Strontium aluminumate compound, afterglow-emitting particles comprising the same, and method for producing afterglow-emitting particles

Abstract

This invention provides a novel strontium aluminate compound having afterglow luminescence based on strontium aluminate, afterglow luminescent particles comprising the compound, and a method for producing afterglow luminescent particles. [Solution] A strontium aluminate compound having residual luminescence and doped with at least europium, silicon, and nitrogen, wherein in the XPS spectrum, the maximum peak of the 2p electron binding energy of aluminum is in the range of 70 eV to 75 eV, two peaks including the maximum peak of the 3d electron binding energy of strontium are in the range of 130 eV to 137 eV, and the maximum peak of the 2p electron binding energy of silicon is in the range of 101 eV to 105 eV.

Description

[Technical Field]

[0001] The present invention relates to a europium, silicon, and nitrogen-doped strontium aluminate compound having afterglow emission properties, afterglow emission particles comprising the same, and a method for producing afterglow emission particles. [Background technology]

[0002] Afterglow-emitting particles absorb light from illumination or sunlight, becoming excited and storing light energy. After the light supply is cut off, the electron transition from the excited state to the ground state continues for a certain period, meaning they continue to emit light for a certain time. Such afterglow-emitting particles are used in various technologies such as paints, coatings, inks, and plastics, and are applied in various fields such as signs, disaster prevention equipment, interiors, lighting, and toys. Research is also being conducted on applications such as biotechnology and X-ray absorption light conversion, taking advantage of their wavelength conversion afterglow properties. As one example of such afterglow-emitting particles, a strontium aluminate compound having afterglow-emitting properties is known, obtained by doping strontium aluminate with lanthanide rare earth elements, as shown in Patent Document 1. In Patent Document 1, this afterglow-emitting strontium aluminate compound is produced by mixing a strontium compound, an aluminum compound, and a europium compound with boric acid as a flux, and then calcining the mixture. Furthermore, Patent Document 2 describes a strontium aluminate compound having afterglow emission properties obtained by doping strontium aluminate with europium, and states that when a boron compound (including boric acid) is added and calcined, the afterglow emission properties are enhanced. In other words, in the production of strontium aluminate compounds with afterglow luminescence, the addition of boric acid provides a dual effect: it accelerates the calcination process and enhances the afterglow luminescence properties.

[0003] The applicant has also proposed various improvements using a strontium aluminate compound with afterglow emission properties, which is produced by heating and sintering a raw material powder, consisting of spherical γ-Al2O3, SrCO3, Eu2O3, and Dy2O3 mixed with a predetermined amount of H3BO3 (boric acid) as a flux, at 1350-1450°C. For example, Patent Documents 3 and 4 propose a method for producing a phosphorescent material with afterglow emission properties by performing a predetermined surface treatment on the strontium aluminate compound in order to impart excellent afterglow brightness characteristics. Furthermore, Patent Document 5 proposes highly water-resistant afterglow emission particles in which the surface of the strontium aluminate compound is coated with a composite oxide containing aluminum atoms and silicon atoms in order to impart aqueous and afterglow brightness characteristics. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-11250 [Patent Document 2] Japanese Patent Publication No. 2006-152242 [Patent Document 3] Patent No. 5967787 [Patent Document 4] Patent No. 7345949 [Patent Document 5] Patent No. 7345948 [Patent Document 6] Special Publication No. 2022-541147 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, when boric acid is added during the production of strontium aluminate compounds to promote sintering, it is known that the particles tend to form in clumps, requiring robust mechanical grinding during the production process. Such mechanical grinding can break the crystal structure and affect the afterglow brightness. Therefore, it has been difficult to efficiently produce afterglow-emitting particles with a large luminescence area and small particle size with little variation. In addition, a sintering temperature of 1300°C or higher is required, but there has been a need for a manufacturing method at a lower temperature due to equipment and efficiency considerations.

[0006] On the other hand, Patent Document 6 discloses a method for producing porous strontium aluminate at low temperatures without calcination using boric acid. Figure 1 of Patent Document 6 discloses strontium aluminate with a particle size of 10 μm or less and having a spongy microstructure or a porous skeletal microstructure. Because these porous particles of strontium aluminate exhibit a spongy microstructure or a porous skeletal microstructure, they can be easily broken during the grinding process. Therefore, by using this strontium aluminate, it is possible to produce strontium aluminate particles with small particle sizes with little variation without destroying the crystalline structure. Furthermore, Patent Document 6 describes doping this porous strontium aluminate with europium and / or dysprosium. However, while doping the strontium aluminate compound described in Patent Document 6 with europium can produce residual luminescence, scattered non-luminescent regions were observed on the particle surface. Therefore, there is a need for a particle with a higher overall luminescence area. This invention has been made in view of these circumstances, and aims to provide a novel strontium aluminate compound having afterglow emission properties based on strontium aluminate, afterglow emission particles comprising the compound, and a method for producing afterglow emission particles. [Means for solving the problem]

[0007] The inventors, after diligent research, concluded that conventional strontium aluminate compounds produced using boric acid as a flux are doped with boron, and that this boron determines the oxygen sharing state between strontium and aluminum. In other words, the parent crystals of strontium aluminate are SrAl2O4, SrAl4O7, Sr3Al2O6, SrAl 12 O 19 It is a mixed crystal composed of various elements, and it is known to exhibit various structures due to the presence of tetrastructured alumina, octostructured alumina, and strontium capable of bonding with nine oxygen atoms. The inventors hypothesized that when boron is doped into this strontium aluminate, the boron takes on one of the following structures: B2O7 / BO2 / BO3 / BO5·BO2, bonding between aluminum and strontium via oxygen to form orthorhombic SrAl2B2O7. They further hypothesized that this crystal significantly influences the afterglow brightness characteristics. Furthermore, we hypothesized that by incorporating crystals of the same shape as SrAl2B2O7 within a mixed crystal of strontium aluminate, we could obtain afterglow luminescence characteristics at least equivalent to those of conventional afterglow luminescent particles made from strontium aluminate compounds produced with boric acid as a flux. Based on these considerations, the inventors focused on SrAl2SiN2O3, which has an orthorhombic structure containing tetra-structured alumina and octo-structured alumina. They discovered that doping strontium aluminate with silicon (Si) and nitrogen (N) along with europium (Eu) produces a strontium aluminate compound with afterglow emission properties. Furthermore, it was found that crystals of this strontium aluminate compound can be formed at the nanoscale. It was also found that afterglow emission particles containing these strontium aluminate compound crystals have a large emission area. Moreover, it was found that the particle size of the afterglow emission particles can be controlled. Strontium aluminate compounds with such residual luminescence properties can be used not only in their existing applications such as lighting, displays, sensors, photoelectric elements, and stress-induced luminescence materials, but also in biomedical applications. In particular, these nanoscale crystals can be used, for example, in bioimaging to analyze the distribution and localization of cells and tissues by supporting them on cells or tissues; as photosensitizers to attack cancer cells in photodynamic therapy; as drug carriers in cancer chemotherapy; as substrates to absorb ionizing radiation in radiotherapy for cancer; as electrodes to ablate affected areas in ablation therapy for arrhythmias; and as part of cell culture substrates in optogenetics to control proteins.

