Patent Publication Number: US-2022228290-A1

Title: Crucible, crystal body, and optical element

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a crucible that is used in, for example, a micro pulling-down method (hereinafter, also referred to as “μ-PD method”) or the like, a crystal body that is grown by using the crucible, and an optical element using the crystal body. 
     2. Description of the Related Art 
     The μ-PD method is a kind of method in which a raw material melt passing through a nozzle hole formed in the bottom of a crucible is brought into contact with a seed crystal, and then the seed crystal is moved downward to grow a crystal. Since the uniform raw material melt in the crucible is continuously and forcibly discharged from the nozzle hole for crystallization, there is a characteristic in which a composition fluctuation in a crystal growth direction is small. 
     In addition, the nozzle hole is provided, and a shape of a crystal growth surface can be defined by a shape of a nozzle surface on which the raw material melt that has passed through the nozzle hole and has been discharged to the outside of the crucible wets and spreads, and thus a crystal with high shape accuracy during crystal growth can be obtained. 
     With regard to a single crystal material, a hetero-element (dopant) other than a single crystal constituent element is added as a means for applying desired material characteristics in many cases. Particularly, in optical crystals such as an optical crystal for a laser, a nonlinear optical crystal, a luminescent crystal for a scintillator, and a fluorescent crystal, optical characteristics greatly vary due to the dopant, and thus a dopant concentration distribution in the crystal greatly acts on the optical characteristics of the entirety of the crystal. 
     In a crucible described in JP 2008-239352 A, a plurality of nozzle holes are provided in an end surface of a nozzle so as to make an additive element in a crystal uniform. However, with regard to a configuration of the crucible in the related art, the present inventors have found that a variation of the additive element in a grown crystal is large, particularly, in a case where an element having a segregation coefficient less than 1 is set as the additive element. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration such circumstances, and an object thereof is to provide a crucible capable of obtaining a crystal body in which a variation of an additive element in the crystal body is small, a crystal body obtained by using the crucible, and an optical element using the crystal body. 
     As a result of thorough investigation for accomplishing the object, the present inventors have found that when surface roughness of an inner surface of a nozzle hole is set to a predetermined value or less, particularly, even in an additive element having a segregation coefficient less than 1, the additive element is uniformly dispersed inside a crystal body, and they accomplished the present invention. 
     That is, according to an aspect of the present invention, there is provided a crucible including: 
     a melt reservoir storing a melt to be a raw material of a crystal; and 
     a nozzle portion controlling a shape of the crystal, 
     The nozzle portion includes a nozzle hole guiding the melt from the melt reservoir to an end surface of the nozzle portion. 
     A surface roughness of an inner peripheral surface of the nozzle hole is 10 μm or less. 
     According to the crucible of the present invention, since the surface roughness of the inner peripheral surface of the nozzle hole is set to a predetermined value or less, particularly, even in an additive element having a segregation coefficient less than 1, the additive element can be uniformly dispersed into the crystal body. Although the reason for this is not clear, for example, it is considered as follows. 
     In order to uniformly disperse an additive element into the crystal body, a configuration in which a plurality of nozzle holes are provided in a nozzle end of the crucible, and a melt is ejected from the nozzle holes onto a crystal growth plane is suggested. However, in a crucible in the related art, since attention was not paid to surface roughness of an inner peripheral surface of the nozzle holes, it was difficult to uniformly disperse an additive element into the crystal body due to occurrence of a difference in the flowing amount of the melt between the nozzle holes, and the like. 
     In the crucible of the present invention, since the surface roughness of the inner peripheral surface of the nozzle holes is set to a predetermined value or less, flowing-out of the melt from the nozzle holes becomes stable, and the amount of the melt flowing from the nozzle holes becomes approximately uniform. Accordingly, it is considered that the additive element is uniformly and easily dispersed into the crystal body. Furthermore, even in a case where a single nozzle hole is formed in a nozzle end of the crucible, flowing-out of the melt from the nozzle hole becomes more stable in comparison to a crucible in the related art in which the surface roughness of the inner peripheral surface of the nozzle hole is not managed, and thus it is easy to uniformly disperse the additive element into the crystal body. 
     Preferably, the nozzle portion is an assembly of divided parts, and the nozzle holes are formed by combining grooves formed in matching surfaces of the divided parts. 
     The crucible is required to have heat resistance to withstand a temperature of the melt, possibility of inductive heating, and the like, and thus the crucible is constituted, for example, by a metal that is difficult to be machined, or the like in many cases. Therefore, machining of the nozzle holes formed in the crucible becomes difficult, and it is difficult to set the surface roughness of the inner peripheral surface of the nozzle holes to 10 μm or less. 
     In a preferred aspect of the present invention, grooves which constitute the nozzle holes are formed in matching surfaces of divided parts, and the nozzle holes are formed by combining the divided parts. Differently from machining of a hole, when machining a groove, since a machining surface is exposed to the outside, it is easy to obtain accuracy of the surface roughness, and it is easy to set the surface roughness to 10 μm or less, 5 μm or less, or 1 μm or less. Accordingly, grooves are combined to form the nozzle holes by combining the divided parts, and it is easy to set the surface roughness of the inner peripheral surface of the nozzle holes to a predetermined value or less. 
     A plurality of grooves may be formed in the matching surfaces of the divided parts, and the divided parts may be combined to form a plurality of nozzle holes. Due to machining of the grooves, it is easy to obtain accuracy of surface roughness and it is also easy to make accuracy of the surface roughness of a plurality of grooves substantially uniform. Accordingly, the amount of the melt flowing from the nozzle holes becomes substantially uniform, and thus it is easier to uniformly disperse an additive element into the crystal body. 
     Preferably, the grooves extend from the melt reservoir to the end surface of the nozzle portion in the middle of the matching surfaces or at end corners, and the grooves define a part of the inner peripheral surface of the nozzle holes. According to this configuration, it is easy to set the surface roughness of the inner peripheral surface of the nozzle holes to a predetermined value or less. 
     Preferably, the divided parts comprise a first part having an outer side surface of the nozzle portion, and a second part that is combined to the first part. When combining the second part to the first part that constitutes the outer side surface of the nozzle portion, it is possible to easily form the nozzle portion including nozzle holes having a smooth inner peripheral surface of which surface roughness is a predetermined value or less. Note that, the second part may be formed by combining divided parts. 
     Preferably, the first part is integrated with the melt reservoir, and the second part is formed to be detachable from the melt reservoir. According to this configuration, the nozzle portion can be easily formed. In addition, since the melt reservoir and the first part are integrated with each other, the melt reliably leaks from the end surface of the nozzle portion. 
     Preferably, an inner side surface of the first part is inclined from the melt reservoir toward a direction close to the center of the end surface of the nozzle portion. 
     An outer side surface of the second part is inclined in correspondence with the inner side surface of the first part. 
     The inner side surface of the first part and the outer side surface of the second part are faced to each other and are combined. 
