JP3062753B1 - Method for producing bulk single crystal of fluoride - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To use a fluoride powder raw material of lower purity (for example, 99.9% by weight) than a conventional method,
Provided is a manufacturing method capable of manufacturing a high-quality fluoride single crystal. SOLUTION: While maintaining a high vacuum of 10 ^-6 torr or more, a powdery fluoride raw material is heated from room temperature to a temperature within a range of 500 ° C. or more and a predetermined temperature or less, and the water contained in the raw material After removing oxygen and melting the raw materials, a fluorocarbon gas is introduced into the production furnace, and impurities generated on the surface of the melt or the solution and impurities present in the melt or solution, and the fluorocarbon gas in the production furnace, Is reacted for a time sufficient to remove the impurities, thereby removing the impurities, and producing a bulk fluoride single crystal from the resulting melt or solution by a melt growth method. Method for producing crystals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a method for producing a bulk single crystal of fluoride. According to the production method of the present invention, a high-quality fluoride single crystal for laser can be produced.

[0002]

2. Description of the Related Art Fluoride-based single crystal materials have attracted great expectations as laser crystals because of their properties such as high transmittance over a wide range, a small crystal field, and a negative temperature coefficient of refractive index. However, the fluoride single crystal has a manufacturing atmosphere, a manufacturing temperature, control of the purity and composition of the raw materials, etc.
There are many factors that make fabrication difficult. YLiF ₄ (YLF) single crystal is one of the excellent materials used for laser oscillation in the ultraviolet and infrared regions, but the conditions for its production were not clear.

Conventionally, in producing a fluoride bulk single crystal, a powdery raw material having a purity of 99.999% by weight (hereinafter referred to as "5N" because five are arranged in 9; the same applies to "3N" hereinafter). , Or a powder raw material having a water content of 1 ppm or less. For this reason, a method for producing a bulk fluoride single crystal by zone-purifying the starting material or purifying the starting material by removing water and the like in a stream of dry hydrogen fluoride (hereinafter referred to as HF), or A method for producing a bulk fluoride single crystal in dry HF has been proposed.

[0004]

However, these methods require the use of a high-purity fluoride powder raw material and require complicated processing steps. Therefore, it is simpler than the method of the prior art, and for example, has a purity of 3N (9
9.9% by weight) grade fluoride powder raw material,
There is a need for a method that can produce high quality single crystals.

[0005]

Means for Solving the Problems The present inventors have developed a method for producing a high-quality bulk single crystal of a fluoride which is useful for an all solid-state (variable wavelength) ultraviolet / infrared (near infrared / far infrared) region laser. As a result of the investigation, it has been found that the use of a fluorocarbon-based gas is effective for producing a high-quality single crystal even when using a fluoride powder raw material whose purity is not as high as the left. That is, a commercially available fluoride powder is not subjected to zone purification or high purification such as removal of water in a dry HF gas stream, or even without performing crystal preparation in an HF atmosphere, using a method comprising the following steps. Thus, it has been found that high quality bulk single crystals of fluoride can be produced.

That is, according to the method for producing a bulk single crystal of fluoride of the present invention, a powdery fluoride raw material is heated from room temperature to a temperature in the range of 500 to 1000 ° C. while maintaining a high vacuum of 10 ⁻⁶ torr or more. After removing water and oxygen contained in the raw material, melting the raw material, introducing a Freon-based gas into the production furnace, and removing impurities generated on the surface of the melt or solution and impurities present in the melt or solution. The impurities are removed by reacting with the fluorocarbon gas in the production furnace for a time sufficient to remove the impurities, and a fluoride bulk single crystal is produced from the resulting melt or solution by the melt growth method. It is characterized by doing.

[0007] According to the above manufacturing method, for example, 3N purity
Even when a (99.9% by weight) -grade fluoride powder raw material is used, a high-quality single crystal can be produced more easily than in the method of the related art.

[0008] The method for producing a bulk fluoride single crystal of the present invention comprises the step of growing a bulk fluoride single crystal from a melt or a solution obtained by removing impurities by a melt growth method in an atmosphere of an inert gas such as Ar. It is preferable to make it. By doing so, it is possible to more effectively prevent impurities from being mixed when growing and producing a bulk fluoride single crystal by the melt growth method.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for producing a bulk fluoride single crystal of the present invention will be described below in more detail. Dissolution of powdered fluoride raw material and removal of water and oxygen While maintaining a high vacuum of 10 ^-6 torr or more, the powdered fluoride raw material is heated from room temperature to a predetermined temperature in the range of 500 to 1000 ° C. To remove moisture and oxygen contained in.