[0008] The strontium aluminate compound of the present invention is a strontium aluminate compound having residual luminescence and doped with at least europium, silicon, and nitrogen, characterized in that, in the XPS spectrum, the maximum peak of the binding energy of the 2p electrons of aluminum is in the range of 70 eV to 75 eV, there are two peaks including the maximum peak of the binding energy of the 3d electrons of strontium in the range of 130 eV to 137 eV, and the maximum peak of the binding energy of the 2p electrons of silicon is in the range of 101 eV to 105 eV.

[0009] The strontium aluminate compound of the present invention is preferably doped with dysprosium and has a maximum binding energy peak at 150 eV to 155 eV that is attributed to the 4d electrons of the dysprosium. The strontium aluminate compound of the present invention is preferably one in which the maximum peak of the bonding energy of the silicon's 2p electrons is in the range of 101.5 eV to 102.5 eV. The strontium aluminate compound of the present invention is preferably one having a bond energy peak of 395 eV to 397 eV for the 1s electron of the nitrogen atom.

[0010] The afterglow luminescent particles of the present invention are characterized by comprising the strontium aluminate compound of the present invention. Such afterglow luminescent particles are preferably porous.

[0011] The method for producing the afterglow luminescent particles of the present invention comprises a step of preparing base particles containing strontium aluminate, a step of preparing a suspension by adding the base particles to an alkaline solution containing ammonium ions, a step of adding an acidic solution containing aluminum ions, silicate ions and nitrate ions to the suspension, a step of adding europium nitrate to the suspension, a step of evaporating ammonia, and a step of further evaporating moisture. The method for producing the afterglow luminescent particles of the present invention, wherein the acidic solution preferably contains at least one selected from barium nitrate, calcium nitrate and zinc nitrate. Further, the method wherein the acidic solution contains at least one selected from silver nitrate, cerium nitrate, terbium nitrate and yttrium nitrate is preferable. [Effect of the Invention]

[0012] The strontium aluminate compound of the present invention is a new compound having afterglow luminescent properties. In particular, crystals can be formed in the nano unit. The afterglow luminescent particles of the present invention emit light over the entire particle surface, so the luminescent area is large. In particular, the afterglow luminescent particles comprising the strontium aluminate compound in the nano unit can emit afterglow luminescence even at several microns. The method for producing the afterglow luminescent particles of the present invention can produce afterglow luminescent particles containing the strontium aluminate compound of the present invention with high production efficiency. In particular, it is preferable that the particle size and porosity of the afterglow luminescent particles can be controlled. The afterglow luminescent particles of the present invention can be applied not only to the conventional uses such as lighting, display, sensor, optoelectronic device, stress luminescent material, etc., but also to biomedicine. [Brief Description of the Drawings]

[0013] [Figure 1]Fig. 1a is a SEM image showing the afterglow-emitting particles of Example 1 after ultraviolet irradiation, and Fig. 1b is a camera image showing the afterglow-emitting particles of Comparative Example 1. [Figure 2] Figs. 2a to i are XPS spectrum diagrams of the afterglow-emitting particles of Example 1, respectively. [Figure 3] Figs. 3a to i are XPS spectrum diagrams of the afterglow-emitting particles of Example 2, respectively. [Figure 4] Figs. 4a to i are XPS spectrum diagrams of the particles of Comparative Example 2, respectively. [Figure 5] Fig. 5a is a SEM image of the afterglow-emitting particles of Example 3, and Fig. 5b is a partially enlarged image thereof. [Figure 6] Fig. 6 is a SEM image of the afterglow-emitting particles of Example 4.

Mode for Carrying Out the Invention

[0014] The strontium aluminate compound of the present invention is a compound having afterglow-emitting properties in which strontium aluminate is doped with at least europium, silicon, and nitrogen. Here, the afterglow-emitting property means that it emits light when irradiated with a D65 light source of at least 200 Lux and shows afterglow after 10 minutes of irradiation, preferably after 20 minutes. The confirmation of the afterglow is performed by magnifying the emission by at least 5000 times with a microscope, an electron microscope, etc. and confirming the emission. The emission color during irradiation and the emission color after irradiation may be different, but it is preferably substantially the same color.

[0015] [Strontium Aluminate] Strontium aluminate is composed of alumina having a tetra structure, alumina having an octa structure, etc., and strontium capable of bonding with nine oxygens, such as SrAl2O4, SrAl4O7, Sr3Al2O6, SrAl 12 0 19 、Sr4Al 14 O 25 Or Sr x Al y O zThis material contains an oxide represented by [formula], and is preferably a mixed oxide containing two or more oxides. This strontium aluminate is preferably formed by bonding strontium to an aluminum alkoxide. By bonding strontium to an aluminum alkoxide, the amount of aluminum oxide with a corundum structure, which causes lattice defects, can be minimized. Such strontium aluminate can be formed by reacting a strontium compound with an alumina suspension, as described later.

[0016] [Strontium aluminate compounds] The strontium aluminate compound of the present invention is obtained by doping strontium aluminate with europium, silicon, and nitrogen. More specifically, strontium aluminate is doped with silicon and nitrogen, at least as silicon oxynitride (Si-ON). Therefore, it is thought that silicon and nitrogen bond with tetrastructured alumina, octostructured alumina, and strontium to form orthorhombic SrAl2SiN2O3. The strontium aluminate compound of the present invention is manufactured without a calcination process, and in particular, it is not manufactured by adding a boron compound (especially boric acid) and calcining it. Therefore, it is preferable that the compound does not contain boron as an element, or does not contain boron as an element unless it is inevitably mixed in during the raw material or manufacturing process. In addition, the strontium aluminate compound of the present invention may be doped with one or more elements other than boron, selected from dysprosium, lanthanides, barium, calcium, zinc, yttrium, silver, cerylium, and terbium. In particular, stable crystals of strontium aluminate compounds can be obtained by doping with barium and / or calcium. Furthermore, by doping with at least one of silver, cerylium, and terbium, the afterglow-emitting particles comprising the strontium aluminate compound of the present invention can be made into porous particles. Moreover, the emission wavelength can be changed by doping with these materials.

