JPH08262512A - Nonlinear optical material and production - Google Patents

Abstract

PURPOSE: To obtain a nonlinear optical material of a thin film form which is uniformly dispersed with fullerenes in a matrix and has excellent heat resistance by forming the fullerene-contg. gel uniformly dispersed with the fullerenes in the oxide gel matrix by using a sol-gel method. CONSTITUTION: Alcohol, such as methanol, is added into metal alkoxide M(OR)n to prepare a soln. mixture. Next, an aq. soln. of the fullerenes or an alcohol soln. is added to this soln. The fullerenes are added in the form of the aq. soln., etc., to the soln. mixture in the case of forming precursors in such a manner, by which the fullerenes are uniformly dispersed. The formed precursors are rested for a suitable period of time from room temp. to 80 deg.<=, as required, to advance hydrolysis and polycondensation reaction, by which the wet gel is formed. The wet gel is applied on a substrate by dip coating right after the prepn. of the precursors in the case where thin films are formed. The wet gel or the precursors applied on the substrate are dried in vacuum or suitable atmosphere, by which the thin films of the dry gel are obtd.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an optical switch, an optical memory,
The present invention relates to a non-linear optical material used for an optical logic element, an optical limiter, etc. and a method for manufacturing the same.

[0002]

2. Description of the Related Art Basket-like carbon cluster molecules (C _x , x = 60, 70, 76, 78, 82, 84) having a π-conjugated electron system.
...) are called fullerenes, and are expected to be applied as superconducting materials, electronic materials, secondary battery materials, photoelectrochemical elements, and the like.

Since fullerenes contain abundant π electrons in the molecular skeleton, they are expected to be applied as nonlinear optical materials. C ₆₀ having a sphere-symmetric structure is expected to have a third-order nonlinear effect, and the third-order nonlinear susceptibility χ ⁽³⁾ has been experimentally measured using a C ₆₀ solution or a thin film. According to the measurement result by the third harmonic generation (THG) method, the value of χ ⁽³⁾ is about 10 ^-10 to 10 ^-11 esu in the three-photon resonance region and 1 in the non-resonance region.
About 0 ^-12 esu, and 10 ^{-10 -10 -11 of} polydiacetylene, which is most promising as a third-order nonlinear optical material.
Values comparable to esu have been reported.

As an application of the non-linear optical effect of fullerene, an optical limiter utilizing the third-order non-linear optical effect is used.
have been proposed by Utt et al. and experimentally confirmed that C ₆₀ and C ₇₀ solutions function as optical limiters (NATURE, 356, 225 (199).
2)).

When fullerene is applied as a non-linear optical material, it is difficult to prepare a device using a fullerene solution, and a fullerene thin film is deteriorated in characteristics due to oxidation in the atmosphere, and when a high-power laser is used, a fullerene molecule Sublimation becomes a problem. JP-A-6-25461 proposes an optical limiter using a resin composition composed of fullerene and a transparent resin. This is a resin composition comprising a transparent resin having a light transmittance of 50% or more and 0.001 to 10% by weight of fullerene with respect to the transparent resin. The optical limiter that does.

Another example of an optical limiter using fullerenes is one in which C ₆₀ is confined in a gel matrix. (Appl. Phys. Lett., 62, 1
721 (1993)). This relates to a bulk in which C ₆₀ is confined in an oxide gel containing Si and Zr as components, and it has been experimentally confirmed that this bulk body has an optical limiter function. As a manufacturing method,
A method is used in which C ₆₀ is added to a mixed solution of alkoxide and benzene, which are Si source and Zr source, respectively, and dried in a steam atmosphere at room temperature.

Lin et al. Have proposed fullerene-doped glass in which fullerene is confined in a glass matrix as a nonlinear optical material using fullerene, and glass raw material powder and C ₆₀ and C ₇₀ are confined in a closed container.
By heating at 0K, C ₆₀ + C ₇₀ is 0.1 wt%
The following fullerene-doped glasses are being manufactured (App
l. Phys. Lett. , 65, 2522 (199
4)).

The sol-gel method is a method in which a wet gel formed by hydrolysis of a metal alkoxide from a solution containing a metal alkoxide and a polymerization reaction is dried to form a dry gel or a heat treatment to form glass or ceramics, which is mainly an oxide glass. It is used as a method for producing ceramics. It is possible to synthesize at a lower temperature than the conventional manufacturing method using melting and sintering, and it is possible to form thin films and fibers by adjusting the viscosity and components of the raw material solution (precursor) as well as the synthesis of bulk materials. There are advantages such as being present. It is also used as a method for producing an organic dispersion gel in which organic molecules are dispersed in an oxide gel matrix or a semiconductor fine particle-doped glass in which semiconductor fine particles are dispersed in a glass matrix.

