthesized in such a manner that they are defined by a crystalline nucleous, which is covered by a non¬ crystalline amorphous or metastable shell. In the present disclosure the nucleous is referred to as core portion and the shell as shell portion.
An example of the shell portion is schematically depicted in Fig. Ib, which shows very enlarged outer layer (shell portion) obtained on a nucleus (core portion) consisting of Sb2S3. The shell portion is comprised Of Bi2S3 that is obtained by partial substitution of Sb3+ ions by Bi3+ in Sb2S3.
Fig. Ic demonstrates the stable structure Of Bi2S3 formed upon laser pulse radiation of Sb2S3/Bi2S3 mixed sulfide. In practice diameter of the nanoparticles varies from 5 to 50 nm. The thickness of the shell portion lies between 10 and 30 % of the nanoparticle diameter. The concentration of the nanoparticles in the polymer matrix lies between 5xlO'3 and 5xlO'2 M being preferably 1x10"2 M. The nanoparticles are substantially homogeneously distributed within the matrix and center-to-center distance between adjacent particles lies between 20 and 100 nm. The nanoparticles have round shape or slightly elliptical shape. In accordance with the invention either the core portion or the shell portion consists of a compound, which is capable to produce heat upon exposure to pulsed laser radiation and to undergo phase transformation. Among such compounds are for example chalcogene- containing compounds. The particular chemical composition of the core portion and the shell portion usually is dissimilar, but might be also identical. By virtue of this provision the structure of the shell portion is similar to the structure of the core portion. Under laser heating the metastable crystalline phase and amorphous phase changes its structure and refraction index. This change is accompanied by producing of heat and therefore the nanoparticles temperature depends less on the heating rate and the rate of heat diffusion. Inasmuch recording occurs due to the phase transition, the photo refractive material of the invention exhibits threshold properties, namely recording occurs when the energy of the laser pulse exceeds some value. Due to the heat, which accompanies the phase transition, this threshold value is significantly lowered. It can be readily appreciated that by virtue of this provision lasers with less power would be required for recording. On the other hand, light beams with smaller energy could be used for reading of the recorded information, which means that photo refractive material of the invention would be not sensitive to prolonged exposure to daylight and therefore the media manufactured from this material would not need any treatment after recording. Concentration of nanoparticles within the matrix, their chemical composition and size are chosen to obtain recording medium with the necessary resolution, the highest number of pages in the hologram, and with the high photosensitivity.
In the present invention the nanoparticles are composed from chemical compounds, which produce heat upon pulsed laser irradiation. It has been found that it is especially advantageous for this purpose if the nanoparticles are composed of sulfides, selenides or tellurides as well of chemical compounds containing two or more metallic chalcogene, e.g. sulfur and selenium, sulfur and tellurium, selenium and tellurium. It should be born in mind, however, that the nanoparticles could be composed also from other compounds if these compounds are capable to produce heat upon laser irradiation and undergo phase transformation from metastable form to stable crystalline form accompanied by the change of refraction index. For example the nanoparticles may contain the core portion comprised of azides, like Cu(N3)2 or Cd(N3)2 covered by the shell portion composed of sulfide. Under laser heating the azide decomposes while producing energy that maintains phase transformation of sulfide in the shell portion. The nanoparticles with required chemical composition are produced by virtue of chemical reaction between soluble salts of transition or non-transition metals and chalcogene containing compounds, i.e. compounds containing sulfur, selenium and tellurium. This reaction is carried out in a solution containing a stabilizer, polymer or a hardening compound. The reaction can be conducted at ambient temperature, however it is advantageous if this reaction is conducted at elevated temperature. The obtained photorefractive materials can be used for holographic data recording and storage. It has been found that photo refractive materials of the invention exhibit very small shrinkage, which is about 0.01%. This can be explained by the fact that the phase transition cannot essentially change the small size of nanoparticles in the matrix. Non-limiting list of suitable