[0017] [XPS analysis] XPS analysis uses an AlKα X-ray source from ULVAC-PHI (PHI5000) VersaProbe2. The elements identified in a survey scan with a beam spot of 200 μm, acceleration energy of 15 kev, and a specified scan speed of 20 msec for the specified energy range are measured for 15 cycles at 20 msec each, and the resulting spectral diagram is obtained by integrating these measurements.

[0018] [Al2p] The strontium aluminate compound of the present invention exhibits a maximum peak of the 2p electron binding energy of aluminum (Al) in the range of 70 eV to 75 eV in XPS analysis (for example, corresponding to P1 in Figures 2b and 3b). According to the NIST XPS database, the bond energy between the 2p electrons of aluminum and nitrogen (Al-N) is 74.3 eV. Therefore, the peak in this range indicates that the strontium aluminate compound of the present invention has an Al-N bond.

[0019] [Sr3d] The strontium aluminate compound of the present invention exhibits two peaks in the range of 130 eV to 137 eV, particularly 132 eV to 135 eV, in XPS analysis, including the peak with the maximum binding energy of the strontium (Sr) 3d electrons (corresponding to P2 and P3 in Figures 2c and 3c). Either of the two peaks may be the maximum peak. Here, the bond energy between the 3d electrons of Sr and oxygen is 133.8 (±0.3) eV, and the bond energy between the 3d electrons of Sr and nitrogen is 134.9 (±0.3) eV. Therefore, it is presumed that the two peaks (P3 and P2), including the maximum peak, originate from the bond energies between the 3d electrons of Sr and oxygen, and between the 3d electrons of Sr and nitrogen, respectively. In other words, these peaks indicate that the strontium aluminate compound of the present invention has a Sr-N bond. Furthermore, the two peaks of the 3d electrons of Sr in this strontium aluminate compound are presumed to be significantly involved in the afterglow emission. In other words, upon irradiation with ultraviolet light, Eu+ undergoes plasmon vibration with aluminate, releasing 4f electrons from Eu and causing emission. At this time, these 4f electrons are released via nitrogen, which is bonded to the 3d electrons of Sr, which have a high bond energy. On the other hand, irradiation with ultraviolet light creates a hole in the ground state of Eu, and this hole is supplied to Dy via oxygen, which is bonded to the 3d electrons of Sr, which have a low bond energy. After irradiation with ultraviolet light, the hole is thermally released and returns to the ground state of Eu2+, producing afterglow. Thus, it is presumed that these two peaks are significantly involved in the afterglow emission. Furthermore, depending on the crystal structure, Eu2+, after emitting its 4f electrons, transitions back to the ultraviolet absorption region of Dy+, where it undergoes plasmon formation with Dy+, emitting light via nitrogen bonded to the 3d electrons of Sr. This light is then trapped as a hole in the alumina of strontium aluminate, ultimately becoming Eu3+, the fundamental state of Eu, and (ideally) balancing the emission as aluminoxystrontium. Therefore, it is presumed that the crystal's durability is also improved.

[0020] [Si2p] The strontium aluminate compound of the present invention exhibits a maximum peak of the silicon (Si) 2p electron bond energy in the range of 10¹eV to 10⁵eV in XPS analysis (corresponding to P4 in Figures 2d and 3d). In particular, it is preferable that the maximum peak of the silicon 2p electron bond energy is in the range of 10¹.5eV to 10³eV, especially 10¹.5eV to 10².5eV. According to the NIST XPS database, the bond energy of Si₃N₄ for silicon 2p electrons is 10².1eV, and the bond energy of SiO₂ is 10³.2eV. Therefore, a peak in this range is considered to be a peak detected due to the presence of both Si-N and Si-O bonds. In other words, this peak indicates the presence of Si-N bonds.

[0021] [N1s] The strontium aluminate compound of the present invention exhibits a peak in the binding energy of the nitrogen (N) 1s electron in XPS analysis, specifically within the range of 395 eV to 398 eV, and particularly within the range of 397 eV to 398 eV (corresponding to P5 in Figures 2e and 3e). This is thought to be due to Si3N4 or Si-NO bonding. Furthermore, the strontium aluminate compound of the present invention has a bond energy peak for the nitrogen (N) 1s electron in the range of 398 eV to 400 eV, particularly 398 eV to 399 eV (corresponding to P6 in Figures 2e and 3e). This is thought to be due to the N-Al bond.

[0022] [Dy4d] The strontium aluminate compound of the present invention, doped with dysprosium (Dy), has a maximum peak of the binding energy of the 4d electrons of dysprosium (Dy) in the range of 150 eV to 155 eV in XPS analysis (corresponding to P7 in Figures 2f and 3f). Doping with dysprosium (Dy) can improve the afterglow emission characteristics.

[0023] [Ba3d] The strontium aluminate compound of the present invention, doped with barium (Ba), exhibits two peaks in XPS analysis within the range of 777eV to 782eV, corresponding to the 3d electron bond energy of barium (Ba). The peak with the higher bond energy (corresponding to P8 in Figures 2g and 3g) is thought to be based on the bond energy of BaN (or BaNOx), preferably in the range of 780eV to 782.5eV, and particularly in the range of 780eV to 781.5eV. The peak with the lower bond energy (P9 in Figures 2g and 3g) is thought to be based on the bond energy of BaO, preferably in the range of 777eV to 780eV, and particularly in the range of 778 to 780eV. Thus, a mixture of BaN (or BaNOx) and BaO bonds is preferred. In particular, the peak value of the low-bonding-energy peak (BaO) is 0.8 to 1.2 times greater than the peak value of the high-bonding-energy peak (BaN (or BaNOx)), with a lower limit of 0.85 times or more, particularly preferably 0.9 times or more, and an upper limit of 1.15 times or less, particularly preferably 1.1 times or less.

[0024] [Ca2p] The strontium aluminate compound of the present invention exhibits a peak in the binding energy range of the calcium (Ca) 2p electrons in XPS analysis within the range of 345 eV to 347 eV (corresponding to P10 in Figures 2h and 3h).