[0009]

[Patent Document 1] Japanese Patent Application Laid-Open No. 6-25461
The non-linear optical material composed of fullerene and transparent resin is not suitable for use when the laser output of the light source is large because it lacks heat resistance. The example in which C ₆₀ is confined in the gel matrix relates to the bulk, and its application as an optical limiter is the subject of research. Since the fullerene-doped glass proposed by Lin et al. Uses a sintering method as a manufacturing method and the heat treatment temperature is high, it has been confirmed that a substance believed to be C ₆₀ O due to the oxidation of fullerene is contained, and the original characteristics of C ₆₀ are exhibited. Probably not done. Further, in this method, fullerene cannot be uniformly dispersed in the matrix, so that a homogeneous material cannot be obtained. Furthermore, it is difficult to form a thin film by this method.

[0010]

In order to solve the above-mentioned problems, the inventors have conducted experiments and studies on a nonlinear optical material using fullerenes and a method for producing the same, and have obtained the following results. That is, as a homogeneous nonlinear optical material with excellent heat resistance using fullerene, fullerene-containing glass and fullerene-containing gel or fullerene-containing glass in which fullerenes are dispersed in a glass matrix prepared using the sol-gel method are formed on a substrate. We propose a nonlinear optical material that is characterized by

Further, a method of forming a fullerene-containing gel or a fullerene-containing glass by a sol-gel method from a precursor prepared by mixing an alcoholic solution or an aqueous solution of fullerene in a solution containing at least a metal alkoxide, and further the above-mentioned precursor We propose a method of forming a fullerene-containing gel on the substrate by coating on a substrate by dip coating or spin coating and then drying, and a method of forming a fullerene-containing glass by heat treatment.

[0012]

The present invention utilizes the excellent non-linear characteristics of fullerenes, and the fullerene is uniformly dispersed in the oxide gel matrix by the sol-gel method in order to obtain a material that can be applied to devices without impairing the characteristics. By using a fullerene-containing glass in which a fullerene is uniformly dispersed in a fullerene-containing gel or a glass matrix, a homogeneous nonlinear optical material having excellent heat resistance is realized. Furthermore, as a method for producing glass, the sol-gel method is capable of low-temperature synthesis and can be made into a thin film as compared with a conventional method using sintering or melting, and fullerenes are mixed in a solution containing at least a metal alkoxide. By the method of forming a fullerene-containing gel or a fullerene-containing glass by a sol-gel method from the precursor prepared by, to prevent desorption and oxidation of fullerene, it becomes possible to obtain a nonlinear optical material in which fullerene is uniformly dispersed, further The precursor can be applied on the substrate by dip coating or spin coating, and then dried and heat-treated to form a thin film of these materials.

The fullerenes used in the present invention include C ₆₀
Fullerene (C _x , x
= 60, 70, 76, 78, 82, 84 ...), as well as various chemical modifications thereof, metal-encapsulated fullerenes such as La @ C ₈₂ in which a metal is included in the carbon skeleton. can do. These fullerenes may be used alone or in combination of a plurality of types depending on the purpose.

When only C ₆₀ having a sphere-symmetric structure is used, only a third-order nonlinear optical effect can be expected, and when a noncentrosymmetric fullerene such as C ₇₀ is used, a third-order effect is added to obtain a second-order nonlinear optical effect. A nonlinear optical effect can also be expected. As the second-order nonlinear optical effect and its application, it can be used for a laser wavelength conversion element using the second harmonic (SHG) generation, an optical modulator using the electro-optical effect, and the like. The third-order nonlinear optical effect and its applications include optical memory utilizing optical bistable,
It can be used for an optical logic element, an optical limiter, an optical switch using a nonlinear refractive index effect, an optical logic element, and the like.

As the sol or glass matrix for confining the fullerenes, SiO ₂ , B ₂ O ₃ , Al ₂ O
Those containing oxides such as ₃ , TiO ₂ , ZrO ₂ , Na ₂ O, CaO and SrO as components can be used. These can be used alone or in combination of two or more.
Since these substances are optically transparent, they are suitable for applications in optical elements.

