CRUCIBLE AND CRYSTAL GROWTH EQUIPMENT

Provided is a crucible capable of improving uniformity of a temperature distribution of a melt drawn by a seed crystal and obtaining a crystal having a more uniform composition, and a crystal growth equipment including the crucible. The crucible includes a melt storage portion 24 that stores a melt that is a raw material of a crystal, and a die unit 34 that controls a shape of the crystal. The die portion 34 includes a die flow path 36 through which the melt 30 is passed from a storage portion outlet 32 provided on a bottom surface of the melt storage portion 24 toward a die outlet 38 provided on an end surface of the die portion 34. The die flow path 36 includes a narrow portion 36a1 whose flow path cross-sectional area is smaller than an opening area of the die outlet 38.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a crucible used for, for example, a micro-pulling down method (hereinafter referred to as a ≅PD method), and a crystal growth equipment including the crucible.

Description of the Related Art

In a ≅PD method, a melt of a single crystal material flowing out from a pore of a crucible comes into contact with a seed crystal arranged below the pore, and a desired single crystal grows on the seed crystal as the melt cools. By pulling down a seed crystal holder that holds the seed crystal according to a growth rate of the single crystal, the single crystal can be grown in a pulling down direction of the seed crystal.

As the crucible used in the ≅PD method, for example, a crucible shown in Patent Literature 1 (J P-A-2005-35861) is known. In the crucible shown in Patent Literature 1, by devising a shape of an outer bottom surface of the crucible, increasing the number of pores, providing an after-heater, and the like, attempts have been made to achieve uniformity of a temperature distribution of the melt drawn by the seed crystal and to obtain a crystal having a uniform composition.

However, it has become clear that it is difficult to sufficiently achieve the uniformity of the temperature distribution of the melt drawn by the seed crystal with a configuration of the crucible in the related art.

SUMMARY OF THE INVENTION

The present invention is made in view of such a circumstance and an object thereof is to provide a crucible capable of improving uniformity of a temperature distribution of a melt drawn by a seed crystal and obtaining a crystal having a more uniform composition, and a crystal growth equipment including the crucible.

In order to achieve the above object, a crucible according to the present invention is

a crucible including a melt storage portion for storing a melt of a raw material of a crystal; and a die portion defining a shape of the crystal, in which

the die portion includes a die flow path through which the melt is passed from a storage portion outlet provided on a bottom surface of the melt storage portion toward a die outlet provided on an end surface of the die portion, and

the die flow path includes a narrow portion having a flow path cross-sectional area smaller than an opening area of the die outlet.

As a result of earnest investigation on the uniformity of the temperature distribution, the present inventor has found that the uniformity of the temperature distribution of the melt drawn by the seed crystal (particularly uniformity of the temperature distribution at a solid-liquid interface along a plane perpendicular to a drawing direction of the melt) can be achieved by providing the narrow portion in a middle of the die flow path when passing the melt from the melt storage portion to the die flow path of the crucible. Thus, the present invention has been completed. According to experiments of the present inventor, it has been confirmed that a crystal having a more uniform composition (particularly a uniform composition along a plane perpendicular to a drawing direction of the crystal) can be obtained by using the crucible.

Preferably, the die flow path includes a divergent portion whose flow path cross-sectional area increases from the narrow portion toward the die outlet along a pulling down direction of the melt With such a configuration, the uniformity of the temperature distribution of the melt drawn by the seed crystal and the uniformity of the composition of the obtained crystal are improved.

The die flow path may include an introduction portion whose inlet is a connected to the storage portion outlet and a flow path main body portion communicating with the introduction portion, and it is preferable that an outlet of the flow path main body portion is connected to the die outlet. The die flow path may not include the introduction portion and may include only the flow path main body portion, but it is preferable that the die flow path includes the introduction portion.

The introduction portion may have a flow path cross-sectional area that changes along a flow direction, but preferably, the introduction includes is a straight body portion having a substantially constant flow path cross-sectional area along the flow direction of the melt. The term “substantially constant” means that the cross-sectional area may be changed to some extent, and the cross-sectional area is less changed than the divergent portion formed at the flow path main body portion. In the introduction portion, the flow path may be slightly expanded or slightly narrowed from the storage portion outlet toward the flow path main body portion.