     According to this configuration, when the second part is inserted into an opening of the first part and is dropped down, the second part does not fall down, and the nozzle portion can be easily formed. In addition, the outer side surface of the second part and the inner side surface of the first part become matching surfaces, and the grooves are formed in the matching surfaces, and thus the nozzle holes inclined toward a direction close to the center of an end surface of the nozzle portion from the melt reservoir can be easily formed by combining the first part and the second part. 
     Preferably, the inner peripheral surface is coated with a wettability improving layer having high wettability with the melt stored in the melt reservoir. According to this configuration, it is easy for the melt to flow out to the end surface after passing through the nozzle holes, and thus a variation of an additive element in a crystal body can be effectively suppressed. 
     Preferably, the crucible is made from iridium, rhenium, molybdenum, tantalum, tungsten, platinum, or alloys thereof. The metals (including the alloys) are excellent in heat resistance, are easily inductively heated, and are preferably used as a crucible. In addition, when using the crucible formed from the materials, a crystal with a high melting point can be manufactured. 
     However, typically, the materials are difficult to be machined, but in the configuration of the preferred crucible of the present invention, a hole is not formed by machining the metals, grooves are formed in an outer surface of divided parts, and the nozzle holes are formed by combining the divided parts. Accordingly, it is easy to machine the surface roughness of the inner peripheral surface of the nozzle holes with accuracy of a predetermined value or less. 
     According to another aspect of the present invention, there is provided a crystal body (preferably, a single crystal) that is manufactured by using the crucible. The crystal body may contain an additive element having a segregation coefficient less than 1. A crystal that is grown by using the crucible according to the present invention has a shape close to an ideal columnar shape. Furthermore, a different phase is less likely to be mixed in the crystal body, and the crystal body is further less likely to be polycrystallized. 
     In addition, according to still another aspect of the present invention, there is provided a method of manufacturing a crystal body, including: 
     a process of causing a melt that becomes a raw material of a crystal to flow out from nozzle hole outlets of nozzle holes which are formed in a nozzle portion and in which surface roughness of an inner peripheral surface is 10 μm or less. 
     According to the manufacturing method of the present invention, even in a case where an additive element having a segregation coefficient less than 1 is contained, it is possible to obtain a crystal body in which a concentration variation of the additive element is suppressed. In the crystal body obtained by the manufacturing method of the present invention, crystallinity is improved, a single crystal is likely to be obtained, polycrystallization can be suppressed, and occurrence of cracks is also suppressed. 
     In addition, the crystal body obtained by using the manufacturing method of the present invention is preferably used as an optical element. 
     Furthermore, when using the method of the present invention, stabilization of crystal growth is secured, and shape accuracy of the crystal body is improved. Accordingly, a machining loss of the crystal body decreases, and a crystal body with high quality can be manufactured with high efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of a crystal manufacturing device including a crucible according to an embodiment of the present invention; 
         FIG. 2  is an enlarged cross-sectional view of a portion II of the crucible illustrated in  FIG. 1 ; 
         FIG. 3  is a partial cross-sectional perspective view of the crucible illustrated in  FIG. 1 ; 
         FIG. 4A  is a schematic exploded perspective view illustrating a configuration of a nozzle portion illustrated in  FIG. 2  in detail; 
         FIG. 4B  is a plan view taken along line IVB-IVB of an end surface of the nozzle portion illustrated in  FIG. 2 ; 
         FIG. 5A  is a plan view of an end surface of a nozzle portion in a crucible according to another embodiment of the present invention; 
         FIG. 5B  is a plan view of an end surface of a nozzle portion in a crucible according to still another embodiment of the present invention; 
         FIG. 6  is an enlarged cross-sectional view of a crucible according to still another embodiment of the present invention; and 
         FIG. 7  is a graph illustrating comparison of a deviation in concentration of an additive element related to examples of the present invention and a comparative example. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the present invention will be described on the basis of embodiment illustrated in the accompanying drawings. 
     First Embodiment 
     As illustrated in  FIG. 1 , a crystal manufacturing device  2  of this embodiment includes a crucible  4  and a refractory furnace  6 . The crucible  4  will be described later. The refractory furnace  6  is constituted by a refractory material, and covers the periphery of the crucible  4  in a dual manner. An observation window for observing a pulling-down state of a melt from the crucible  4  may be formed in the refractory furnace  6 . 
     The refractory furnace  6  is further covered with an outer casing  8 , and a main heater  10  configured to heat the entirety of the crucible  4  is provided at an outer periphery of the outer casing  8 . In this embodiment, the outer casing is formed from, for example, a quartz tube, and an inductive heating coil  10  is used as the main heater  10 . A seed crystal  14  held by a seed crystal holding jig  12  is disposed on a downward side of the crucible  4 . As the seed crystal  14 , the same crystal or the same kind of crystal as a crystal to be manufactured is used. For example, in a case where the crystal to be manufactured is a Ce-doped YAG crystal, a YAG single crystal or the like that does not contain an additive is used. 
     A material of the seed crystal holding jig  12  is not particularly limited, and it is preferable that the material is composed of dense alumina or the like that is less affected in the vicinity of 1900° C. that is a use temperature. A shape and a size of the seed crystal holding jig  12  are not particularly limited, but a rod-shape having a diameter that does not contact with the refractory furnace  6  is preferable. 
     A tubular after-heater  16  is provided at an outer periphery of a lower end of the crucible  4 . An observation window may be formed in the after-heater  16  at the same position as in the observation window of the refractory furnace  6 . The after-heater  16  is used in a state of being connected to the crucible  4 , and is disposed so that a nozzle hole outlet  38  of a nozzle portion  34  of the crucible  4  illustrated in  FIG. 2  is located in an internal space of the tubular after-heater  16  so as to heat a melt that is pulled down from the nozzle portion  34  and the nozzle hole outlet  38 . For example, the after-heater  16  illustrated in  FIG. 1  is constituted by a similar material (it is not necessary to be the same) as in the crucible  4 , or the like. When the after-heater  16  is inductively heated by the high-frequency coil  10  in a similar manner as in the crucible  4 , radiant heat is generated from an outer surface of the after-heater  16 , and the inside of the heater  16  can be heated. 
     Note that, although not illustrated in the drawings, the crystal manufacturing device  2  is provided with a pressure reducing unit configured to reduce a pressure inside the refractory furnace  6 , a pressure measuring unit configured to monitor the pressure reduction, a temperature measuring unit configured to measure a temperature of the refractory furnace  6 , and a gas supply unit configured to supply an inter gas to the inside of the refractory furnace  6 , and the like. 