As a manufacturing procedure, first, a metal alkoxide M (OR) _n (M: Si, B,
A metal such as Al or Ti, R: an alkyl group such as CH ₃ , C ₂ H ₅ , or C ₃ H ₇ , n: an oxidation number of the metal) is added with an alcohol such as methanol or ethanol to prepare a mixed solution. The metal alkoxide is, for example, TEOS (etraethoxysilane, Si (OC ₂ H ₅ ) when SiO ₂ is the matrix.
₄ ), TMOS (tetramethoxysilane, Si (OC
H ₃ ) ₄ ) or the like may be used. Na of the above oxides
₂ O and CaO are usually used in combination with other oxides as subcomponents of 30 mol% or less, and these may be made of hydroxide as a raw material in addition to metal alkoxide.

Next, an aqueous solution of fullerenes or an alcohol solution is added to this solution. As a method of confining the fullerenes in a glass matrix or a gel matrix, by adding the fullerenes as an aqueous solution or an alcohol solution when forming the precursor in this way, the fullerenes can be uniformly dispersed, and thus a large Non-linearity can be obtained.

Although fullerenes are almost insoluble in water and alcohol, they become soluble by adding 0.1 to 20 wt% of a surfactant in a solvent. As the surfactant, polyvinylpyrrolidone (PVP), cyclodextrin, aromatic hydroxy compounds such as phenol, polyvinyl alcohol, higher alcohols, higher fatty acids, polyethers such as diethylene glycol, triethylene glycol, polyethylene oxide and the like can be used. . Among them, PVP and cyclodextrin are particularly effective because they can dissolve a large amount of fullerenes in water or alcohol as compared with other surfactants.

The method for adding the surfactant is to add it directly to water or alcohol, or to add the surfactant to P
In the case of a solid such as VP or cyclodextrin, a solution of fullerenes dissolved in a solvent having a high solubility of fullerenes such as benzene and toluene and a solution of a surfactant dissolved in an appropriate organic solvent are mixed and dried. There is a method of dissolving the soaked product in water or alcohol.

Water is required for the hydrolysis of the metal alkoxide. When an aqueous solution of fullerene is added, it also serves as water for hydrolysis, but when an alcohol solution is added, it is necessary to add water separately.

Hydrochloric acid, sulfuric acid, nitric acid, as a catalyst for hydrolysis,
An acid such as acetic acid or an alkali such as ammonia may be added. When producing a bulk material, formamide or dimethylformamide (DMF) may be added in order to prevent cracks, ruptures, and foaming during drying or heat treatment. These operations may be performed at room temperature.

By this method, a precursor in which fullerenes are uniformly dispersed is formed, and a material in which fullerenes are uniformly dispersed can be obtained even in a gel or glass produced through the subsequent processes. The mixing procedure of each raw material does not necessarily need to follow the above-mentioned method, and can also be performed by other procedures.

The thus-prepared precursor is left as it is at room temperature to 80 ° C. for an appropriate period of time to proceed with hydrolysis and polycondensation reaction to form a wet gel. In the case of forming a thin film, it is coated on the substrate by dip coating or spin coating immediately after the precursor is prepared or after reacting for an appropriate time to adjust the viscosity.
As the substrate, semiconductor single crystals and polycrystals such as Si and GaAs, metals such as glass, Cu, Ni, Ag, Au, and Fe can be used. By selecting an appropriate substrate, the desired element Can be formed.

In the present invention, it is easy to form a thin film of fullerene-containing glass or fullerene-containing gel on a substrate as described above, and by using a nonlinear optical material formed on the substrate, not only an optical limiter but also an optical switch. , Optical memory,
It can be applied to optical logic devices, optical modulators, etc.

The wet gel or the precursor coated on the substrate is dried in vacuum or in a suitable atmosphere to obtain a bulk or thin film of a dry gel in which fullerenes are uniformly dispersed. Since the drying can be performed in the range of room temperature to 150 ° C., it is possible to prevent desorption and oxidation of the fullerenes due to sublimation.

By heating the dried gel, vitrification of the gel occurs, and a bulk or thin film of glass in which fullerenes are uniformly dispersed can be obtained. The heat treatment temperature varies depending on the composition of the glass and is generally 300 to 1200 ° C., but it is desirable to perform the heat treatment at 500 ° C. or less in order to prevent desorption and oxidation due to sublimation of the fullerenes during the heat treatment. When forming a thin film, heat treatment may be performed without drying after applying the precursor.

The bulk or thin film of the fullerene-containing gel or the fullerene-containing glass thus produced has a homogeneous structure in which the fullerene is uniformly dispersed in the matrix, and the fullerene is desorbed or oxidized by sublimation during the heat treatment process. Therefore, excellent characteristics can be expected as an excellent nonlinear optical material. The non-linear optical material preferably contains 0.001 to 10 wt% of fullerenes. The fullerene-containing gel or fullerene-containing glass of the present invention can be applied to various nonlinear optical elements described above by forming it as a thin film on a bulk or a substrate, if necessary, and performing appropriate processing.