chalcogene containing compounds comprises hydrides of sulfur, selenium, and tellurium, soluble sulfides of alkaline metals, selenosulfites, tellurides etc. The chemical reaction can be conducted in the presence of stabilizers like sodium polyphosphate, trioctyl phosphine oxide or mercaptoacetic acid, which prevent the produced nanoparticles from aggregation during precipitation. Polymers like polyvinyl alcohol or gelatin can also be used as stabilizers. In accordance with the invention the chemical reaction can be conducted in such a manner that the produced nanoparticles consist of compounds containing a single chalcogene element or more than one chalcogene element. This is achieved by precipitation or by substitution reactions. In the first case a source of sulfur, selenium or tellurium is added to the solution containing salts of two or more metals. An example of _• αitable reaction can be . interaction of sodium sulfide with acidic solution of bismuth and antimony chlorides. In the second case ions capable to form insoluble chalcogene containing compounds on the surface of the core portion are added to dispersion of nanoparticles in water and in the presence of a stabilizer. This reaction results in the nanoparticles having the core portion and the shell portion, which differ in chemical composition. For example, if bismuth chloride is added to dispersion of Sb2S3 nanoparticles, bismuth replaces antimony in the surface layer of the partciles and mixed sulfide is formed. Eventually the core portion of the nanoparticles is composed Of Sb2S3 and the shell portion is composed Of Bi2S3. This reaction can take place if the second sulfide has much smaller solubility product as compared with the sulfide constituent of the core portion. For manufacturing of the recording medium solid holographic films can be produced by evaporation of the solvent from the dispersion with nanoparticles distributed within a vehicle, which is a polymer or a polymerizable compound. In the lat er case the solid film is hardened photochemically or thermally. Hardening of polymerizable compound can be carried out with the aim of a photoinitiator upon irradiation by the UV light or by visible light or with the aim of a proper thermoinitiator.
Non-limiting list of polymers suitable for manufacturing of the present photo refractive material and the holographic media of the invention comprises acrylic and vinyl polymers, alkyd, coumarone-indene, epoxy and phenolic resins, fluoropolymers, aminoplasts, polyacetals, polyacrylics, polyalkylenes, polyalkenyles, polyalkynyles, polyamicacids, polyamides, polyanhydrides, polyarylenealkenyles, polyarylenealkylenes, polyarylenes, polyazomethynes, polybenzimidazoles, polybenzothiazoles, polybenzoxazinones, polybenzoxazoles, polybenzyls, polycarbodiimides, polycarbonates, polycarboranes, polycarbosilanes, polycyaurates, polydienes, polyesters, polyurethanes, polyethereketones, polyethers, polyuretanes, polyhydrazides, polyimidazoles, polyimides, polyimines, polyisocyanurates, polyketones, polyolefins, polyoxadiazoles, polyoxides, polyoxyalkylenes, polyoxyarylenes, polyoxymethylenes, polyoxyphenylenes, polyoxyphenyls, polyphosphazenes, polyquinolines, polyquinooxalines, polysilanes, polysilazanes, polysiloxazanes, polysilsesquioxanes, polythioethers, polysulfonamides, polysulfones, polythiazoles, polythoalkylenes, polythioarylenes, polythiomethylenes, polyureas, polyurethanes, polyvinyl acetals, polyvinyl butyrals and polyvinyl formals etc. Non-limiting limiting list of suitable polymerizable compounds comprises acrylates, metacrylates or epoxides. Examples of suitable commercially available products are polyether or polyester urethane acrylates like BR-200, BR- 300, BR- 400 manufactured by Aldrich Inc. or bifunctional polyester or polyether urethane acrylates or metacrylates manufactured by Bomar Specialties Inc To improve optical characteristics of the recording medium plasticizers can be introduced in the photo refractive material. Non-limiting list of suitable plasticizers comprises alkyl phthalates, phosphates, adipates and sebacates, polyethers, epoxides, etc. As suitable substrate one can use transparent inorganic glasses, polycarbonate, polymethylmethacrylate, polymethylacrylate, and polystyrene etc. The non-limiting examples below illustrate preparation of the photo refractive material of the present invention. Example 1.
10 ml OfNa2S in 10% solution of polyvinyl alcohol (PVA) with typical Mw 9,000 - 10,000 was first prepared (0.15 ml of 1 M aqueous Na2S solution to 10 ml of PVA solution). Then to this solution 0.1 ml of 1 M SbCl3 acidic (HCl) aqueous solution was added successively. Temperature of the Na2S in PVA solution was 25 0C.
The reaction resulted in formation of nanoparticles having shell portion composed of amorphous Sb2S3.