     The material of the crucible  4  is preferably iridium, rhenium, molybdenum, tantalum, tungsten, platinum, or an alloy thereof because a melting point of a crystal is high. In addition, the crucible  4  may be formed from carbon. In a case where the crucible  4  is indirectly heated by heat generation of a member other than the crucible  4 , it is preferable that the crucible  4  does not react with a melt of a material that is crystallized, and a phenomenon such as softening at a melting point, or the like does not occur in the crucible  4 . In a case where the crucible  4  becomes a heat generating body due to inductive heating (high-frequency heating) or the like, a material that further has electrical conductivity and is heated by an external magnetic field is preferable. Examples thereof include iridium (Ir), molybdenum (Mo), tungsten (W), rhenium (Re), platinum (Pt), and a platinum alloy. In addition, it is more preferable to use iridium (Ir) as the material of the crucible  4  in order to prevent foreign matters from being mixed into a crystal due to oxidation of the material of the crucible  4 . 
     Note that, in a case where a material having a melting point of 1500° C. or lower is set as a target, Pt can be used as the material of the crucible  4 . In addition, in a case of using Pt as the material of the crucible  4 , crystal growth in the air is possible. In a case where a material having a high melting point higher than 1500° C., since Ir or the like is used as the material of the crucible  4 , crystal growth is preferably performed under an inert gas atmosphere such as Ar. A material of the refractory furnace  6  is not particularly limited, but the material is preferably alumina from the viewpoint of a heat retention property, an operating temperature, and prevention of mixing of impurities into a crystal. 
     Next, the crucible  4  that is used in the crystal manufacturing device  2  of this embodiment will be described in detail. As illustrated in  FIG. 2 , the crucible  4  according to this embodiment includes a melt reservoir  24  configured to store a melt  30  that becomes a raw material of a crystal, and a nozzle portion  34  that controls a crystal shape. Note that, in a case where the crucible  4  has a large size, a plurality of members may be jointed in the middle of a longitudinal direction of the melt reservoir  24  so as to constitute the crucible  4 . The melt reservoir  24  includes a bottomed tubular accommodation wall  26 . A constant amount of melt  30  can be stored in the melt reservoir  24  on an inner surface of the accommodation wall  26 . 
     In this embodiment, the crucible  4  is used in a μ-PD method, the nozzle portion  34  is located on a lower side of the melt reservoir  24  in a vertical direction, and the melt  30  stored in the melt reservoir  24  is pulled down by the seed crystal  14  from the nozzle hole outlet  38  formed in the lower end surface  35  of the nozzle portion  34  to a lower side in the vertical direction. 
     The nozzle portion  34  includes a nozzle outer side surface  37  that protrudes from approximately the central portion of a bottom outer surface  28  of the accommodation wall  26  that constitutes the melt reservoir  24 . The lowest end of the nozzle outer side surface  37  intersects the lower end surface  35  of the nozzle portion  34 , and a corner located at a boundary between the lower end surface  35  and the outer side surface  37  becomes an outer peripheral edge  35   a  of the lower end surface  35 . 
     As a result, the lower end surface  35  of the nozzle portion  34  protrudes by a predetermined distance Z 1  from the bottom outer surface  28  of the accommodation wall  26  toward a vertical direction (pulling-down direction Z). The predetermined distance Z 1  is preferably determined in order for the melt pulled down from the nozzle hole outlet  38  not to adhere to the bottom outer surface  28 . The predetermined distance Z 1  is preferably 1 to 5 mm, and more preferably 1 to 2 mm. The nozzle portion  34  includes a nozzle hole  36  that allows the melt to flow out from the melt reservoir  24  that stores the melt to the lower end surface  35  of the nozzle portion  34 . The lower end surface  35  of the nozzle portion  34  is a surface that is substantially orthogonal to the pulling-down direction Z and is flat. 
     A bottom inner surface of the accommodation wall  26  that constitutes the melt reservoir  24  includes an inclined surface that is inclined in a taper shape toward the nozzle portion  34  located at the center, and the melt  30  stored in the reservoir  24  flows in toward a nozzle hole inlet  32  of each of a plurality of the nozzle holes  36  formed in the nozzle portion  34 . Each of the nozzle holes  36  includes the nozzle hole inlet  32  opened toward the bottom of the melt reservoir  24 , and the nozzle hole outlet  38  that is opened at the lower end surface  35  of the nozzle portion  34 . 
     As illustrated in  FIG. 3 , the nozzle portion  34  is constituted by an assembly of a first part  50  and a second part  56 . The first part  50  is a divided part that is approximately integrated with the accommodation wall  26  of the melt reservoir  24  and has an approximately quadrangular tubular shape, and is a frame having an approximately quadrangular columnar opening on an inner side. The second part  56  has an approximately quadrangular columnar shape to be fitted into the opening of the first part  50 , and is formed by combining two divided parts  56   a  having an approximately triangular columnar shape. The second part  56  is fitted into the opening of the first part  50 , thereby forming the nozzle portion  34 . 
     The first part  50  having an approximately quadrangular tubular shape protrudes from an approximately central portion of the bottom outer surface  28  of the accommodation wall  26  that constitutes the melt reservoir  24 , and constitutes the nozzle outer side surface  37  of the nozzle portion  34 . As illustrated in  FIG. 2  and  FIG. 3 , the nozzle hole  36  is formed between the first part  50  and the second part  56 , and between the divided parts  56   a  of the second part  56 . 
     As illustrated in  FIG. 4A , grooves  54  leading to the lower end surface  35  from the melt reservoir  24  are formed in four corners of an inner peripheral surface (inner side surface)  52  of an opening of the first part  50  having an approximately quadrangular tubular shape. A cross-section of each of the grooves  54  has a partial shape of a circle (an arc shape of approximately ¾ of the circle). Grooves  62   a  and  62   b  in which a cross-section has a partial shape of a circle (an arc shape that becomes a nozzle hole by complementing the arc of the groove  54 ) are formed in four corners of the second part  56  having a quadrangular columnar shape at positions corresponding to the grooves  54  in a direction that is approximately parallel to the pulling-down direction Z (may be slightly inclined. The same shall apply hereinafter). 
     Note that, each of two grooves  62   a  is formed in an intersecting corner of a pair of outer side surfaces  58  (one end of the outer side surfaces  58 ) of each of the two divided parts  56   a  having an approximately triangular columnar shape, and other two grooves  62   b  are formed by combining matching surfaces  60  and  60  of the divided parts  56   a . The grooves  62   b  are formed by combining divided grooves  62   b   1  which are formed in both ends of the matching surfaces  60  of the two divided parts  56   a  having an approximately triangular columnar shape. The divided grooves  62   b   1  are formed in intersecting corners of the matching surfaces  60  and the outer side surface  58  along a direction that is approximately parallel to the pulling-down direction Z. 
     In addition, a groove  62   c  is formed in the middle of each of the matching surfaces  60  (in the vicinity of the center in the drawing) of the divided parts  56   a  of the second part  56  along a direction that is approximately parallel to the pulling-down direction Z. With regard to the grooves  62   c , when the matching surfaces  60  of the divided parts  56   a  are assembled, the grooves  62   c  are combined to form the nozzle hole  36  located at the center as illustrated in  FIG. 2 . 
