Method for growing crystal of multi-color crystal

Abstract

To provide a method for growing a crystal that grows a multi-collar crystal in which a grown single crystal exhibits two or more colors by only regulating concentration of oxygen contained in an atmosphere gas in crystal growth.SOLUTION: A method for growing a crystal includes a step of increasing or decreasing concentration of oxygen contained in an atmosphere gas in crystal growth in a step wise of one or more steps or slope wise in a plurality of predetermined concentrations between 100 vol% and 0.0 vol% to change an oxidation state of an impurity ion that causes pigmentation in a crystal, thereby growing a multi-collar crystal in which a single crystal exhibits two or more colors.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This invention relates to a method for growing multi-color crystals, in which the oxygen (O2) concentration in the atmospheric gas during crystal growth is adjusted between 100 vol% and 0.0 vol%, changing the oxidation number of the impurity ions contained in the crystal to change the color of the crystal, thereby growing crystals that exhibit two or more colors. [Background technology]

[0002] Crystals used for jewelry include natural crystals grown in nature and artificially grown crystals. Natural crystals are rare, while artificial crystals are characterized by their high quality, uniformity, and mass production. Conventional methods for growing artificial crystals include the floating zone (FZ) method, the Cz method (Czochralski crystal pulling method), the Verneuil method (flame fusion method), the Bridgman method, the flux method, the skull melt method, the Bagdasorov method, and the EFG method (Edge-defined Film-fed Growth). These artificial crystals were monochromatic. Natural crystals such as tourmaline (tourmaline), which exhibit multiple colors, were prized as bicolor crystals due to their rarity. On the other hand, there was no crystal growth technology capable of growing multicolor crystals such as bicolor crystals or tricolor crystals, which exhibit multiple colors.

[0003] Both natural and artificial spinel have been used as spinel (MgAl2O4) for jewelry. Conventional methods for growing artificial spinel crystals include the Verneuil method, the Cz method, the flux method, and the FZ method. These artificial spinel crystals were monochromatic crystals that exhibited one color throughout the crystal. Natural spinel that exhibits multiple colors was known as bicolor crystals and was highly valued for its rarity. On the other hand, there was no technology to grow artificial spinel that exhibits multiple colors, such as bicolor spinel or tricolor spinel.

[0004] In the case of monochromatic artificial spinel crystals, where the entire crystal exhibits one color, spinels of various colors have been artificially grown. For example, Non-Patent Document 1 reports that when growing spinel crystals containing added MnO, it is possible to grow crystals in colors such as yellow, pink, and green by changing the O2 concentration in the atmospheric gas and the composition ratio of the spinel raw materials (MgO / Al2O3). In addition, YAG crystals containing added Eu (Y3Al5O 12 It has been reported in Non-Patent Document 2 that purple or colorless crystals can be grown by changing the O2 concentration in the atmospheric gas when growing crystals of . The methods described in Non-Patent Document 1 and Non-Patent Document 2 are crystal growth methods for obtaining monochromatic crystals in which the entire crystal exhibits one color. With conventional crystal growth techniques, it was impossible to grow multi-colored crystals that exhibit multiple colors in a single crystal. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Toru Katsumata, Hiromasa Mitomi, Hijiri Nagayama, Yuka Orihara, Mina Aoki, Ayaka Yoshida, Kasumi Shiratake, Shunsuke Minowa, Takashi Sakuma, Hiroaki Aizawa, Shuji Komuro, “Compositional variations in optical characteristics of Mn doped spinel crystals” , J.Crystal Growth,468 (2017) 387-390.

[0006] [Non-Patent Document 2] Yuka Kiyokawa, Hirofumi Inoue, Toru Katsumata, Shuji Komuro, Hiroaki Aizawa, “Thermal stability and annealing behavior of photoluminescence from Eu doped YAG”, Optical Materials, 37 (2014) 493-497. Summary of the Invention [Problem to be solved by the invention]

[0007] This invention provides a crystal growth technology for artificially producing multi-color crystals in which one crystal exhibits two or more colors. Natural crystals contain multiple impurities, and the color of the crystal can change in various ways as the concentration of each impurity changes during crystal growth. However, with conventional artificial crystal growth technology, it was difficult to grow crystals while changing the type and concentration of impurities during crystal growth. For this reason, there was no effective technology to artificially grow multi-color crystals that exhibit multiple colors. [Means for solving the problem]