Resulting solution was deposited on hydroxylized glass plate and then the plate was dried in a closed box at room temperature for 4 days.
Example 2.
10 ml OfNa2S in 20% PVA solution was first prepared (0.15 ml of 1 M aqueous Na2S solution to 10 ml of PVA solution). Then to this solution 0.3 ml of 0.2 M aqueous . thioglycolic acid solution, 0.1 ml of 1 M BiCl3 acidic (HCl) aqueous solution was added successively. Temperature of the Na2S in PVA solution was 25 0C.
The reaction resulted in formation of nanoparticles having shell portion composed of amorphous Bi2S3.
Resulting solution was deposited on hydroxylized glass plate and then the plate was dried in a closed box at room temperature for 4 days.
Example 3.
10 ml OfNa2S in 10% PVA solution was first prepared (0.15 ml of 1 M aqueous Na2S solution to 10 ml of PVA solution). Then to this solution 0.05 ml of 1 M SbCl3 acidic
(HCl) aqueous solution and 0,05 ml of 1 M BiCl3 acidic (HCl) aqueous solution were added successively. Temperature of the Na2S in PVA solution was 22 C.
The reaction resulted in formation of nanoparticles with core portion consisting Of Sb2S3 and shell portion consisting Of Bi2S3.
Resulting solution was deposited on hydroxylized glass plate and then the plate was dried in a closed box at room temperature for 4 days.
Example 4.
10 ml OfNa2S in 10% PVA solution was first prepared (0.15 ml of 1 M aqueous Na2S solution to 10 ml of PVA solution). Then to this solution 0.1 ml of 1 M SbCl3 acidic (HCl) aqueous solution was added successively. Temperature of the Na2S in PVA solution was 70 0C. Then 0.01 ml of 1 M BiCl3 acidic (HCl) aqueous solution wa^ added successively. The reaction resulted in formation of nanoparticles with core portion consisting Of Sb2S3 and shell portion consisting Of Bi2S3. Resulting solution was deposited on hydroxylized glass plate and then the plate was drying in a closed box at room temperature for 4 days.
Example 5.
0.038 ml of 0.2 M solution OfNa2SeSO3 was added to 5ml of 15% PVA solution under stirring. Than 0.07 ml of 0.1 M aqueous solution of Cu(C104)2 was added drop wise at 70
C. Solution was mixed during 30 min.
The reaction resulted in formation of nanoparticles having both the core portion and the shell portion consisting of copper selenide
Resulting solution was deposited on hydroxylized glass plate and then the plate was dried in a closed box at room temperature for 4 days.
Example 6.
10 ml of 1 M aqueous solution of Cu(C104)2 was added dropwise to 1 M solution OfNaN3 in aqueous 15% solution of polyvinylpyrrolidone under intense stirring. After that 1 ml of 0.1 M solution OfNa2S was added to dispersion of Cu(N3)2 nanoparticles.
The reaction resulted in formation of nanoparticles with core portion consisting of Cu(N3 )2 and shell portion consisting of CuS.
Resulting solution was deposited on hydroxylized glass plate and then the plate was dried in a closed box at room temperature for 4 days.
Holograms were recorded with the aim of the medium prepared from the photo refractive material of the invention. In Fig.2 is shown dependence of diffraction effrciency η of the holograms on the energy of laser pulse. Diffraction efficiency is the ratio of the power in the diffracted beam to the power in the incident beam. It is clearly seen that this dependence has a threshold, i.e. the recording is achieved after the laser pulse energy reaches certain minimum value and this efficiency increases until some maximum value.
With reference to Fig.3 it is shown that diffraction efficiency increases when concentration of the nanoparticles rises. With the above dependences it is possible to find optimal condition in terms of minimum recording energy and concentration, which would be required for recording a hologram with highest diffraction efficiency.
It has been empirically revealed that maximum value of diffraction efficiency η can range up to 80%. The maximum value of diffraction efficiency corresponds to change of the refraction index by about 0.005.
Dynamic range, photosensitivity and diffraction efficiency of the photo refractive materials of the present invention are summarized in the non-limiting Tables 1 and 2 below. This data is presented along with the factors, which influence on these properties. Among these factors are concentration of nanoparticles (as shown in Fig. 3), temperature of synthesis of nanoparticles and pH of the solution.