     In this embodiment, the matching surfaces  60  of the pair of divided parts  56   a  are combined with each other to form the second part  56 , and the outer side surface  58  of the second part  56  are combined with the inner side surface  52  of the first part  50  to form the nozzle portion  34 . In this regard, the outer side surface  58  of the second part  56  and the inner side surface  52  of the first part  50  can be referred to as “matching surface”. Accordingly, the grooves  54 ,  62   a ,  62   b , and  62   c , which constitute parts of the nozzle holes  36  illustrated in  FIG. 2  and are illustrated in  FIG. 4A , extend from the melt reservoir  24  to the lower end surface  35  of the nozzle portion  34  in the middle of the matching surfaces  60 ,  58 , and  52 , or at end corners, thereby forming parts of inner peripheral surfaces of the nozzle holes  36 . 
     Surface roughness of inner surfaces of the grooves  54 ,  62   a ,  62   b   1 , and  62   c  is polished to 10 μm or less, preferably 5 μm or less, and more preferably 1 μm or less. In addition, the outer side surface  58  and the inner side surface  52 , which become matching surfaces in a similar manner as in the matching surfaces  60 , have surface roughness similar to or less than the surface roughness of the grooves, and are polished to 10 μm or less, preferably 5 μm or less, and more preferably 1 μm or less. Although not particularly limited, examples of a polishing means include electrolytic polishing, chemical polishing, composite polishing in which the polishing methods and a physical polishing method are combined, and the like. 
     In the matching surfaces  60  of the divided parts  56   a , surface roughness is preferably small at a portion other than the grooves  62   c  for close contact in order for the melt  30  illustrated in  FIG. 2  not to leak. In addition, since the outer side surface  58  of the second part  56  and the inner side surface  52  of the first part  50  become matching surfaces, as in the case of the matching surfaces  60 , the surface roughness is preferably small in a portion other than the grooves  62   a ,  62   b   1 , and  62   c  for close contact in order for the melt  30  illustrated in  FIG. 2  not to leak. 
     In this embodiment, the inner side surface  52  of the first part  50  is slightly inclined inward from the melt reservoir  24  toward the vicinity of the center of the end surface  35 . In addition, the outer side surface  58  of the second part  56  is preferably inclined so as to correspond to the inclination of the inner side surface  52 . According to this configuration, it is easy to insert the second part  56  into an opening of the first part  50  from an upper side, and it is possible to suppress the second part  56  from being dropped downward from the first part  50 . Note that, in a state in which the second part  56  is combined to the first part  50 , a lower end surface of the second part  56  is flush with a lower end surface of the first part  50 , and the lower end surfaces integrally constitute the lower end surface  35 . 
     Note that, a wettability improving layer (not illustrated) may be formed on inner surfaces of the grooves  54 ,  62   a ,  62   b   1 , and  62   c . Examples of the wettability improving layer include an aluminum oxide layer and a rare-earth garnet compound that does not contain aluminum in a rare-earth aluminum and garnet compound, a rare-earth oxide layer contained in the same composition in a rare-earth silicic acid oxide compound, and a fluoride layer (CaF 2  or BaF 2 ) of an alkali metal contained in the same composition in fluorides containing an alkali-earth metal such as LiCaAlF 6  and BaLiF 3 . It is preferable that the wettability improving layer is formed only on the inner surfaces of the grooves  54 ,  62   a ,  62   b   1 , and  62   c , but it is preferable that the wettability improving layer is also formed on an upper end surface and a lower end surface of the second part  56 , and a lower end surface of the first part  50 . It is preferable that the melt  30  does not flow to the matching surface  60  and the outer side surface  58  of the divided parts  56   a , and the inner side surface  52  of the first part  50 , but the wettability improving layer may be formed thereon. 
     As illustrated in  FIG. 4B , in this embodiment, an external shape viewed from the lower end surface  35  of the nozzle portion  34  is a rectangular shape, and the outer peripheral edge  35   a  of the lower end surface  35  also has a rectangular shape. However, a shape of the outer peripheral edge  35   a  is not limited to the rectangular shape, and may be a circular shape, a hexagonal shape, other polygonal shapes, an elliptical shape, or other different shapes. The shape of the outer peripheral edge  35   a  defines a shape of an outer side surface of a crystal manufactured by the μ-PD method using the crucible  4  illustrated in  FIG. 2 . 
     In this embodiment, for example, as illustrated in  FIG. 4B , the nozzle hole outlet  38  in the lower end surface  35  of the nozzle hole  36  is formed near the center of the lower end surface  35  and four corners. Five pieces of the nozzle hole outlets  38  pass through the nozzle holes  36  illustrated in  FIG. 2  and are connected to the corresponding nozzle hole inlets  32 . 
     In this embodiment, a flow passage cross-section of each of the nozzle holes  36  has a circular shape in combination with the inlet  32  and the outlet  38 , and each of the nozzle holes  36  extends in parallel to the pulling-down direction Z of a crystal. However, a cross-sectional shape of each of the nozzle hole outlets  38  is not limited to the circular shape, and can be set to a polygonal shape, an elliptical shape, or the other shapes. 
     The crystal manufacturing device  2  including the crucible  4  of this embodiment as illustrated in  FIG. 1  is preferably used in the μ-PD method. A raw material that is put into the melt reservoir  24  of the crucible  4  is heated by the main heater  10  or the like and becomes the melt  30  illustrated in  FIG. 2 , passes through the nozzle holes  36  of the nozzle portion  34 , is drawn out from the nozzle hole outlets  38  by the seed crystal  14 , and the seed crystal  14  is pulled down to grow a crystal, thereby obtaining a crystal body. 
     Next, a method of manufacturing a crystal by using the crystal manufacturing device  2  of this embodiment will be briefly described. In the crystal manufacturing device  2  of this embodiment, first, a raw material of a crystal body to be obtained is put into the melt reservoir  24  of the crucible  4  illustrated in  FIG. 1 , and the main heater  10  is activated to heat the melt reservoir  24 . When the melt reservoir  24  is heated, the raw material is melted and becomes the melt  30  in the melt reservoir  24 , and flows from the nozzle hole inlets  32  of the nozzle portion  34  to the nozzle holes  36 . The melt  30  passes through the nozzle holes  36  and comes into contact with an upper end of the seed crystal  14  at the nozzle hole outlets  38 . 
     Before or after the heating, the after-heater  16  is also activated to heat the vicinity of the nozzle portion  34 . When using the crucible  4  of this embodiment, the melt  30  ejected from the nozzle hole outlets  38  of the nozzle holes  36  formed in the nozzle portion is crystallized due to pulling-down of the seed crystal  14 . 