Preferably, the introduction portion (including the storage portion outlet, a middle of the introduction portion, or a boundary between the introduction portion and the flow path main body portion) includes the narrow portion. When the introduction portion is a straight body portion, the narrow portion is formed at a middle of the straight body portion, the storage portion outlet, or the boundary between the introduction portion and the flow path main body portion. Since the narrow portion is formed at the introduction portion, it becomes easy to adjust a flow rate of the melt stored in the storage portion passing through the die flow path. The melt can be drawn from the die outlet at a stable speed, and the uniformity of the composition of the crystal (uniformity in the drawing direction) is improved.

The flow path main body portion may includes the narrow portion. When the narrow portion is formed at the flow path main body portion, a divergent portion whose flow path cross-sectional area increases from the narrow portion toward the die outlet is formed. An intermediate-expanded portion having a cross-sectional area larger than that of the introduction portion and the narrow portion may be formed between the narrow portion formed at the flow path main body portion and the introduction portion.

Preferably, a ratio (S2/S1) of the opening area (S2) of the die outlet to the flow path cross-sectional area (S1) of the narrow portion is 3 to 3000. Within such a range, the uniformity of the temperature distribution of the melt drawn by the seed crystal and the uniformity of the composition of the obtained crystal are improved.

Preferably, a flat end peripheral surface that is substantially perpendicular to the drawing direction of the melt is provided at the end surface of the die portion around the die outlet With such a configuration, an outer peripheral surface shape of the crystal obtained by using the crucible can be easily controlled.

A ratio (S2/(S2+S3)) of the opening area (S2) of the die outlet to a sum of the opening area (S2) of the die outlet and an area (S3) of the end peripheral surface is preferably 0.1 to 0.95, and more preferably 0.50 to 0.90. With such a configuration, the uniformity of the temperature distribution of the melt drawn by the seed crystal and the uniformity of the composition of the obtained crystal are further improved.

The crucible is made of a heat-resistant material, such as iridium, rhenium, molybdenum, tantalum, tungsten, platinum, or an alloy thereof, or carbon.

A crystal growth equipment according to the present invention includes any one of the above crucibles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described based on embodiments shown in the drawings.

First Embodiment

As shown inFIG. 1, a crystal growth equipment2according to the present embodiment includes a crucible4and refractory furnaces6. The crucible4will be described later. The refractory furnaces6cover a periphery of the crucible4doubly. The refractory furnaces6are formed with observation windows18,20for observing a pulling down state of a melt from the crucible4.

The refractory furnaces6are further covered with an outer casing8, and a main heater10for heating the entire crucible4is provided on an outer periphery of the outer casing8. In the present embodiment, the outer casing is formed by, for example, a quartz tube, and an induction heating coil10is used as the main heater10. A seed crystal14held by a seed crystal holding jig12is arranged below the crucible4. As the seed crystal14, a crystal of the same or the same type as a crystal to be produced is used. For example, if the crystal to be produced is a Ce-doped YAG crystal, a YAG single crystal containing no additives is used.

A material of the seed crystal holding jig12is not particularly limited, but the seed crystal holding jig12is preferably made of dense alumina or the like, which has little influence at an operating temperature of around 1900° C. A shape and a size of the seed crystal holding jig12are not particularly limited, but a rod shape having a diameter so that the jig does not come into contact with the refractory furnace6is preferred.

As shown inFIG. 2A, a cylindrical after-heater16is installed on an outer periphery of a lower end of the crucible4. The after-heater16is formed with an observation window22at the same position as the observation window20of the refractory furnace6. The after-heater16is used by being connected to the crucible4, and is arranged so that a die outlet38of a die portion34of the crucible4is located in an inner space of the cylindrical after-heater16, so as to heat the melt drawn from the die portion34and the die outlet38. The after-heater16is made of, for example, the same material as the crucible4(it does not have to be the same). When the after-heater16is induced and heated by the high frequency coil10similar to the crucible4, radiant heat is generated from an outer surface of the after-heater16, and an inside of the after-heater16can be heated.

Although not shown, the crystal growth equipment2includes a decompression unit for decompressing an inside of the refractory furnace6, a pressure measuring unit for monitoring the decompression, a temperature measuring unit for measuring a temperature of the refractory furnace6, and a gas supply unit for supplying an inert gas to the inside of the refractory furnace6.