[0025] The aluminum that makes up strontium aluminate exists in a certain proportion as aluminum oxide in a corundum structure, and it is thought that this forms lattice defects in strontium aluminate. Barium and calcium are thought to stabilize the crystal by filling these lattice defects.

[0026] [O1s] The strontium aluminate compound of the present invention exhibits a maximum peak of 530 eV to 535 eV for the 1s electron binding energy of oxygen (O) in XPS analysis (corresponding to P11 in Figures 2i and 3i).

[0027] The strontium aluminate compound of the present invention is a novel compound that possesses afterglow luminescence properties.

[0028] Next, we will describe the afterglow-emitting particles comprising crystals of the strontium aluminate compound of the present invention. The average particle size (D50) of the afterglow-emitting particles of the present invention can be selected depending on the application and is not particularly limited, but is between 0.1 μm and 200 μm. The preferred lower limit of the average particle size for control as a crystalline powder is 2 μm or more, particularly 3 μm or more, and the preferred upper limit of the average particle size is 100 μm or less, particularly 50 μm or less, and can also be 5 μm or less. The afterglow-emitting particles of the strontium aluminate compound of the present invention, comprising crystals, are preferably porous. In particular, those with a pore radius of 15 to 500 Å and a pore volume of 0.001 ml / g or more and less than 0.05 ml / g, measured by mercury intrusion, and those with a pore radius of 300 to 5000 Å and a pore volume of 0.7 to 1.5 ml / g are preferred. Furthermore, the BET surface area is 0.1 m². 2 / g or more, preferably 1m 2 / g or more, 40m 2 A value of less than / g is preferable.

[0029] The crystal size of this strontium aluminate compound is 50 nm or more and 5 μm or less, with a preferred lower limit of 60 nm or more, particularly 120 nm or more, and a preferred upper limit of 3 μm or less, particularly 1 μm or less. Here, "crystal size" can be defined as the diameter equivalent to a perfect circle of the crystal (the region observed two-dimensionally in the image) confirmed when a specific particle is observed with SEM or TEM.

[0030] The afterglow-emitting particles of the present invention can be produced with a relatively small average particle size and have a large luminescence area. The afterglow-emitting particles using the strontium aluminate compound of the present invention are expected to have applications not only in lighting, displays, sensors, photoelectric elements, stress-induced luminescence materials, and other fields, but also in biomedical applications.

[0031] [Method for producing afterglow-emitting particles] Next, the method for producing the afterglow-emitting particles of the present invention will be described. The present invention provides a method for producing afterglow-emitting particles, comprising: a first step of preparing base particles containing strontium aluminate; a second step of preparing a suspension containing the base particles; a third step of adding a predetermined acidic solution to the suspension; a fourth step of adding europium to the suspension; a fifth step of evaporating ammonia; and a sixth step of further evaporating water.

[0032] [1st step] The first step is to prepare substrate particles containing strontium aluminate. Strontium aluminate is composed of tetrastructured alumina, octostructured alumina, and strontium that can bond with 9 oxygen atoms, resulting in SrAl2O4, SrAl4O7, Sr3Al2O6, and SrAl 12 0 19 , Sr4Al 14 O 25 These contain oxides such as the above. Preferably, this strontium aluminate is formed by bonding strontium to an aluminum alkoxide. By bonding strontium to an aluminum alkoxide, the amount of aluminum oxide with a corundum structure, which causes lattice defects, can be minimized. Such strontium aluminate can be formed by reacting a strontium compound with an alumina suspension, as described later. The average particle size (D50) is between 50 nm and 1 μm, with a preferred lower limit of 80 nm and above, particularly 100 nm and above, and a preferred upper limit of 800 nm and below, particularly 700 nm and below. The size of the nanocrystals containing strontium aluminate is 50 nm or more and 5 μm or less, with a preferred lower limit of 60 nm or more, particularly 120 nm or more, and a preferred upper limit of 3 μm or less, particularly 1 μm or less. Here, "nanocrystal size" can be defined as the diameter equivalent to a perfect circle of the nanocrystal (the region observed two-dimensionally in the image) confirmed when a specific particle is observed with SEM or TEM. The substrate particles containing strontium aluminate nanocrystals are preferably porous with a spongy microstructure. In particular, it is preferable that the pore volume is 0.001 ml / g or more and less than 0.05 ml / g for pore radii of 15 to 500 Å, as measured by mercury intrusion, and 0.7 to 1.5 ml / g for pore radii of 300 to 5000 Å. Furthermore, the BET surface area is 1 m². 2 / g or more, 20m 2 A value of less than / g is preferable.

[0033] A method for producing porous substrate particles containing strontium aluminate, as disclosed in Patent Document 6, comprises the following steps: 1-1 step of preparing a Sr-Al suspension by adding a strontium compound to an alumina suspension; 1-2 step of subjecting the Sr-Al suspension to hydrothermal treatment to produce a precursor of a mixed oxide of strontium aluminate; and 1-3 step of calcining the precursor of the mixed oxide of strontium aluminate. The alumina suspension in step 1-1 may be a suspension of aluminum hydroxide oxide (AlO(OH)), aluminum hydroxide (Al(OH)3), aluminum oxide (Al2O3), or a combination thereof, with aqueous suspension being preferred. This causes aluminum alkoxide to form on the surface of the solid. The strontium compound in step 1-1 may include strontium salts such as strontium acetate and strontium carbonate, strontium oxide, strontium hydroxide, or combinations thereof. In other words, the Sr-Al suspension in step 1-1 is a state in which strontium is bound to the aluminum alkoxide on the solid surface of the suspension. The hydrothermal treatment in steps 1 and 2 can be carried out by heating at a temperature of 100°C to 250°C for 0.5 to 14 hours. The hydrothermal treatment should be performed at a pH of 5 to 12. A precursor of strontium aluminate mixed oxide can be obtained by drying a hydrothermally treated Sr-Al suspension. The calcination process in steps 1-3 involves heating at a temperature of 900°C to 1100°C for 0.5 to 5 hours to produce strontium aluminate. The strontium aluminate produced by these processes becomes porous substrate particles containing strontium aluminate crystals (especially nanocrystals). The base particles containing the mixed oxide of strontium aluminate produced in the first step are preferably pulverized, for example, by wet grinding, until the average particle size (D50) is 50 nm or more and 1 μm or less.