A measure for the data-storage capacity of holographic media is defined by so-called M- number (M#), which was determined using the following formula
v r ^ 2π * Anl * d , 2π ■ ^" A Δnw,, M#--
;=1 ' it /l *cos#, λ t ttf cosø, where: d— thickness of photosensitive layer θ — angle between reference and object beams λ - wavelength of recording light η, - diffraction efficiency of each hologram.
The photo sensitivity S was calculated according to the following formula:
S = η05/Eod in cm/mJ, where:
Eo- the flux energy Ep/A where Ep is the pulse energy and A is the spot area (A=O.5 mm2 ) d— Thickness of the sample η - Diffraction efficiency of the hologram Table 1.
Properties of photo refractive materials containing nanoparticles composed ofSbySi and
CuSe.
Photosensitivity of the present photo refractive materials is not worse than photosensitivity of the known in the art photo polymerizable materials. For example, photo refractive material developed by Aprilis Ventrures demonstrates photosensitivity between 2.5 and 4.5 cm/mJ.
At the same time the present photo refractive materials have significant advantage over the known in the art materials since they do not shrink and have much shorter recording time.
Non-limiting Table 2 displays how photosensitivity of the present photo refractive material depends on the temperature of the synthesis.
Table 2.
Diffraction efficiency of photo refractive material comprising nanoparticles composed of Sb2S3 core portion and Sh2S3/BiiS3 shell portion
The present invention has been described using non-limiting detailed description of various embodiments thereof. It should be appreciated that the present invention is not limited by the above-described embodiments and that one ordinarily skilled in the art can make changes and modifications without deviation from the scope of the invention as will be defined below in the appended claims.
It should also be appreciated that features disclosed in the foregoing description, and/or in the foregoing drawings and/or following claims both separately and in any combination thereof, be material for realizing the present invention in diverse forms thereof.
When used in the following claims, the terms "comprise", "include", "have" and their conjugates means "including but not limited to".

Claims

CLAIMS:
1. A photosensitive material comprising a matrix with distributed therein discrete particles of a hosted material, said hosted material is capable to change its refractive index in response to laser beam irradiation, said particles comprise a core portion and a shell portion surrounding the said core portion, wherein said shell portion is capable to undergo a phase transformation from an amorphous or a metastable crystalline state to a stable crystalline state, wherein said phase transformation is accompanied by change of refractive index.
2. The photosensitive material as defined in claim 1 , in which said particles have diameter D of about 5-50 nanometers and concentration of said particles within the matrix is between 0.005 and 0.05 M.
3. The photosensitive material as defined in claim 1 , in which thickness of the shell portion is about (0.1 -03)D.
4. The photosensitive material as defined in claim 1 , in which said matrix is made of an organic material and said particles are made of an inorganic material.
5. The photosensitive material as defined in claim 4, in which said inorganic material is capable to produce heat in response to laser beam irradiation, wherein said heat sustains the phase transformation.
6. The photosensitive material as defined in claim 5, in which said inorganic material is capable to change refractive index in response to pulsed laser radiation with energy less than 3 mJ/mm2 and with duration of the pulse from 1 up to 50 ns.
7. The photosensitive material as defined in claim 6, in which said inorganic material is a chemical compound, which contains at least one element selected from the group VIb of the Periodical Classification of the Elements and at least one metal selected from the group Ib, Ub, Vb, VIIb and VIIIb of the Periodical Classification of the Elements.
8. The photosensitive material as defined in claim 7, in which said organic material is an organic polymer selected from the group consisting of acrylic and vinyl polymers, alkyd, coumarone-indene, epoxy and phenolic resins, fluoropolymers, aminoplasts, polyacetals, polyacrylics, polyalkylenes, polyalkenyles, polyalkynyles, polyamicacids, polyamides, polyanhydrides, polyarylenealkenyles, polyarylenealkylenes, polyarylenes, polyazomethynes, polybenzimidazoles, polybenzothiazoles, polybenzoxazinones, polybenzoxazoles, polybenzyls, polycarbodiimides, polycarbonates, polycarboranes, polycarbosilanes, polycyaurates, polydienes, polyesters, polyurethanes, polyethereketones, polyethers, polyuretanes, polyhydrazides, polyimidazoles, polyimides, polyimines, polyisocyanurates, polyketones, polyolefins, polyoxadiazoles, polyoxides, polyoxyalkylenes, polyoxyarylenes, polyoxymethylenes, polyoxyphenylenes, polyoxyphenyls, polyphosphazenes, polyquinolines, polyquinooxalines, polysilanes, polysilazanes, polysiloxazanes, polysilsesquioxanes, polythioethers, polysulfonamides, polysulfones, polythiazoles, polythoalkylenes, polythioarylenes, polythiomethylenes, polyureas, polyurethanes, polyvinyl acetals, polyvinyl butyrals and polyvinyl formal s
9. The photosensitive material as defined in claim 8, in which chemical composition of said core portion is identical with chemical composition of the shell portion.
