Patent Publication Number: US-2023142721-A1

Title: Composite of Silicate-Based Base Material and Rare-Earth Compound, Light-Emitting Nanoparticle, Cell Detection Method, Treating Method for Treating Non-Human Animal, Medical Device, and Method for Producing Composite of Silicate-Based Base Material and Rare-Earth Compound

Description:
TECHNICAL FIELD 
     The present invention relates to a composite of a silicate-based base material and a rare-earth compound, a method for producing a composite of a silicate-based base material and a rare-earth compound, light-emitting nanoparticles, a cell detection method, an animal treating method, and a medical device. 
     BACKGROUND ART 
     In recent years, there has been a demand for a technique of detecting tumors such as cancer cells or the like with high sensitivity at a cellular level by a marker material having high biocompatibility. 
     Patent Document 1 discloses, as a bioimaging material, a two-photon absorbing material consisting of a water soluble dendrimer in which a dye having a two-photon absorbing property and a fluorescence property and a dendron are bonded. 
     Patent Document 2 discloses use of a water-dispersible quantum dot in which a surface of the quantum dot is coated with a surfactant-type polymerization initiator including a hydrophobic group and a polar group, as a particle for in-vivo bioimaging. 
     Patent Document 3 discloses a production method of a bioimaging nanoparticle including producing a hydrophobic nanoparticle which maintains individual dispersibility in a nonpolar organic solvent, wherein in a hydrophobic inorganic nanoparticle having a core or core/shell structure protected by a surfactant, the surfactant is partially substituted by adding 1 to 30 equivalents of an organic ligand wherein a thiol group and a hydrophilic group are bonded by a hydrocarbon chain having a carbon number of 8 to 20, and the surface of the nanoparticles is surface-modified so that only one part is hydrophilic, by forming a metal thiolate (M-S) bond, and the like. 
     Patent Document 4 discloses a fluorescent particle used for bioimaging, which is a fluorescent particle having upconversion characteristics as a phenomenon of obtaining visible light fluorescence with the use of a low energy light such as an infrared light or the like as an excitation light, and the material of the fluorescent particles is one material, or a combination of two or more materials among Y 2 O 3 :Er 3+ , Yb 3+ , Y 2 O 3 :Er 3+ , NaYF 4 :Er 3+ , and Yb 3+ . 
     Patent Document 5 discloses a semiconductor nanoparticle to be used for molecule/cell imaging, which is a semiconductor nanoparticle having an average particle size of 1 to 20 nm, containing an atom pair of a main component atom constituting the same, and an atom pair of the corresponding differing atom or a differing atom having an equivalent valence electron arrangement, and further the dopant distributed on the semiconductor nanoparticle surface or in the vicinity thereof. 
     Patent Document 6 discloses a fluorescent labeling agent for pathological diagnosis including fluorescent material encapsulated nanoparticles including a first fluorescent substance, and a second fluorescent substance having a distinguishable excitation/light-emitting property from the first fluorescent substance. 
     Patent Document 7 discloses a fluorescent labeling agent including a rare-earth fluorescent complex-containing silica particle containing rare-earth fluorescent complex, and a target molecule measurement kit. 
     Furthermore, Non-Patent Documents 1 to 4 also disclose use of quantum dots, fluorescent dyes, or the like, for bioimaging. 
     As described above, in recent years, there has been a demand for a technique of detecting tumors such as cancer cells with high sensitivity at the cellular level by a marker material having high biocompatibility. For example, in the cancerization of a cell, before a morphological change occurs, an activity change at the molecular level occurs. For example, a cancer cell tends to consume a large amount of glucose compared with a normal cell. At the same time, folate receptors are overexpressed on the cell membrane, resulting in tendency of specifically binding to / taking up folic acid molecules. High sensitivity imaging of such changes at the molecular level of a cell would make it possible to realize very early stage detection of cancer cells and the like. 
     However, in the case of using an organic molecule as an imaging material for imaging, the rate of degradation/fading is high, for example, there has been the problem that light-emitting particles become quenched or the like by photoirradiation after several tens of minutes under fluorescence observation. Furthermore, in the case of using an inorganic material such as quantum dots as a bioimaging material, highly toxic elements such as cadmium may be included, and there have been problems with biocompatibility and the like. 
     Thus, the present inventors created a composite particle wherein a light-emitting molecule or ion is included in an inorganic material, and developed a light-emitting nanoparticle provided with light emitting stability and light resistance, and having low biological toxicity (Patent Document 8). 
     
         
         Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2010-133887 
         Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2009-190976 
         Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2009-107106 
         Patent Document 4: Japanese Unexamined Patent Application, Publication No. 2013-14651 
         Patent Document 5: PCT International Publication No. WO2009/066548 
         Patent Document 6: Japanese Unexamined Patent Application, Publication No. 2013-57037 
         Patent Document 7: PCT International Publication No. WO2005/023961 
         Patent Document 8: PCT International Publication No. WO2017/170531 
       
    
     
         
         Non-Patent Document 1: “Selective molecular imaging of viable cancer cells with pH-activatable fluorescence probes” Nature Medicine 15, 104 (2009) 
         Non-Patent Document 2: “Quantum Dot Bioconjugates for Ultrasensitive Nonisotopic Detection.” Science 281, 2016 (1998) 
         Non-Patent Document 3: “Nucleic Acid-Passivated Semiconductor Nanocrystals: Biomolecular Templating of Form and Function.” Accounts of Chemical Research, 43, 173 (2010) 
         Non-Patent Document 4: “Multimodal-Luminescence Core-Shell Nanocomposites for Targeted Imaging of Tumor Cells.” Chem. Eur. J., 15, 3577 (2009) 
       
    
     DISCLOSURE OF THE INVENTION 
     Problems to Be Solved by the Invention 
     In order to achieve bioimaging with high sensitivity, light-emitting intensity of light-emitting particles is desirably high. However, in Patent Document 8, light-emitting molecules/ions may agglomerate, or the amount of light-emitting molecules is small and the light-emitting intensity may be degraded. Note here that high light-emitting intensity is similarly demanded for applications other than bioimaging, and the problem that when light-emitting molecules/ions agglomerate or the amount of light-emitting substance is small, the light-emitting intensity may be degraded similarly occurs in applications other than bioimaging. 
     The present invention has been made in view of the above-mentioned problem, and has an object to provide a composite of a silicate-based base material and a rare-earth compound, having high light-emitting intensity and capable of being used as light-emitting particles, and light-emitting nanoparticle including the same, a cell detection method, a method for treating an animal, a medical device, and a method for producing the composite of a silicate-based base material and a rare-earth compound. 
     Means for Solving the Problems 
     The present inventors have completed the present invention based on the finding that when a composite of a silicate-based base material and a rare-earth compound includes the silicate-based base material containing elemental silicon (Si) and elemental oxygen (O) and the rare-earth compound, the rare-earth compound includes at least one selected from a chloride of a rare-earth element and a fluoride of a rare-earth element, and the silicate-based base material has a solid  29 Si-NMR spectrum satisfying Q 4 /Q 3  of 1.6 to 3.9 where Q 4  represents a peak area derived from Si(OSi) 4  and Q 3  represents a peak area derived from HO—Si(OSi) 3 , an amount of a light-emitting rare-earth element such as Eu is sufficient, agglomeration of light-emitting rare-earth ions is suppressed, and the light-emitting intensity is high. In other words, the present invention includes the following configurations. 
     [1] A composite of a silicate-based base material and a rare-earth compound, the silicate-based base material containing elemental silicon (Si) and elemental oxygen (O), in which the rare-earth compound includes at least one selected from a chloride of a rare-earth element and a fluoride of a rare-earth element, and 
     the silicate-based base material has a solid  29 Si-NMR spectrum satisfying Q 4 /Q 3  of 1.6 to 3.9 where Q 4  represents a peak area derived from Si(OSi) 4  and Q 3  represents a peak area derived from HO—Si(OSi) 3 . 
     [2] The composite of a silicate-based base material and a rare-earth compound as described in the above [1], in which the rare-earth element is at least one selected from europium (Eu) and terbium (Tb). 
     [3] The composite of a silicate-based base material and a rare-earth compound as described in the above [2], in which the rare-earth compound includes at least one compound selected from compounds represented by the following chemical formulae (1) to (4): 
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
      (in the formula (1), x is 0.05 or more and 5 or less). 
     [4] The composite of a silicate-based base material and a rare-earth compound as described in the above [3], in which the rare-earth compound has a powder X-ray diffraction pattern having a first diffraction peak in a diffraction angle (2θ) range of 34.3° to 36.1° in which a half value width of the first diffraction peak is 1.8° or less, and/or having a second diffraction peak in a diffraction angle (2θ) range of 28.6° to 29.6° and a third diffraction peak in a diffraction angle (2θ) range of 36.8° to 38.4° in which a half value width of the second diffraction peak is 1.0° or less and a half value width of the third diffraction peak is 1.6° or less. 
     [5] The composite of a silicate-based base material and a rare-earth compound as described in the above [2], in which the rare-earth compound includes a compound represented by the following chemical formula (5) or a compound represented by the following chemical formula (6), and a mixed crystal of at least one compound selected from the compound represented by the chemical formula (5) and the compound represented by the chemical formula (6) and amorphous silica. 
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     [6] The composite of a silicate-based base material and a rare-earth compound as described in the above [5], in which the rare-earth compound has a powder X-ray diffraction pattern having a fourth diffraction peak in a diffraction angle (2θ) range of 26.6° to 28.6°, a fifth diffraction peak in a diffraction angle (2θ) range of 44.8° to 46.8°, and a sixth diffraction peak in a diffraction angle (2θ) range of 24.3° to 26.3° in which a half value width of the fourth diffraction peak is 0.3° or less, a half value width of the fifth diffraction peak is 0.57° or less, and a half value width of the sixth diffraction peak is 0.22° or less, and/or having the fourth diffraction peak, the fifth diffraction peak, and a seventh diffraction peak in a diffraction angle (2θ) range of 30.8° to 32.8° in which a half value width of the fourth diffraction peak is 0.3° or less, a half value width of the fifth diffraction peak is 0.57° or less, and a half value width of the seventh diffraction peak is 0.38° or less. 
     [7] A composite of a silicate-based base material and a rare-earth compound as described in any one of the above [1] to [6], in which the rare-earth element is on a surface of the silicate-based base material. 
     [8] A composite of a silicate-based base material and a rare-earth compound as described in any one of the above [1] to [7], including a molecule containing elemental carbon on a surface thereof. 
     [9] The composite of a silicate-based base material and a rare-earth compound as described in any one of the above [1] to [8], in which a percentage of a number of moles of the rare-earth element with respect to a total number of moles of the elemental silicon and the rare-earth element is 0.1 mol% or more and 7 mol% or less. 
     [10] The composite of a silicate-based base material and a rare-earth compound as described in any one of the above [1] to [9], in which the silicate-based base material is a base material including silica or a silicate. 
     [11] The composite of a silicate-based base material and a rare-earth compound as described in any one of the above [1] to [10], in which the silicate-based base material is an amorphous. 
     [12] The composite of a silicate-based base material and a rare-earth compound as described in any one of the above [1] to [11], in which the silicate-based base material is powder having an average particle diameter of 50 nm or more and 470 nm or less. 
     [13] A light-emitting nanoparticle including a composite of the silicate-based base material and the rare-earth compound as described in the above [12], the rare-earth compound being a light-emitting substance. 
     [14] The light-emitting nanoparticle as described in the above [13] being used for bioimaging. 
     [15] A cell detection method, including allowing the light-emitting nanoparticle as described in the above [13] to be taken into a cell, irradiating the light-emitting nanoparticle with light, and observing the cell. 
     [16] A treating method for treating a non-human animal, the method including administering the light-emitting nanoparticle as described in the above [13] to the animal, irradiating the light-emitting nanoparticle with light, and treating the animal. 
     [17] A medical device including a testing portion for carrying out testing of an internal cell, a diagnosis portion for carrying out diagnosis of the internal cell, and/or a treatment portion 
     for carrying out treatment of the internal cell, and   further including a light irradiating portion for introducing the light-emitting nanoparticle as described in the above [13] into an internal cell and irradiating the light-emitting nanoparticle with light, when the testing, the diagnosis, and/or the treatment are carried out.   

     [18] A method for producing the composite of a silicate-based base material and a rare-earth compound as described in any one of the above [1] to [12], the method including:
     mixing a silicate-based base material and a raw material of a rare-earth compound with each other to carry out a solid-phase mechanochemical reaction,   in which the silicate-based base material has a solid  29 Si-NMR spectrum satisfying Q 4 /Q 3  of 1.6 to 3.9 where Q 4  represents a peak area derived from Si(OSi) 4  and Q 3  represents a peak area derived from HO—Si(OSi) 3 .   

     [19] A method for producing the composite of a silicate-based base material and a rare-earth compound as described in any one of the above [1] to [12], the method including: 
     dissolving a surface of the silicate-based base material in a basic atmosphere, and   reacting the silicate-based base material in which the surface is dissolved with a raw material of the rare-earth compound,   in which the silicate-based base material has a solid  29 Si-NMR spectrum satisfying Q 4 /Q 3  of 1.6 to 3.9 where Q 4  represents a peak area derived from Si(OSi) 4  and Q 3  represents a peak area derived from HO—Si(OSi) 3 .   

     [20] A mixed crystal including at least one compound selected from a compound represented by the following chemical formula (5) and a compound represented by the following chemical formula (6), and amorphous silica, the mixed crystal having a powder X-ray diffraction pattern having a fourth diffraction peak in a diffraction angle (2θ) range of 26.6° to 28.6°, a fifth diffraction peak in a diffraction angle (2θ) range of 44.8° to 46.8°, and a sixth diffraction peak in a diffraction angle (2θ) range of 24.3° to 26.3°, in which a half value width of the fourth diffraction peak is 0.3° or less, a half value width of the fifth diffraction peak is 0.57° or less, and a half value width of the sixth diffraction peak is 0.22° or less, and/or having the fourth diffraction peak, the fifth diffraction peak, and a seventh diffraction peak in a diffraction angle (2θ) range of 30.8° to 32.8°, in which a half value width of the fourth diffraction peak is 0.3° or less, a half value width of the fifth diffraction peak is 0.57° or less, and a half value width of the seventh diffraction peak is 0.38° or less. 
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     Effects of the Invention 
     The present invention can provide a composite of a silicate-based base material and a rare-earth compound having high light-emitting intensity and being usable as a light-emitting particle, a light-emitting nanoparticle using the same, a cell detection method, a method for treating an animal, a medical device, and a method for producing a composite of a silicate-based base material and a rare-earth compound. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic sectional view showing an example of a composite of a silicate-based base material and a rare-earth compound. 
         FIG.  2    shows a solid  29 Si-NMR spectrum of the silicate-based base material. 
         FIG.  3    shows a powder X-ray diffraction pattern of the silicate-based base material. 
         FIG.  4 A  and  FIG.  4 B  show measurement results of an average particle size by a field emission type scanning electron microscope (FE-SEM) of a silicate-based base material. 
         FIG.  5    is a schematic side view for illustrating a production device used for a production method by a mechanochemical method. 
         FIG.  6    shows powder X-ray diffraction patterns of particles of Examples and Comparative Examples. 
         FIG.  7 A  and  FIG.  7 B  show excitation spectrums and fluorescence spectrums of particles of Examples. 
         FIG.  8 A  and  FIG.  8 B  show transmission electron microscope (TEM) observation images of particles of Examples. 
         FIG.  9 A  and  FIG.  9 B  show calculation results of average particle sizes of the particles of Examples by a field emission type scanning electron microscope (FE-SEM) observation. 
         FIG.  10    shows powder X-ray diffraction patterns of particles of Examples. 
         FIG.  11    is a view showing measurement results of cell densities of Examples and Comparative Examples. 
         FIG.  12    is a view showing measurement results of fluorescence densities (PL) of Examples and Comparative Examples. 
         FIG.  13    is a view showing measurement results of fluorescence densities (PL) of Examples and Comparative Examples. 
         FIG.  14    is a schematic side view for illustrating a production method by gas phase method. 
         FIG.  15    shows powder X-ray diffraction patterns of particles of Examples. 
         FIG.  16    shows powder X-ray diffraction patterns of particles of Examples and Comparative Examples. 
         FIG.  17    shows fluorescence spectrum of particles of Examples. 
     
    
    
     PREFERRED MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, the present invention will be described in more detail. 
     Composite of Silicate-Based Base Material and Rare-Earth Compound 
     A composite of a silicate-based base material and a rare-earth compound of the present invention includes a silicate-based base material containing elemental silicon (Si) and elemental oxygen (O), and a rare-earth compound. The rare-earth compound includes at least one selected from chloride of a rare-earth element and fluoride of a rare-earth element. Furthermore, the silicate-based base material has a solid  29 Si-NMR spectrum satisfying Q 4 /Q 3  of 1.6 to 3.9 where Q 4  represents a peak area derived from Si(OSi) 4  and Q 3  represents a peak area derived from HO—Si(OSi) 3 . 
     In this way, a composite of a specific silicate-based base material and a rare-earth compound including chloride of the rare-earth element or fluoride of the rare-earth element, as shown in the below-mentioned Examples, agglomeration of rare-earth element ions as light-emitting substance is suppressed and a supporting amount of the rare-earth element into the silicate-based base material becomes appropriate, fluorescence intensity (light-emitting intensity) becomes high. On the other hand, when Q 4 /Q 3  is less than 1.6, since the supporting amount of the rare-earth element is large, agglomeration occurs, and fluorescence intensity is deteriorated. Furthermore, when Q 4 /Q 3  is more than 3.9, since the supporting amount of the compound of the rare-earth element is small, the fluorescence intensity is deteriorated. 
     The “composite of a silicate-based base material and a rare-earth compound” is not a simple mixture obtained by mixing a silicate-based base material and a rare-earth compound, but is a structure body having a rare-earth compound, for example, on a surface of the silicate-based base material, and a structure body in which a silanol group of a silicate-based base material and an oxygen atom of a siloxane bond, and rare-earth ions constituting the rare-earth compound are chemically bonded one another by, for example, a coordination bond. 
     The rare-earth ions constituting the rare-earth compound are not particularly limited but are preferably at least one type selected from the group consisting of trivalent Ce, tetravalent Ce, trivalent Pr, trivalent Nd, trivalent Pm, trivalent Sm, divalent Eu, trivalent Eu, trivalent Gd, trivalent Tb, trivalent Dy, trivalent Ho, trivalent Er, trivalent Tm, trivalent Yb, trivalent Lu, and trivalent Tb. Any of these are a light-emitting substance. Among these, Eu 3+  that is trivalent Eu is preferable. This is preferable because Eu 3+  is excited and emits light in the visible light region. For example, a crystal of a europium compound excites and emits light in a visible light region, and the excitation wavelength λ ex  is, for example, 395 nm and 464 nm, and the fluorescence wavelength λ em  is, for example, 615 nm. 
     The rare-earth compound may be an amorphous but is preferably a crystal. When the rare-earth compound is a crystal, as compared with an amorphous, elusion of ions such as a chloride ion and a fluoride ion does not easily occur, so that an adverse effect by the elusion of ions is suppressed. Therefore, cytotoxicity is low, and can be preferably used for bioimaging. 
     The silicate-based base material contains elemental silicon (Si) and elemental oxygen (O). The molar ratio (O/Si) that is a ratio of O to Si in the silicate-based base material, is preferably 2.0 to 2.2. The silicate-based base material is a material as a skeleton of the composite of the silicate-based base material and the rare-earth compound. Examples of the silicate-based base material include silicon oxide such as silica, a base material including silicate. These may be a crystal but is preferably an amorphous from the viewpoint of biotoxicity. 
     Furthermore, the silicate-based base material has a solid  29 Si-NMR spectrum satisfying Q 4 /Q 3  of 1.6 to 3.9 where Q 4  represents a peak area derived from Si(OSi) 4  and Q 3  represents a peak area derived from HO—Si(OSi) 3 . The Q 4 /Q 3  is preferably 2.0 to 3.9, and more preferably 2.2 to 2.6. 
     Such a silicate-based base material containing elemental silicon (Si) and elemental oxygen (O) and satisfying Q 4 /Q 3  of 1.6 to 3.9 can be obtained as a particulate substance (a soot body or a by-product) generated in a method for producing silica glass by a conventionally known soot method (for example, a production method of silica glass by Vapor phase Axial Deposition (VAD)). For example, when silica glass is produced as porous synthetic quartz glass (soot body) by hydrolyzing silicon tetrachloride in an oxygen-hydrogen flame using silicon tetrachloride as a raw material, particles which are hydrolyzed in the oxygen-hydrogen flame and then desorbed from the flame and do not become porous synthetic quartz glass can be the silicate-based base material. By adjusting the above conditions, the above silicate-based base material is obtained. For example, silicon tetrachloride as a raw material is introduced into the central portion of the oxygen-hydrogen flame burner to adjust a flame temperature zone length and gas balance of oxygen-hydrogen gas. Specifically, nucleation and grain growth are adjusted, for example, in a range of the flame temperature zone length at 1000° C. or more: 100 mm or more and 800 mm or less, and volume ratio of hydrogen to oxygen (H 2 /O 2 ): 1.0 or more and 2.5 or less. As the flame temperature zone length is increased, Q 4 /Q 3  tends to increase, and as H 2 /O 2  increases, Q 4 /Q 3  tends to decrease. 
     The shape of the silicate-based base material is not particularly limited. The shape may be, for example, a spherical shape (powdery) or may be a plate shape, but the shape is preferably spherical shape because the cytotoxicity is low. Also, the size of the silicate-based base material is not particularly limited. When the composite of the silicate-based base material and the rare-earth compound is used for bioimaging, from the viewpoint of cytotoxicity, it is preferable that the silicate-based base material has a spherical shape and an average particle size of 50 nm or more and 470 nm or less and is amorphous. 
     When the silicate-based base material has a spherical shape, as shown in a schematic sectional view of  FIG.  1    showing an example of the composite of the silicate-based base material and the rare-earth compound, the composite of the silicate-based base material and the rare-earth compound (hereinafter, also referred to as “composite”) is a structure body in which a surface of the silicate-based base material 1 is covered with the rare-earth compound 2. Furthermore, when a silicate-based base material having a plate shape is used, a composite in which at least a part of the surface of the silicate-based base material of the plate shape is covered with the rare-earth compound 2 is obtained. The thickness of the layer including the rare-earth compound 2 covering the silicate-based base material 1 is not particularly limited, but the thickness is, for example, 5 nm or more and 25 nm or less, and preferably, 10 nm or more and 20 nm or less. Note here that  FIG.  1    shows a composite in which an entire surface of the silicate-based base material 1 having a spherical shape is covered with the rare-earth compound 2, but the rare-earth compound 2 is only required to cover at least a part of the surface of the silicate-based base material 1. 
     In the composite, a percentage of the number of moles of the rare-earth element with respect to a total number of moles of the elemental silicon and the rare-earth element (number of moles of rare-earth element / (number of moles of rare-earth element + number of moles of Si)) is preferably 0.1 mol% or more and 7 mol% or less, and more preferably 4 mol% or more and 7 mol% or less. 
     When the rare-earth compound includes the chloride of the rare-earth element, the rare-earth compound includes, for example, compounds represented by the following chemical formulae (1) to (4). 
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
      (In the formula (1), x is 0.05 or more and 5 or less.) 
     Furthermore, it is preferable that the compounds represented by the above chemical formulae (1) to (4) have a powder X-ray diffraction pattern having a first diffraction peak in a diffraction angle (2θ) range of 34.3° to 36.1° in which a half value width (half width) of the first diffraction peak is 1.8° or less, and/or having a second diffraction peak in a diffraction angle (2θ) range of 28.6° to 29.6° and a third diffraction peak in a diffraction angle (2θ) range of 36.8° to 38.4° in which a half value width of the second diffraction peak is 1.0° or less and a half value width of the third diffraction peak is 1.6° or less. The compounds represented by the chemical formulae (1) to (4) may have a first diffraction peak in a diffraction angle (2θ) range of 34.3° to 36.1° in which a half value width of the first diffraction peak is 1.8° or less; may have a second diffraction peak in a diffraction angle (2θ) range of 28.6° to 29.6°and a third diffraction peak in a diffraction angle (2θ) range of 36.8° to 38.4° in which a half value width of the second diffraction peak is 1.0° or less and a half value width of the third diffraction peak is 1.6° or less; and also may have a first diffraction peak in a diffraction angle (2θ) range of 34.3° to 36.1° in which a half value width of the first diffraction peak is 1.8° or less, a second diffraction peak in a diffraction angle (2θ) range of 28.6° to 29.6° and a third diffraction peak in a diffraction angle (2θ) range of 36.8° to 38.4° in which a half value width of the second diffraction peak is 1.0° or less and a half value width of the third diffraction peak is 1.6° or less. The half value width of the first diffraction peak is preferably 1.1° or less. The half value width of the second diffraction peak is preferably 0.6° or less. The half value width of the third diffraction peak is preferably 1.0° or less. The first diffraction peak is derived from a crystal of the compound represented by the chemical formula (1) or (2). The second diffraction peak and the third diffraction peak are derived from a crystal of the compound represented by the chemical formula (3) or (4). In the chemical formula (1), x is preferably 0.2 or more and 0.6 or less. 
     The description “having a diffraction peak in a diffraction angle (2θ) range of a° to b°” means that a peak top position of the diffraction peak (a diffraction peak top position) is within a range of a° to b°. Therefore, for example, in a broad peak, all of the peaks from an end portion to another end portion are not necessarily required to be included within a range of a° to b°. 
     Furthermore, the crystal bodies of the compounds represented by the chemical formulae (1) to (4) may have a different peak other than the above specific diffraction peak. For example, the compound represented by the chemical formula (1) or (2) may also have a diffraction peak in a diffraction angle (2θ) range of 25.9° to 26.5° and a diffraction peak in a diffraction angle (2θ) range of 31.6° to 32.2°. The diffraction peak in a diffraction angle (2θ) range of 25.9° to 26.5° and the diffraction peak in a diffraction angle (2θ) range of 31.6° to 32.2°respectively have preferably a half value width of 0.6° or less, and further preferably 0.4° or less. Furthermore, the crystal bodies of the compound represented by the chemical formula (3) or (4) may also have a diffraction peak in a diffraction angle (2θ) range of 39.0° to 40.2°. The half value width of the diffraction peak in a diffraction angle (2θ) range of 39.0° to 40.2° is preferably 1.2° or less, and further preferably 0.8° or less. 
     Conventionally, crystal bodies of the compounds represented by the above chemical formulae (1) to (4) have not been known. However, as will be described in detail later, when a specific silicate-based base material and europium chloride (III) hexahydrate are subjected to a solid-phase mechanochemical reaction under specific conditions, crystals of compounds represented by chemical formulae (1) to (4) having the specific diffraction peaks can be obtained. Note here that the “crystal” means a substance not being amorphous, and a substance having crystallinity represented by the following formula (7) of more than 0. The crystallinity is preferably more than 0.10.  Crystallinity = {crystal diffraction peak area / amorphous halo diffraction peak area} (7) (In the formula (7), the “crystal diffraction peak area” is a sum of the areas of the diffraction peaks derived from the crystal in 2θ = 20° to 55°; the “amorphous halo diffraction peak area” is a value obtained by subtracting the crystal diffraction peak area from the sum of the areas of all the diffraction peaks observed in 2θ = 20° to 55°.) 
     When the rare-earth compound includes a fluoride of a rare-earth element, the rare-earth compound includes, for example, a compound represented by chemical formula (5) or (6). A mixed crystal of at least one compound selected from compounds represented by chemical formulae (5) and (6) and silica derived from a silicate-based base material may be used. 
     
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
     
     Furthermore, it is preferable that the compound represented by the above chemical formula (5) or (6) has a powder X-ray diffraction pattern having a fourth diffraction peak in a diffraction angle (2θ) range of 26.6° to 28.6°, a fifth diffraction peak in a diffraction angle (2θ) range of 44.8° to 46.8°, and sixth diffraction peak in a diffraction angle (2θ) range of 24.3° to 26.3, in which a half value width of the fourth diffraction peak is 0.3° or less, a half value width of the fifth diffraction peak is 0.57° or less, a half value width of the sixth diffraction peak is 0.22° or less, and/or and having the fourth diffraction peak, the fifth diffraction peak, and a seventh diffraction peak in a the diffraction angle (2θ) range of 30.8° to 32.8°, in which a half value width of the fourth diffraction peak is 0.3° or less, a half value width of the fifth diffraction peak is 0.57° or less, and a half value width of the seventh diffraction peak is 0.38° or less. The fourth diffraction peak, the fifth diffraction peak, and the seventh diffraction peak are derived from the crystal of the compound represented by the formula (5). Furthermore, the fourth diffraction peak, the fifth diffraction peak, and the sixth diffraction peak are derived from the crystal of the compound represented by the formula (6). 
     The rare-earth compound may be, for example, terbium chloride (TbCl 3 ), and terbium fluoride (TbF 3 ). 
     Note here that in the present invention, the rare-earth compound may have a different peak other than the above-specified diffraction peak. 
     The composite of the silicate-based base material and the rare-earth compound of the present invention preferably includes a molecule containing a carbon element on a surface thereof. The amount of molecule containing a carbon element is not particularly limited, but, for example, the percentage of the number of moles of carbon atoms with respect to the number of moles of silicon atoms included in the composite of the silicate-based base material and the rare-earth compound (number of moles of C / number of moles of Si) is preferably 0.05 mol% to 160 mol%, and more preferably 6 mol% to 9 mol%. 
     Method for Producing Composite of Silicate-Based Base Material and Rare-Earth Compound 
     A composite of the silicate-based base material and the rare-earth compound of the present invention can be produced by a production method including mixing a silicate-based base material and a raw material of a rare-earth compound with each other to carry out a solid-phase mechanochemical reaction, in which the silicate-based base material has a solid  29 Si-NMR spectrum satisfying Q 4 /Q 3  of 1.6 to 3.9 where Q 4  represents a peak area derived from Si(OSi) 4  and Q 3  represents a peak area derived from HO—Si(OSi) 3 . 
     The silicate-based base material is described in the above-mentioned &lt;Composite of the silicate-based base material and rare-earth compound&gt;. 
     Examples of the raw material of the rare-earth compound include europium chloride (III) hexahydrate, europium chloride (III) anhydride in a case where the rare-earth compound is chloride of the rare-earth element and include europium fluoride (III) hexahydrate and europium fluoride (III) anhydride in a case where the rare-earth compound is fluoride of the rare-earth element. 
     Such a silicate-based base material and a raw material of a rare-earth compound are mixed and subjected to a solid-phase mechanochemical reaction under a load (for example, under a load of 2 N or more and 24 N or less, and preferably 2 N or more and 12 N or less). A method for subjecting a silicate-based base material and a raw material of a rare-earth compound to a solid-phase mechanochemical reaction is not particularly limited. For example, a powdery silicate-based base material and a raw material of a rare-earth compound may be placed in a mortar and pulverized by rotating a pestle while applying a load of 2 N or more and 24 N or less to the pestle. When the above operation is carried out with the mortar mounted on the electronic balance (electronic scale), the load value can be read by the metric indicator of the electronic balance. By increasing the load to be loaded, minute particulate composite is produced. The silicate-based base material and the rare-earth compound are composed (bonded) at a load of 2 N or more, and the rare-earth compound starts to be crystalized at a load of 4 N or more. By increasing the load, crystallinity can be enhanced. Note here that when the load exceeds 12 N, peeling of the rare-earth compound (light-emitting layer) accompanying pulverization tends to progress to cause phase separation and refinement (less than 50 nm). Therefore, the load is preferably 12 N or less. Furthermore, pulverization may be carried out by mounting europium chloride (III) on a surface of the plate-shaped silicate-based base material and moving the pestle while applying a load of 4 N or more and 24 N or less, and preferably 2 N or more and 12 N or less. In this case, by carrying out the above-mentioned operation while a plate-shaped silicate-based base material is mounted on an electronic balance, the load value can be read with a metric indicator of the electronic balance. 
     The percentage of the silicate-based base material and the raw material of the earth compound is not particularly limited, but the percentage of the number of moles of the rare-earth element with respect to the total number of moles of Si and the rare-earth element (number of moles of rare-earth element) / (number of moles of rare-earth element + number of moles of Si)) is preferably 0.1 mol% or more and 7.0 mol% or less. When europium chloride (III) hexahydrate is used as the raw material of the rare-earth compound, when the amount of Eu with respect to Si is increased, the compound represented by the chemical formula (3) tends to be generated through the compound represented by the chemical formula (4). Furthermore, when europium fluoride (III) hexahydrate is used as the raw material of the rare-earth compound, the compound represented by the chemical formula (5) is generated when the amount of Eu with respect to Si is small, and when the amount of Eu with respect to Si is increased, the compound represented by the chemical formula (5) is generated and at the same time, the compound represented by the chemical formula (6) tends to remain. 
     In the solid-phase mechanochemical reaction using the silicate-based base material satisfying Q 4 /Q 3  of 2.0 to 3.9, europium chloride (III) hexahydrate is added such that the percentage of the number of moles of the europium element with respect to the total number of moles of elemental silicon and a europium element is 1.0 mol% or more and, and the above reaction is carried out under a load at 4 N or more and 24 N or less. Thus, a composite of the crystal of a europium compound and the silicate-based base material can be produced. The percentage of the number of moles of the europium element with respect to the total number of moles of the elemental silicon and a europium element is preferably 1.0 mol% or more and 7.0 mol% or less. 
     The europium compound is conventionally difficult to be made separately, but according to the above-mentioned production method, the compounds represented by chemical formulae (1) to (4) can be separated based on the amount of Eu in the solid-phase mechanochemical reaction. Specifically, in a state in which the concentration of europium during a solid-phase mechanochemical reaction is low (in a state in which OH during the reaction is small in amount), the compound represented by the chemical formulae (1) and (2) coexist, and when a multilayer structure starts to be formed according to increase in concentration of europium during reaction, the compound represented by the chemical formula (1) and the compound represented by the chemical formula (2) interact with each other, and tend to be changed into the compounds represented by the chemical formulae (3) and (4). Therefore, the compounds represented by the chemical formulae (1) to (4) can be made separately based on the amount of Eu in the solid-phase mechanochemical reaction. 
     Furthermore, in the solid-phase mechanochemical reaction using the silicate-based base material satisfying Q 4 /Q 3  of 2.0 to 3.9, europium fluoride is added such that the percentage of the number of moles of the europium element with respect to the total number of moles of elemental silicon and a europium element is 1.0 mol% or more and, and the above reaction is carried out under a load at 4 N or more and 24 N or less. Thus, a composite of the crystal of a europium compound and the silicate-based base material can be produced. 
     A solid-phase mechanochemical reaction is carried out, and then baking is carried out, and then washing with organic solvent or water is carried out as necessary. 
     With this production method, the rare-earth compound is formed on a surface of the silicate-based base material. For example, when the spherical-shaped silicate-based base material is used, a composite having a rare-earth compound covering at least a part of the surface of the spherical-shaped silicate-based base material is obtained. It is inferred that the rare-earth compound strongly binds to the silicate-based base material by some kind of chemical bonds such as a coordination bond between oxygen atoms existing on the surface of the silicate-based base material and the rare-earth atoms contained in the rare-earth compound. 
     The above-mentioned composite of the silicate-based base material and the rare-earth compound can be produced also by the gas phase method. Specifically, the composite of the silicate-based base material and the rare-earth compound can be produced by a production method including a step of dissolving the surface of the silicate-based base material in an basic atmosphere, and a step of reacting the silicate-based base material having a surface dissolved with the raw material of the rare-earth compound, in which the silicate-based base material has a solid  29 Si-NMR spectrum satisfying Q 4 /Q 3  of 1.6 to 3.9 where Q 4  represents a peak area derived from Si(OSi) 4  and Q 3  represents a peak area derived from HO—Si(OSi) 3 . 
     Firstly, the surface of a silicate-based base material is dissolved in a basic atmosphere. The reactivity with the raw material of the rare-earth compound can be enhanced by dissolving the surface of the silicate-based base material in a basic atmosphere. Examples of the basic atmosphere include an atmosphere including ammonia vapor. The silicate-based base material is similar to that described for the solid phase mechanical method. In the case where the silicate-based base material is spherical (powdery), the surface of the silicate-based base material may be dissolved by mixing and pulverizing the silicate-based base material and the raw material of the rare-earth compound and placing the obtained mixed and pulverized product in a basic atmosphere. 
     Next, a silicate-based base material having a surface that has been dissolved is allowed to react with the raw material of the rare-earth compound. Thus, the silicate-based base material such as silica that has been dissolved is deposited again and Eu 3+  coprecipitates. Thereby, a crystal of the rare-earth compound and NH 4 Cl is formed on the surface of the silicate-based base material. The raw material of the rare-earth compound is the same as those described for the solid phase mechanical method. After the reaction is carried out by a gas phase method, baking is carried out, and washing with organic solvent or water may be carried out as necessary. 
      Note here that as described above, without using a surfactant, a composite in which agglomeration of the rare-earth ions is suppressed can be produced. 
     Use of Light-Emitting Nanoparticle and Light-Emitting Nanoparticle 
     A composite of a silicate-based base material and a rare-earth compound of the present invention has low cytotoxicity, and has the rare-earth compound formed on the surface of the silicate-based base material functioning as a light-emitting substance, so that the composite can be preferably used for bioimaging technique. For example, the composite of the silicate-based base material and the rare-earth compound of the present invention can be used as the light-emitting nanoparticle for the bioimaging technique. 
     The average particle size of the light-emitting nanoparticle is preferably 50 nm to 470 nm. By making the average particle size within this range, it becomes easy for the particles to be taken up by the target cells, and also tends to be suitable in observing the cells. On the other hand, it is not preferable that the average particle size is small because there is a tendency to cause toxicity problems by acting on the active function of the cell. The average particle size of the light-emitting nanoparticle is preferably 100 nm to 400 nm. Note here that in the case where the light-emitting nanoparticles are not used, for example, for cell imaging, the average particle size may be larger than 470 nm. 
     The light-emitting nanoparticle to be used for bioimaging technique preferably includes a hydroxyl group (OH group) on the surface thereof. Also preferably, the surface of the light-emitting nanoparticle is modified by an amino group, and, for example, may also be formed using a silane coupling agent containing an amino group. When silicate-based base material has pores, the OH group and the amino group may be on the inner surface of the pores, but preferably on the outer surface of the pores. When the OH group or the amino group is fixed by a hydrogen bond or a covalent bond by a condensation polymerization to the cell binding molecule, and the surface of the light-emitting nanoparticle is modified by the cell binding molecule, the cell binding molecule can specifically bind to a cancer cell or a normal cell. When the cell binding molecule specifically binds to a cell, the light-emitting nanoparticle is taken up into the cell. Thus, the light-emitting nanoparticle is made to emit light inside the cell, and a cancer cell or the like can be detected. 
     Examples of the cell binding molecule include an HER2 antibody, antibodies specifically binding to human epidermal growth factor receptor, cancer-specific antibodies, phosphorylation protein antibodies, folic acid, antibodies specifically binding to folic acid receptor β, vascular endothelial cell-specific antibodies, tissue-specific antibodies, transferrin, transferrin-bonding peptide, proteins having affinity to sugar chains, and the like. Among these, folic acid, having a tendency to be taken up by cancer cells, is preferably used as the cell binding molecule. Folic acid receptors are over-expressed on cell membranes for cancer cells, resulting in a tendency of selectively binding to and taking up folic acid molecules. 
     Furthermore, the surface of the light-emitting nanoparticle may be modified by an anticancer agent molecule. When the anticancer agent molecule specifically binds to the cancer cell, the light-emitting nanoparticle will be taken up into the cell. In this way, the light-emitting nanoparticle inside the cell is allowed to emit light and can detect cancer cells. Further, the anticancer agent is also taken up by the cell, and the anticancer agent molecule can act, and the proliferation of cancer cells can be suppressed. 
     The cell binding molecule or anticancer agent molecule are preferably modified and fixed to the surface of the light-emitting nanoparticle by a chemical bond. Examples of the chemical bond include a peptide bond (—CO—NH—), a hydrogen bond, or the like. 
     The excitation wavelength and the light-emission wavelength of the light-emitting nanoparticles are preferably in the visible light region. When the excitation wavelength and the light-emission wavelength are in the visible light wavelength or higher, degradation of biological tissue and labeling material can be reduced due to irradiating with light. Furthermore, light scattering of a sample surface can be reduced, and the observation sensitivity can be increased. Note here that in an application using the light-emitting nanoparticles, when it is not necessary to consider damage to biological tissue and labeling material, the excitation wavelength and the light-emission wavelength are not necessarily in the visible light region. 
     Use of the light-emitting nanoparticles permits detection of cells, and treatment of animals. Specifically, the cell detection method of the present invention includes introducing the light-emitting nanoparticle into a cell, irradiating the light-emitting nanoparticle with light, and observing the cell. According to this detection method, because the light-emitting nanoparticle of the present embodiment has high fluorescence intensity and high sensitivity, observation of cells can be observed more easily. 
     The treatment method of an animal of the present invention is a method for treating a non-human animal. The method includes steps of administering the light-emitting nanoparticle to a non-human animal, irradiating light onto the light-emitting nanoparticle, and treating the animal. According to this treatment method, the light-emitting nanoparticle of the present embodiment has high fluorescence intensity and high sensitivity, and further, high biocompatibility, a condition of disease in an animal body can be detected with high sensitivity, and safely. Thus, it becomes possible to suitably treat a disease of a non-human animal. 
     Furthermore, the medical device of the present invention includes a testing portion for carrying out testing of an internal cell, a diagnosis portion for carrying out diagnosis of the internal cell, and/or a treatment portion for carrying out treatment of the internal cell, and further include a light irradiation portion which introduces the light-emitting nanoparticles into the internal cell, and irradiates the light-emitting nanoparticles with light in carrying out the testing, diagnosis, and/or treatment. Herein, examples of the testing portion for carrying out testing of an internal cell include a fluorescence endoscope for carrying out precision image diagnosis. Furthermore, examples of the diagnosis portion for carrying out diagnosing of an internal cell include a device for carrying out tissue biopsies. Furthermore, examples of the treatment portion for carrying out treatment of an internal cell include a device for extracting a tumor site by endoscopy. Furthermore, examples of the internal cell include cancer cells pertaining to oral cavity cancer, pharyngeal cancer, esophageal cancer, large intestinal cancer, small intestinal cancer, lung cancer, breast cancer, and bladder cancer. According to this medical device, the light-emitting nanoparticle of the present embodiment have high fluorescence intensity and high sensitivity, and high biocompatibility, whereby it becomes possible to carry out testing, diagnosis, and treatment of an internal cell with high sensitivity, and safely. 
     Other Applications 
     Furthermore, the silicate-based base material and the rare-earth compound of the present invention can be used for applications other than the bioimaging application, and, for example, applications of light emitting devices such as a light emitting diode are expected. 
     EXAMPLES 
     Hereinafter, the present invention will be described with reference to Examples in more detail, but the present invention is not necessarily limited by these examples. 
     Production of Silicate-Based Base Material 1 
     Silicon tetrachloride as a raw material was subjected to hydrolysis reaction sufficiently in an oxygen-hydrogen flame to produce silica glass as porous synthetic quartz glass (soot body). At this time, particles that did not become porous synthetic quartz glass after hydrolysis in an oxygen-hydrogen flame and desorbed from the flame were used as the silicate-based base material 1. Note here that silicon tetrachloride was introduced from the center portion of the oxygen-hydrogen flame burner, and the length of the flame temperature zone of 1000° C. or more was 400 mm, and the volume ratio (H 2 /O 2 ) of hydrogen to oxygen was 1.5. 
     Production of Silicate-Based Base Material 2 
     Ultrapure water (22.8 mL), hexadecylammonium chloride (0.10 g), and 2N-sodium hydroxide aqueous solution (0.35 mL) were added to a screw tube, then 50 mg of silicate-based base material 1 was added thereto, and the obtained product was subjected to dispersion treatment by carrying out perform ultrasonic irradiation for 5 minutes. Tetraethoxysilane (0.55 mL) was then added and stirred at 1500 rpm for 48 hours at room temperature. Then, centrifugation (3000 rpm, 20 min) was carried out, washing was carried out twice with ultrapure water, dried at 120° C. for two hours, and baked at 550° C. for six hours. Thereafter, the obtained product was washed with 40 mL of ethanol, and subjected to solid-liquid separation by centrifugation, and the solid phase was dried at 120° C. for two hours to obtain a silicate-based base material 2. 
      Production of Silicate-Based Base Material 3 
     A silicate-based base material 3 was obtained in the same manner as described above (production of the silicate-based base material 2) except that hexadecylammonium chloride and the silicate-based base material 1 were not added and the baking temperature was set at 750° C. 
     Production of Silicate-Based Base Material 4 
     A silicate-based base material 4 was obtained in the same manner as described above (production of the silicate-based base material 2) except that the silicate-based base material 1 was not added. Note here that all of the obtained silicate-based base materials 1 to 4 were spherical-shaped powders. 
     (Q 4 /Q 3  of silicate-based base material in solid  29 Si-NMR spectrum) 
     For the obtained silicate-based base materials 1 to 4, the solid  29 Si-NMR spectrum was measured in the following conditions. The results are shown in  FIG.  2   . 
     Measurement Conditions 
     Name of device: Bruker Advance 300 wbs spectrometer (manufactured by BRUKER) Measurement method: DD (Dipolar Decoupling) method
     Sample tube: 7 mm   Number of revolution of sample: 5000 rpm   Resonance frequency: 59.62 MHz   Pulse width: 4.5 msec.   Waiting time: 60 sec   Multiplication time: 1000 times   Reference sample: hexamethylcyclotrisiloxane (-9.55 ppm)   &lt;Peak separation method&gt;   (Formation method of base line)   Operation (1): An average value 1 of strength in a range of -70 to -79 ppm, and an average value 2 of strength in a range of -131 to -140 ppm are measured   Operation (2): A straight line passing through two points (-70 ppm, average value 1) and (-140 ppm, average value 2) is defined as a base line   Operation (3): The base line value is deleted from the spectrum   (Peak separation method)   

     Separation method: Solver function of Microsoft Office 2016 Excel (registered trademark) Used function: Gaussian function (in the formula, A denotes a peak height, B denotes a peak position, and C denotes a half value width) 
     
       
         
           
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     Peak assignment:
     Q 2 : -91 ± 2 ppm, two ΞSi—O—SiΞ bonds and two ΞSi—OH bonds   Q 3 : -100 ± 2 ppm, three ΞSi—O—SiΞ bonds and one ΞSi—OH bond   Q 4 : -110 ± 2 ppm, four ΞSi—O—Si bonds   Initial conditions of A, B, and C:   Q 2 : A=100000, B=-91, C=4   Q 3 : A=400000, B=-100, C=5.5   Q 4 : A=960000, B=-110, C=5.5   

     From  FIG.  2   , for each silicate-based base material, the obtained spectrum was defined as raw data, and the raw data were subjected to spectrum separation as mentioned above. Q 4  / Q 3  obtained when a peak area derived from Si(OSi) 4  was defined as Q 4  and the peak area derived from HO—Si(OSi) 3  was defined as Q 3  in the solid-state  29 Si-NMR spectrum was 2.4 for the silicate-based base material 1, 1.6 for the silicate-based base material 2, 4.0 for the silicate-based base material 3, and 1.3 for the silicate-based base material 4. Not here that Q 2  shown in  FIG.  2    is a peak derived from (HO) 2 —Si(OSi) 2 . 
     Measurement of Powder X-Ray Diffraction Pattern of Silicate-Based Base Material 
     For the silicate-based base materials 1 to 4, the powder X-ray diffraction (XRD) patterns were measured. The measurement was carried out using a sample horizontal type X-ray diffractometer (XRD) (Smart Lab manufactured by Rigaku Corporation), under the conditions of X radiation source: CuKα radiation source (λ: 1.5418 Å), output: 40 kV/30 mA, scanning speed: 3.0°/min, sampling width: 0.01°, and measurement mode: continuous. As an example, the result of the silicate-based base material 1 is shown in  FIG.  3   . As a result, in the silicate-based base materials 1 to 4, the half value width of the amorphous halo pattern appearing in the vicinity of 2θ = 20° was large such as 6.7° to 8.3°, and a peak derived from crystal was not observed, showing an amorphous. 
     Measurement of Average Particle Size of Silicate-Based Base Material 
     The silicate-based base materials 1 to 4 (particle powder) were fixed to a sample stand for observation with carbon paste, and dried. Next, particles were observed under a field emission scanning electron microscope (FE-SEM) (SU8230 manufactured by Hitachi High-Technologies, Ltd.), 100 or more of particle diameters were measured, and the average particle size was calculated. Specifically, for 300 particles, the longer diameter and the shorter diameter of each particle were measured, and “(longer diameter + shorter diameter) / 2” was defined as a particle diameter (particle size) of each particle. An average value of the particle diameter of each particle (a value obtained by dividing the total values of the particle diameter of each particle by number of particles (300)) was defined as an average particle size (Ave.), and coefficient of variance (Cv.) was calculated. As an example, the result of silicate-based base material 1 is shown in  FIGS.  4 A and  4 B . As a result, the silicate-based base material 1 had an average particle size of 151 nm, and the coefficient of variance of 45%. The silicate-based base material 2 had an average particle size of 124 nm, and the coefficient of variance of 52%. The silicate-based base material 3 had an average particle size of 143 nm, and the coefficient of variance of 44%. The silicate-based base material 4 had an average particle size of 129 nm, and the coefficient of variance of 52%. 
     Example 1 
       FIG.  5    is a schematic side view for illustrating a production device used in the production method of Example 1. As shown in  FIG.  5   , pulverization was carried out in an agate mortar  11  having a hemispherical recess space (diameter: 65 mm, and depth: 30 mm) and an 80-mm pestle  12  having a hemispherical protrusion (tip-end diameter: 20 mm, and height: 5 mm), the silicate-based base material and the europium chloride (III) hexahydrate were subjected to a solid-phase mechanochemical reaction under the load of 4 N. Specifically, europium chloride hexahydrate (EuCl 3  · 6H 2 O, manufactured by Wako Pure Chemical Industries, Ltd., special grade agent, purity: 99.9 wt.%) was added to 0.4 g (6.66 mmol) of the silicate-based base material 1 which had been dried at 120° C. for 24 hours in the mortar  11 , such that the percentage of the number of moles of Eu with respect to the total number of moles of Si and Eu (number of moles of Eu / (number of moles of Si + number of moles of Eu)) was 5.0 mol%. Then, for 5 minutes, the pestle  12  was revolved on the circumference of a radius of 25 mm in the recessed space in the mortar  11  by the pestle  12  without rotating the pestle  12  itself. The pestle  12  was revolved at 120 rotating/min with load of 4 N applied to the pestle  12 . Note here that the above operation was carried out in a state in which the mortar  11  was mounted on an electronic balance  13 , the load value was read by using the metric indicator  14  of the electronic balance  13 . The obtained powder was dried at 120° C. for two hours, and then baked at 550° C. for 6 hours. Thereafter, the obtained product was washed with 40 mL of ethanol, and subjected to solid-liquid separation by centrifugation, and the solid phase was dried at 120° C. for two hours to obtain the particles (spherical-shaped powder) of Example 1. 
     Example 2 
     Particles of Example 2 were obtained by carrying out the same operation as in Example 1 except that europium chloride hexahydrate was added such that the percentage of the number of moles of Eu with respect to the total number of moles of Si and Eu was 2.5 mol%. 
     Example 3 
     Particles of Example 3 were obtained by carrying out the same operation as in Example 1 except that europium chloride hexahydrate was added such that the percentage of the number of moles of Eu with respect to the total number of moles of Si and Eu was 1.25 mol%. 
     Example 4 
     Particles of Example 4 were obtained by carrying out the same operation as in Example 1 except that the europium chloride hexahydrate was added such that the percentage of the number of moles of Eu with respect to the total number of moles of Si and Eu was 0.625 mol%. 
     Example 5 
     Particles of Example 5 were obtained by carrying out the same operation as in Example 1 except that the silicate-based base material 2 was used instead of the silicate-based base material 1. 
     Comparative Example 1 
     Europium chloride hexahydrate was used as particles for Comparative Example 1. 
     Comparative Example 2 
     Particles of Comparative Example 2 were obtained by carrying out the same operation as in Example 1 except that the silicate-based base material 3 was used instead of the silicate-based base material 1. 
     Comparative Example 3 
     Particles of Comparative Example 3 were obtained by carrying out the same operation as in Example 1 except that the silicate-based base material 4 was used instead of the silicate-based base material 1. 
     Powder X-Ray Diffraction (XRD) 
     Particles of Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to measurement of powder X-ray diffraction (XRD) pattern in the following conditions. Measurement was carried out using the sample horizontal type X-ray diffractometer (XRD, Smart Lab manufactured by Rigaku Corporation) under conditions of X radiation source: CuKα radiation source (λ: 1.5418 Å), output: 40 kV/30 mA, scanning speed: 3.0°/min, sampling width: 0.01°, and measurement mode: continuous. The diffraction peak position, diffraction angle, and half-value width were obtained by software (manufactured by Rigaku Corporation, software name: PDXL) attached to the device. The diffraction peaks were detected by the automatic profiling process of PDXL, by the second-order differential method (a method of detecting a region in which the peak second-order differential is negative (convex upward) as a peak), by removing the background, removing the Kα 2  line, and smoothing in this order, and fitting with the B-spline function (the split pseudo-Voigt function). The threshold (cut value of the standard deviation) in detecting the diffraction peak was 3.0. The threshold means that the diffraction peak is not regarded as a diffraction peak when the intensity of the diffraction peak is 3.0 times or less of its error. Three points were selected in descending order of the diffraction peak intensity (the height of the diffraction peak) and used for identification of the crystal. Furthermore, the crystallinity was calculated by the above formula (7). The results are shown in Table 1 and  FIG.  6   . In Table 1, in the upper stage, “m ± n” indicating the diffraction angle 2θ in which each diffraction peak is located indicates that the peak top position (diffraction peak top position) of the diffraction peak is m (°), the start point of the diffraction peak is m - n (°), and the end point of the diffraction peak is m + n (°). Specifically, the diffraction peak top was defined as the maximum intensity (maximum height) between the start point and the end point of each diffraction peak when a baseline is drawn from the start point to the end point. The position of the diffraction peak top (diffraction angle) was defined as the diffraction peak top position. In Table 1, the parentheses in the lower row indicate the half value width of each diffraction peak. The half value width indicates the width between diffraction peak positions having an intensity (height) of 50% of the diffraction peak top within the range of “m - n”° to “m + n”°. 
     As shown in Table 1 and  FIG.  6   , Examples 2 to 3 have the powder X-ray diffraction pattern having a diffraction peak (first diffraction peak) in a diffraction angle (2θ) range of 34.3° to 36.1° in which a half value width of the diffraction peak in a diffraction angle (2θ) range of 34.3° to 36.1° was 1.8° or less and included a crystal of the compounds represented by the chemical formula (1) or (2). Note here that x in the chemical formula (1) was 0.2 or more and 0.6 or less. Furthermore, Examples 2 to 3 have a diffraction peak in a diffraction angle (2θ) range of 25.9° to 26.5° and in a diffraction angle (2θ) range of 31.6° to 32.2° in which the half value width of the diffraction peaks both in a diffraction angle (2θ) range of 25.9° to 26.5° and a diffraction angle (2θ) range of 31.6° to 32.2° was 0.6° or less. 
     Furthermore, Example 1 included a crystal of a compound represented by the chemical formula (3) or (4) having a powder X-ray diffraction pattern including diffraction peaks (second diffraction peak and third diffraction peak) in the diffraction angle (2θ) range of 28.6° to 29.6° and a diffraction angle (2θ) range of 36.8° to 38.4° in which the half-value width of the diffraction peak in the diffraction angle (2θ) range of 28.6° to 29.6° was 1.0° or less and the half-value width of the diffraction peak in the diffraction angle (2θ) range of 36.8° to 38.4° was 1.6° or less. Furthermore, Example 1 had diffraction peaks in the diffraction angle (2θ) range of 39.0° to 40.2° in which the half-value width of the diffraction peak in the diffraction angle (2θ) range of 39.0° to 40.2° was 1.2° or less. Furthermore, as shown in Table 1 and  FIG.  6   , in the particles obtained in Examples 1 to 3, crystallinity was more than 0, and the crystal of the europium compound was formed on the surface, while the particles of Example 4 to 5 and Comparative Examples 1 to 3 were amorphous. Note here that in any of Examples 1 to 5, a europium compound was bonded to the surface of each silicate-based base material.  
     
       
         
          TABLE 1
           
               
               
               
               
               
               
               
               
               
             
               
                   
                 Example 
                 Comparative Example 
               
               
                 1 
                 2 
                 3 
                 4 
                 5 
                 1 
                 2 
                 3 
               
             
            
               
                 Diffraction angle (2θ) in which diffraction peak is located: degree (Half value width: degree) 
                 24.8 ± 0.4 (0.50) 
                 26.2 ± 0.3 (0.34) 
                 26.2 + 0.3 (0.34) 
                 - 
                 - 
                 - 
                 - 
                 - 
               
               
                 27.5 ± 0.3 (0.37) 
                 31.9 + 0.3 (0.37) 
                 31.9 ± 0.3 (0.36) 
                   
                   
                   
                   
                   
               
               
                 28.3 ± 0.3 (0.38) 
                 35.2 ± 0.9 (1.06) 
                 35.2 ± 0.9 (1.09) 
                   
                   
                   
                   
                   
               
               
                 29.1 ± 0.5 (0.59) 
                 45.9 + 0.5 (0.61) 
                 45.9 ± 0.5 (0.59) 
                   
                   
                   
                   
                   
               
               
                 31.6 + 0.6 (0.73) 
                   
                   
                   
                   
                   
                   
                   
               
               
                 34.5 ± 0.4 (0.49) 
                   
                   
                   
                   
                   
                   
                   
               
               
                 37.6 ± 0.8 (0.95) 
                   
                   
                   
                   
                   
                   
                   
               
               
                 39.6 ± 0.6 (0.73) 
                   
                   
                   
                   
                   
                   
                   
               
               
                 41.4 ± 0.6 (0.72) 
                   
                   
                   
                   
                   
                   
                   
               
               
                 48.1 ± 0.4 (0.50) 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Crystallinity 
                 0.41 
                 0.12 
                 0.11 
                 0.000 
                 0.000 
                 0.000 
                 0.000 
                 0.000 
               
            
           
         
       
     
     Light-Emitting Property 
     An excitation spectrum and a fluorescence spectrum of particles of Examples 1 to 5 and Comparative Examples 1 to 3 were measured in the following conditions. As an example, the results of Examples 1 to 3 are shown in  FIG.  7 A  and  FIG.  7 B .  FIG.  7 A  shows an excitation spectrum, and  FIG.  7 B  shows a fluorescence spectrum. 
     Excitation Spectrum 
     The excitation spectrum was obtained by fixing the detection wavelength (615 nm) with a spectrophotometer (PL, FP-8500 manufactured by JASCO Corporation). The measurement conditions were atmosphere: air, excitation/detection slit size: 2.5 nm/2.5 nm, step width: 1.0 nm, sample weight: 20 mg, shape: pellet. 
     Fluorescence Spectrum 
     The sample was irradiated with excitation light from the Xe lamp using a spectrophotometer (PL, FP-8500 manufactured by JASCO Corporation) at room temperature (excitation wavelength: 395 nm), and a PL spectrum (fluorescence spectrum) was obtained. The measurement conditions were atmosphere: air, excitation/detection slit size: 2.5 nm / 2.5 nm, step width: 1.0 nm, sample weight: 20 mg, shape: pellet. 
     As a result, as shown in  FIG.  7 A  and  FIG.  7 B , in all of Examples 1 to 5 and Comparative Examples 1 to 3, excitation peak derived from Eu(III) ion( 7 F 0 → 5 D 4  transition,  7 F 0 → 5 G 4  transition,  7 F 0 → 5 L 6  transition,  7 F 0 → 5 D 2  transition, and  7 F 0 → 5 D 1  transition) and light-emitting peak ( 5 D 0 → 7 F 1  transition,  5 D 0 → 7 F 2  transition,  5 D 0 → 7 F 3  transition,  5 D 0 → 7 F 4  transition) were observed. Furthermore, from  FIGS.  7 A and  7 B , the internal quantum yields of the particles of particles of Examples 1 to 5 and Comparative Examples 1 to 3 at the excitation wavelength λ ex  = 395 nm and the emission wavelength λ em  = 615 nm were respectively 1.0 to 4.0%. 
     Chemical Composition (X-Ray Fluorescence Analysis (XRF)) 
     Particles of Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to the X-ray fluorescence analysis (XRF) in the following conditions. A sample pellet obtained by pressurizing about 100 mg of sample powder which had not been diluted was subjected to XRF analysis using the fluorescent X-ray analyzer (XRF, manufactured by Rigaku Corporation, device name: ZSX PrimusII) and software attached to the device (manufactured by Rigaku Corporation, name of the software: EZ scan program). In measurement, without using a primary filter and a calibration curve, semi-quantitative analysis was carried out using the measurement program attached to the device is used. Analysis results and results converted in element ratios are shown in Tables 2 to 5.  
     
       
         
          TABLE 2
           
               
               
               
               
               
               
               
             
               
                   
                 Si (mol%) 
                 O (mol%) 
                 Eu (mol%) 
                 C (mol%) 
                 Cl (mol%) 
                 Other element (mol%) 
               
             
            
               
                 Example 1 
                 30.7 
                 64.1 
                 1.57 
                 2.67 
                 0.959 
                 0.001 
               
               
                 Example 2 
                 32.0 
                 64.4 
                 0.844 
                 2.22 
                 0.494 
                 0.042 
               
               
                 Example 3 
                 32.0 
                 65.0 
                 0.404 
                 2.41 
                 0.239 
                 - 
               
               
                 Example 4 
                 32.1 
                 63.5 
                 0.195 
                 2.01 
                 0.045 
                 2.15 
               
               
                 Comparative Example 1 
                 - 
                 25.6 
                 21.5 
                 - 
                 52.9 
                 0 
               
            
           
         
       
     
     
       
         
          TABLE 3
           
               
               
               
               
               
             
               
                   
                 Eu/Si (mol%) 
                 Cl/Eu (mol%) 
                 C/Si (mol%) 
                 C/Eu (mol%) 
               
             
            
               
                 Example 1 
                 5.11 
                 61.1 
                 8.70 
                 170 
               
               
                 Example 2 
                 2.64 
                 58.5 
                 6.94 
                 263 
               
               
                 Example 3 
                 1.26 
                 5 9.2 
                 7.53 
                 597 
               
               
                 Example 4 
                 0.607 
                 23.1 
                 6.26 
                 1031 
               
               
                 Comparative Example 1 
                 - 
                 246 
                 - 
                 - 
               
            
           
         
       
     
     
       
         
          TABLE 4
           
               
               
               
               
               
               
               
               
             
               
                   
                 Si (mol%) 
                 O (mol%) 
                 Eu (mol%) 
                 C (mol%) 
                 Cl (mol%) 
                 N (mol%) 
                 Other element (mol%) 
               
             
            
               
                 Example 1 
                 30.7 
                 64.1 
                 1.57 
                 2.67 
                 0.959 
                 - 
                 0.001 
               
               
                 Example 5 
                 22.5 
                 45.0 
                 1.16 
                 30.6 
                 0.139 
                 0.560 
                 0.041 
               
               
                 Comparative Example 2 
                 30.1 
                 63.6 
                 0.505 
                 5.81 
                 0.0216 
                 - 
                 - 
               
               
                 Comparative Example 3 
                 20.4 
                 45.2 
                 1.52 
                 32.5 
                 0.0869 
                 0.179 
                 0.114 
               
            
           
         
       
     
     
       
         
          TABLE 5
           
               
               
               
               
               
             
               
                   
                 Eu/Si (mol%) 
                 Cl/Eu (mol%) 
                 C/Si (mol%) 
                 C/Eu (mol%) 
               
             
            
               
                 Example 1 
                 5.11 
                 61.1 
                 8.70 
                 170 
               
               
                 Example 5 
                 5.16 
                 12.0 
                 136 
                 2638 
               
               
                 Comparative Example 2 
                 1.68 
                 4.28 
                 19.3 
                 1150 
               
               
                 Comparative Example 3 
                 7.45 
                 5.72 
                 159 
                 2138 
               
            
           
         
       
     
     Transmission Electron Microscope (TEM) Observation 
     Particles of Examples 3 to 4 were observed under transmission electron microscope (TEM). Firstly, the particles were dispersed in ethanol at a concentration of 0.1 mass%, subjected to ultrasonication for 15 minutes, and dried on a carbon microgrid. Then, the center portion of the particle membrane was evaluated and analyzed under transmission electron microscopy (TEM) (HT 7700, manufactured by Hitachi High-Technologies, Ltd.). As an example of the results, the result of Example 1 is shown in  FIG.  8 A , and the result of Example 2 is shown in  FIG.  8 B . As a result, in Examples 1 and 2, a layer covering the surface of the silicate-based base material was observed, and the covering layer has a thickness of 19 to 25 nm in Example 1, and 8 to 12 nm in Example 2. Note here that in Examples 3 and 4, formation of a clear layer was not observed. 
     Measurement of Average Particle Size of Particles 
     For the particles of Examples 1 to 4, 100 or more particle diameters were measured using the field emission-type scanning electron microscope (FE-SEM), and an average particle size was calculated. Note here that for 300 particles, the longer diameter and the shorter diameter of each particle were measured, respectively, and “(longer diameter + shorter diameter) / 2” was defined as a particle diameter of each particle. An average value of the particle diameters of each particle (a value obtained by dividing the total values of the particle diameters of each particle by the number of particles (300)) was defined as an average particle size (Ave.). As an example, Example 1 is shown in  FIG.  9 A , and Example 2 is shown in  FIG.  9 B . As a result, the average particle size of the particles of Example 1 was 189 nm, and the thickness of the silicate-based base material 1 was 151 nm, from these values, the thickness of the layer was calculated to be (189-151)/2 of 19 nm. The average particle size of the particles of Example 2 was 172 nm, and the thickness of the silicate-based base material 1 was 151 nm, from these values, the thickness of the layer was calculated to be (172-151)/2 of 10 nm. An average particle size of the particles of Example 3 was 160 nm. An average particle size of the particles of Example 4 was 155 nm. 
     Example 6 
     Particles of Example 6 were obtained by the same operation as in Example 1 except that the load was made to be 8.0 N. 
     Example 7 
     Particles of Example 7 were obtained by the same operation as in Example 1 except that the load was made to be 12.0 N. 
     For the particles of Examples 6 to 7, results obtained in the same manner as in &lt;Powder X-ray diffraction (XRD)&gt; mentioned above are shown in Table 6 and  FIG.  10   . As shown in Table 6 and  FIG.  10   , both Examples 6 to 7 included a crystal of the compound represented by the chemical formula (3) or (4) having diffraction peaks (a second diffraction peak and a third diffraction peak) in a diffraction angle (2θ) range of 28.6° to 29.6° and the diffraction angle (2θ) range of 36.8° to 38.4°, in which a half value width of the diffraction peak in the range of the diffraction angle (2θ) range of 28.6° to 29.6° was 1.0° or less, a half value width of the diffraction peak in the range of the diffraction angle (2θ) range of 36.8° to 38.4° was 1.6° or less. Furthermore, both Examples 6 to 7 had a diffraction peak in a diffraction angle (2θ) range of 39.0° to 40.2° in which a half value width in a diffraction angle (2θ) range of 39.0° to 40.2° was 0.8° or less. As shown in Table 6 and  FIG.  10   , particles obtained in both of Examples 6 to 7 had crystallinity of more than 0 and had a crystal of a europium compound on the surface of the particle. As shown in Table 6 and  FIG.  10   , it is found that as the load is increased, the crystallinity can be enhanced.  
     
       
         
          TABLE 6
           
               
               
               
             
               
                   
                 Example 6 
                 Example 7 
               
             
            
               
                 Diffraction angle (2θ) in which diffraction peak is located : degree (Half value width : degree) 
                 24.8 ± 0.6 (0.70) 
                 24.8 ± 0.5 (0.61) 
               
               
                 27.0 + 0.1 (0.14) 
                 27.0 ± 0.1 (0.13) 
               
               
                 27.5 ± 0.3 (0.31) 
                 27.5 ± 0.3 (0.37) 
               
               
                 28.3 ± 0.3 (0.30) 
                 28.3 ± 0.3 (0.36) 
               
               
                 29.1 + 0.5 (0.54) 
                 29.1 ± 0.5 (0.54) 
               
               
                 31.3 ± 0.3 (0.41) 
                 31.3 ± 0.3 (0.41) 
               
               
                 34.5 ± 0.5 (0.64) 
                 34.5 ± 0.3 (0.38) 
               
               
                 37.4 ± 0.6 (0.73) 
                 37.4 ± 0.7 (0.84) 
               
               
                 39.4 ± 0.5 (0.60) 
                 39.4 ± 0.6 (0.72) 
               
               
                 41.6 ± 0.5 (0.58) 
                 41.6 + 0.6 (0.72) 
               
               
                 46.4 ± 0.7 (0.79) 
                 46.4 ± 0.8 (0.91) 
               
               
                 48.2 + 0.5 (0.54) 
                 48.2 ± 0.5 (0.54) 
               
               
                 50.6 ± 0.3 (0.40) 
                 50.6 ± 0.4 (0.48) 
               
               
                 51.8 ± 0.5 (0.64) 
                 51.8 ± 0.4 (0.52) 
               
               
                 Crystallinity 
                 0.51 
                 0.52 
               
            
           
         
       
     
     Toxicity Evaluation 
     Particles of Examples 1 to 4 or Comparative Example 1 were subjected to toxicity evaluation by cancer cell imaging and a fluorescence intensity measurement by the following methods. 
     Modification of Cancer Cell Binding Molecule (Folic Acid Derivative FA-NHS) to Particle 
     To 250 mg of the particles of Examples 1 to 4 or Comparative Example 1, 12 ml of an HCl aqueous solution (pH = 2) was added, and ultrasonic treatment was carried out. Next, a solution containing 0.78 ml (3.3 mmol) of 3-aminopropyltriethoxysilane (APTES) in 5 mL of ethanol was prepared and added to the ultrasonic-treated solution to obtain a mixed solution. The mixed solution was stirred for 20 hours at 40° C. (pH &lt; 6.5). After stirring was completed, the mixed solution was centrifuged and washed with ethanol. After washing, drying was carried out under reduced pressure to obtain 150 mg of particles having a surface modified with APTES. To 150 mg of these particles having a surface modified with APTES, 25 mL of a 50 mM phosphate buffer solution (pH = 7.0) was added, and ultrasonic treatment was carried out. Next, a solution containing 430 mg (0.8 mmol) of FA-NHS (folic acid derivative) in 12 mL of dimethylsulfoxide (DMSO) was prepared, and the prepared solution was added to the ultrasonic-treated solution to obtain a mixed solution. The mixed solution was stirred for 3 hours at room temperature. After stirring was completed, the mixed solution was centrifuged and washed with water. After washing, drying was carried out under reduced pressure to obtain FA (folic acid)-modified particles of Examples 1 to 4 or Comparative Example 1. 
     Cell Culture 
     Hela cancer cells were cultured in a PS flask (dissemination density: 100 × 10 4  cells/37 cm 2 ). Thawing and dissemination were carried out for 7 days. The cells were peeled off and separated. The Hela concentration was (0.99 ± 0.07) × 10 5  cells/mL. Concentration of the cells was adjusted, and 10 vol% FBS (fetal bovine serum) was cultured in DMEM (Dulbecco modification nutrient medium). The obtained cells were 7.5 × 10 4  cells per 1 mL. An amount of 2.25 mL/TCPS was disseminated to polystyrene dishes (TCPS) (cultivation area: 9.6 cm 2 ), and the dissemination density was 1.8 × 10 4  cells/cm 2 . (Microscope observation). Thereafter, culturing was carried out (temperature: 37° C., CO 2  concentration: 5%, humidity: 100%). After 12 hours, FA (folic acid)-modified particles of Examples 1 to 4 or Comparative Example 1 were added to 10 vol% DMEM, and dispersed, and the concentration was adjusted to 100 mg/mL. 
     For living cell imaging, at 3 hours, 12 hours, 24 hours, 36 hours and 48 hours after spraying FA (folic acid)-modified particles on the cell surface, the medium was removed. 
     Measurement of Cell Density 
     After the above cells were cultured, a polystyrene dish (TCPS) including cells was washed twice with 1 ml of phosphate buffered saline (PBS), then FA (folic acid)-modified particles which had not taken up by the cells were removed, 0.1 ml of 0.05% Trypsin-EDTA was placed in a TCPS including cells, followed by allowing to stand still in a CO 2  incubator for 12 minutes, and cells were peeled off from TCPS. Peeling was observed, a suspension including cells was taken into a 50-ml conical tube and subjected to centrifugation (2000 rpm, 2 min). After centrifugation, a supernatant was discarded, 7 ml of culture medium was added to the tube, overturning stirring was carried out about 10 times, and then centrifugation (2000 rpm,2 min) was carried out. Thereafter, the supernatant was discarded, 20 ml of medium was added to the tube, pipetting was carried out about 20 times, 1 ml was aliquoted into 15 ml-tubes, the cell suspension was placed into a disposable hemocytometer using a micropipette outside a clean bench, the cell number was confirmed under a microscope, and the average value (cell/cm 2 ) was calculated. At 3 hours, 12 hours, 24 hours, 36 hours, and 48 hours after spraying FA (folic acid)-modified particles on the cell surface, the average value of cell density was calculated, and the results are shown in  FIG.  11   . 
     Measurement of Fluorescence Intensity (PL) 
     Using an integrating sphere (ISF834 manufactured by JASCO Corporation), PL spectrum measurement was carried out by a spectrophotometer (PL; FP-8500 manufactured by JASCO Corporation), under the conditions: atmosphere: air, excitation/detection slit size: 10 nm/10 nm, a step width: 1.0 nm. Specifically, TCPS including cells after cell culture and FA (folic acid)-modified particles was washed with 1 ml of phosphate buffered saline twice, FA (folic acid)-modified particles which had not been taken up by the cells were removed, and further washing with 1 ml of ultrapure water twice. TCPS after washing (i.e., TCPS including cells which had taken up FA (folic acid)-modified particles) were freeze-dried. After drying, the cell layer present in the TCPS was peeled off to form a powder, and the powder was placed into a powder cell holder. Then, the PL spectrum was measured. The excitation wavelength herein was 395 nm, and integrated light-emission intensity centered on the peak top of 5 D 0 → 7 F 2  transition was calculated. Specifically, the PL spectrum area integrated light-emission intensity in the wavelength region between 600 to 635 nm was obtained. Note here that light emission from TCPS was not observed in this wavelength region. The results are shown in  FIG.  12   . 
     As shown in  FIG.  11   , Examples 1 to 3 in which crystal of a europium compound were formed on the surface, exhibited a normal cell proliferation behavior and no cytotoxicity. In other words, it can be said that, in a case of compounding (compositing) into a spherical silicate-based base material as a crystal, no cytotoxicity was observed. On the other hand, in Comparative Example 1, a normal cell proliferation behavior is not observed, and it is considered that since the amorphous EuCl 3 ·6H 2 O elemental substance is an unstable chloride, it eluted into the cell culture solution to form Eu ion or Eu chloride ion and reacted directly with the cells. Similarly, also when the amorphous of Example 4 were used, it is considered that the amorphous particles were eluted into the cell culture solution to form Eu ions or Eu chloride ions and reacted directly with the cells. Therefore, in the case of an amorphous, it can be said that there is cytotoxicity due to the elution. 
     As shown in  FIG.  12   , for the fluorescence property, in Comparative Example 1 showing a non-crystal, the fluorescence intensity associated with binding and uptake into cells by elution and toxicity was low in culture time of 48 hours, but in Examples 1 to 3 showing crystal, the fluorescence intensity in culture time of 48 hours was higher than in Comparative Example 1 because there was no elution and no toxicity. 
     Measurement of Fluorescence Integrated Intensity 
     PL spectra of particles of Examples 1 and 5 and Comparative Examples 2 and 3 were measured. A PL spectrum (fluorescence spectrum) was obtained by irradiating a sample with excitation light (excitation wavelength: 394 nm) from the Xe lamp using a spectrophotometer (PL, FP-8500 manufactured by JASCO Corporation) at room temperature under the conditions: atmosphere: air, excitation/detection slit size: 2.5 nm / 2.5 nm, a step width: 1.0 nm, sample mass: 20 mg, shape: pellet. Thereafter, the integrated light-emission intensity centered on the peak top of the  5 D 0 → 7 F 2  transition (left vertical axis in  FIG.  13   ) was calculated. Specifically, the calculation was carried out using the PL spectrum area in the wavelength region between 600 nm to 635 nm. Furthermore, from the results of XRF, the amount of Eu 3+  in particles (in 20 mg each) was obtained, and integrated light-emission intensity per mole (right vertical axis in  FIG.  13   ) was obtained. For the integrated emission intensity per mole, the highest integrated emission intensity was fixed at 1 and the relative intensities of the other samples were calculated. The results are shown in  FIG.  13   . 
     As shown in  FIG.  13   , Examples 1 and 5 in which Q 4 /Q 3  was 1.6 to 3.9 showed high fluorescence intensity. In more detail, Example 1 in which Q 4 /Q 3  was 2.4 had especially high fluorescence intensity. This is because the support amount is optimized, Eu(III) ions are present in monodisperse on the surface of the silicate-based base material (silica sphere). In Example 5 in which Q 4 /Q 3  was 1.6, the fluorescence intensity is high but lower than that of Example 1. This is because the amount of silanol group in the silicate-based base material (silica sphere) was larger than in Example 1 and Eu(III) ions agglomerated more than in Example 1. On the other hand, in Comparative Examples 2 and 3 in which Q 4 /Q 3  was out of a range of 1.6 to 3.9, the fluorescence intensity was low. In more detail, in Comparative Example 3 in which Q 4 /Q 3  was 1.3, the fluorescence intensity was low. This is because the amount of silanol group in the silicate-based base material was large, the support amount of the Eu compound became too large, and Eu(III) ions agglomerated. In Comparative Example 2 in which Q 4 /Q 3  was 4.0, the fluorescence intensity was low. This is because the amount of the silanol group in the silicate-based base material is small, and the support amount of Eu(III) ions is small. 
     Example 8 
     As shown in  FIG.  14    being a schematic side view for illustrating a production method of Example 8, into a hermetically-sealable cylindrical-shaped container  21  made of PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer) having a volume of 30 mL, 2.5 mL of ammonia water was placed, and a stand  25  was mounted in the container  21  so that the 10 mL-screw tube  23  was placed to be higher than a liquid surface  24  of ammonia water  22 . A mixed and pulverized product  30  was obtained by mixing and pulverizing 10 mg of a silicate-based base material (silicate-based base material 1) and 10 mg of europium chloride (III) hexahydrate. The obtained mixed and pulverized product  30  was placed in a 10-mL screw tube  23 , the screw tube  23  was mounted on the stand  25  of the container  21  with the upper portion opened without being lidded, and the container  21  was sealed and allowed to stand still at 60° C. for 24 hours. Thus, the inside of the container  21  was saturated with ammonia vapor, and the surface of the silicate-based base material was dissolved by deliquescence and ammonia vapor. Thereafter, the screw tube  23  was taken out form the container  21 . Thus, the dissolved silicate-based base material was deposited again and coprecipitated with Eu 3+  on the surface of the silicate-based base material, and thereby, a rare-earth compound and NH 4 Cl as a crystal were deposited on the surface of the silicate-based base material. The obtained powder was dried at 120° C. for 2 hours and baked at 550° C. for 6 hours. Thereafter, the obtained product was washed with 40 mL of ethanol, solid-liquid separated by centrifugation, and the solid phase was dried at 120° C. for two hours to obtain spherical-shaped powder of Example 8. 
     Example 9 
     A mixed dispersion was obtained by mixing 10 mg of silicate-based base material (silicate-based base material 1), and 1.0 mL of europium chloride (III) aqueous solution having a concentration of 10 g/L, followed by ultrasonication for 2 minutes. Particles of Example 9 were obtained by carrying out the same operation as in Example 8 except that 0.1 mL of the obtained mixed dispersion was used instead of the mixed and pulverized product. 
     Example 10 
     Particles of Example 10 were obtained by carrying out the same operation as in Example 9 except that the amount of mixed dispersion was made to be 1.0 mL. 
     Powder X-Ray Diffraction (XRD) 
     For particles of Examples 8 to 10, results obtained in the same manner as in the above &lt;Powder X-ray diffraction (XRD)&gt; are shown in Table 7 and  FIG.  15   . 
     As shown in Table 7 and  FIG.  15   , in Examples 8 to 10, a crystal of NH 4 Cl was formed on the surface of the silicate-based base material. Note here that in all of Examples 8 to 10, a europium compound was bonded to the surface of the silicate-based base material.  
     
       
         
          TABLE 7
           
               
               
               
               
             
               
                   
                 Example 8 
                 Example 9 
                 Example 10 
               
             
            
               
                 Diffraction angle (28) in which diffraction peak is located : degree (Half value width : degree) 
                 22.9 ± 0.01 (0.013) 
                 32.6 ± 0.02 (0.025) 
                 32.6 + 0.02 (0.025) 
               
               
                 32.6 ± 0.02 (0.025) 
                   
                   
               
               
                 40.3 ± 0.05 (0.060) 
                   
                   
               
               
                 46.8 ± 0.03 (0.038) 
                   
                   
               
               
                 52.8 ± 0.05 (0.060) 
                   
                   
               
               
                 54.1 ± 0.04 (0.050) 
                   
                   
               
               
                 Crystallinity 
                 0.060 
                 0.012 
                 0.0039 
               
            
           
         
       
     
     Chemical Composition (X-ray Fluorescence Analysis (XRF)) 
     For particles of Examples 8 to 10, an X-ray fluorescence analysis (XRF) was carried out as in Example 1. Results are shown in Tables 8 and 9.  
     
       
         
          TABLE 8
           
               
               
               
               
               
               
               
               
             
               
                   
                 Si (mol%) 
                 O (mol%) 
                 Eu (mol%) 
                 C (mol%) 
                 Cl (mol%) 
                 N (mol%) 
                 other element (mol%) 
               
             
            
               
                 Example 8 
                 22.2 
                 65.4 
                 1.02 
                 6.28 
                 4.96 
                 0.0638 
                 0.0762 
               
               
                 Example 9 
                 27.2 
                 66.2 
                 0.179 
                 5.54 
                 0.868 
                 0.0527 
                 - 
               
               
                 Example 10 
                 23.8 
                 69.6 
                 0.034 
                 6.7 0 
                 0.152 
                 0.0302 
                 - 
               
            
           
         
       
     
     
       
         
          TABLE 9
           
               
               
               
               
               
             
               
                   
                 Eu/Si (mol%) 
                 Cl/Eu (mol%) 
                 C/Si (mol%) 
                 C/Eu (mol%) 
               
             
            
               
                 Example 8 
                 4.59 
                 486 
                 28.3 
                 616 
               
               
                 Example 9 
                 0.658 
                 485 
                 20.4 
                 3095 
               
               
                 Example 10 
                 0.143 
                 447 
                 28.2 
                 19706 
               
            
           
         
       
     
     Example 11 
     Particles of Example 11 were produced by using a production device of  FIG.  5   . As shown in  FIG.  5   , pulverization was carried out in an agate mortar  11  having a hemispherical recess space (diameter: 65 mm, and depth: 30 mm) and an 80-mm pestle  12  having a hemispherical protrusion (tip-end diameter: 20 mm, and height: 5 mm), the silicate-based base material 1 and europium fluoride were subjected to a solid-phase mechanochemical reaction under the load of 4 N. Specifically, europium fluoride (EuF 3 , manufactured by Wako Pure Chemical Industries, Ltd., special grade agent, purity: 99.9 wt.%) was added to 0.4 g (6.66 mmol) of the silicate-based base material 1 which had been dried at 120° C. for 24 hours in the mortar  11  such that the percentage of the number of moles of Eu with respect to the total number of moles of Si and Eu was 1.3 mol%. Then, for 5 minutes, the pestle  12  was revolved on the circumference of a radius of 25 mm in the recessed space in the mortar 1 by the pestle  12  without rotating the pestle  12  itself. The pestle  12  was revolved at 120 rotating/min with load of 4 N applied to the pestle  12 . Note here that the above operation was carried out in a state in which the mortar  11  was mounted on an electronic balance  13 , the load value was read by using the metric indicator  14  of the electronic balance  13 . The obtained powder was dried at 120° C. for two hours, and then baked at 550° C. for 6 hours. Thereafter, the obtained product was washed with 40 mL of ethanol, and subjected to solid-liquid separation by centrifugation, and the solid phase was dried at 120° C. for two hours to obtain the particles (spherical-shaped powder) of Example 11. 
     Example 12 
     Particles of Example 12 were obtained by carrying out the same operation as in Example 11 except that europium fluoride was added such that the percentage of the number of moles of Eu with respect to the total number of moles of Si and Eu was 2.5 mol%. 
     Example 13 
     Particles of Example 13 were obtained by carrying out the same operation as in Example 11 except that europium fluoride was added such that the percentage of the number of moles of Eu with respect to the total number of moles of Si and Eu was 5.0 mol%. 
     Comparative Example 4 
     Europium fluoride was used as a particle of Comparative Example 4. 
     Powder X-Ray Diffraction (XRD) 
     For the particles of Examples 11 to 13 and Comparative Example 4, results obtained in the same manner as in the &lt;Powder X-ray diffraction (XRD)&gt; mentioned above are shown in Table 10 and  FIG.  16   .  FIG.  16    also shows the powder X-ray diffraction pattern of only silicate-based base material 1. 
     As shown in Table 10 and  FIG.  16   , Examples 12 and 13 included a crystal of a compound represented by the formula (5) having a powder X-ray diffraction pattern having a diffraction peak (fourth diffraction peak) in a diffraction angle (2θ) range of 26.6° to 28.6°, a diffraction peak (fifth diffraction peak) in a diffraction angle (2θ) range of 44.8° to 46.8°, and a diffraction peak (seventh diffraction peak) in a diffraction angle (2θ) range of 30.8° to 32.8°, respectively, in which a half value width of the fourth diffraction peak was 0.3° or less, a half value width of the fifth diffraction peak was 0.57° or less, and a half value width of the seventh diffraction peak was 0.38° or less, and a crystal of a compound represented by the formula (6) having a powder X-ray diffraction pattern having a diffraction peak (fourth diffraction peak) in a diffraction angle (2θ) range was 26.6° to 28.6°, a diffraction peak (fifth diffraction peak) in a diffraction angle (2θ) range was 44.8° to 46.8°, and a diffraction angle (2θ) was 24.3 to 26.3 (sixth diffraction peak), respectively, in which a half value width of the fourth diffraction peak was 0.3° or less, a half value width of the fifth diffraction peak was 0.57° or less, and a half value width of the sixth diffraction peak was 0.22° or less. Example 11 is a crystalline monophase of a compound represented by the formula (5) having a powder X-ray diffraction pattern having a diffraction peak (fourth diffraction peak) in a diffraction angle (2θ) range of 26.6° to 28.6°, a diffraction peak (fifth diffraction peak) in a diffraction angle (2θ) range of 44.8° to 46.8°, and a diffraction peak (seventh diffraction peak) in a diffraction angle (2θ) range of 30.8° to 32.8°, respectively, in which a half value width of the fourth diffraction peak was 0.3° or less, a half value width of the fifth diffraction peak was 0.57° or less, and a half value width of the seventh diffraction peak was 0.38° or less. The particles of Examples 12 to 13 are said to be a mixed crystal of the compound represented by the formula (5), the compound represented by the formula (6), and an amorphous silica. Furthermore, in Examples 11 to 13, the diffraction peak (2θ) were observed in 39.1° to 39.7°. In  FIG.  16   , they are described as “Δ”, and used in calculation of the crystallinity of Table 10. [0145]  
     
       
         
          TABLE 10
           
               
               
               
               
               
             
               
                   
                 Example 11 
                 Example 12 
                 Example 13 
                 Comparative Example 4 
               
             
            
               
                 Diffraction angle (2θ) in which diffraction peak is located : degree (Half value width: degree) 
                 27.6 ± 0.1 (0.11) 
                 24.3 ± 0.05 (0.060) 
                 24.3 ± 0.03 (0.033) 
                 24.3 ± 0.04 (0.048) 
               
               
                 28.0 ± 0.1 (0.12) 
                 25.4 ± 0.05 (0.066) 
                 25.4 ± 0.05 (0.054) 
                 25.4 ± 0.05 (0.054) 
               
               
                 32.4 ± 0.06 (0.072) 
                 27.5 ± 0.09 (0.11) 
                 27.5 ± 0.07 (0.084) 
                 27.5 ± 0.04 (0.048) 
               
               
                 46.1 ± 0.1 (0.12) 
                 29.8 ± 0.04 (0.048) 
                 29.8 ± 0.04 (0.045) 
                 29.8 ± 0.04 (0.047) 
               
               
                 46.7 ± 0.1 (0.11) 
                 31.7 ± 0.1 (0.12) 
                 31.7 ± 0.13 (0.16) 
                 35.4 ± 0.04 (0.047) 
               
               
                 54.7 ± 0.1 (0.12) 
                 35.4 ± 0.04 (0.048) 
                 35.4 ± 0.04 (0.045) 
                 41.0 ± 0.04 (0.048) 
               
               
                   
                 41.0 ± 0.04 (0.048) 
                 41.0 ± 0.04 (0.045) 
                 42.8 ± 0.04 (0.048) 
               
               
                   
                 42.8 ± 0.04 (0.046) 
                 42.8 ± 0.05 (0.057) 
                 45.5 ± 0.05 (0.054) 
               
               
                   
                 45.5 ± 0.3 (0.36) 
                 45.5 ± 0.3 (0.33) 
                 47.6 ± 0.05 (0.054) 
               
               
                   
                 47.6 ± 0.07 (0.084) 
                 47.6 ± 0.05 (0.053) 
                 51.6 ± 0.04 (0.048) 
               
               
                   
                 51.6 ± 0.05 (0.066) 
                 51.6 ± 0.05 (0.054) 
                 52.1 ± 0.05 (0.057) 
               
               
                   
                 53.3 ± 0.05 (0.060) 
                 53.3 ± 0.05 (0.054) 
                 ± 0.04 53.3 (0.048) 
               
               
                   
                 54.5 ± 0.1 (0.13) 
                 54.5 ± 0.2 (0.21) 
                   
               
               
                 Crystallinity 
                 0.076 
                 0.11 
                 0.12 
                 0.044 
               
            
           
         
       
     
     Light-Emitting Property 
     For particles of Examples 11 to 13, an excitation spectrum and a fluorescence spectrum were measured in the same manner as in Example 1. As an example of the results, fluorescence spectrum is shown in  FIG.  17   . 
      As a result, in all of Examples 11 to 13, an excitation peak (395 nm) and a light-emitting peak (613 nm) derived from an Eu(III) ion were observed. Furthermore, for particles of Examples 11 to 13, when internal quantum yields of the particles were obtained where excitation wavelength λ ex  was 395 nm and light-emission wavelength λ em  was 613 nm, the yield was 1.47 in Example 11, 5.39 in Example 12, and 6.70% in Example 13. 
     Chemical Composition (X-Ray Fluorescence Analysis (XRF)) 
     For the particles of Examples 11 to 13 and Comparative Example 4, the X-ray fluorescence analysis (XRF) was carried out in the same manner as in Example 1. Results are shown in Tables 11 and 12. [0149]  
     
       
         
          TABLE 11
           
               
               
               
               
               
               
               
             
               
                   
                 Si (mol%) 
                 O (mol%) 
                 Eu (mol%) 
                 C (mol%) 
                 F (mol%) 
                 Other element (mol%) 
               
             
            
               
                 Example 11 
                 31.7 
                 65.3 
                 0.391 
                 2.36 
                 0.214 
                 0.035 
               
               
                 Example 12 
                 31.6 
                 64.0 
                 0.860 
                 2.18 
                 1.35 
                 0.010 
               
               
                 Example 13 
                 31.1 
                 61.4 
                 1.50 
                 2.01 
                 3.99 
                 - 
               
               
                 Comparative Example 4 
                 - 
                 - 
                 23.7 
                 - 
                 76.3 
                 - 
               
            
           
         
       
     
      [0150]  
     
       
         
          TABLE 12
           
               
               
               
               
               
             
               
                   
                 Eu/Si (mol%) 
                 F/Eu (mol%) 
                 C/Si (mol%) 
                 C/Eu (mol%) 
               
             
            
               
                 Example 11 
                 1.23 
                 54.7 
                 7.44 
                 604 
               
               
                 Example 12 
                 2.72 
                 157 
                 6.90 
                 253 
               
               
                 Example 13 
                 4.82 
                 266 
                 6.46 
                 134 
               
               
                 Comparative Example 4 
                 - 
                 322 
                 - 
                 - 
               
            
           
         
       
     
     Measurement of Average Particle Size 
     For particles of Examples 11 to 13, 100 or more particle diameters were measured using the field emission-type scanning electron microscope (FE-SEM), and an average particle size was calculated. Note here that for 300 particles, the longer diameter and the shorter diameter of each particle were measured, respectively, and “(longer diameter + shorter diameter) / 2” was defined as a particle diameter of each particle. An average value of the particle diameter of each particle (a value obtained by dividing the total values of the particle diameter of each particle by number of particles (300)) was defined as an average particle size. As a result, an average particle size of the particles of Example 11 was 140 nm, an average particle size of the particles of Example 12 was 149 nm, and an average particle size of the particles of Example 13 was 151 nm. 
     Toxicity Evaluation 
     Toxicity evaluation was carried out using the particles of Examples 11 to 13 and Comparative Example 4 by the same method as in Example 1. As a result, Examples 11 to 13, in which crystal of a europium compound were formed, exhibited normal cell proliferation behavior and no cytotoxicity. On the other hand, in Comparative Example 4, since fluoride was unstable, this eluted into a cell culture solution, and was formed into Eu ion or Eu fluoride ion and reacted with cells directly, resulting in showing substantially the same level of toxicity as in Comparative Example 1. Note here that for the fluorescence property of the particles which have taken up by the cells, since the crystal did not elute into the cell culture solution, finally, after 48 hours of culture, high fluorescence intensity which was higher than the result of Comparative Example 4 was shown. 
     As mentioned above, it is shown that when composite particles having a chloride of the rare-earth element or a fluoride of the rare-earth element on a surface of a specific silicate-based base material is used, cells grow well, and the particles can be taken up by the cells and visualized. Since agglomeration of the rare-earth element as a light-emitting substance is suppressed, and the support amount of the rare-earth element is appropriate, the fluorescence intensity is high, and detection can be carried out with high sensitivity.  
     
       
         
           
               
               
             
               
                 EXPLANATION OF REFERENCE NUMERALS 
               
             
            
               
                 1 
                 Silicate-based base material (spherical shape) 
               
               
                 2 
                 Rare-earth compound 
               
               
                 21 
                 Container 
               
               
                 22 
                 Ammonia water 
               
               
                 23 
                 Screw tube 
               
               
                 24 
                 Liquid surface of ammonia water 
               
               
                 25 
                 Stand