[0008] In this invention, in a crystal growth technique using the FZ method, the valence of impurity ions inside the crystal was changed by adjusting the O2 concentration in the atmospheric gas, and crystals exhibiting multiple colors were successfully grown. By using a spinel doped with an element whose ion's oxidation number changes depending on the O2 concentration during crystal growth, crystals could be grown while changing the O2 concentration in the atmospheric gas during crystal growth. By adjusting the O2 concentration in the spinel's atmospheric gas during crystal growth between 100 vol% and 0.0 vol%, the oxidation number of the impurity ions in the crystal was changed, changing the color of the crystal. By using this crystal growth method, multi-colored crystals exhibiting multiple colors could be grown using spinels doped with MnO and spinels doped with Fe2O3.

[0009] In the crystal growth method of the present invention, it is possible to grow multi-colored crystals exhibiting multiple colors by increasing or decreasing the O2 concentration in the atmospheric gas in a step-like or slope-like manner during crystal growth. Therefore, it is possible to apply this method to all crystal growth methods that allow the O2 concentration in the atmospheric gas to be increased or decreased during crystal growth. This crystal growth method of the present invention can be applied to crystal growth methods such as the FZ method, Cz method, Bernoulli method, Bridgman method, flux method, Skullmelt method, Bagdasorov method, and EFG method.

[0010] In the crystal growth method of the present invention, a multi-color crystal exhibiting multiple colors can be grown by increasing or decreasing the O2 concentration in the atmospheric gas in a step-like or slope-like manner during crystal growth. Any element whose oxidation state changes depending on the O2 concentration can be used as the impurity element that causes coloration in the growing crystal. Therefore, the method can be applied to the growth of multi-color crystal exhibiting multiple colors in a crystal to which at least one or more elements selected from Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Tm, Yb, Ti, V, Cr, Mn, Fe, Co, and Ni are added. Effect of the Invention

[0011] Since crystals exhibiting multiple colors can be grown by adjusting the O2 concentration in the atmospheric gas, this method has the advantage that no special equipment is required; simply connect O2 gas and argon (Ar) gas, O2 gas and nitrogen (N2) gas, or air and N2 gas, or air and Ar gas to a conventional crystal growth apparatus. If this method is applied to the growth of crystals containing elements as impurities whose ion oxidation numbers change with changes in O2 concentration, it is possible to grow multi-colored crystals in which a single crystal exhibits multiple colors by precisely adjusting the O2 concentration during crystal growth between 100 vol% and 0.0 vol%. [Brief description of the drawings]

[0012] [Figure 1] Crystal growth method using the floating zone (FZ) method [Diagram 2] Behavior of O2 during crystal growth and oxidation state of impurity ions in the melt [Diagram 3] Decreasing pattern of O2 concentration in the atmospheric gas during growth [Figure 4] Differences in color of crystals grown in atmospheric gases with different O2 concentrations [Diagram 5] Color change of crystals with a stepwise decrease in O2 concentration [Figure 6] Change in crystal color with decreasing O2 concentration in a ramp or two-step manner [Figure 7] Increase pattern of O2 concentration in the atmosphere gas during growth [Figure 8] Multicolored crystals cut for jewelry DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The crystal growth method using the FZ method is shown in Figure 1. The crystal growth technology of this invention can be applied to all crystal growth methods that can increase or decrease the O2 concentration of the atmospheric gas during crystal growth, such as the FZ method, Cz method, Bernoulli method, Bridgman method, flux method, Skalmelt method, Bagdasorov method, and EFG method. The FZ method crystal growth apparatus to which this invention is applied is shown in Figure 1.

[0014] A grown crystal 2 can be obtained by solidifying the melt 3 produced by melting a raw material rod 1 for crystal growth. The melt 3 is produced by concentrating light from a heating light source 6 installed in the center of a quartz tube 4 placed at the focal position of an elliptical mirror 5. The inside of the quartz tube 4 is filled with atmospheric gas adjusted to the desired O2 concentration, which is a mixture of O2 gas, carbon dioxide (CO2) gas, or air 7 and Ar gas, or N2 gas, or a mixed gas 8 of Ar gas and N2 gas. The mixed gas 8 of O2 gas, CO2 gas, air 7 and Ar gas, or N2 gas, or Ar gas and N2 gas, adjusted to the desired pressure by a pressure regulator 10, is introduced into the inside of the quartz tube 4 through a gas piping 9, with the amount of the mixture adjusted by a flow regulator or mass flow meter 11.