[0034] [Second process] The second step is to prepare an alkaline suspension containing base particles that include strontium aluminate. The suspension is prepared by adding base particles containing strontium aluminate to an alkaline solution containing ammonium ions. As an alkaline solution containing ammonium ions, an alkaline buffer solution containing ammonium ions is preferred, and in particular, an ammonium nitrate buffer solution with a pH of 8 to 10 is preferred. The particulate concentration of strontium aluminate is between 10 g / l and 80 g / l, with a preferred lower limit of 20 g / l and a preferred upper limit of 50 g / l.

[0035] [3rd step] The third step involves adding an acidic solution containing aluminum ions, silicate ions, and nitrate ions to the suspension. Specifically, an acidic solution containing aluminum salt, silicon dioxide, and nitrate is added to the suspension. This coats the surface of the substrate particles with Si-O. Metal elements are also supported on this coating. The pH of the acidic solution is 2 or higher and 6 or lower, with a preferred lower limit of 3 or higher, particularly 4 or higher, and a preferred lower limit of 5 or lower, particularly 4.5 or lower. The aluminum salt is not particularly limited, but aluminum phosphate is preferred. The concentration of the aluminum salt is 0.1 mol / l or more and 0.2 mol / l or less, with a preferred lower limit of 0.12 mol / l or more, and particularly 0.15 mol / l or more. Examples of silicate ions include colloidal silica, with acidic silica sol with a pH of 3-6 being particularly preferred. The silicate ion concentration is 0.2 mol / l or higher and 0.4 mol / l or lower, with a preferred lower limit of -2 mol / l or higher, particularly 0.25 mol / l or higher, and a preferred upper limit of 0.35 mol / l or lower, particularly 0.3 mol / l or lower. The molar ratio of aluminum to silicon (Al / Si) is between 0.00001 and 0.01, with a preferred lower limit of 0.0001 and particularly 0.0003, and a preferred upper limit of 0.001 and particularly 0.0007. Examples of nitrates include nitrates of alkaline earth metals (other than strontium), such as barium nitrate (Ba(NO3)2) and calcium nitrate (Ca(NO3)2). The nitrate concentration is 0.05 mol / l or higher and 0.1 mol / l or lower, with a preferred lower limit of 0.05 mol / l or higher, particularly 0.06 mol / l or higher, and a preferred upper limit of 0.75 mol / l or lower, particularly 0.5 mol / l or lower. As mentioned above, the aluminum constituting strontium aluminate exists in a certain proportion as aluminum oxide in a corundum structure, which is thought to form lattice defects in strontium aluminate. Alkaline earth metals such as barium and calcium are thought to stabilize the crystal by filling these lattice defects. Other nitrates may also be added to the acidic solution. Examples include zinc nitrate (Zn(NO3)2) and yttrium nitrate (Y(NO3)3). The concentrations of these nitrates can range from 0.05 mol / l to 0.1 mol / l, with a preferred lower limit of 0.05 mol / l or higher, particularly 0.06 mol / l or higher, and a preferred upper limit of 0.75 mol / l or lower, particularly 0.5 mol / l or lower. These nitrates may be included in the acidic solution or added to the suspension as a separate, independent solution.

[0036] The respective concentrations can be appropriately selected depending on the amount of each element doped into the strontium aluminate. The amount of silicon (Si) doping is between 5 mol% and 20 mol% relative to strontium, with a preferred lower limit of 8 mol% and a preferred upper limit of 15 mol%. The nitrogen (N) doping amount is 3 mol% or more and 15 mol% or less relative to strontium, with a preferred lower limit of 5 mol% or more and a preferred upper limit of 15 mol% or less. The amount of barium (Ba) doping is between 1 mol% and 20 mol% relative to strontium, with a preferred lower limit of 2 mol% or more, a particularly preferred lower limit of 3 mol% or more, and a preferred upper limit of 15 mol% or less. The amount of calcium (Ca) doping is between 1 mol% and 20 mol% relative to strontium, with a preferred lower limit of 2 mol% or more, particularly preferred of 3 mol% or more, and a preferred upper limit of 15 mol% or less. The particle size (D50) of the porous particles coated with silicon dioxide is 5 nm or more and 0.2 μm or less, with a particularly preferred size of 20 nm or less, and most preferably 15 nm or less.

[0037] The acidic solution is preferably added dropwise to the suspension. Specifically, the acidic solution is added to the suspension while titrating, forming a xerogel-like primary crystal by the sol-gel method. This creates a silicon dioxide coating on the surface of the porous strontium aluminate particles in the suspension, resulting in a xerogel state. The coating also contains nitrate metal.

[0038] Silver nitrate, cerium nitrate, or terbium nitrate may be added as the nitrate in the third step. In this case, granulation of the strontium aluminate compounds is promoted, and the porosity of the afterglow-emitting particles can be improved. The amount of silver (Ag) doping is between 1 mol% and 20 mol% relative to strontium, with a preferred lower limit of 2 mol% or more, a particularly preferred lower limit of 3 mol% or more, and a preferred upper limit of 15 mol% or less. The amount of cerium (Ce) doping is 0.5 mol% or more and 10 mol% or less relative to strontium, with a preferred lower limit of 1 mol% or more, a particularly preferred lower limit of 2 mol% or more, and a preferred upper limit of 10 mol% or less. The doping amount of terbium (Tb) is 0.5 mol% or more and 10 mol% or less relative to strontium, with a preferred lower limit of 1 mol% or more, a particularly preferred lower limit of 2 mol% or more, and a preferred upper limit of 10 mol% or less. These nitrates may be included in the acidic solution, or they may be added to the suspension as a separate, independent solution.

[0039] [4th step] The fourth step is to add europium nitrate to the suspension. This supports europium on the porous strontium aluminate particles. Europium nitrate is preferably added after adding the acidic solution, but it may also be added before adding the acidic solution. In addition, nitrates of rare earth elements such as dysprosium nitrate and / or lanthanide nitrates may be added along with europium nitrate. In particular, it is preferable to add at least europium nitrate and dysprosium nitrate. By adding nitrates of rare earth elements, the strontium aluminate compound can be doped with rare earth elements. Europium nitrate and nitrates of rare earth elements are preferably diluted with water and added together with an ammonium nitrate buffer solution with a pH of 8-10. The amount of europium element supported should be 5 mol% or more and 30 mol% or less relative to strontium, with a preferred lower limit of 8 mol% or more, particularly 10 mol% or more, and a preferred upper limit of 20 mol% or less, particularly 15 mol% or less. The amount of dysprosium element supported is 0.5 mol% or more and 10 mol% or less relative to strontium, with a preferred lower limit of 1 mol% or more, a particularly preferred lower limit of 2 mol% or more, and a preferred upper limit of 10 mol% or less. The amount of lanthanide elements supported is between 1.5 mol% and 20 mol% relative to strontium, with a preferred lower limit of 2 mol% or more, a particularly preferred lower limit of 3 mol% or more, and a preferred upper limit of 10 mol% or less.