In this case, the powdery fluoride raw material is appropriately selected and used according to the desired composition of the single crystal. The particle size and the like are not particularly limited and are within a range that can be appropriately set by those skilled in the art.
The high vacuum of 10 ^-6 torr or more is intended to facilitate removal of moisture and oxygen. 10 ^-6 torr
If it is less than this, water cannot be sufficiently removed.

The powdery fluoride raw material is heated from room temperature to a predetermined temperature in the range of 500 ° C. or more, for example, 1000 ° C., to remove moisture and oxygen contained in the raw material. If the temperature is lower than 500 ° C., a sufficient effect cannot be expected, and the upper limit temperature is set from the viewpoint of removing moisture and oxygen, for example, 1000 ° C.

Removal of impurities After melting the raw material, a fluorocarbon-based gas is introduced into the production furnace, and impurities generated on the surface of the melt or the solution and impurities present in the melt or the solution are mixed with the fluorocarbon gas in the production furnace. Are reacted for a time sufficient to remove the impurities, thereby removing the impurities. As long as a fluorocarbon-based gas can be used in this step, for example, CF ₄ can be used. Also, a mixed gas of a chlorofluorocarbon-based gas and another gas, for example, C ₂ H ₆ can be used. The “sufficient time for removing impurities” can be, for example, within 30 minutes. Note that the case where the composition of the grown crystal is equal to the composition of the liquid is called “melt”, and the case where it is not is called “solution”.

Production of Fluoride Bulk Single Crystal by Melt Growth Method From the obtained melt or solution, a fluoride bulk single crystal is produced by a melt growth method.

Hereinafter, preferred embodiments of the method for producing a bulk fluoride single crystal of the present invention will be specifically described. As a raw material component, in order to obtain a desired single crystal chemical composition, for example, CaF ₂ , AlF ₃ , LiF, BaF ₂ , YF ₃ , CeF _3, etc., purity 99.95%
The commercially available fluoride powder raw material is appropriately selected and blended in a predetermined amount. The powdered fluoride mixed raw material is pushed into the crucible with a spoon or the like, and is placed in a single crystal production furnace as it is. Here, vacuum is drawn to about 10 ^-6 torr, and 500
The temperature is raised to a temperature in the range of -1000 ° C., for example, about 700 ° C., and the mixture is heated in a vacuum state to remove water and oxygen in the powdery fluoride raw material.

Here, a fluorocarbon gas such as CF ₄ is introduced into a single crystal production furnace. Thereafter, the temperature is further raised to melt the powder raw material and kept in a liquid state for 30 minutes. At this time,
Impurities (oxides, oxyfluorides, carbon, etc.) appearing on the liquid surface due to the influence of moisture or the like existing in the powder raw material or in the furnace are completely eliminated by reacting with the chlorofluorocarbon-based gas. As a result, a melt (or solution) free of impurities is obtained. By producing a single crystal from this melt (or solution) by a solution growth method, a high quality fluoride bulk single crystal can be obtained.

There are various methods for producing a single crystal. For example, the pulling method is performed as follows. The temperature of the melt is kept close to the melting point of each compound, and by pulling the seed crystal at a speed of 0.1 to 10 mm / h while rotating at 1 to 50 rpm, the crystal is transparent and free of bubbles and scattering centers. High quality single crystals can be obtained. As another single crystal manufacturing method, the Bridgman method or the like can be considered.

[0018] In the phase of the resulting single crystal X-ray powder analysis (XRD), also OH ^- presence or absence of groups FR-IR
Investigated by

[0019]

EXAMPLES Examples of the present invention will be described below with reference to comparative examples.

Example 1 Commercial powdery materials of 3N purity LiF, CaF ₂ , AIF ₃ were prepared at a molar ratio of 1: 1: 1, and they were filled in a crucible without mixing. The total weight of the raw materials was 140 g.
Place the crucible in the single crystal production furnace as it is, 10 ^-6 Torr
The mixture was evacuated to a vacuum and heated under vacuum to about 700 ° C. to remove water and oxygen in the mixture.

Here, CF ₄ gas is introduced into a single crystal production furnace,
Heat and melt the powder raw material in CF ₄ gas atmosphere,
Minutes, kept in liquid state. At this time, all impurities appearing on the liquid surface disappeared by reacting with the CF ₄ gas. Next, the seed crystal is brought into contact with the melt, and pulled up in the c-axis direction at a speed of 1 mm / h.
A single crystal was grown and produced at a rotation speed of 15 rpm. The produced crystal was a transparent and high-quality LiCaAIF ₆ single crystal having a diameter of about 20 mm and a length of about 80 mm without bubbles, cracks, and scattering centers. No existence of OH ^- groups or the like which cause deterioration of laser characteristics was observed in the crystal.