A material of the crucible4is preferably iridium, rhenium, molybdenum, tantalum, tungsten, platinum, or an alloy thereof for reasons such as a high melting point of the crystal. The crucible4may be made of carbon. It is more preferable to use iridium (Ir) as the material of the crucible4in order to prevent foreign substances from being mixed into the crystal due to oxidation of the material of the crucible4.

When a substance having a melting point of 1500° C. or lower is targeted, Pt can be used as the material of the crucible4. When Pt is used as the material of the crucible4, crystal growth in atmosphere is possible. When a substance having a high melting point exceeding 1500° C. is targeted, Ir or the like is used as the material of the crucible4, and therefore the crystal growth is preferably carried out in an inert gas atmosphere such as Ar. A material of the refractory furnace6is not particularly limited, but alumina is preferred from viewpoints of heat retention, operating temperature, and prevention of impurities from being mixed into the crystal.

Next, the crucible4used in the crystal growth equipment2according to the present embodiment will be described in detail. A s shown inFIG. 2A, the crucible4according to the present embodiment incudes a melt storage portion24for storing a melt30, which is a raw material of the crystal, and the die portion34for controlling a shape of the crystal, and the melt storage portion24and the die portion34are integrally formed. When the crucible4is large, a plurality of members may be joined in a middle of a longitudinal direction of the melt storage unit24to configure the crucible4.

In the present embodiment, the crucible4is used for the ≅PD method. The die portion34is located below the melt storage portion24in a vertical direction, and the melt30stored in the melt storage portion24is drawn from the die outlet38, which is formed in a lower end surface42of the die portion34, by the seed crystal14downward in the vertical direction.

The melt storage portion24includes a cylindrical side wall26and a bottom wall28continuously formed with the side wall26. A certain amount of the melt30can be stored in the melt storage portion24by an inner surface of the side wall26and an inner surface of the bottom wall28. A storage portion outlet32is formed at a substantially central portion of the bottom wall28. The storage portion outlet32communicates with a die flow path36formed at the die portion34. The die flow path36will be described later.

The inner surface of the bottom wall28is a reverse-tapered inclined surface whose inner diameter decreases downward, and the melt30in the melt storage portion24can easily flow toward the storage portion outlet32. An outer surface of the bottom wall28is preferably flush with an outer surface of the side wall26, and is more preferably flush with the outer surface of the after-heater16. A lower surface28aof the bottom wall28is a flat plane substantially perpendicular to a flow direction (also referred to as a drawing direction or a pulling down direction) Z of the melt30, and the after-heater16is connected to an outer peripheral portion thereof.

At least a part of the die portion34is formed to protrude downward at a substantially central portion of the lower surface28aof the bottom wall28. As shown inFIG. 2A1, the lower end surface42of the die portion34protrudes from the lower surface28aof the bottom wall28at a predetermined distance Z1. The die outlet38formed at a substantially central portion of the lower end surface42of the die portion34and the storage portion outlet32formed at the substantially central portion of the bottom wall28are connected via the die flow path36formed at the die portion34.

Into the present embodiment, the die flow path36includes an introduction portion36awhose inlet is the storage portion outlet32, and a flow path main body portion36bcommunicating with the introduction portion36a, in which an outlet of the flow path main body portion36bis the die outlet38. The die flow path36may not include the introduction portion36a, and may have only the flow path main body portion36b, but it is preferable that the die flow path36includes the introduction portion36a.

In the present embodiment, the introduction portion36amay have a flow path cross-sectional area (a cross-sectional area perpendicular to the flow direction) that changes along the flow direction, but preferably, the introduction portion36ais a straight body portion having a substantially constant flow path cross-sectional area along the drawing direction Z. In the present embodiment, the term “substantially constant” means that the cross-sectional area may be changed to some extent, but the cross-sectional area is less changed than a divergent portion40formed at the flow path main body portion36b. A change in the cross-sectional area is preferably within approximately ĕ10%, and more preferably within ĕ5%. In the introduction portion36a, the flow path may be slightly expanded or slightly narrowed from the storage portion outlet32toward the flow path main body portion36b.