[0040] [5th ​​step] The fifth step is to evaporate the ammonium from the mixed solution. As the ammonia evaporates, the Si-O coating on the substrate particles combines with N, doping the strontium aluminate as silicon oxynitride (Si-ON). This forms an orthorhombic strontium aluminate compound. At the same time, barium (Ba), calcium (Ca), and europium (Eu) supported on the surface of the substrate particles along with Si-O are doped into the crystal, and crystallization progresses. One method of evaporation is to heat the mixed solution to, for example, 50°C to 70°C, particularly 60°C. However, natural evaporation is also possible.

[0041] [6th step] The sixth step involves evaporating the ammonium followed by evaporating the water. By evaporating the water, the Si doped in strontium aluminate combines with the Si in other particles, forming Si-O-Si and granulating the particles. This allows for control of the particle size of the afterglow-emitting particles containing crystals of the strontium aluminate compound. Furthermore, because granulation occurs, the porosity of the luminescent particles can also be controlled. Methods of evaporation include natural evaporation and heating the mixed solution to, for example, 50°C or higher and 150°C or lower. For example, spraying the solution into a space under a 150°C atmosphere using a spray nozzle. The average particle size (D50) of the afterglow-emitting particles produced by this process is between 100 μm and 2 μm, with a preferred lower limit of 200 nm and above, particularly 300 nm and above, and a preferred upper limit of 1 μm and below, particularly 900 nm and below.

[0042] [Effects of manufacturing method for afterglow-emitting particles] The present invention's method for producing afterglow-emitting particles allows for europium doping of strontium aluminate at a relatively lower temperature (maximum 900°C to 1100°C in the first step) compared to conventional methods. Furthermore, the present invention's method for producing afterglow-emitting particles allows for control of the average particle size (D50). In particular, it enables the production of particles with relatively small average particle sizes with minimal variation. Moreover, the present invention's method for producing afterglow-emitting particles can generate afterglow-emitting particles in which crystals of a strontium aluminate compound with high afterglow-emitting properties are densely formed on the particle surface. In particular, nanoscale crystals can be uniformly and densely arranged. Furthermore, the present invention's method for producing afterglow-emitting particles can produce porous luminescent particles. That is, it can produce lightweight, high-quality afterglow-emitting particles that are porous and have small crystals uniformly arranged. In this case, raw material requirements can be reduced, and production efficiency is high. [Examples]

[0043] [Afterglow luminescence test] The presence or absence of afterglow emission was determined by irradiating the particles with a 200 Lux D65 light source and confirming whether they emitted light and exhibited afterglow after irradiation. [XPS analysis] XPS analysis was performed using an AlKα X-ray source on the ULVAC-PHI PHI5000 VersaProbe2. Elements identified by a survey scan with a beam spot of 50W, acceleration energy of 15Kev, and a specified scan speed of 20msec for the specified energy range were measured for 15 cycles at the same 20msec scan speed, and the resulting spectral diagram was obtained by integrating the results.

[0044] "Example 1" Porous wet particles (SrDopeAlumina, manufactured by Sasol) consisting of a mixed oxide of strontium aluminate with an average particle size D50 of 2.5 μm were prepared and added to pure water to a solid content concentration of 35%. Then, the mixture was wet-milled with 50 μm zirconia beads, and the beads were separated to prepare porous base particles with an average particle size D50 of 0.6 μm (Step 1). These porous substrate particles were added to an ammonium nitrate buffer solution at pH 8.8 to prepare a suspension (step 2). An acidic solution was prepared by mixing 8 g of aluminum phosphate (AlPO4), 72 g of colloidal silica sol from EVERGREEN (Al2O3 / SiO2 molar ratio 0.0010), 61 g of pure water, 30 g of barium nitrate (Ba(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt% diluted with water), 30 g of calcium nitrate (Ca(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt% diluted with water), and 30 g of zinc nitrate (Zn(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt% diluted with water). Then, an acidic solution was added dropwise to the above suspension so that Ba(NO3)2, Ca(NO3)2, Zn(NO3)2, and silica sol were present in amounts of 2 wt%, 2 wt%, 2 wt%, and 4 wt% relative to the substrate particles, respectively (third step). Next, europium nitrate solution (Eu(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries) (5 wt% diluted with water), dysprosium nitrate solution (Dy(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries) (5 wt% diluted with water), and lanthanide nitrate solution (La(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries) (5 wt% diluted with water) were prepared, respectively. Acidic solutions were added dropwise to the above suspensions so that Eu(NO3)3, Dy(NO3)3, and La(NO3)3 were present at concentrations of 1.0 wt%, 2.0 wt%, and 1.2 wt% relative to the substrate particles, respectively (Step 4). Next, the mixed solution was sprayed to dry the ammonia in an environment below 70°C (step 5). Then, the water was evaporated in that environment (step 6). The particles produced by this process will be referred to as Example 1.

[0045] "Comparative Example 1" Porous particles (Sasol AS-3) made from a mixed oxide of strontium aluminate were prepared and added to pure water to a solid content of 35%. Then, the mixture was wet-milled with 50 μm zirconia beads, and the beads were separated to prepare a suspension containing the porous substrate particles. Next, we prepared a solution of europium nitrate (Eu(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries) (5 wt% diluted with water) and a solution of dysprosium nitrate (Dy(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries) (5 wt% diluted with water). Then, Eu(NO3)3 solution and Dy(NO3)3 solution were added dropwise to the suspension at concentrations of 1 wt% and 2 wt%, respectively, relative to the substrate particles. Furthermore, a mixed solution was prepared by adding ammonium nitrate buffer at pH 8.8. This mixed solution was dried and calcined at 1350°C for 3 hours under a nitrogen atmosphere to produce luminescent particles. In other words, particles were prepared by doping europium with strontium aluminate without doping it with silicon and nitrogen. This will be referred to as Comparative Example 1.