[0021]

[Comparative Example 1] Commercial powdery raw materials of LiF, CaF ₂ and AIF _{3 having} a purity of 5N were prepared at a molar ratio of 1: 1: 1, and they were mixed.
The mixture was filled in a crucible. The total amount of the raw materials was 130 g. Place the crucible in the single crystal production furnace and
Vacuum to about ^-2 torr, about 700 ° C in vacuum
Heated to the extent.

Here, an Ar gas (or CF ₄ gas) was charged into a single crystal production furnace and kept flowing at a flow rate of 1 l / min. Thereafter, when the temperature was raised to melt the powder raw material, a large amount of impurities were generated on the liquid surface. So once cool down to room temperature,
The impurities on the surface were removed. Thereafter, the temperature was raised again by the same process, but the same impurities were generated again. Then, a seed crystal was brought into contact with the liquid to produce a single crystal at a pulling rate of 1 mm / h and a rotation speed of 15 rpm in the c-axis direction. As a result, a LiCaAIF ₆ crystal having a large amount of impurities attached to the crystal surface was obtained.

[0023]

[Example 2] YF ₃ , LiF, CeF _{3 with a} purity of 3N
₃ : Prepared as LiF = 0.48: 0.52 (molar ratio),
They were filled into crucibles without mixing. The total weight of the raw materials was 250 g. Place the crucible in the single crystal production furnace as it is and evacuate it to about 10 ^-6 torr,
It was heated in a vacuum to about 0 ° C.

Here, CF ₄ gas was introduced into a single crystal production furnace.
Thereafter, the temperature was raised to melt the powder raw material, and kept in a liquid state for 30 minutes. At this time, all impurities appearing on the liquid surface disappeared by reacting with the CF ₄ gas. A seed crystal was brought into contact with the liquid, and a single crystal was pulled in the c-axis direction at a pulling speed of 1 mm / h and a rotation speed of 15 rpm. The prepared single crystal has a diameter of about
It was a transparent, high-quality single crystal of Ce: YLiF _{4 having} a size of 20 mm and a length of about 90 mm, free of bubbles, tarts, scattering centers and the like. OH which causes deterioration of laser characteristics in the crystal
Was not observed at all.

[0025]

[Comparative Example 2] YF ₃ , LiF, CeF _{3 with} 5N purity
₃ : Prepared as LiF = 0.48: 0.52 (molar ratio),
After mixing them, they were filled in a crucible. The total weight of the raw materials was 250 g. The crucible was placed in a single crystal production furnace as it was, and the crucible was evacuated to about 10 ^-2 torr and heated to about 700 ° C. in a vacuum.

Here, an Ar gas (or CF ₄ gas) was charged into a single crystal production furnace, and kept flowing at a flow rate of 1 l / min. Thereafter, when the temperature was raised to melt the powder raw material, a large amount of impurities were generated on the liquid surface. Then, it was once cooled to room temperature to remove impurities on the surface. Thereafter, the temperature was raised again by the same process, but the same impurities were generated again. Then, the seed crystal is brought into contact with the liquid, the pulling speed is 1mm / h in the c-axis direction,
As a result of producing a single crystal pulled at pm, it became completely cloudy, Ce:
Crystals containing YLiF ₄ and a mixture of YOF and CeOF were obtained.

──────────────────────────────────────────────────続 き Continuing from the front page (56) References Shinichiro Tozawa et al., “Creating CaF2 Single Crystal for Ultraviolet Laser Glass by Cz Method,” Technical Research Report, Technical Department, Institute of Metals, Tohoku University, 1999. Month, pp. 29-32 I. M. Ranieri et al. , “Growth of LiYF 4 crystals doped with holmium, erbium and thulium,”, Journal of Crystal Growth, vol. 166. 1996, pp. 423-428 (58) Fields investigated (Int. Cl. ⁷ , DB name) C30B 1/00-35/00 CA (STN)

Claims (2)

(57) [Claims] 1. While maintaining a high vacuum of 10 ^-6 torr or more, a powdery fluoride raw material is heated from room temperature to a temperature in a range of not less than 500 ° C. and not more than a predetermined range. After removing oxygen and melting the raw material, a fluorocarbon gas is introduced into the production furnace, and impurities generated on the surface of the melt or solution and impurities present in the melt or solution, and fluorocarbon gas in the production furnace are mixed with each other. Is reacted for a time sufficient to remove the impurities, thereby removing the impurities, and producing a bulk fluoride single crystal from the resulting melt or solution by a melt growth method. Method for producing crystals. 2. A fluoride bulk single crystal is produced from a melt or a solution obtained by removing impurities by a melt growth method in an atmosphere of an inert gas such as Ar. Production method. [0001]