JPH0369598A - Method for growing organic nonlinear optical single crystal - Google Patents

Abstract

PURPOSE:To suppress polycrystallization by using a solvent mixture prepd. by mixing plural solvents which are respectively different in solubility as the solvent for the soln. of an org. nonlinear optical material. CONSTITUTION:The org. nonlinear optical material, such as 2-(alpha- methylbenzylamino)-5-nitropyridine, (hereafter expressed as the 'optical material') is weighed and put into a glass vessel 1. The solvent mixture composed of the solvent, such as acetone, having the high solubility of the optical material and the solvent, such as n-hexane, the small solubility of the optical material is added to the vessel and heated up to completely dissolve the material. This soln. is filtered by a filter to remove impurities; thereafter, the glass vessel 1 is disposed in a thermostatic water chamber 5 to slowly cool the soln. to a prescribed temp. A single crystal 4 of the optical material attached to a platinum wire is hung in this growing soln. 6 and is rested still. Gaseous N2 3 is made flow into a glass tube 2 installed in the upper part of the glass vessel 1 from one end thereof to control the evaporation rate of the soln. The crystal is grown for about 3 to 5 days. The single crystal of the optical material is thus obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for growing organic nonlinear optical single crystals that can be applied to optoelectronic devices used for optical harmonic generation, optical parametric oscillation, etc. It is.

[Prior Art] It has been known for a long time to convert the frequency of light by utilizing nonlinear polarization in a nonlinear crystal, but in recent years, the development of organic materials as this type of optical material has progressed.

Among nonlinear optical materials, those with second-order nonlinearity (
polarization proportional to the square of the electric field) is applied to second harmonic generation and optical parametric oscillation, but most of the crystal structures of these materials do not have inversion symmetry. ing. However, the lack of inversion symmetry means that the crystal has low symmetry, and since the properties of each crystal plane are different, the growth rate of the crystal or the shape of the crystal planes will be inconsistent, resulting in a good single crystal. becomes very difficult to obtain. Therefore, it is very difficult to crystallize organic materials with large nonlinear optical coefficients, and this is the reason why there are very few examples of growing large single crystals in organic nonlinear optical materials.

Under these circumstances, methods for single-crystallizing organic nonlinear optical materials include the sublimation method, in which the organic nonlinear optical material is crystallized by sublimation, and the method in which crystals are obtained by slowly cooling the molten organic nonlinear optical material. Melt method (e.g. Bridgman method, Djochralski method, etc.) or organic nonlinear optical material dissolved in an organic solvent to create a saturated solution.
Conventionally, a solution method has been used in which crystals are precipitated by cooling 8ti and the difference in solubility between hot and cold conditions is used, or by evaporating the solvent from the solution to precipitate crystals.

[Problems with the prior art] However, in the conventional method for growing organic nonlinear optical single crystals as described above, when crystals are produced by sublimation, relatively high purity can be obtained, but it is difficult to suppress the generation of miscellaneous products. The drawback is that it is extremely difficult to produce large crystals. In addition, in crystal growth methods from melt such as the Bridgman method and the Czochralski method, organic nonlinear optical materials are heated to a temperature higher than the melting point of the material and held at that temperature for a long time. The disadvantage is that thermal decomposition of the nonlinear optical material is unavoidable, resulting in the formation of by-products or coloring of the crystals based on the formation of by-products.

On the other hand, in the solution method, problems such as the growth of by-products due to thermal decomposition, which are seen in the melt method, are not so common. However, when a cooling method is used in the solution method, the following problems arise in addition to the slow growth rate of crystals.

In other words, the solvent used in the solution method must satisfy the conditions that the solubility of the organic nonlinear optical material must be very high when heated, and the solubility must be quite low when cold. The types of solvents available are very limited, and the range of solvent selection is extremely narrow. In the solution method, since a second component called a solvent is added, the properties of the added solvent have a much greater effect than the properties of the organic nonlinear optical material itself, and the crystal form differs depending on the type of solvent. The smaller the amount, the more limited the shape of the crystal becomes, causing the problem that the expected crystal cannot be obtained.

On the other hand, if we widen the selection range to include solvents that have high solubility even when cold, the solution will not reach saturation and crystallization will occur unless the amount of organic nonlinear optical material dissolved in the solvent is increased, but under these conditions many It has the disadvantage that it tends to crystallize.

The present invention has been made in view of the above, and an object of the present invention is to provide a simple method for growing a crystal by which a good large-sized organic nonlinear optical single crystal can be obtained.

[Means for Solving the Problems] In the present invention, in a method of growing an organic nonlinear optical single crystal by precipitating it from a solution in which an organic nonlinear optical material is dissolved, as a solvent for the solution, a solution having a solubility of the organic nonlinear optical material is The above problems are achieved by using a mixed solvent in which a plurality of different solvents are mixed.