[0028]

【Example】

Example 1 A bulk of fullerene-containing gel in which C ₆₀ was dispersed in a SiO ₂ gel matrix was prepared by the sol-gel method. First, TEOS and ethanol were mixed at a molar ratio of 1: 4.3 to prepare a metal alkoxide solution. Toluene: hexane = 1: from soot obtained by arc evaporation method
C ₆₀ obtained by isolation by high performance liquid chromatography using 1 mixed solvent was polyvinylpyrrolidone (PV
P) was dissolved in pure water containing 5 wt% to obtain a C ₆₀ aqueous solution. A C ₆₀ aqueous solution and hydrochloric acid as a catalyst were mixed with the metal alkoxide solution to prepare a precursor. T in the precursor
The molar ratio of EOS: water: C ₆₀ : HCl is 1: 4.6: 4.
6 × 10 ⁻⁵ : 0.07. The precursor was transferred to a petri dish, allowed to stand at 25 ° C. for gelation and drying to obtain a disk-shaped dry gel. C in gel calculated from raw material ratio
The content of ₆₀ is 0.06 wt%.

When the infrared absorption spectrum of the prepared dry gel was measured, four peaks attributable to C ₆₀ were observed, and it was found that C ₆₀ was confined in the gel. No precipitate was observed by observation with an optical microscope or a transmission electron microscope, and it was confirmed that C ₆₀ was uniformly dispersed in the gel.

When the third-order nonlinear susceptibility χ ⁽³⁾ of the prepared gel was evaluated by the third harmonic generation (THG) method, the value of χ ⁽³⁾ was 3.2 × 10 ^-10 esu in the resonance region. , A good value of 5.4 × 10 ⁻¹² esu was shown in the non-resonance region.

Example 2 A thin film of a fullerene-containing gel in which C ₆₀ was dispersed in a SiO ₂ gel matrix was prepared on silica glass by the sol-gel method. The precursor prepared in the same manner as in Example 1 was allowed to stand at 25 ° C. to adjust the viscosity, and one side of the silica glass substrate was coated by dip coating. By leaving at 25 ° C. for gelation and drying, a dried gel thin film was obtained on the substrate. The content of C ₆₀ in the gel calculated from the raw material ratio is 0.06 wt% as in Example 1.

When the infrared absorption spectrum of the produced dry gel thin film was measured, four peaks attributable to C ₆₀ were observed, and it was found that C ₆₀ was confined in the gel. No precipitate was observed by observation with an optical microscope or a transmission electron microscope, and it was confirmed that C ₆₀ was uniformly dispersed in the gel.

When the third-order nonlinear susceptibility χ ⁽³⁾ of the prepared gel was evaluated by the third harmonic generation (THG) method, the value of χ ⁽³⁾ was 3.3 × 10 ^-10 esu in the resonance region. , A good value of 5.2 × 10 ^-12 esu was shown in the non-resonance region.

Example 3 A bulk of fullerene-containing glass in which C ₆₀ was dispersed in a SiO ₂ glass matrix was prepared by the sol-gel method. First, TMOS and DMF were mixed at a molar ratio of 1: 1 to prepare a solution. Toluene from soot obtained by the arc evaporation method: hexane = 1: 1 to C ₆₀ obtained was isolated by high performance liquid chromatography using a mixed solvent, polyvinylpyrrolidone (PVP) 5w
It was dissolved in pure water added with t% to obtain a C ₆₀ aqueous solution. Methanol, a C ₆₀ aqueous solution, and ammonia as a catalyst were mixed with the metal alkoxide solution to prepare a precursor. The molar ratio of TMOS: methanol: water: C ₆₀ : ammonia in the precursor was 1: 2.2: 10: 1 × 10 ⁻⁴ : 4 × 10 ⁻⁴ . The precursor was transferred to a petri dish, allowed to stand at 25 ° C. for gelation and drying to obtain a disk-shaped dry gel. This dried gel was heat-treated at 500 ° C. in the atmosphere using an electric furnace to form glass. The content of C ₆₀ in the glass calculated from the raw material ratio is 0.12 wt%.

When the infrared absorption spectrum of the produced glass was measured, four peaks due to C ₆₀ were observed, and it was found that C ₆₀ was confined in the glass. No precipitate was observed by observation with an optical microscope or a transmission electron microscope, and it was confirmed that C ₆₀ was uniformly dispersed in the glass.