[0046] [Evaluation of afterglow emission area] The particles of Example 1 were irradiated with a 200 Lux D65 light source, and their state after 20 seconds was photographed with a Keyence VHX6000 stereomicroscope (5000x magnification). Figure 1a is an image of the particles of Example 1. On the other hand, Figure 1b is a camera image of the particles of Comparative Example 1 (inside a crucible) when irradiated with a 200 Lux D65 light source. The particles in Example 1 emitted light without any gaps throughout. Even under magnification, the light-emitting elements were densely arranged, with almost no areas that did not emit light. In contrast, the particles in Comparative Example 1 showed areas that did not emit light even when observed at 1:1 magnification. Furthermore, the emission was faint. Thus, it was found that the afterglow-emitting particles comprising the strontium aluminate compound of the present invention have elements with afterglow-emitting properties densely arranged throughout the entire particle.

[0047] Example 2 A suspension was prepared from the first and second steps of Example 1. An acidic solution was prepared by mixing 12 g of aluminum phosphate (AlPO4), 85 g of colloidal silica sol manufactured by EVERGREEN (Al2O3 / SiO2 molar ratio 0.0010), 70 g of pure water, 30 g of barium nitrate (Ba(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt% diluted with water), 30 g of calcium nitrate (Ca(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt% diluted with water), and 30 g of zinc nitrate (Zn(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt% diluted with water). Then, an acidic solution was added dropwise to the suspension so that Ba(NO3)2, Ca(NO3)2, Zn(NO3)2, and silica sol were present in amounts of 4 wt%, 5 wt%, 4 wt%, and 8 wt% relative to the substrate particles, respectively (third step). Next, steps 4 to 6 of Example 1 are performed, and the resulting particles are designated as Example 2.

[0048] "Comparative Example 2" A suspension was prepared from the first and second steps of Example 1. As an acidic solution, 10 g of aluminum phosphate (AlPO4), 85 g of colloidal silica sol manufactured by EVERGREEN (Al2O3 / SiO2 molar ratio 0.0010), 70 g of pure water, 30 g of barium nitrate (Ba(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt% diluted with water), 30 g of calcium nitrate (Ca(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt% diluted with water), and 30 g of zinc nitrate (Zn(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt% diluted with water) were mixed. Then, an acidic solution was added dropwise to the suspension so that Ba(NO3)2, Ca(NO3)2, Zn(NO3)2, and silica sol were present in amounts of 1 wt%, 1 wt%, 1 wt%, and 5 wt% relative to the substrate particles, respectively (third step). Next, steps 4 to 6 of Example 1 are performed, and the resulting particles are designated as Comparative Example 2.

[0049] Next, the particles of Example 1, Example 2, and Comparative Example 2 were subjected to afterglow luminescence tests. In conclusion, the particles in Examples 1 and 2 exhibited afterglow emission, while the particles in Comparative Example 2 did not. The details are as follows. The particles in Example 1 emitted green light upon irradiation with ultraviolet light. The emission was observed throughout the entire particle without any gaps. After irradiation with ultraviolet light, the particles emitted a yellowish-green light (afterglow emission) that was different from the initial emission. This afterglow emission was also observed throughout the entire particle without any gaps. After 20 minutes, the afterglow emission disappeared. The particles in Example 2 emitted green light upon irradiation with ultraviolet light. The emission was observed throughout the entire particle without any gaps. After irradiation with ultraviolet light, the particles emitted a yellowish-green light (afterglow emission) that was different from the initial emission. This afterglow emission was also observed throughout the entire particle without any gaps. After 20 minutes, the afterglow emission disappeared. The particles in Comparative Example 2 emitted blue light when irradiated with ultraviolet light. The emission was observed without any gaps throughout the entire particle. However, no afterglow was observed after irradiation with ultraviolet light.

[0050] Next, XPS analysis was performed on the particles of Example 1, Example 2, and Comparative Example 2. The results are shown in Figures 2 to 4.

[0051] "XPS analysis of particles in Example 1" The XPS analysis of the particles from Example 1 is shown below. The spectral diagrams for each element are shown in Figures 2a to 2i. Figure 2a is the spectral diagram obtained by the survey scan, and Figures 2b to 2i are detailed spectral diagrams for each element. The maximum bond energy peak for the 2p electrons of aluminum (Al) (P1 in Figure 2b) was detected at 73.4 eV. A peak to the left of peak P1 (indicating a higher bond energy) is also observed. This is presumed to be an Al-OH bond, suggesting the presence of a region that has not crystallized. Peaks representing the 3d electron binding energies of strontium (Sr) were detected at 132.5 eV (P3 in Figure 2c) and 134.5 eV (P2 in Figure 2c). Of the two, the peak with the lower binding energy (P3, the peak originating from the silicon-oxygen bond) was detected as the largest peak. The maximum bond energy peak for silicon (Si) 2p electrons was detected at 101.8 eV (P4 in Figure 2d). This indicates the presence of both Si-N and Si-O bonds. The bond energy peak for the 1s electron of nitrogen (N) was detected at 397.5 eV (P5 in Figure 2e). The maximum bond energy peak for the 1s electron of nitrogen (N) was detected at 398.8 eV (P6 in Figure 2e). The maximum binding energy peak for the 4d electrons of dysprosium (Dy) was detected at 152.7 eV (P7 in Figure 2f). Since the measurement was performed while irradiating with X-rays, it is presumed that Eu / Dy absorbed the X-rays and emitted light, indicating that Dy was oxidized. The bond energy peak for barium (Ba) 3d electrons in BaN (BaNOx) was detected at 780.9 eV (P8 in Figure 2g), and the bond energy peak for BaO was detected at 778.0 eV (P9 in Figure 2g). In particular, the latter peak value was 1.1 times higher than the former peak value. A peak representing the 2p electron bond energy of calcium (Ca) was detected at 346.5 eV (P10 in Figure 2h). The maximum peak of the 1s electron bond energy of oxygen (O) was detected at 531.5 eV (P11 in Figure 2i).