10. The photosensitive material as defined in claim 8, in which chemical composition of said core portion is not identical with chemical composition of the shell portion.
11. The photosensitive material as defined in claim 8, in which said core portion is composed Of Sb2S3 and said shell portion is composed Of Bi2S3
12. The photosensitive material as defined in claim 8, in which said shell portion is composed Of Sb2S3 and said core portion is composed Of Bi2S3
13. The photosensitive material as defined in claim 8, in which said core portion is composed of Cu(N3)2 and said shell portion is composed of CuS.
14. A method for preparation of photosensitive material comprising a matrix with distributed therein discrete particles of a hosted material, said hosted material is capable to change its refractive index in response to laser beam irradiation, said method comprises chemical interaction of soluble salts of transition and nontransition metals selected from the group Ib, lib, Vb, VIb, VIIb and VIIIB of the Periodic Classification of the Elements with at least one chemical compound selected from the group consisting of a sulfide, selenium and tellurium containing compounds, wherein said chemical interaction is carried out in a solution of an organic or inorganic compound, capable to form a film with distributed therein particles, resulting from the said chemical interaction.
15. The method as defined in claim 14, in which said soluble salts are selected from the group consisting of salts of copper, silver, zinc, cadmium, mercury, manganese, iron, cobalt, nickel, platinum, palladium, thallium, indium, gallium, aluminum, germanium, tin, lead, bismuth, antimony, arsenic, scandium, yttrium, lanthanum and lanthanides, uranium.
16. The method as defined in claim 14, wherein said sulfide is selected from the group consisting of sulfide of ammonium, lithium, sodium, potassium, rubidium, cesium, calcium, strontium, barium, aluminum, germanium, aluminum, gallium, indium, scandium, yttrium lanthanum and lanthanides, zinc, cadmium, mercury, bismuth, arsenic, antimony, tin, lead, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, cobalt, nickel, copper, zinc, cadmium, silver, palladium, platinum, πienium, ruthenium, platinum, uranium.
17. The method as defined in claim 14, in which said selenium containing compounds are selected from selenides and selenosulfates.
18. The method as defined in claim 14, in which said tellurium containing compounds are selected from tellurides.
19. The method as defined in claim 14, in which said organic compound is an organic polymers.
20. The method as defined in claim 14, in which said inorganic compound is inorganic silicate.
21. The method as defined in claim 14, in which said organic compound is formed by hydrolysis of metallorganic polymers.
22. The method as defined in claim 14, in which said chemical interaction is carried out in a solvent, which is selected from the group consisting of water, liquid gases and organic solvents.
23. The method as defined in claim 14, in which said film is formed by evaporation of the solvent.
24. The method as defined in claim 14, in which said chemical interaction is between water-soluble azides and salts of transition metals.
25. The method as defined in claim 14, in which a photopolymerizable compound is added to the solution.
26. The method as defined in claim 14, in which said film is formed by hardening of the organic compound upon irradiation of the solution by UV or visible light.
27. The method as defined in claim 26, in which a photoinitiator is added to the solution to accelerate the hardening.
28. The method as defined in claim 27, in which said is photoinitiator is selected from the group consisting of aromatic or alkyl ketones, organic or inorganic peroxides,
29. The method as defined in claim 14, in which a plasticizer is odded to said solution to facilitate softening and melting of the film.
30. A storage medium comprising photosensitive material of claim 1.
31. The storage medium of claim 30, said medium comprises CD write-once (CDR), DVD write-once (DVDR) discs, cards and tapes.
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