When the third-order nonlinear susceptibility χ ⁽³⁾ of the produced glass was evaluated by the third harmonic generation (THG) method, the value of χ ⁽³⁾ was 4.8 × 10 ^-10 esu in the resonance region. , A good value of 6.1 × 10 ⁻¹² esu was shown in the non-resonance region.

Example 4 A thin film of fullerene-containing glass in which C ₆₀ was dispersed in a SiO ₂ glass matrix was produced on silica glass by the sol-gel method. First TE
OS and ethanol were mixed at a molar ratio of 1: 6.8 to prepare a metal alkoxide solution. C obtained by isolation from soot obtained by the arc evaporation method by liquid high performance chromatography using a mixed solvent of toluene: hexane = 1: 1
₆₀ was dissolved in pure water containing 5 wt% of polyvinylpyrrolidone (PVP) to obtain a C ₆₀ aqueous solution. A C ₆₀ aqueous solution and hydrochloric acid as a catalyst were mixed with the metal alkoxide solution to prepare a precursor. TEOS in the precursor: water: C ₆₀ :
The molar ratio of HCl is 1: 11: 1.1 × 10 ⁻⁴ : 0.07.
And The prepared precursor was allowed to stand at 25 ° C. to adjust the viscosity, and spin coating was applied to one side of the silica glass substrate. The glass substrate coated with the precursor was heat-treated at 500 ° C. in the atmosphere using an electric furnace to form a glass thin film on the substrate. The content of C ₆₀ in the glass calculated from the raw material ratio is 0.13 w
t%.

When the infrared absorption spectrum of the produced glass thin film was measured, four peaks due to C ₆₀ were observed, and it was found that C ₆₀ was confined in the glass thin film. No precipitate was observed by observation with an optical microscope or a transmission electron microscope, and it was confirmed that C ₆₀ was uniformly dispersed in the glass thin film.

When the third-order nonlinear susceptibility χ ⁽³⁾ of the produced glass thin film was evaluated by the third harmonic generation (THG) method, the value of χ ⁽³⁾ was 4.7 × 10 ^{-10 in the} resonance region. es
u, a good value of 6.3 × 10 ⁻¹² esu was shown in the non-resonance region.

[0040]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, the heat resistance is higher than that of the conventional non-linear optical material composed of fullerene and transparent resin, and further, desorption or oxidation due to sublimation of fullerenes does not occur in the matrix. It is possible to provide a homogeneous non-linear optical material in which fullerenes are evenly dispersed and a method for producing the same, which facilitates thin film formation.

Claims (10)

[Claims] 1. A non-linear optical material comprising a fullerene-containing gel in which fullerenes are dispersed in an oxide gel matrix formed on a substrate. 2. The oxide gel serving as a matrix is SiO 2.
₂ , B ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , Na ₂ O, C
The non-linear optical material according to claim 1, comprising at least one component selected from aO and SrO. 3. A non-linear optical material, characterized in that fullerene-containing glass, in which fullerenes are dispersed in a glass matrix, is formed on a substrate. 4. The glass serving as a matrix is SiO ₂ ,
B ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , Na ₂ O, Ca
The nonlinear optical material according to claim 3, comprising at least one component selected from O and SrO. 5. A method for producing a fullerene-containing glass, which comprises forming a fullerene-containing glass by a sol-gel method from a precursor prepared by mixing a fullerene with a solution containing at least a metal alkoxide. 6. A precursor prepared by mixing fullerenes in a solution containing at least a metal alkoxide is applied onto a substrate by dip coating or spin coating, and then dried to form a fullerene-containing gel on the substrate, or A method for producing a non-linear optical material, characterized in that glass containing fullerene is formed on a substrate by heat treatment. 7. The fullerene-containing material according to claim 5, wherein a fullerene-containing precursor is uniformly dispersed by adding an alcoholic solution or an aqueous solution of the fullerene to a solution containing at least a metal alkoxide. A method for producing glass or the nonlinear optical material according to claim 6. 8. A precursor in which fullerenes are uniformly dispersed is prepared by adding an alcohol solution or an aqueous solution of fullerenes to a solution containing at least a metal alkoxide, and a fullerene-containing gel is formed from the precursor. A method for producing a fullerene-containing gel, which is characterized. 9. The fullerene-containing glass or the nonlinear optical material according to claim 7, wherein the fullerene alcohol solution or aqueous solution is prepared by adding the fullerene to a surfactant-containing solvent. Item 9. A method for producing a fullerene-containing gel according to Item 8. 10. A surfactant selected from polyvinylpyrrolidone (PVP) and cyclodextrin.
10. The method for producing a fullerene-containing gel or a fullerene-containing glass or a non-linear optical material according to claim 9, wherein