[Operation] When solvents with different solubility of the organic nonlinear optical material are mixed, the solubility of the nonlinear optical material in the mixed solvent changes depending on the mixing ratio. That is, when a solvent with low solubility is added to a solvent with high solubility, the solubility of the nonlinear optical material at a constant temperature in the solvent with high solubility changes (decreases).
Therefore, the saturation temperature can be set to a desired temperature (the upper and lower limits are limited to the saturation temperature when each solvent is used alone). Being able to freely set the saturation temperature in this way is very effective in considering conditions for growing a good single crystal.

In addition, since it is a solvent that dissolves organic nonlinear optical materials very well, solvents that could not be used as crystallization solvents due to polycrystallization can now be used by mixing them with solvents with low solubility, making it possible to select solvents. The range of information is expanded.

In the present invention, suitable solvents with low solubility include halogenated hydrocarbon solvents such as methylene chloride, chloroborm, and carbon tetrachloride; alcoholic solvents such as methanol, ethanol, n-propanol, and i-propanol; Ether solvents such as 2-methylfuran, tetrahydrofuran, dimethoxyethane, ketone solvents such as acetone, methyl ethyl ketone, γ-butyrolactone, ester solvents such as methyl formate, ethyl formate, methyl acetate, ethyl acetate, formic acid, acetic acid, etc. Examples include fatty acid solvents, nitrogen compound solvents such as nitromethane, diethylamine, acetonitrile, pyridine, and ethylenediamine, among which acetone, chloroform, 2-methylfuran, tetrahydrofuran, methyl formate, ethyl formate, and methyl acetate are preferably used. .

In addition, examples of solvents with low solubility for organic nonlinear optical materials include hydrocarbon solvents such as n-hexane, isooctane, hensen, and toluene, carbon tetrachloride, triethylamine, and isopropyl ether, among which n
-Hexane is preferably used.

The above-mentioned combination of a solvent with high solubility and a solvent with low solubility is appropriately selected depending on the solute (organic optical material), but it is preferable that the difference in solubility between the two is at least 20 or more. Note that the solvents constituting the mixed solvent are not necessarily two.
It doesn't have to be a type, but depending on the situation, it can be 3F! Solvents of the same type or higher may be mixed.

Further, in the present invention, the method of precipitating the crystals is not particularly limited, and the crystals may be precipitated by evaporating the solvent, or the crystals may be precipitated by cooling the solution and using the difference in solubility of the solution. It's okay. However, from the viewpoint of precipitation rate, ease of temperature control, etc., it is preferable to maintain the solution at a saturation temperature, evaporate the solvent as the crystals grow, and precipitate the crystals while keeping the degree of saturation of the solution constant. At this time, if the solvent is selected so that the boiling point of the solvent with higher solubility is lower than the boiling point of the solvent with lower solubility, redissolution of the grown single crystal can be suppressed.

[Example] The method for growing an organic nonlinear optical single crystal of the present invention will be explained in detail in the following example with reference to FIG.

Example: 1 First, sufficiently purified 2-(
Weighed 10 g of α-methylhensylamino)-5-nitroviridine (hereinafter abbreviated as MBA-NP), and
00 ml of glass container 1, and then add a mixed solvent of 40 ml of sufficiently purified acetone (boiling point 56.5°C) and 280 ml of n-hexane (boiling point 69°C).
The temperature of the seven products was raised to 50 degrees Celsius for seven nights to completely dissolve the MBA-NP.

After filtering this solution to remove impurities,
The glass container 1 was placed in a constant water tank 5, and the liquid temperature was gradually lowered to 14 degrees Celsius. Then, in this solution, a seed crystal 4 of MBA-NP (confirmed as a single crystal by X-ray diffraction, etc.) attached to a platinum wire (diameter 0.5 mm) was suspended.
I left it still. Further, the amount of evaporation of the solvent was adjusted to 10 to 30 m1/day by removing nitrogen gas 3 from one side of the glass tube 2 (diameter 3.5 mm) installed on the top of the glass container 1.

By the above-mentioned growing method, MBA-NPs with a size of about 10 x 10 x 15 mm can be grown in 3 to 5 days.
A single crystal was obtained. Analysis using X-ray diffraction and polarized light microscopy revealed that it was a single crystal whose outer shape roughly aligned with the dielectric axis of the crystal.

A single crystal having such a structure is a very good single crystal that is easy to handle when processed into an optoelectronic device.

Example 2 Weighed 10g of sufficiently purified MBA-NP, and
00ml glass container 1, and then add a mixed solvent of 48ml fully purified ethyl formate (boiling point 54.3°C) and 80ml n-hexane (boiling point 69°C), and raise the liquid temperature to 50°C. , the MBA-NPs were completely dissolved.