[0015] The behavior of O2 molecules during crystal growth and the oxidation state of impurity ions in the melt are shown in Figure 2. The partial pressure of O2 molecules 12 in the ambient gas during crystal growth is in equilibrium with the partial pressure of O2 evaporating from the melt 3, and affects the O2 concentration in the melt. For this reason, the O2 gas concentration in the atmosphere affects the concentration of impurity ions 13 in a high oxidation state or impurity ions 14 in a low oxidation state contained in the melt 3. These impurity ions with different oxidation states are taken up from the melt 3 into the crystal 2 according to the magnitude of the segregation coefficient at the interface between the melt and the crystal as the crystal grows. The color of the grown crystal changes because the concentrations of impurity ions with different oxidation states in the crystal change depending on the O2 concentration in the ambient gas.

[0016] The pattern of the decrease in the O2 concentration of the atmospheric gas during growth is shown in Figure 3. The color of the crystal grown in an atmosphere containing a high concentration of O2 and the color of the crystal grown in an atmosphere containing a low concentration of O2 or no O2 are determined by the oxidation number of the impurity ions contained in the grown crystal. By changing the O2 concentration during crystal growth, it was possible to grow a multi-color crystal in which one crystal exhibits multiple colors. Figure 3 shows the change in the O2 concentration of the atmospheric gas when the O2 concentration contained in the atmospheric gas is decreased during crystal growth. Possible adjustment patterns include an O2 concentration adjustment pattern 15 in which the O2 concentration of the atmospheric gas is changed in a single step during crystal growth, a pattern 16 in which the O2 concentration is decreased in a single step, a slope-like O2 concentration adjustment pattern 17, and a slope-like O2 concentration decrease pattern 18. Furthermore, it is also possible to change the O2 concentration of the atmospheric gas in multiple steps during crystal growth, such as a multiple-step O2 concentration adjustment pattern 19, or a multiple-step O2 concentration decrease pattern 20.

[0017] Figure 4 shows the difference in color of crystals grown in atmospheric gases with different O2 concentrations. When a crystal is grown along the crystal growth direction 21 while keeping the O2 concentration in the atmosphere constant, the colors of the grown crystals differ, such as crystal 22 grown with a high O2 concentration and crystal 23 grown with a low O2 concentration. This is because the oxidation number of the ions that cause coloring and are incorporated into the crystal is affected by the O2 concentration of the atmospheric gas. For this reason, it was possible to grow crystals of different colors by changing the O2 concentration contained in the atmospheric gas during crystal growth.

[0018] Figure 5 shows the change in crystal color as the O2 concentration in the atmospheric gas during crystal growth is reduced to a single step shape 15, 16. The O2 concentration can be changed to a single step shape 15, 16, a slope shape 17, 18, or multiple steps 19, 20, depending on the length of the grown crystal or the elapsed time from the start of growth. The color of the crystal changed with each change in O2 concentration. This crystal growth method can be applied to spinel doped with one or more transition metal elements such as Ti, V, Cr, Mn, Fe, Co, and Ni, and YAG doped with rare earth metal elements such as Eu or transition metal elements such as Cr or Ti, and by adjusting the O2 concentration during growth, it is possible to grow multi-colored crystals that exhibit multiple colors. By changing the O2 concentration in the atmospheric gas during crystal growth, it was possible to grow multi-color crystals in which a single crystal exhibits multiple colors, such as a crystal 22 grown at a high O2 concentration along the crystal growth direction 21, a crystal 23 grown at a low O2 concentration, and a crystal 24 grown at an O2 concentration intermediate between the high and low O2 concentrations.

[0019] Figure 6 shows the change in crystal color when the O2 concentration is decreased in a slope shape 17, 18 or in a two-step shape 19, 20. The O2 concentration can be changed to a single step shape, a slope shape, or multiple steps with respect to the length of the grown crystal or the elapsed time from the start of growth. The color of the crystal changed as shown in Figure 6 with each change in O2 concentration. This crystal growth method can be applied to spinel doped with one or more transition metal elements such as Ti, V, Cr, Mn, Fe, Co, and Ni, and YAG doped with rare earth metal elements such as Eu or transition metal elements such as Cr or Ti, and by adjusting the O2 concentration during growth, it is possible to grow multi-colored crystals that exhibit multiple colors. By changing the O2 concentration contained in the atmospheric gas during crystal growth, it was possible to grow multi-colored crystals that exhibit multiple colors, such as a crystal 22 grown with a high O2 concentration along the crystal growth direction 21, a crystal 23 grown with a low O2 concentration, and a crystal 24 grown with an O2 concentration intermediate between the high and low O2 concentrations.

[0020] As an application example, a pattern in which the O2 concentration of the atmospheric gas during crystal growth is gradually increased with the length of the grown crystal or the elapsed time from the start of growth is shown in Figure 7. Possible patterns include O2 concentration adjustment patterns 25 and 26 in which the O2 concentration of the atmospheric gas is increased in a single step during crystal growth, O2 concentration adjustment patterns 27 and 28 in which the O2 concentration is increased in a sloped manner, and O2 concentration adjustment patterns 29 and 30 in which the O2 concentration is increased in multiple steps. With this application, it is possible to reverse the color change of the multi-colored crystal with growth to that of the multi-colored crystal grown with the adjustment pattern of decreasing the O2 concentration in Figure 3.

[0021] Gases that can be mixed with O2 include Ar gas, N2 gas, and air. Also, CO2 gas can be used instead of O2 gas to adjust the O2 concentration. When CO2 gas is used instead of O2 gas, O2 is generated from CO2 through the chemical reaction (CO2 → CO + 1 / 2O2) at the crystal growth temperature, so the O2 concentration of the atmospheric gas can be adjusted.

[0022] Multi-colored crystals cut for jewelry use are shown in Figure 8. Jewelry designs that take advantage of the color changes in multi-colored crystals are possible, as shown in top view 31 of a multi-colored crystal cut as a table cut (emerald cut) for jewelry use and top view 32 of a multi-colored crystal cut as a brilliant cut for jewelry use. The color changes in the multi-colored crystals can be emphasized by processing them into a polygonal prism shape, such as a cylinder, square prism, triangular prism, pentagonal prism, hexagonal prism, or octagonal prism, as shown in multi-colored crystal cut into a cylindrical shape for jewelry use 33 or multi-colored crystal cut into a square prism shape for jewelry use 34. EXAMPLES

[0023] Fe2O3-added spinel was grown using the FZ method crystal growth apparatus shown in Figure 1. The Fe2O3 concentration was adjusted to be between 0.05 mol% and 2.5 mol%. The spinel composition ratio (x = MgO / Al2O3) was adjusted to be between x = 0.3 and x = 1.0. The atmospheric gas used was a mixture of Ar gas and O2 gas with different ratios. The O2 concentration of the atmospheric gas was adjusted to be between 0.0 vol% and 100 vol%. The crystal growth rate was 10 mm / h, and the feed rod and seed crystal rod were rotated in opposite directions at 30 rpm.

[0024] When spinel crystals were grown with a composition ratio of x between 0.3 and 1.0, with the O2 concentration in the atmospheric gas kept constant during crystal growth, crystals of different colors were able to grow for each O2 concentration, as shown in Figure 4. When crystals were grown in an atmospheric gas with an O2 concentration of 0.0 vol%, the grown crystals were pink. On the other hand, when crystals were grown in an atmospheric gas with an O2 concentration of 0.1 vol%, the grown crystals were blue. When crystals were grown in an atmospheric gas with an O2 concentration of 10.0 vol% or more and 100 vol% or less, the grown crystals were green. EXAMPLES

[0025] Fe2O3-added spinel was grown using the FZ method crystal growth apparatus shown in Figure 1. The Fe2O3 concentration was adjusted to be 0.05 mol% or more and 2.5 mol% or less. The composition ratio of the spinel (x = MgO / Al2O3) was adjusted to be x = 0.3 or more and x = 1.0 or less. The atmosphere gas used was a mixture of Ar gas and O2 gas with different mixing ratios. The O2 concentration of the atmosphere gas was adjusted to be 0.0 vol% or more and 100 vol% or less. The O2 concentration of the atmosphere gas during crystal growth was reduced in a single step as shown in Figure 3, using patterns 15 and 16 to grow the crystal. The crystal growth speed was 10 mm / h, and the feed rod and seed crystal rod were rotated in opposite directions at 30 rpm.

[0026] Crystal growth was performed with an Fe2O3 concentration of 1.0 mol% and a spinel composition ratio (x = MgO / Al2O3) of x = 0.3. The atmosphere gas used was a mixture of Ar gas and O2 gas with different ratios. As shown in Figure 3, the O2 concentration of the atmosphere gas during growth was reduced in one step from 100 vol% to 0.0 vol%, in patterns 15 and 16. The grown Fe2O3-doped spinel crystal was a bicolor spinel that exhibited two colors, green and pink, in one crystal. The color of the grown crystal changed from transparent green to transparent pink as the O2 concentration decreased from 100 vol% to 0.0 vol%. EXAMPLES

[0027] The Fe2O3-added spinel was grown using the FZ method crystal growth apparatus shown in Fig. 1. The Fe2O3 concentration was adjusted to 0.05 mol% or more and 2.5 mol% or less. The composition ratio of the spinel (x = MgO / Al2O3) was adjusted to x = 0.3 or more and x = 1.0 or less. The atmosphere gas was used with different mixture ratios of Ar gas and O2 gas. The O2 concentration of the atmosphere gas was adjusted to 0.0 vol% or more and 100 vol% or less. As shown in Fig. 3, the O2 concentration of the atmosphere gas during crystal growth was reduced in a single step pattern 15, 16, reduced in a slope pattern 17, 18, and reduced in multiple steps pattern 19, 20. The crystal was grown at a growth speed of 10 mm / h, and the feed rod and seed crystal rod were rotated in opposite directions at a rotation speed of 30 rpm.

[0028] Crystal growth was performed with an Fe2O3 concentration of 1.0 mol% and a spinel composition ratio (x = MgO / Al2O3) of x = 0.3. The mixture ratio of Ar and O2 gases was changed for the atmospheric gas. As shown in Figure 3, the O2 concentration of the atmospheric gas during growth was reduced in multiple steps from 100 vol% to 0.0 vol%, in a pattern 19, 20. The grown Fe2O3-doped spinel crystal was a tricolor spinel that exhibited three colors, green, blue, and pink, in one crystal. The color of the grown crystal changed from transparent green to transparent blue as the O2 concentration decreased from 100 vol% to 0.1 vol%, and from transparent blue to transparent pink as the O2 concentration decreased from 0.1 vol% to 0.0 vol%. EXAMPLES

[0029] MnO-added spinel was grown using the FZ method crystal growth apparatus shown in Figure 1. The MnO concentration was adjusted to be 0.1 mol% or more and 5.0 mol% or less. The composition ratio of the spinel (x = MgO / Al2O3) was adjusted to be x = 0.3 or more and x = 1.0 or less. The atmosphere gas used was a mixture of Ar gas and O2 gas with different mixing ratios. The O2 concentration of the atmosphere gas was adjusted to be 0.0 vol% or more and 100 vol% or less. The O2 concentration of the atmosphere gas during crystal growth was reduced in one step as shown in Figure 3, using patterns 15 and 16 to grow the crystal. The crystal growth speed was 10 mm / h, and the feed rod and seed crystal rod were rotated in opposite directions at 30 rpm.

[0030] Crystal growth was performed with an MnO concentration of 1.0 mol% and a spinel composition ratio (x = MgO / Al2O3) of x = 0.3. The atmosphere gas used was a mixture of Ar gas and O2 gas with different mixture ratios. As shown in Figure 3, the O2 concentration of the atmosphere gas during growth was reduced in one step from 100 vol% to 0.0 vol%, as shown in patterns 15 and 16. The grown MnO-doped spinel crystal was a bicolor spinel that exhibited two colors, pink and brown, in one crystal. The color of the grown crystal changed from transparent pink to transparent brown as the O2 concentration decreased from 100 vol% to 0.0 vol%. EXAMPLES

[0031] MnO-added spinel was grown using the FZ method crystal growth apparatus shown in Figure 1. Crystal growth was performed by adjusting the MnO concentration to 3.0 mol% and the spinel composition ratio (x = MgO / Al2O3) to x = 1.0. The atmospheric gas used was a mixture of Ar gas and O2 gas with different mixture ratios. As shown in Figure 3, the O2 concentration of the atmospheric gas during growth was reduced in one step from 100 vol% to 0.0 vol%, using patterns 15 and 16 to grow the crystal. The crystal growth speed was 10 mm / h, and the feed rod and seed crystal rod were rotated in opposite directions at 30 rpm.

[0032] The grown MnO-doped spinel was a bicolor spinel exhibiting two colors, yellow and light green, in one crystal. The color of the grown crystal changed from transparent yellow to transparent light green with decreasing O2 concentration from 100 vol% to 0.0 vol%. EXAMPLES

[0033] Multicolor spinels with Fe2O3 concentrations of 0.5 mol%, 1.0 mol%, 1.5 mol%, and 2.0 mol%, and composition ratios (x = MgO / Al2O3) of x = 0.3 and 1.0, grown using an FZ method crystal growth apparatus, and multicolor spinels with MnO concentrations of 1.0 mol% and 3.0 mol%, and composition ratios (x = MgO / Al2O3) of x = 1.0 and 0.3, were processed for jewelry use. A fine cutter (made by Imahashi) and a faceter (made by Imahashi) were used to process the multicolor spinels. The color changes of the multicolor spinels processed into table cuts (emerald cuts)31, brilliant cuts32, cylindrical shapes33, and square prism shapes34 could be emphasized. The crystal growth technology for multicolor crystals has opened up new application fields for artificial gemstones. EXAMPLES

[0034] A crystal growth apparatus for carrying out the above-described crystal growth will be described. The apparatus is composed of a quartz tube 1, a holder for holding raw material for crystal growth inside the quartz tube (not shown in FIG. 1, but a jig for holding raw material for crystal growth 3), a heating unit 6 for heating the quartz tube 4, a gas pipe 9 for supplying gas to the quartz tube, a flow rate regulator 11 for adjusting the gas components of the gas flowing into the gas pipe, and an input unit (not shown in FIG. 1) for inputting information specifying the O2 concentration of the gas together with time. Here, the flow rate regulator 11 uses the input information to control the O2 concentration of the gas in a stepwise or sloped manner in response to the time. For example, the valve of the cylinder of the gas containing O2 and the valve of the cylinder containing the other gas are adjusted in degree of opening and closing of the valve (the O2 concentration increases when the valve of the cylinder of the gas containing O2 is opened widely) and the opening and closing time using the input O2 concentration and time information. This control may be performed manually using the input information, or may be performed by computer control using the input information that has been recorded. With this device, if the material is set in the holder and the gas to be supplied is set in the cylinder, the flow rate regulator changes the oxygen concentration over time when information is input to the computer, so that by changing the input information, crystals with various colors can be easily manufactured. In this configuration, a pressure regulator (10 in FIG. 1) is not included, but this pressure regulator can be used when the gas pressure flowing into the flow rate regulator is not constant. In addition, in this explanation, the flow rate regulator 11 is described as one, but when the gas containing oxygen and the gas not containing oxygen are separately adjusted and the two gases are mixed in the gas piping, it is easy to control by providing a flow rate regulator and a pressure regulator for each system of the gas containing oxygen and the gas not containing oxygen, as shown in FIG. 1. Furthermore, a flow rate regulator and a pressure regulator may be provided for each type of gas, and by doing so, a device capable of fine control can be provided. The control can be performed by computer control using the information input for each system. [Industrial Applicability]

[0035] This invention makes it possible to grow crystals with desired light absorption and emission characteristics simply by adjusting the O2 concentration in the ambient gas around the growing crystal. This technology can be applied to many crystal growth techniques. Crystals grown using this technology can be used as rare multi-color gemstones, such as bicolor and tricolor gemstones. It can also be applied to the growth of optical filters and phosphor crystals that change emission color. [Explanation of symbols]

[0036] 1 Raw material rod for crystal growth 2. Grown crystals 3. Melt 4 Quartz tube 5. Elliptical Mirror 6. Heating light source 7 O2 gas or CO2 gas or air 8 Ar gas or N2 gas or a mixture of Ar gas and N2 gas 9 Gas piping 10 Pressure Regulator 11 Flow regulator or mass flow meter 12 O2 molecules in the atmospheric gas during crystal growth 13 Highly oxidized impurity ions 14 Impurity ions in low oxidation states 15 One-step O2 concentration adjustment pattern 16 A pattern that reduces O2 concentration in one step 17 Slope-like O2 concentration regulation pattern 18 Slope-like decrease in O2 concentration 19 Multiple stepwise O2 concentration adjustment pattern 20 A pattern of decreasing O2 concentration in multiple steps 21 Crystal growth direction 22 Crystals grown at high O2 concentrations 23 Crystals grown at low O2 concentrations 24 Crystals grown at intermediate O2 concentrations between high and low O2 concentrations 25 One-step O2 concentration adjustment pattern 26 A pattern in which the O2 concentration is increased in a single step 27 Slope-like O2 concentration regulation pattern 28 Pattern of increasing O2 concentration in a slope 29 Multiple stepwise O2 concentration adjustment pattern 30 A pattern in which O2 concentration is increased in multiple steps 31 Top view of multi-colored table cut (emerald cut) crystals for jewelry 32 Top view of multicolored crystals cut for jewelry by brilliant cut 33 Multi-colored crystals cut into cylindrical shapes for jewelry 34 Multi-colored crystals cut into square prisms for jewelry

Claims

1. A method for growing multi-color crystals, characterized in that the concentration of oxygen contained in the atmospheric gas during crystal growth is decreased or increased in a stepwise or sloped manner between multiple predetermined concentrations of 0.0 vol.% or more and 100 vol.% or less relative to the elapsed time of crystal growth or the growth amount of the crystal, thereby controlling the oxidation number of the impurity ions added to the crystal, thereby growing crystals that exhibit two or more colors.

2. The growing crystal is a spinel containing an impurity element M at a concentration of 0.1 mol % or more and 5.0 mol % or less, and its chemical formula is Mg ｘ (M ｙ , Al １－ｙ ) ２ O ３＋ｘ Or, (M ｙ , Mg １－ｙ ) ｘ A ２ O ３＋ｘ Or, yMO.(1-y)Mg ｘ A ２ O ３＋ｘ Or, yM ２ O ３ (1-y) Mg ｘ A ２ O ３＋ｘ Or, yMO ２ (1-y) Mg ｘ A ２ O ３＋ｘ The method for growing multi-color crystals according to claim 1, characterized in that the chemical formula is represented by the formula: x=0.3 or more and x=1.0 or less, y=0.001 or more and y=0.05 or less, and the impurity element M is a mixture of at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, and Ni.

3. The growing crystal has a chemical formula (Eu ｘ , Y １－ｘ ) ３ A ５ O １２ 2. The method for growing multi-color crystals according to claim 1, wherein the garnet is represented by the formula: where x is 0.001 or more and x is 0.05 or less.

4. The method for growing a multi-color crystal according to any one of claims 1 to 3, characterized in that the crystal growth method used for growing the crystal is any one of the following crystal growth methods: floating zone method (FZ method), Cz method (Czochralski crystal pulling method), Bernoulli method (flame fusion method), Bridgman method, flux method, skull melt method, Bagdazorov method, and EFG method (Edge-defined Film-fed Growth).

5. The method for growing a multi-color crystal according to any one of claims 1 to 4, characterized in that the concentration of oxygen contained in the atmospheric gas during crystal growth is adjusted by mixing either argon gas, nitrogen gas, or a mixture of argon gas and nitrogen gas with oxygen or air in a predetermined ratio.

6. The growing crystal is Fe ２ O ３ or FeO or Mn ２ O ３ Spinel (MgAl ２ O ４ 6. The method for growing a multi-color crystal according to any one of claims 1 to 5, characterized in that the concentration of oxygen contained in the atmospheric gas during crystal growth is decreased or increased in a stepwise or multiple stepwise or sloped manner relative to the elapsed time of crystal growth or the amount of crystal growth, thereby growing a spinel exhibiting multiple colors in one crystal.

7. A quartz tube; A holder for holding a crystal growth raw material inside the quartz tube; A heating unit that heats the quartz tube; a gas pipe for supplying gas to the quartz tube; A flow rate regulator that regulates the gas components of the gas flowing into the gas pipe; and The O ２ An input unit for inputting information for specifying a concentration together with time, The flow rate regulator adjusts the O of the gas using the input information. ２ A crystal growth apparatus characterized in that the concentration is controlled in a stepwise or sloped manner in response to the time.

8. The gas component is O ２ Gas or carbon dioxide (CO ２ ) gas or air and Ar gas or N ２ Gas or Ar gas and N ２ 8. A crystal growing apparatus as claimed in claim 7, further comprising a gas.

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