     In the crucible  4  of this embodiment, since surface roughness of the inner peripheral surface of the nozzle holes  36  is set to a predetermined value or less, flowing-out of the melt from the nozzle holes  36  is stabilized, and the amount of the melt flowing out from the nozzle holes  36  becomes substantially uniform, and thus it is easy to uniformly disperse an additive element into the crystal body. Note that, even in a case where a single nozzle hole  36  is formed in the nozzle end surface  35  of the crucible  4 , flowing-out of the melt from the nozzle hole  36  becomes more stable in comparison to a crucible in the related art in which the surface roughness of the inner peripheral surface of the nozzle hole  36  is not managed, and thus it is easy to uniformly disperse the additive element into the crystal body. 
     In this embodiment, the nozzle portion  34  is an assembly of a plurality of the divided parts  50 ,  56   a , and  56   a , and the nozzle holes  36  are formed when the grooves  62   a ,  62   b   1 ,  62   c , and  54  formed in the matching surfaces  60 ,  58 , and  52  of the divided parts  50 ,  56   a , and  56   a  are combined. 
     The crucible  4  is required to have heat resistance to withstand a temperature of the melt, possibility of inductive heating, and the like, and thus the crucible  4  is constituted, for example, by a metal that is difficult to be machined, or the like in many cases. Therefore, machining of the nozzle holes  36  formed in the crucible  4  becomes difficult, and it is difficult to set the surface roughness of the inner peripheral surface of the nozzle holes  36  to 10 μm or less. 
     In this embodiment, the grooves  62   a ,  62   b   1 ,  62   c , and  54  which constitute the nozzle holes  36  are formed in the matching surfaces  60 ,  58 , and  52  of the divided parts  50 ,  56   a , and  56   a , and the divided parts  50 ,  56   a , and  56   a  are combined to form the nozzle holes  36 . Differently from machining of a hole, when machining a groove, since a machining surface is exposed to the outside, it is easy to obtain accuracy of the surface roughness, and it is easy to set the surface roughness to 10 μm or less, 5 μm or less, or 1 μm or less. Accordingly, when the divided parts  50 ,  56   a , and  56   a  are combined, the grooves  62   a ,  62   b   1 ,  62   c , and  54  are combined to form the nozzle holes  36 , and it is easy to set the surface roughness of the inner peripheral surface of the nozzle holes  36  to a predetermined value or less. 
     In this embodiment, a plurality of the grooves  54  are formed in the inner side surface (inner peripheral surface)  52  of the first part  50 , and the second part  56  including a plurality of the divided parts  56   a  is inserted into an opening of the first part  50  to be combined, thereby forming a plurality of the nozzle holes  36 . In addition, the second part  56  is formed by combining the plurality of divided parts  56   a , and the grooves  62   c  formed in the matching surfaces  60  are combined to form the nozzle holes  36 . Due to machining of the grooves  62   a ,  62   b   1 , and  54 , it is easy to obtain accuracy of surface roughness and it is also easy to make accuracy of the surface roughness of a plurality of grooves substantially uniform. Accordingly, the amount of the melt  30  flowing from the nozzle holes  36  becomes substantially uniform, and thus it is easier to uniformly disperse an additive element into a crystal body. 
     Furthermore, in this embodiment, the inner side surface  52  of the first part  50  is inclined from the melt reservoir  24  toward a direction close to the center of the lower end surface  35  of the nozzle portion  34 , and the outer side surface  58  of the second part  56  is inclined in correspondence with the inner side surface  52  of the first part  50 . According to this configuration, when the second part  56  is inserted into the opening of the first part  50  and is dropped down, the second part  56  does not fall down, and the nozzle portion  34  can be easily formed. In addition, the outer side surface  58  of the second part  56  and the inner side surface  52  of the first part  50  become matching surfaces, and the grooves  62   a  and  62   b  are formed in the matching surfaces, and thus the nozzle holes  36  inclined toward a direction close to the center of the lower end surface  35  of the nozzle portion  34  from the melt reservoir  24  can be easily formed by combining the first part  50  and the second part  56 . 
     In addition, in this embodiment, the inner peripheral surface of the nozzle holes  36  are coated with the wettability improving layer with high wettability with the melt  30  stored in the melt reservoir  24 . According to this configuration, it is easy for the melt  30  to flow out to the lower end surface  35  after passing through the nozzle holes  36 , and thus a variation of an additive element in a crystal body can be further effectively suppressed. 
     In addition, in this embodiment, typically, a hole is not formed by machining a metal that is difficult to be machined. The grooves  62   a  and  62   b  are formed in the outer side surface  58  of the divided parts  56   a  and  56   a , the grooves  54  are formed in inner corers of the inner side surface  52  of the first part  50 , or the groove  62   c  is formed in the center of the matching surface  60 . In addition, the divided parts are combined to form the nozzle holes  36 . Accordingly, it is easy to machine the surface roughness of the inner peripheral surface of the nozzle holes  36  with accuracy of a predetermined value or less. 
     The crystal body (preferably, a single crystal) according to this embodiment is manufactured by using the crucible  4  described above, and may contain an additive element having a segregation coefficient less than 1. A crystal that is grown by using the crucible  4  according to this embodiment has a shape close to an ideal columnar shape. In addition, a different phase is less likely to be mixed in the crystal body, and the crystal body is further less likely to be polycrystallized. 
     In addition, when using the crucible  4  according to this embodiment, a concentration distribution of a composition (containing an activator) in the crystal body that is grown from the nozzle hole outlets  38  becomes substantially uniform, particularly, in a plane orthogonal to the pulling-down direction Z. In addition, the concentration distribution becomes substantially uniform also in a plane parallel to the pulling-down direction Z. For example, in a case of manufacturing YAG:Ce by using the device  2  of this embodiment, it is possible to obtain a crystal body of YAG:Ce or the like in which an activator such as Ce is uniformly dispersed. 
     In addition, the method of manufacturing a crystal body according to this embodiment includes a process of causing the melt  30  that becomes a raw material of a crystal to flow out from the nozzle hole outlets  38  of the nozzle holes  36  which are formed in the nozzle portion  34  and in which surface roughness of an inner peripheral surface is 10 μm or less. According to the manufacturing method of this embodiment, even in a case where an additive element having a segregation coefficient less than 1 is contained, it is possible to obtain a crystal body in which a concentration variation of the additive element is suppressed. In the crystal body obtained by the manufacturing method of this embodiment, crystallinity is improved, a single crystal is likely to be obtained, polycrystallization can be suppressed, and occurrence of cracks is also suppressed. 
     In addition, a crystal body that is obtained by using the manufacturing method of this embodiment is preferably used as an optical element. Furthermore, when using the method of this embodiment, stabilization of crystal grown is secured, and shape accuracy of the crystal body is improved. Accordingly, a machining loss of the crystal body decreases, and a crystal body with high quality can be manufactured with high efficiency. 
     Second Embodiment 
     As illustrated in  FIG. 5A , a crystal manufacturing device according to this embodiment is different from the first embodiment only in divided parts (second part) of the nozzle portion  34 , and description of a common portion will be omitted. Hereinafter, different portions will be mainly described in detail. A portion that is not described below is similar to description of the first embodiment. 
     The nozzle portion  34  of a crucible according to this embodiment is an assembly of the first part  50  and a second part  156 . In the second part  156 , four quadrangular columnar divided parts  156   a  are combined and the resultant assembly is inserted into an inner side of the first part  50  having a quadrangular tubular shape to form the nozzle portion  34 . 
     A nozzle hole  136  is formed between an outer side surface  58  (matching surface) of the second part  156  and the inner side surface  52  (matching surface) of the first part  50 , and between matching surfaces  60  of the divided parts  156   a  which constitute the second part  156 . The nozzle hole  136  is formed by combining grooves formed in the matching surfaces of the parts in a similar manner as in the first embodiment. An arrangement and the number of the nozzle hole  136  and a nozzle hole outlet  138  can be freely determined. 
     Third Embodiment 
     As illustrated in  FIG. 5B  and  FIG. 6 , the crystal manufacturing device according to this embodiment is different from the first or second embodiment only in divided parts (a first part and a second part) of a nozzle portion  34 , and thus description of a common portion will be omitted. Hereinafter, different portions will be mainly described in detail. A portion that is not described below is similar to description of the first or second embodiment. 
     A nozzle portion  34  of a crucible according to this embodiment is an assembly of the first part  50  and a single second part  256 . The second part  256  is a divided part having a size of being inserted into an inner opening of the first part  50  having a quadrangular frame shape through just fit. The second part  256  is fitted into an inner side of the first part  50  to form the nozzle portion  34 . 
     Nozzle holes  236  are formed between an outer side surface  58  (matching surface) of the second part  256  and the inner side surface  52  (matching surface) of the first part  50 . The nozzle holes  236  are formed by combining grooves formed in the matching surfaces of the parts in a similar manner as in the first or second embodiment. An arrangement and the number of the nozzle holes  236  can be freely determined. 
     In this embodiment, the outer side surface  58  of the second part  256  illustrated in  FIG. 5B  is inclined from the melt reservoir  24  illustrated in  FIG. 6  toward the lower end surface  35  of the nozzle portion  34  in a direction close to the center  42  of the lower end surface  35  of the nozzles. In addition, the inner side surface  52  of the first part  50  is also inclined in conformity to the inclination. As a result, as illustrated in  FIG. 6 , the nozzle holes  236  according to this embodiment are inclined from nozzle hole inlets  232  toward nozzle hole outlets  238  and toward a direction close to the center  42  of the end surface  35 . 
     In addition, according to this embodiment, in the nozzle holes  236 , the entirety of a flow passage is inclined in order for the nozzle hole outlets  238  to be closer to the center of the lower end surface  35  in comparison to the nozzle hole inlets  232  opened to the melt reservoir  24 . According to this configuration, a raw material melt ejected from the nozzle hole outlets  38  is likely to be directed to an inner side from an outer side of a crystal along a crystal growth plane. 
     In addition, in this embodiment, as illustrated in  FIG. 5B , the nozzle hole outlets  238  in the lower end surface  35  of the nozzle holes  236  are arranged in a nozzle hole forming region  40  located close to the outer peripheral edge  35   a  of the lower end surface  35 . In addition, in this embodiment, the nozzle hole outlets  238  are constituted by a plurality of individual outlets  238  formed intermittently with predetermined interval along a peripheral direction within a range of the nozzle hole forming region  40 . The plurality of outlets  238  are connected to a plurality of corresponding nozzle hole inlets  232  after passing through the plurality of individual nozzle holes  236  illustrated in  FIG. 6 . 
     In this embodiment, a flow passage cross-section of each of the nozzle holes  236  has a circular shape in combination with the inlets  232  and the outlets  238 , and the flow passage cross-section of the nozzle hole  236  is constant from the inlets  232  to the outlets  238 , but it is not necessary for the flow passage cross-section to be constant. For example, in this embodiment, only the outlets  238  may be constituted by a plurality of individual outlets  238  along a peripheral direction, and the nozzle holes  236  may be set as a single ring-shaped hole connecting the plurality of outlets  238  along the peripheral direction. In addition, with regard to the nozzle hole inlets  232  may be set as a single ring-shaped opening connecting the plurality of outlets  238  along the peripheral direction in a similar manner as in the nozzle holes  236 . 
     In this case, in the vicinity of the melt reservoir  24 , a ring-shaped gap or opening may be formed between the matching surfaces of the first part  50  and the second part  256 . The ring-shaped gap or opening may be approximately parallel to the pulling-down direction Z. Alternatively, in the vicinity of the melt reservoir  24 , the second part  256  may not be formed, and a columnar space may exist. However, in the vicinity of the lower end surface  35  of the nozzle portion  234 , the matching surfaces of the first part  50  and the second parts  256  are preferably in contact with each other in a portion other than the nozzle holes  236  in order for the melt not to be leaked, but the melt may be slightly leaked. In addition, a cross-sectional shape of the individual nozzle hole outlets  238  may be set to have a polygonal shape, an elliptical shape, and other shapes without limitation to a circular shape. The deformation is also applicable to the first embodiment and the second embodiment. 
     As illustrated in  FIG. 5B , in this embodiment, a region including the center  42  of the lower end surface  35  located on an inner side of the nozzle hole forming region  40  is a nozzle hole not-formed region  44  in which the nozzle hole outlets  38  are substantially not formed. Note that, in this embodiment, the center  42  of the lower end surface  35  represents the geometric center or the center of gravity of a planer shape of the lower end surface  35 . For example, in a case where a shape of the outer peripheral edge  35   a  of the lower end surface  35  is a circle, the center  42  of the lower end surface  35  represents the center of the circle. In addition, as illustrated in  FIG. 5B , in a case where the shape of the outer peripheral edge  35   a  is a polygonal shape such as a square and a hexagon, an elliptical shape, or the other different shapes, the center  42  represents the center of gravity of the lower end surface  35 . The lower end surface  35  includes a lower end surface of the first part  50  and a lower end surface of the second part  256 . 
     As illustrated in  FIG. 5B , the nozzle hole forming region  40  is located within a range between a virtual boundary line  46  that connects ½ of a distance R from the center  42  of the lower end surface  35  to the outer peripheral edge  35   a  in a peripheral direction, and the outer peripheral edge  35   a . More preferably, the nozzle hole forming region  40  is located within a range between the virtual boundary line  46  that connects ⅔ (more preferably ¾) of the distance R from the center  42  of the lower end surface  35  to the outer peripheral edge  35   a  in a peripheral direction, and the outer peripheral edge. 
     Note that, the distance from the center  42  of the virtual boundary line  46  can be expressed as α×R. α is preferably ½ or greater, more preferably ⅔ or greater, and still more preferably ¾. The upper limit of a is less than 1, and is determined so that the nozzle hole outlets  38  are formed within a range of the nozzle hole forming region  40  expressed by (R−α×R). The nozzle hole outlets  238  are preferably formed close to the outer peripheral edge  35   a  as much as possible. 
     An inner diameter (or an opening area) of the nozzle hole outlets  238  is not particularly limited, and is determined so that the nozzle hole outlets  238  are within the range (R−α×R) of the nozzle hole forming region  40 . In a case where the nozzle hole outlets  238  have a circular shape, the inner diameter of the outlets  238  is, for example, approximately 1/10 to 9/10 of (R−α×R). In addition, although not particularly limited, the number of the nozzle hole outlets  238  arranged within the range of the nozzle hole forming region  40  is, for example, preferably 4 or greater along a peripheral direction, more preferably 6 or greater, and still more preferably 8 or greater. 
     In a case where the shape of the outer peripheral edge  35   a  is a circle, the shape of the virtual boundary line  46  also becomes a circle, and the size of a radius of the circle of the virtual boundary line  46  becomes a times the distance (radius) R of the outer peripheral edge  35   a . Furthermore, in a case where the shape of the outer peripheral edge  35   a  is a hexagon, the shape of the virtual boundary line  46  also becomes a hexagon, and the shape of the virtual boundary line  46  becomes a similar shape that is a times the shape of the outer peripheral edge  35   a . In addition, as illustrated in  FIG. 5B , in a case where the shape of the outer peripheral edge  35   a  is a square, the shape of the virtual boundary line  46  also becomes a square, and the shape of the virtual boundary line  46  becomes a similar shape that is a times the shape of the outer peripheral edge  35   a . Even in a case where the shape of the outer peripheral edge  35   a  is the other different shapes, the shape of the virtual boundary line  46  becomes a similar shape that is a times the shape of the outer peripheral edge  35   a.    
     Note that, an inner region (a region including the center  42 ) of the virtual boundary line  46  becomes the nozzle hole not-formed region  44 , and the nozzle hole outlet  38  are substantially not formed in the region. The meaning of “nozzle hole outlets  38  are substantially not formed” will be described later. 
     When using the crucible  4  of this embodiment, a melt that is pulled down from the nozzle hole outlets  38  disposed in the nozzle hole forming region  40  located close to the outer peripheral edge  35   a  of the end surface  35  of the nozzle portion  34  by the seed crystal  14  flows toward the center  42  of the nozzle hole not-formed region  44  along the lower end surface  35 , and crystal growth is performed. 
     That is, when using the crucible  4  of this embodiment, crystal growth starts from a site close to the outer peripheral edge  35   a  of the end surface  35  of the nozzle portion  34  and proceeds toward an inner side. Accordingly, even in a case where an additive element having a segregation coefficient less than 1 is contained in the melt, the additive element is less likely to be mixed in a crystal and is concentrated during a growing process, and thus it is possible to effectively suppress a phenomenon in which the additive element segregates to an outer edge portion at an initial stage of growing. 
     Accordingly, in a crystal body obtained by using the crucible  4  of this embodiment, even in a case where an additive element having a segregation coefficient less than 1 is contained, surplus segregation of the additive element (dopant) at a site close to an outer side surface of the crystal body is suppressed. In the crystal body of this embodiment, crystallinity is improved, a single crystal is likely to be obtained, polycrystallization can be suppressed, and occurrence of cracks is also suppressed. 
     In addition, the crystal body obtained by using the crucible  4  of this embodiment can suppress dilution of the concentration of the additive element (dopant) in the vicinity of the center of the crystal body, and an effect of adding a dopant to the crystal body increases. The obtained crystal body is preferably used as an optical element. Furthermore, when using the crucible  4  of this embodiment, stability of crystal growth is secured, and shape accuracy of the crystal body is improved. Accordingly, a machining loss of the crystal body decreases, and a crystal body with high quality can be manufacture with high efficiency. 
     In addition, in this embodiment, the nozzle hole forming region  40  is disposed close to the outer peripheral edge  35   a  in the lower end surface  35  of the nozzle portion  34 , and an inner side thereof is set as the nozzle hole not-formed region  44 . Accordingly, after the raw material melt passes through the nozzle hole outlets  38 , a flow of the melt moving along a crystal growth plane is likely to be directed toward an inner side from an outer peripheral side of a crystal. As a result, a crystal that is grown by using the crucible  4  according to this embodiment has a shape close to an ideal columnar shape. In addition, a different phase is less likely to be mixed in the crystal body, and the crystal body is further less likely to be polycrystallized. 
     Note that, in this embodiment, description of “nozzle hole outlet is substantially not formed” in the nozzle hole not-formed region  44  represents that a nozzle hole outlet smaller than an inner diameter of the nozzle hole outlets  38  formed in the nozzle hole forming region  40  can be slightly formed. Alternatively, the description represents that even though the inner diameter of the nozzle hole outlets  38  is the same in each case, the nozzle hole outlets  38  can be slightly formed in the nozzle hole not-formed region  44  in a number less than the number of the nozzle hole outlets  38  formed in the nozzle hole forming region  40 , for example, in a number less than the number by approximately 1/10 or less. 
     EXAMPLES 
     Hereinafter, the present invention will be further described on the basis of detailed example, but the present invention is not limited to the examples. 
     Example 1 
     A fluorescent substance formed from a single crystal of Ce:YAG (Ce doped YAG) was manufactured by using the crystal manufacturing device  2  illustrated in  FIG. 1 . The crucible  4  used in growth was formed from iridium and had a cylindrical shape having an outer diameter of 20 mm, an inner diameter of 18 mm, and a height of 50 mm. The device  2  included the nozzle portion  34  having a structure illustrated in  FIG. 2  to  FIG. 4B , the nozzle hole outlets  38  of a total of five nozzle holes  36  were arranged at four corners of the nozzle end surface  35  at a position on an inner side by 1.0 mm from the outer peripheral edge  35   a  and at the center of the nozzle end surface  35 , and penetrated in the vertical direction (pulling-down direction). The nozzle end surface  35  has a square shape (R=2.5 mm) having dimension of 5.0 mm×5.0 mm, and an inner diameter of the nozzle holes  36  was 0.4 mm. 
     (Evaluation of Surface Roughness) The inner peripheral surface  36   a  of the nozzle holes  36  was measured ten times with respect to the inner peripheral surface  36   a  of the nozzle holes  36  by using a laser microscope (LEXT-OLS4100) manufactured by Olympus Corporation, and arithmetic mean roughness Ra was obtained. 
     The arithmetic mean roughness Ra of the inner peripheral surface  36   a  of the nozzle holes  36  according to this example was 6 to 9 μm. 
     (Preparation of Specimen) Respective oxide powders of Al 2 O 3 , Y 2 O 3 , and CeO 2  with purity of 99.99% were blended in a composition ratio of Y 2 O 3 :Al 2 O 3 =3.0:5.0, or CeO 2 /(CeO 2 +(1/2)Y 2 O 3 )=0.01 in terms of a molar ratio to obtain a raw material in a total amount of 10 g, and the resultant raw material was set as a raw material for crystal growth. The crucible  4  filled with the same raw material was provided in the single crystal growing device  2 , and was heated up to approximately 2000° C. for one hour. 
     In an N 2  gas flow atmosphere, a Y3Al5O12 single crystal in which a crystal orientation &lt;111&gt; is set as a longitudinal direction was used as the seed crystal  14 , and as illustrated in  FIG. 2 , a tip end of the seed crystal  14  was brought into contact with the nozzle portion  34  provided in the lower end of the crucible  4 , after the raw material melt flowing out from the nozzle hole outlets  38  of the nozzle portion  34  wets and spreads on the tip end of the seed crystal  14 , the seed crystal  14  was gradually lowered to perform crystal growth at a pulling-down rate of 0.20 mm per minute. 
     A Ce:YAG single crystal having a quadrangular columnar shape of approximately 5 mm square and 40 mm in length was obtained. The single crystal was deep yellow and transparent, and thus precipitates such as an inclusion were not observed in the crystal with naked eyes. Four side surfaces of the crystal body were smooth, and a cross-section orthogonal to the pulling-down direction had an approximately square shape over the entirety of the crystal. 
     With respect to the obtained crystal body, specimens for evaluation were sampled as follows, and the following evaluation was performed. 
     (Sampling of Specimen for Evaluation) 
     Ten crystals grown by a micro pulling-down method were grown. Three samples for evaluation were prepared from one crystal at positions different in the pulling-down direction. The respective samples were prepared by cutting a specimen at a cut plane orthogonal to the pulling-down direction in a state in which an outer side surface of the crystal body during the pulling-down growth is set as an outer peripheral edge. Furthermore, both surfaces were mirror polished so that the inside of the crystal can be observed, thereby preparing a flat specimen for evaluation in a thickness of approximately 1 mm. A composition variation of the grown crystal was evaluated by using a total of 30 samples. 
     (Evaluation of Composition Variation) 
     With regard to a composition distribution inside the grown crystal, an additive element Ce was evaluated by laser ablation ICP mass spectrometry by using an ICP-MS analyzer (7500S, manufactured by Agilent Technologies, Inc.). Quartiles were statically obtained from composition distribution measurement results of the respective samples, and comparison evaluation for a deviation in concentration of Ce was performed. 
     It was determined that the smaller a difference between the maximum value and the minimum value in the samples is, the smaller the composition variation is. Results obtained with respect to the 30 samples are shown in  FIG. 7 . 
     Example 2 
     A Ce:YAG single crystal was grown by the micro pulling-down method by using a crucible including the same nozzle portion  34  as in Example 1 except that the arithmetic mean roughness Ra of the inner peripheral surface  36   a  of the nozzle holes  36  is within a range of 3 to 4 μm. 
     Crystal growth was performed by the same raw material and under the same growing conditions as in Example 1, and the same evaluation as in Example 1 was performed. Results are shown in  FIG. 7 . 
     Example 3 
     A Ce:YAG single crystal was grown by the micro pulling-down method by using a crucible that is formed from the same material and has the same shape as the crucible  1  used in Example 1 except that the arithmetic mean roughness Ra of the inner peripheral surface  36   a  of the nozzle holes  36  is within a range of 0.6 to 0.8 μm. 
     Crystal growth was performed by the same raw material and under the same growing conditions as in Example 1, and the same evaluation as in Example 1 was performed. Results are shown in  FIG. 7 . 
     Example 4 
     With respect to a crucible having the same specifications as in Example 3, the inner peripheral surface  36   a  of the nozzle holes  36  was coated with Al 2 O 3  at a film forming temperature of 150° C. with an atomic layer deposition (ALD) device (AFALD-8, manufactured by JSW-AFTY. CO. JP) by using trimethyl aluminum (TMA) as a precursor gas and oxygen (O 2 ) as an oxidizing agent. A Ce:YAG single crystal was grown by the micro pulling-down method by using a crucible that is formed from the same material and has the same shape as in Example 3 except that the inner peripheral surface  36   a  of the nozzle holes  36  is coated with Al 2 O 3 . 
     Crystal growth was performed by the same raw material and under the same growing conditions as in Example 1, and the same evaluation as in Example 1 was performed. Results are shown in  FIG. 7 . 
     Comparative Example 1 
     A crucible including a typical nozzle portion was used, and the nozzle holes were formed by wire electric discharge machining. The arithmetic mean roughness Ra of the inner peripheral surface  36   a  of the nozzle holes  36  was within a range of 12 to 18 μm. Crystal growth was performed by using the same raw material and device, and under the same atmosphere and growing conditions as in Example 1, and the same evaluation as in Example 1 was performed. Results are shown in Table 7. 
     Evaluation 
     As illustrated in  FIG. 7 , from the results in Examples 1 to 4, it could be seen that a difference between a maximum value and a minimum value of the concentration of Ce in samples is smaller and a composition variation is smaller in comparison to results in Comparative Example 1. Particularly, satisfactory results were obtained in the order of Examples 4, 3, 2, and 1. 
     EXPLANATIONS OF LETTERS OR NUMERALS 
     
         
         
           
               2  CRYSTAL MANUFACTURING DEVICE 
               4  CRUCIBLE 
               6  REFRACTORY FURNACE (REFRACTORY MATERIAL) 
               8  OUTER CASING 
               10  MAIN HEATER 
               12  SEED CRYSTAL HOLDING JIG 
               14  SEED CRYSTAL 
               16  AFTER-HEATER 
               24  MELT RESERVOIR 
               26  ACCOMMODATION WALL 
               28  BOTTOM OUTER SURFACE 
               30  MELT 
               32 ,  232  NOZZLE HOLE INLET 
               34 ,  134 ,  234  NOZZLE PORTION 
               35  END SURFACE 
               35   a  OUTER PERIPHERAL EDGE 
               36 ,  136 ,  236  NOZZLE HOLE 
               36   a  INNER PERIPHERAL SURFACE 
               37  OUTER SIDE SURFACE 
               38 ,  138 ,  238  NOZZLE HOLE OUTLET 
               40  NOZZLE HOLE FORMING REGION 
               42  CENTER 
               44  NOZZLE HOLE NOT-FORMED REGION 
               46  VIRTUAL BOUNDARY LINE 
               50  FIRST PART (DIVIDED PART) 
               52  INNER SIDE SURFACE (MATCHING SURFACE) 
               54  GROOVE 
               56 ,  156 ,  256  SECOND PART (DIVIDED PART) 
               56   a ,  156   a ,  256   a  DIVIDED PART 
               58  OUTER SIDE SURFACE (MATCHING SURFACE) 
               60  MATCHING SURFACE 
               62   a ,  62   b ,  62   c  GROOVE