After filtering this solution to remove impurities,
This container was placed in a thermostatic water tank 5, and the liquid temperature was gradually lowered to 12 degrees Celsius. In this solution, a platinum wire (
MBA-NP seed crystal (diameter 0.5 mm) attached to
(confirmed to be a single crystal by X-ray diffraction etc.) was hung and allowed to stand still. Further, by flowing nitrogen gas 3 from one side of the glass tube 2 (diameter 3.5 mm) installed above the glass container 1, the evaporation amount of the solvent was adjusted to 10 to 30 m1/day.

By the above-mentioned growing method, MBA-NPs with a size of about 12 x 15 x 15 mm can be grown in 3 to 5 days.
A single crystal of was obtained. Analysis using X-ray diffraction, polarizing microscope, etc. revealed that it was a very good single crystal with a crystal outer shape almost aligned with the dielectric axis of the crystal.

0 Example 3 Weighed 10 g of sufficiently purified MBA-NP, and added 5
00ml glass container 1, and add a mixed solvent of 50ml fully purified methyl acetate (boiling point 575°C) and 80ml n-hexane (boiling point 69°C).
The temperature was raised to 50 degrees Celsius to completely dissolve the MBA-NPs.

After filtering this solution to remove impurities,
This glass container 1 was placed in a constant temperature water tank S, and the liquid temperature was gradually lowered to 12 degrees Celsius. And in this solution,
A seed crystal 4 of MBA-NP (confirmed to be a single crystal by X-ray diffraction, etc.) attached to a platinum wire (diameter 0.5 mm) was hung and allowed to stand still. In addition, the adjustment of the amount of evaporation of the solvent was carried out in Example 1.2.
Glass tube 2 (diameter 3.5 m) installed at the top of the container in the same way as
Nitrogen gas is added to m1 from one side so that the amount of evaporation of the solvent is lθ~3o
This was done by flowing the solution at a rate of ml/day.

By the above-mentioned growth method, MBA-NPs with a size of about IOX 20X 25mm can be grown in 3 to 5 days.
A single crystal of was obtained. Analysis using X-ray diffraction, polarizing microscope, etc. revealed that it was a very good single crystal with a crystal outer shape almost aligned with the dielectric axis of the crystal.

Comparative example: 1 6.5 g PP of sufficiently purified MBA-N P was placed in a 50 On + 1 glass container 1, and 50 ml of sufficiently purified ethanol (boiling point 78.3°C) was added, and the liquid temperature was The temperature was raised to 50 degrees Celsius to completely dissolve the MBA-NP.

After filtering this solution to remove impurities,
This glass container 1 was placed in a thermostatic water tank 5, and the liquid temperature was gradually lowered to 19.5 degrees Celsius.

A seed crystal 4 of MBA-NP (confirmed to be a single crystal by X-ray diffraction or the like) attached to a platinum wire (diameter 0.5 mm) was suspended in this solution and allowed to stand still. In addition, to adjust the amount of evaporation of the solvent, as in Example 1, nitrogen gas was introduced from one side into the glass tube 2 (diameter 3.5 mm) installed at the top of the container so that the amount of evaporation of the solvent was 10 to 30 m1/day. This was done by letting it flow.

By the growth method described above, crystals with a size of about 10 x 10 x 8 mm were obtained in a growth time of 3 to 5 days.1 However, the outer shape of the crystal was irregular and the crystal sides were opaque. .

[Effects of the Invention] As described above, in the present invention, by using a mixed solvent in which a plurality of solvents having different solubility are mixed as a crystallization solvent, even solvents that are conventionally unsuitable as a crystallization solvent can be used. This has made it possible to greatly expand the range of solvent selection, and it has also become possible to keep the concentration of organic nonlinear optical materials in solution low and prevent polycrystallization.

That is, the present invention has the effect that a large organic nonlinear optical single crystal with a good crystal structure can be easily obtained, and is very useful for applying organic nonlinear optical materials to various optoelectronic devices. Beneficial.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an organic nonlinear single crystal growth apparatus in an embodiment of the present invention. [Explanation of symbols of main parts] 1 Glass container 2 Glass tube nitrogen gas seed crystal (MBA-NP): Constant temperature water tank growth solution (thirstification solvent 10 MBA-NP)

Claims (1)

[Claims] In the method of precipitating and growing an organic nonlinear optical single crystal from a solution in which an organic nonlinear optical material is dissolved, a mixed solvent in which a plurality of solvents having different solubility of the organic nonlinear optical material are mixed is used as a solvent for the solution. A method for growing an organic nonlinear optical single crystal characterized by: