JPWO2005098096A1 - Self-coated single crystal and manufacturing apparatus and manufacturing method thereof - Google Patents

Abstract

An object of the present invention is to provide a self-coated single crystal whose outer periphery is coated with layers having different characteristics without passing through a special process after crystal growth. The self-coated single crystal of the present invention is obtained by melting a crystal material to be a core and a clad into a single crucible and growing the single crystal in an as-grown manner in the process of crystal growth using a pulling method or a pulling method. In this state, the outer periphery of the crystal is self-coated with a clad having a refractive index lower than that of the core.

Description

  The present invention relates to a so-called self-coated single crystal in which a coating layer (a layer having characteristics different from the inside) has already been formed on the outer periphery in a state in which the single crystal is grown (as growth). The present invention relates to a manufacturing apparatus and a manufacturing method.

Japanese Patent Laid-Open No. 10-265293 JP-A-8-259375 JP 11-278994 A JP-A-10-251098

  Crystals containing optically active ions are used in many luminescent media such as solid state lasers and scintillator devices. Solid lasers have a higher density of laser operating materials than gas lasers, so high power of 100 MW can be obtained with a pulse wave of several tens of nanoseconds. It is also possible to increase the efficiency by using a semiconductor laser as an excitation light source. A laser using Yb has better quantum efficiency than a laser using Nd, and the excitation level and the emission level are the same, so there is little heat generated by the laser oscillation process, and it is promising as a high-power laser.

  However, in any light emitting medium, light is radiated in all directions during the light emission process, and only a small amount of light radiated in the direction of the detector can be extracted, resulting in a substantial loss. Further, the heat generated by the excitation causes a thermal birefringence effect, a thermal lens effect, a decrease in the intensity of output light due to the thermal population, and a deterioration in beam quality. For this purpose, a special coating has been conventionally provided as a post-processing step.

That is, in a crystal without a surface coating of the crystal, light is radiated in all directions during the light emission process, and only a small amount of light radiated in the direction of the detector can be extracted, resulting in a substantial loss. For this reason, in a device with low light emission, such as a scintillator crystal, the surface of the crystal is coated to increase the emission intensity in order to collect the emitted light.

  On the other hand, as methods for growing single crystals of various materials, there are many methods such as Cz method, Bridgman method, EFG method, hydrothermal synthesis method, solution growth, epitaxial growth, and thin film method. This method requires a great deal of cost and days to obtain a single crystal, which hinders the speed of new material development. In addition, since a cutting margin or the like due to the cutting of the crystal after production occurs, the yield is poor, and the entire surface needs to be processed, and the cost of the crystal becomes high.

  As a method for growing the single crystal, a micro pulling-down method is known (Patent Document 1, Patent Document 2, and Patent Document 3). For example, Patent Document 1 describes a specific device in paragraph number (0025) and FIG. Further, FIG. 3 of Patent Document 3 also describes a specific configuration of the apparatus.

  In the techniques described in Patent Document 1 and Patent Document 2, crystal growth is possible at a rate one or two orders of magnitude higher than other melt growth methods. Therefore, the time required for the production of crystals is short, and a single crystal having a significant size and high quality can be obtained with a small amount of raw materials. Further, since the crystal is pulled out from the bottom pore of the crucible, it can be grown without removing impurities floating on the upper surface of the melt.

  However, even in the techniques described in Patent Document 1 and Patent Document 2, when the produced crystal is used as an optical element, the crystal is cut into a target size after the crystal is produced, and the entire crystal is polished and coated. There must be.

  In terms of thermal conductivity, since the thermal conductivity of the crystal is unique to the crystal, the luminescent medium with low thermal conductivity cannot release the heat generated by excitation, the thermal birefringence effect, the thermal lens effect, High output and high quality continuous oscillation is difficult because it causes a drop in output light intensity and beam quality degradation due to thermal population.

  The present inventor has applied this micro-pulling method to fluorides, studied an apparatus and a manufacturing method (Patent Document 1), and succeeded in growing crystals having a diameter of about 1 mm. However, when evaluating whether a crystal grown by the same method is suitable for various applications such as a solid-state laser and a scintillator, it has been found that a crystal having a shape corresponding to the material is necessary.

  In Patent Document 4, an oxide single crystal material constituting a core portion is dissolved in a first crucible to form a first melt, and an oxide single crystal material constituting a clad portion is dissolved in a second crucible. After melting and making the second crucible melt, the first and second melts are brought into contact with the seed crystal, and then the second melt is brought into contact with the first melt while lowering the first melt. And pull it down. Thereby, it pulls down, integrating a core part and a clad part.

However, in this technique, the heating method is difficult, and it is very difficult to determine the conditions. In addition, seeding is separately performed on both the core part and the clad part. However, it is practically very difficult to seed both the core portion and the clad portion.
If the positional relationship between the first crucible and the second crucible is not precisely controlled, the thickness of the clad portion will be uneven.

  An object of the present invention is to provide a self-coated single crystal whose outer periphery is coated with layers having different characteristics without passing through a special process after crystal growth.

  The self-coated single crystal of the present invention is obtained by melting a crystal material to be a core and a clad into a single crucible and growing the single crystal in an as-grown manner in the process of crystal growth using a pulling method or a pulling method. In this state, the outer periphery of the crystal is self-coated with a clad having a refractive index lower than that of the core.

The single crystal is a single crystal grown by a micro pulling method.
The single crystal is a single crystal for a light emitting medium.
The single crystal is a single crystal for a solid laser or a scintillator.

In the above self-coating, the temperature distribution in the vicinity of the melt-crystal interface selectively decreases the solubility of specific constituents in the melt due to the temperature difference, resulting in a clad composition and a temperature distribution that causes self-coating. Therefore, self-coating is realized.
The material to be the cladding material is a material in which a rare earth element or a transition element is added to the material to be the core material.

  Each of the cladding materials is preferably an additive-free material, while the core material is preferably a material to which an activator such as a rare earth element or a transition element is added. In general, the element-added one has a melting point of several degrees C. to several tens of degrees C. Therefore, when the temperature of the outer side (cladding part) is low, an additive-free crystal grows on the outer periphery (cladding part).

  The additive-free crystal has higher thermal conductivity and smaller refractive index, so that heat can be released efficiently and light that is going to go out from the inside also goes out due to the total reflection phenomenon. As a result, there is an advantage that light can be extracted only from the longitudinal direction of the crystal.

Wherein as the core material of the single _{crystal, Yb: YAG (Y 3 Al} 5 O 12), Nd: YAG (Y 3 Al 5 O 12), Yb: LuAG (Lu 3 Al 5 O 12), Nd: LuAG (Lu ₃ Al ₅ O ₁₂ ), Ti: Sapphire (α-Al ₂ O ₃ ), Cr: Sapphire (α-Al ₂ O ₃ ), Ce: GSO (Gd ₂ SiO ₅ ), Ce: LSO (Lu ₂ SiO ₅ ) , Ce: LiCAF (LuCaAlLiF ₆ ), Ho: LuLF (LuLiF ₄ ), HoTm: YLF (YLiF ₄ ), Ce: PrF ₃ , LN (LiNbO ₃ ), LT (LiTaO ₃ ) Features.
For the clad part, an additive-free material is preferably used. For example, it is made of additive-free Al ₂ O ₃ (sapphire).

The method for producing a self-coated single crystal according to the present invention involves melting materials with different melting points in a single crucible, and providing a temperature gradient that lowers the temperature from the center to the edge at the solid-liquid interface. Or crystal growth is performed by a pulling method.
The temperature gradient can be controlled by setting B / S to a predetermined value. That is, the single crystal manufacturing apparatus of the present invention is a single crystal manufacturing apparatus for pulling and growing a single crystal from a hole formed at the bottom of the crucible. A planar protrusion (referred to as a shaper) having an outer diameter (S) not more than 5 times that of B) is provided.

1.2 <(B / S) <5.
It is characterized by 1.5 <B / S <4.5.
Considering the vicinity of the protrusion under the crucible, the protrusion is a part of the crucible, so it itself generates heat, and there is also heat conduction from the crucible Body, so the temperature is high. However, considering the in-plane of the same height, the distribution is such that the temperature decreases near the outer periphery of the protrusion. However, when the outer periphery of the crucible body is sufficiently large, the temperature distribution around the protrusion is also uniform so that the presence or absence of the protrusion can be ignored. It has been found that the threshold value is B / S = 5.

In the method for producing a single crystal of the present invention, a planar protrusion having an outer diameter (S) not more than 5 times the inner diameter (B) of the crucible is provided around the outlet side of the hole formed in the bottom of the crucible. The method for producing a self-coated single crystal according to claim 8, wherein the single crystal is grown.
In the method for producing a single crystal in which the single crystal is pulled and grown from the hole formed in the bottom of the crucible, the outer diameter (S) is not more than three times the inner diameter (B) of the crucible around the outlet side of the hole. A single crystal is grown by providing a planar protrusion.
1.2 <B / S <5.
It is characterized by 1.5 <B / S <4.5.
As the material for the cladding, a material having a higher melting point than the material for the core is used.
By flowing an inert gas from below the crucible, the outside of the melt is cooled to achieve a desired temperature gradient.
Generally, atmospheric gas enters from the crucible information. However, cooling is performed more strongly by supplying atmospheric gas such as nitrogen gas and argon gas from below the after heater. When that happens, it is especially nurtured.

Since the outside of the crystal (ie, the outer periphery when considering the cross section of S) is strongly cooled, the temperature becomes relatively low, and the high-melting point additive-free crystal is preferentially crystallized. become.
The larger the temperature gradient that is formed, the better. By increasing the temperature gradient, the boundary region between the core and the clad is narrowed, and a single crystal having a steeper composition change can be obtained.

  Self-coated rod-like crystals are produced by the micro pull-down method (μ-PD method). The μ-PD method is a method for producing a crystal by pulling a raw material melted in a crucible from a hole at the lower end of the crucible. When the starting material is a composition in which the cation ratio is shifted by about 10% from the light emitting medium intended for the crystal composition, and the temperature gradient in the melt is sufficiently high, the low refractive index phase caused by the composition deviation is melted by convection. It is carried to the end of the liquid and solidifies so as to coat the crystal (FIGS. 1 and 4).

Here, the width of the shaper at the lower end of the crucible is S, the width of the body is B, and S: B = 1: x (FIG. 1). When x <5, there is a steep temperature gradient in the melt and the crystal is coated (FIG. 2), but when x> 5, the melt has no sufficient temperature gradient and the crystal is coated. Not (FIG. 3). In addition, it is necessary to suppress the size of the shaper when producing ultrafine fibers, and x becomes large and self-coating is difficult. In this case, Ar or N ₂ gas is allowed to flow upward from the bottom of the crucible so that the outside of the melt is cooled by the gas, a steep temperature gradient is realized, and crystals can be coated even at x-30.
This technique makes it easy to process a single crystal by using only two surfaces.

  Since the inside of the crystal having a high refractive index is the core and the coating portion is the cladding (FIGS. 2 and 5), it is possible to collect the light radiated from the luminescent medium in all directions by total reflection, and it can be obtained by a detector. A dramatic increase in the amount of luminescence was confirmed.

  By coating the surface of the crystal with a material having a high thermal conductivity, a cooling effect works, and heat generated during the light emission process can be released to the outside of the crystal. As a result, high power excitation, continuous oscillation, and light emission at high temperatures are possible.

  The crystal cutting and processing need only be performed on two surfaces, and the yield is good. Moreover, the labor of processing can be saved greatly, and the setting at a low price is possible.

It is a conceptual diagram which shows the crucible bottom part provided with shaper. In FIG. 1, it is a conceptual diagram which shows the case of 5> x. In FIG. 1, it is a conceptual diagram which shows the case of 5 <x. 4 is an external view of a self-coated LN single crystal in Example 2. FIG. It is a graph which shows the refractive index distribution in the crystal | crystallization in the single crystal shown in FIG.

  The present invention is a method of growing a single crystal by pulling a single crystal from a crucible containing a melt and containing a melt (micro pulling method), and designing the shape of the crucible bottom hole and the crucible bottom. Thus, the shape of the grown crystal can be controlled.

  The melt coming out of the crucible hole travels on the outer surface of the outer bottom of the crucible due to its wettability. The extent to which the melt wets depends on the nature of the crucible (eg, material, surface roughness), the nature of the pores (eg, hole diameter, length), and the nature of the melt (eg, material, temperature). The range of wetting is determined according to the crucible, melt, and hole. If the shaper is designed to have an arbitrary surface shape within the wet range, crystals corresponding to the arbitrary surface shape are grown.

  The shaper shape can be any shape. For example, the shape may be a circle, an ellipse, a square, a rectangle, or another polygon, and the surface shape may be designed to have an arbitrary size larger than the size of the hole as long as the surface is wet.

The shaper may be formed in the crucible itself, or a shaper having a desired shape may be attached to the crucible.
The step in the protrusion (the length in the vertical direction with respect to the lower surface of the protrusion is preferably 1 mm or more. By setting it to 1 mm or more, it is possible to prevent an increase in melt with good wettability, and to form a single crystal of any shape. The upper limit is preferably 5 mm, and if it exceeds 5 mm, the melt passage may be lengthened, and 1.5 to 3 mm is preferable.

  The range of wetting varies depending on the nature of the crucible, the nature of the holes, and the nature of the melt, but each surface may be previously determined by experimentation and the surface shape of the crucible bottom outer surface may be designed accordingly.

  For example, when a platinum crucible is used, the wettability of platinum and fluoride is relatively good. Therefore, if the shape of the crucible is not taken into account, a phenomenon in which the melt rises along the crucible is observed. Conversely, by utilizing this phenomenon and devising the shape of the bottom surface of the crucible, the crystal shape can be controlled. That is, it is possible to grow a crystal having a diameter of 2 mm or more (diameter 2 to 5 mm), which is difficult with a carbon crucible, and also to a crystal having a diameter of 2 mm or less (diameter 0.5 to 2 mm).

  In this case, the bottom hole of the crucible is 0.2 to 0.5 mm, and the bottom surface having the hole, that is, the portion where the melt is transmitted by wetting is set to about 0.5 to 5 mm in diameter, and the melt is transmitted through the crucible. Therefore, a crystal depending on the shape can be grown.

  Further, if the shape of the bottom surface of the crucible is, for example, 0.5 mm wide and 10 mm long, a plate-like crystal can be grown, and if it is, for example, 3 mm square, a square crystal can be grown.

As an example, Yb-added YAG is added with a small amount of Al ₂ O ₃ (sapphire). A small amount of sapphire is light in weight and is easily carried to the end of the melt by convection. Here, since the melting point of sapphire (2050 ° C.) is higher than the melting point of YAG as a melt (1930 ° C.), sapphire is cooled at the end of the melt and solidifies so as to coat the garnet phase. The added Yb enters only the garnet phase and becomes a luminescent medium. When Yb is added, Yb: YAG has a high refractive index and becomes a core, and the outer sapphire phase becomes a clad with a low refractive index. Therefore, the light emitted from the core can be extracted with no loss repeatedly and totally reflected.

  In addition, the thermal conductivity of sapphire in the cladding is higher than that of rare earth oxides among oxides, so that heat generated during the light emission process can be efficiently released, and laser oscillation at high output is possible without the need for a cooling device. This is possible and is expected to reduce the size of the device.

Hereinafter, embodiments of the present invention will be described in detail.
The self-coated crystal was produced by high-frequency induction heating type micro-pulling (μ-PD method). Ir or Pt was used for the crucible material and the after heater. A crucible having a flat shaper at the lower end was used. As shown in FIG. 1, it is assumed that the diameter of the shaper at the bottom of the crucible is S and the radius of the body part is B. When S: B = 1: x, the crystals were self-coated when 1.2 <x <5, preferably 1.5 <x <4.5.
As shown in FIG. 2, when x <5, the temperature difference between the central portion and the edge portion of the shaper is 100 ° C. or more, and the phase caused by the composition deviation at the edge portion due to this steep temperature gradient is crystallized. Solidify to coat. Further, as shown in FIG. 3, when x> 5, the temperature difference between the shaper center and the edge becomes less than 100 ° C., and the crystal is difficult to be coated.
It is necessary to suppress the size of the shaper when producing ultrafine fibers, and x becomes large and self-coating is difficult. In this case, Ar or N ₂ gas is allowed to flow upward from the bottom of the crucible so that the outside of the melt is cooled by the gas, a steep temperature gradient is realized, and crystals can be coated even at x-30.

The self-coated LN single crystal was produced using a Pt crucible and a Pt after heater in an Ar gas or 2% oxygen mixed Ar gas atmosphere. The seed crystal used was an LN single crystal. Li ₂ CO ₃ (4N), Nb ₂ O ₅ (4N), and MnO ₂ (4N) powder were used as raw materials.
The starting material used was such that the cation ratio was matched with LiMn _x Nb _1-x O ₃ (0 <x <0.5) and sintered at 800 ° C. for 24 hours or more. The crucible was charged with 1.0 g of raw material. The crystal was produced at a growth rate of 3.0 mm / min or less. The obtained crystal was a fiber having a diameter of about 1.0 mm to 3.0 mm. When x <0.3, the LiNbO ₃ single crystal was coated with Li (Mn, Nb) O ₃ . The appearance is shown in FIG.
The refractive index distribution of the obtained crystal at 633 nm has a high refractive index at the center as shown in FIG. 5, and a core and a clad are formed.

The self-coated Yb: YAG was produced using Ir as a crucible and an after heater, and was produced in an Ar atmosphere in order to prevent Ir oxidation. YAG <111> single crystal was used as a seed crystal. Y ₂ O ₃ (4N), Yb ₂ O ₃ (4N), Al ₂ O ₃ (5N) powder was used as a raw material.
The starting material was weighed so that the cation ratio was equal to (Yb _x Y _1-x ) ₃ Al ₅ O ₁₂ + yAl ₂ O ₃ (0 <x <1, y <3) and baked at 1450 ° C. for 24 hours or more. Using the ligated material, 2.0 g of the crucible was charged. The crystal was produced at a growth rate of 3.0 mm / min or less.
The obtained crystal was a fiber having a diameter of about 1.0 mm to 3.0 mm. When 0 <x <1, y <1, the Yb: YAG single crystal was coated with Al ₂ O ₃ .

According to the present invention, the following effects are achieved.
1. Since the crystal is produced by the μ-PD method, the crystal shape is selective, and crystal shaping after the production is unnecessary.
2. We established a technique to coat the surface of the crystal with a material having a low refractive index in the crystal production process. In addition, this technique makes it possible to omit the cutting of the crystal and the entire processing after the crystal is produced.
3. By coating the crystal surface with a film having a low refractive index, it is possible to collect light radiated in the forward direction in the crystal to the detector with less loss due to total reflection.
4). By coating the crystal surface with a film with high thermal conductivity, the cooling effect worked, and the heat generated during the light emission process was successfully released outside the crystal. This allowed excitation at high power.
5. The self-coating technique can be used in the production of all optical media such as solid laser crystals and scintillator crystals.
6). Since the coating is performed in the rod-shaped crystal production process by the μ-PD method, the processing after the production is only the cutting of the rod and the processing of the cut surface, and there is a high possibility that it will be supplied at a low cost in the future.
7). In a solid-state laser using a self-coated single crystal, the amount of light emission increases, and loss during the light emission process can be prevented.
8). The light emitting medium is cooled by the coating material, and can be used as a stable high-power laser medium.
9. In a single crystal in which the surface of the luminescent medium is self-coated with a crystalline material having a low refractive index during the crystal preparation process, it is possible to suppress the loss of light caused by the luminescence process due to total reflection, and a substance with high thermal conductivity can be used. A high cooling effect is also realized by coating.
10. There is no need to individually seed both the core and the clad. Further, since only one crucible is used, it is naturally unnecessary to align the first and second crucibles.