In the present embodiment, a narrow portion36a1is formed at the introduction portion36a(including the storage portion outlet32, a middle of the introduction portion36a, or a boundary between the introduction portion36aand the flow path main body portion36b). When the introduction portion36ais a straight body portion, the narrow portion36a1is formed at a middle of the straight body portion, the storage portion outlet32, or the boundary between the introduction portion36aand the flow path main body portion36bat a portion where the flow path cross-sectional area is minimum Since the narrow portion36a1is formed at the introduction portion36a, it becomes easy to adjust a flow rate of the melt stored in the storage portion24passing through the die flow path36, the melt can be drawn from the die outlet38at a stable speed, and uniformity of a composition of the crystal (particularly uniformity in the drawing direction) is improved.

According to the present embodiment, the narrow portion36a1is a portion in the die flow path36whose flow path cross-sectional area is smaller than an opening area of the die outlet38, and having a flow path cross-sectional area equal to or smaller than the opening area on an upstream side thereof and smaller than the opening area on a downstream side thereof along the drawing direction Z. When two or more narrow portions36a1are present along the die flow path36, the narrow portion closest to the die outlet38is the narrow portion36a1according to the present embodiment.

For example, in the present embodiment, as shown inFIG. 2A1, since the introduction portion36ais the straight body portion, the narrow portion36a1is formed at the middle of the introduction portion36a, the storage portion outlet32, or the boundary between the introduction portion36aand the flow path main body portion36b.

In the present embodiment, the flow path main body portion36bincludes the divergent portion40whose flow path cross-sectional area increases from the narrow portion36a1toward the die outlet38along the pulling down direction Z. In the present embodiment, the divergent portion40is formed in a tapered shape in which the flow path cross-sectional area gradually increases from the narrow portion36a1of the introduction portion36atoward the die outlet38.

A length Z2of the introduction portion36aalong the drawing direction Z is preferably 0 mm to 5 mm, and more preferably 0.5 mm to 2 mm. Since the narrow portion36aas the straight body portion is formed, it becomes easy to adjust the flow rate of the melt stored in the storage portion24passing through the die flow path36, the melt can be drawn from the die outlet38at a stable speed, and the uniformity of the composition of the crystal (uniformity in the drawing direction) is improved.

A length Z3of the flow path main body portion36balong the drawing direction Z is determined by, for example, a relation with a total length Z0(=Z2+Z3) of the die flow path36, and a ratio (Z3/Z0) is preferably 0.1 to 1, and more preferably 0.2 to 0.8. Alternatively, the length Z3of the flow path main body portion36balong the drawing direction Z is preferably 1 mm to 5 mm, and more preferably 1.5 mm to 2.5 mm.

The length Z3of the flow path main body portion36balong the drawing direction Z may be the same as or different from the distance Z1from the lower surface28aof the bottom wall28to the lower end surface42of the die portion34. The distance Z1from the lower surface28aof the bottom wall28to the lower end surface42of the die portion34along the drawing direction Z is preferably determined so that the melt drawn from the die outlet38does not adhere to the lower surface28aof the bottom wall28, and is, for example 1 mm to 2 mm.

As shown inFIG. 3A, on the lower end surface42of the die portion34, a flat end peripheral surface42athat is substantially perpendicular to the drawing direction Z (seeFIG. 2A) is formed around the die outlet38. The end peripheral surface42ais formed between an outer shape of the lower end surface42of the die portion34and an outer shape of the die outlet38.

A ratio (S2/(S2+S3)) of an opening area S2 (area perpendicular to the drawing direction Z) of the die outlet38to a sum of an area S3 (area perpendicular to the drawing direction Z) of the end peripheral surface42aand the S2 is preferably 0.10 to 0.95, and more preferably 0.5 to 0.95. A ratio (S2/S1) of the opening area (S2) of the die outlet38to a flow path cross-sectional area (S1) of the narrow portion36a1is preferably 3 to 3000, and more preferably 10 to 2000. In the present embodiment, the flow path cross-sectional area (S1) of the narrow portion36a1is the same as the flow path cross-sectional area of the introduction portion36a, which is the straight body portion, and the area (S1) is determined so that a speed of the melt drawn from the die outlet38of the die flow path36and the like is constant, and is preferably 0.008 mm2to 0.2 mm2.

In the present embodiment, the outer shape of the lower end surface42of the die portion34is rectangular according to a cross-sectional (cross section perpendicular to the pulling down direction Z) shape of an obtained crystal body, and a shape of the die outlet38is circular but is not limited thereto. For example, the outer shape of the lower end surface42of the die portion34may also be a circle, a polygon, an ellipse, or any other shape according to the cross-sectional shape of the obtained crystal body. A cross-sectional shape of the die outlet38is also not limited to a circle, but may be a polygon, an ellipse, or any other shape. Cross-sectional shapes of the introduction portion36aand the flow path main body portion36bare also not limited to a circle, but may be a polygon, an ellipse, or any other shape. The cross-sectional shape of the introduction portion36aand the cross-sectional shape of the flow path main body portion36bmay be the same or different, but are preferably the same.

The crystal growth equipment2including the crucible4according to the present embodiment shown inFIG. 1is preferably used in the ≅PD method or the like. The raw material charged into the melt storage portion24of the crucible4is heated by the main heater10or the like to become the melt30shown inFIG. 2A, and is drawn by the seed crystal14from the die outlet38through the die flow path36of the die portion34, and by pulling down the seed crystal14, the crystal is grown to obtain the crystal body.

Next, a method for producing a crystal using the crystal growth equipment2of the present embodiment will be briefly described. In the crystal growth equipment2of the present embodiment, first, the raw material of the crystal body to be obtained is charged into the melt storage portion24of the crucible4, and the main heater10is activated to heat the melt storage portion24. The melt storage portion24is heated so that the raw material melts in the melt storage portion24to become the melt30, which flows from the storage portion outlet32of the die portion34to the die flow path36. The melt30passes through the introduction portion36aand the flow path main body portion36band then comes into contact with an upper end of the seed crystal14at the die outlet38.

Around this time, the after-heater16is also activated to heat the vicinity of the die portion34. By using the crucible4of the present embodiment, the temperature of the melt pulled down by the seed crystal14via the die outlet38becomes substantially uniform, particularly in a plane perpendicular to the pulling down direction Z.

By using the crucible4according to the present embodiment, a concentration distribution of a composition (containing an activator) in the crystal body grown from the die outlet38is substantially uniform particularly in the plane perpendicular to the pulling down direction Z, and is also substantially uniform in a plane parallel to the pulling down direction Z. When YAG:Ce is to be produced for example, by using the apparatus2of the present embodiment, a crystal body YAG:Ce in which an activator such as Ce is uniformly dispersed can be obtained.

That is, in the present embodiment, the melt30from the melt storage portion24of the crucible4passes through the narrow portion36a1provided in the introduction portion36aof the die flow path36, then passes through the divergent portion40from the narrow portion36a1toward the die outlet38, and is pulled down from the die outlet38together with the seed crystal14. With such a configuration, the uniformity of the temperature distribution of the melt drawn by the seed crystal (particularly the uniformity along the plane perpendicular to the drawing direction of the melt) and the uniformity of the composition of the obtained crystal are improved.

In the present embodiment, since the narrow portion36a1is formed at the introduction portion36a, it becomes easy to adjust the flow rate of the melt stored in the storage portion24passing through the die flow path36. The melt can be drawn from the die outlet38and then crystallized at a stable speed, and the uniformity of the composition of the crystal (particularly uniformity in the drawing direction) is improved.

In the present embodiment, since the flat end peripheral surface42athat is substantially perpendicular to the drawing direction Z of the melt30is provided at the lower end surface42of the die portion36around the die outlet38, an outer peripheral surface shape of the crystal body obtained by using the crucible4can be easily controlled. Furthermore, in the present embodiment, a ratio (S2/S3) of the opening area (S2) of the die outlet38to the area (S3) of the end peripheral surface42ais set within a predetermined range, and the ratio (S2/S1) of the opening area (S2) of the die outlet38to the flow path cross-sectional area (S1) of the narrow portion36a1is also set within a predetermined range. With such configurations, the uniformity of the temperature distribution of the melt drawn by the seed crystal and the uniformity of the composition of the obtained crystal are further improved.

Second Embodiment

As shown inFIG. 2B, in a crystal growth equipment according to the present embodiment, only a configuration of a die portion34aof a crucible4ais different from that of the first embodiment. Some of the same portions will be omitted, and different portions will be described in detail below. Portions not described below are the same as in the description of the first embodiment.

In the die flow path36of the crucible4aaccording to the present embodiment, a shape of a divergent portion40a, whose flow path cross-sectional area increases from a narrow portion36a1formed at an introduction portion36atoward the die outlet38, is not a tapered shape in which the cross-sectional area increases linearly, but a shape in which the cross-sectional area expands in a concave curve. The divergent portion40aof the present embodiment may have a straight body portion having substantially the same cross-sectional area along the pulling down direction Z near the die outlet38, but it is preferable that the straight body portion is short. In the present embodiment, the shape of the divergent portion40amay be a shape in which the cross-sectional area increases in a convex curve or another curve, instead of the shape in which the cross-sectional area increases in a concave curve.

Third Embodiment

As shown inFIG. 2C, in a crystal growth equipment according to the present embodiment, only a configuration of a die portion34bof a crucible4bis different from that of the first or second embodiment Some of the same portions will be omitted, and different portions will be described in detail below. Portions not described below are the same as in the description of the first or second embodiment.

A narrow portion41ais formed at the flow path main body portion36bin the die flow path36of the crucible4baccording to the present embodiment. When the narrow portion41ais formed at the flow path main body portion36b, a divergent portion40bwhose flow path cross-sectional area increases from the narrow portion41atoward the die outlet38is formed. In the present embodiment, an intermediate-expanded portion having a larger cross-sectional area than the introduction portion36aand the narrow portion41amay be formed between the narrow portion41aformed at the flow path main body portion36band the introduction portion36a.

The narrow portion41aof the present embodiment corresponds to the narrow portion36a1of the first or second embodiment described above. The flow path cross-sectional area S1 thereof has the same relation with the opening area S2 of the die outlet38. The distance Z3from the narrow portion41ato the die outlet38has the same relation as in the first or second embodiment described above.

An inner diameter of the introduction portion36aof the present embodiment is preferably equal to or greater than an inner diameter of the narrow portion41a, but may be smaller as long as the melt30can pass through. In the present embodiment, the introduction portion36amay also be formed with a portion having a flow path cross-sectional area smaller than the opening area of the die outlet38. However, in the present embodiment, the portion that greatly contributes to the uniformity of the temperature distribution of the melt drawn by the seed crystal14is the narrow portion41athat is a starting point of the divergent portion40btoward the die outlet38.

Forth Embodiment

As shown inFIG. 2D, in a crystal growth equipment according to the present embodiment, only a configuration of a die portion34cof a crucible4cis different from those in the first to third embodiments. Some of the same portions will be omitted, and different portions will be described in detail below. Portions not described below are the same as in the descriptions of the first to third embodiments.

In the die portion34of the crucible4caccording to the present embodiment, a plurality of (for example, 2 to 8) die flow paths36are formed. Each die flow path36has the same configuration with that of any of the first to third embodiments. It is preferable that the plurality of die flow paths36(for example, 2 to 8) have the same configuration, but may be different. For example, one of the plurality of die flow paths36has the same configuration as the die flow path36of the first embodiment, and the others may have the same configuration with the die flow path36of the second or third embodiment.

The present invention is not limited to the above embodiments, and various modifications can be made within a scope of the present invention. For example, the crystal produced by using the crucible and the crystal growth equipment of the present invention is not limited to a single crystal YAG or LuAG doped with an M element, and single crystals such as Al2O3(sapphire), GAGG (Gd3Al2Ga3O12), GGG (Gd3Ga5O12), and GPS (Gd2Si2O7) are also exemplified. The crystal is not limited to a single crystal, and may be a co-crystal such as YAG-Al2O3or LuAG-Al2O3.

EXAMPLES

Hereinafter, the present invention will be described based on more detailed Examples, but the present invention is not limited to these Examples.

Using the crystal growth equipment2shown inFIG. 1, a phosphor made of a single crystal Ce:YAG (YAG doped with Ce) was produced. An inner diameter of the introduction portion36aas the straight body portion shown inFIG. 2Awas 0.4 mm, and an inner diameter of the die outlet38was 4 mm. The length Z2of the introduction portion36ashown inFIG. 2A1was 0.5 mm, and the length Z3of the flow path main body portion36bwas 2 mm.

FIG. 3Bshows a temperature distribution of the melt (near the solid-liquid interface) immediately after the melt is drawn from the die outlet38of the die portion34using the crystal growth equipment2according to Example 1. T1, T2, T3, and T4each represent a temperature of an indicated region. The temperature is lowest in T1and gradually increases from T2to T3to T4. For example, the temperature T1was 1945° C. to 1953° C.; the temperature T2was 1953° C. to 1961° C.; the temperature T3was 1965° C. to 1973° C.; and the temperature T4was 1973° C. or higher. The temperature distribution was measured by simulation analysis.

As can be seen by comparingFIG. 3AwithFIG. 3B, in a portion corresponding to the die outlet38, an area of the portion where the uniform temperatures T1and T2are obtained is large.FIG. 3Cshows a concentration distribution of Ce in a cross section of Ce:YAG produced by the crystal growth equipment2of Example 1. InFIG. 3C, C1, C2, C3, and C4represent concentrations of Ce (¼ 100/(+), in which an atomic % of Y is defined as, and an atomic % of Ce is defined as in the indicated regions. The concentration is lowest in C1and gradually increases from C2to C3to C4. In Example 1, the concentration C1was 0.94 atomic % to 1.07 (1.00 ĕ 0.07) atomic %; the concentration C2was 1.08 atomic % to 1.22 atomic %; the concentration C3was 1.23 atomic % to 1.37 atomic %; and the concentration C4was 1.38 atomic % or more. The concentration distribution was measured by LA (laser ablation)-ICP mapping.

As shown inFIG. 3C, the concentration of Ce in the cross section of the grown Ce:YAG crystal was distributed so as to correspond to the temperature distribution shown inFIG. 3B. Corresponding to the outlet38of the die flow path36shown inFIG. 3A, an area of a region in which the concentration of Ce was uniform with C1was large, and a size (occupied area) of a largest uniform concentration region was approximately 43.4% of a total cross-sectional area of the obtained crystal body. The region in which the concentration of Ce is uniform with C1is located in a central portion of the crystal body, and is close to a circle. Therefore, a crystal body having a relatively large cross-sectional area and a uniform concentration can be obtained.

Comparative Example 1

A phosphor made of a single crystal Ce:YAG was produced in the same manner as in Example 1 except for that as shown below. The fluophor made of the single crystal Ce:YAG was produced in the same manner as in Example 1 using the same crystal growth equipment as in Example 1 except that a crucible4in the related art shown inFIGS. 4 and 5Awas used.

As shown inFIG. 4, the crucible4used in Comparative Example 1 includes the melt storage portion24and a die portion34. Five storage portion outlets32are formed at the central portion of the bottom wall26of the melt storage portion24. Each storage portion outlet32communicates with each of five die outlets38through a corresponding die flow path36. Each of the five die flow paths36was a straight body portion having the same flow path cross-sectional area from the storage portion outlet32to the die outlet38, and an inner diameter of each die flow path36was the same as the inner diameter of the introduction portion36ain Example 1.

FIG. 5Bshows a temperature distribution of a melt immediately after the melt is drawn from the die outlet38of the die portion34using the crystal growth equipment according to Comparative Example 1. T1a, T2a, T3a, and T4arepresent a temperature of an indicated region. The temperature is lowest in T1aand gradually increases from T2ato T3ato T4a. For example, the temperature T1awas 1972° C. to 1974° C.; the temperature T2awas 1974° C. to 1976° C.; the temperature T3awas 1976° C. to 1977° C.; and the temperature T4awas 1977° C. or higher.

FIG. 5Cshows a concentration distribution of Ce in a cross section of Ce:YAG produced by the crystal growth equipment of Comparative Example 1. InFIG. 5C, C1, C2, C3, and C4each represent a concentration of Ce in the indicated region. The concentration is lowest in C1and gradually increases from C2to C3to C4. Definitions of the concentrations C1, C2, C3, and C4are the same as in Example 1.

As shown inFIG. 5C, a size (occupied area) of a region in which the concentration of Ce was uniform with C1was approximately 30.2% of a total cross-sectional area of the obtained crystal body. As shown inFIG. 5C, the region in which the concentration of Ce is uniform with C1is located in a central portion of the crystal body, but the area thereof is small and a shape thereof is not circular but distorted. Therefore, an amount and a color of fluorescence generated from a surface of the crystal body vary, which makes it difficult to obtain a uniform light emitting state. In Comparative Example 1, a size (occupied area) of a region in which the concentration of Ce is uniform with C4is large, but a distribution thereof varies in a circumferential direction, which also causes variations in the amount and color of the fluorescence generated from the surface of the crystal body, so that it is difficult to obtain a uniform light emitting state.

REFERENCE SIGNS LIST