Claims (20)

In the process of melting the crystal material for the core and clad into a single crucible and growing the single crystal using the pulling or pulling method, the grown single crystal is in the as-gross state and has a refractive index from the core around the crystal. Self-coated single crystal characterized in that the low clad is self-coated. The self-coated single crystal according to claim 1, wherein the single crystal is a single crystal grown by a micro-pulling down method. In the above self-coating, the temperature distribution in the vicinity of the melt-crystal interface selectively decreases the solubility of specific constituents in the melt due to the temperature difference, resulting in a clad composition and a temperature distribution that causes self-coating. The self-coated single crystal according to claim 1, wherein self-coating is realized. The self-coated single crystal according to any one of claims 1 to 3, wherein the single crystal is a single crystal for a light emitting medium. The self-coated single crystal according to any one of claims 1 to 4, wherein the single crystal is a single crystal for a solid laser or a scintillator. The self-coated single crystal according to any one of claims 1 to 5, wherein the material to be the cladding material is a material in which a rare earth element or a transition element is added to the material to be the core material. In the single crystal, the core material is Yb: YAG, Nd: YAG, Yb: LuAG, Nd: LuAG, Ti: Sapphire, Cr: Sapphire, Ce: GSO, Ce: LSO, Ce: LiCAF, Ho: LuLF. The self-coated single crystal according to any one of claims 1 to 6, wherein the single-coated single crystal is made of any one of the following materials: HoTm: YLF, Ce: PrF ₃ , LN, and LT. Self-melting materials with different melting points are melted in a single crucible, and crystal growth is performed by a pulling or pulling method with a temperature gradient that lowers the temperature from the center to the edge at the solid-liquid interface. A method for producing a coated single crystal. A single crystal is grown by providing a planar protrusion having an outer diameter (S) not more than 5 times the inner diameter (B) of the crucible around the outlet side of the hole formed in the bottom of the crucible. A method for producing a self-coated single crystal according to claim 8. 10. The method for producing a self-coated single crystal according to claim 9, wherein 1.2 <(B / S) <5. The method for producing a self-coated single crystal according to claim 10, wherein 1.5 <(B / S) <4.5. 12. The self-coated single crystal according to any one of claims 8 to 11, wherein an inert gas is allowed to flow from the bottom of the crucible to cool the outside of the melt to achieve a desired temperature gradient. Manufacturing method. The self-coated single crystal manufacturing method according to any one of claims 8 to 12, wherein the material for the clad material is a material obtained by adding a rare earth element or a transition element to the material for the core material. Method. The single crystal cores are Yb: YAG, Nd: YAG, Yb: LuAG, Nd: LuAG, Ti: Sapphire, Cr: Sapphire, Ce: GSO, Ce: LSO, Ce: LiCAF, Ho: LuLF, HoTm: YLF. The method for producing a self-coated single crystal according to any one of claims 8 to 13, wherein the material is made of any one of, Ce: PrF ₃ , LN, and LT. The production of a single crystal according to any one of claims 8 to 14, wherein the composition of the starting material is a composition in which the cation ratio is shifted by 5 to 15% with respect to the composition of the intended single crystal. Method. A single crystal manufacturing apparatus for pulling and growing a single crystal from a hole formed in a bottom portion of a crucible, wherein means for providing a temperature gradient in the vicinity of a solid-liquid interface is provided. . The means for giving the temperature gradient is constituted by a planar protrusion having an outer diameter (S) not more than 5 times the inner diameter (B) of the crucible around the outlet side of the crucible hole. The apparatus for producing a single crystal according to claim 16, characterized in that: 18. The apparatus for producing a single crystal according to claim 17, wherein 1.2 <B / S <5. 19. The apparatus for producing a single crystal according to claim 18, wherein 1.5 <B / S <4.5. The apparatus for producing a single crystal according to any one of claims 17 to 19, further comprising means for flowing an inert gas from below the crucible.

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