[0052] "XPS analysis of particles in Example 2" The XPS analysis of the particles from Example 1 is shown below. The spectral diagrams for each element are shown in Figures 3a to 3i. Figure 3a is the spectral diagram obtained by the survey scan, and Figures 3b to 3i are detailed spectral diagrams for each element. The maximum bond energy peak for 2p electrons in aluminum (Al) was detected at 73.3 eV (P1 in Figure 3b). Peaks representing the 3d electron bond energy of strontium (Sr) were detected at 132.5 eV (P3 in Figure 3c) and 134.5 eV (P2 in Figure 3c). Unlike Example 1, the peak with the highest bond energy (P2, a peak originating from the silicon-nitrogen bond) was detected as the maximum peak, although the two peak values ​​were almost the same. From this, it can be inferred that there are more Si-N bonds than in Example 1. The maximum bond energy peak for silicon (Si) 2p electrons was detected at peak 101.9 eV (P4 in Figure 3d). This indicates the presence of both Si-N and Si-O bonds. A peak in the 1s electron binding energy of nitrogen (N) was detected at 397.5 eV (P5 in Figure 3e). Another peak in the 1s electron binding energy of nitrogen (N) was detected at 398.5 eV (P6 in Figure 3e). Note that two peaks are observed at 399.8 eV and 400.5 eV (maximum peak), which are thought to be due to binding with other dopants (e.g., Ba or Ca). The maximum binding energy peak for the 4d electrons of dysprosium (Dy) was detected at 152.4 eV (P7 in Figure 3f). The BaNOx bond energy peak for the 3d electrons of barium (Ba) was detected at 780.2 eV (P8 in Figure 3g), and the BaO bond energy peak was detected at 778.4 eV (P9 in Figure 3g). In particular, the latter peak value was 1.1 times higher than the former peak value. A peak of 346.5 eV (P10 in Figure 3h) representing the 2p electron bond energy of calcium (Ca) was detected. The maximum peak of the 1s electron bond energy of oxygen (O) was detected at 531.4 eV (P11 in Figure 3i). Table 1 shows the weight percentages of each element detected in the XPS analysis of the particles in Example 2 (see Figure 3a).

[0053] [Table 1]

[0054] "XPS analysis of particles in Comparative Example 1" The XPS analysis of the particles from Example 1 is shown below. The spectral diagrams for each element are shown in Figures 4a to 4i. Figure 4a is the spectral diagram obtained by the survey scan, and Figures 4b to 4i are detailed spectral diagrams for each element. The maximum bond energy peak for the 2p electrons of aluminum (Al) was detected at 73 eV (p1 in Figure 4b). A peak to the left of peak P1 (indicating a higher bond energy) is also observed. This is presumed to be an Al-OH bond, and its region is larger than that in Example 1. A single peak representing the 3d electron bonding energy of strontium (Sr) was detected at 133.5 eV (p2 in Figure 4c). Given that there was only one peak, and that its peak value is close to the bonding energy between Sr's 3d electrons and oxygen (133.8 (±0.3) eV), it is presumed that there is almost no bonding between Sr's 3d electrons and nitrogen. The maximum bond energy peak for silicon (Si) 2p electrons was detected at 103.7 eV (p4 in Figure 4d). A peak in the 1s electron bond energy of nitrogen (N) was detected at 396.5 eV (p5 in Figure 4e). Another peak in the 1s electron bond energy of nitrogen (N) was detected at 399.2 eV (p6 in Figure 4e). The maximum peak in the 1s electron bond energy of nitrogen (N) was detected at 401.2 eV, which is thought to be due to bonding with other dopants (e.g., Ba or Ca). The maximum binding energy peak for the 4d electrons of dysprosium (Dy) was detected at 157 eV (p7b in Figure 4f). A peak was also detected at 153.5 eV (p7a in Figure 4f). This is presumed to be due to dysprosium oxide. The BaNOx bond energy peak for the 3d electrons of barium (Ba) was detected at 780.6 eV (Figure 4g, p8), and the BaO bond energy peak was detected at 779.2 eV (Figure 4g, p9). In particular, the latter peak value was 0.75 times that of the former. The bond energy peak of the 2p electrons in calcium (Ca) was detected at 346.5 eV (p10 in Figure 4h). The maximum bond energy peak for the 1s electron of oxygen (O) was detected at 532 eV (p11 in Figure 4i).

[0055] [Consideration] As described above, this analysis revealed that Sr3d electrons are significantly involved in the afterglow emission of the particles. Specifically, for Sr3d electrons, the particles of Examples 1 and 2 showed two peaks in the 130eV-137eV range, including the maximum peak of Sr 3d electrons, indicating the presence of Sr-O and Sr-N. On the other hand, the particles of Comparative Example 1 showed only one peak in the 130eV-137eV range, indicating that almost no Sr-N was detected. Furthermore, the Sr3d electron peak of the particles of Comparative Example 1 was a broader, more bell-shaped peak compared to Examples 1 and 2. This is thought to be because SrOH remained on the surface, preventing sufficient crystallization. Thus, it was found that Sr-N is significantly involved in the afterglow emission of this strontium aluminate compound. Differences were also observed between the examples and comparative examples for Si2p electrons, N1s electrons, Dy4d electrons, and Ba3d electrons. These differences are shown below. Regarding Si2p electrons, the particles in Examples 1 and 2 showed peaks at 101.5 eV to 103 eV, while the particles in Comparative Example 2 showed a slightly shifted peak at 103.7 eV. This is thought to be due to the strong presence of SiO. Regarding N1s electrons, the particles in Examples 1 and 2 showed peaks at 397 eV to 398 eV, while the particles in Comparative Example 2 showed a peak at 396.5 eV. Regarding Dy4d electrons, the particles in Examples 1 and 2 showed a maximum peak around 154 eV. On the other hand, the particles in Comparative Example 2 showed a peak at 154 eV, but also a similar peak at 166 eV. It is presumed that Dy is not doped into strontium aluminate but exists as dysprosium oxide. Regarding Ba3d electrons, in the particles of Examples 1 and 2, the peak attributable to the BaO bond energy (P10) was 1.1 times (more than 0.8 times) greater than the peak attributable to the BaNOx bond energy (P9 in Figures 2g and 3g), while in the comparative example it was 0.75 times greater. It is presumed that the comparative example contains less BaO.

[0056] "Example 3" Porous wet particles (Sasol's AS3 aggregate-improved product) consisting of a mixed oxide of strontium aluminate with an average particle size D50 of 2.5 μm were prepared and added to pure water to a solid content concentration of 35%. Then, the mixture was wet-milled with 50 μm zirconia beads, and the beads were separated to prepare porous core base particles with an average particle size D50 of 0.3 μm (Step 1). These porous substrate particles were added to an ammonium nitrate buffer solution at pH 8.8 to prepare a suspension (step 2). An acidic solution was prepared by mixing 10 g of aluminum phosphate, 85 g of colloidal silica sol from EVERGREEN (Al2O3 / SiO2 molar ratio 0.0010), 70 g of pure water, 30 g of barium nitrate (Ba(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt%) diluted with water, 30 g of calcium nitrate (Ca(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt%) diluted with water, 30 g of zinc nitrate (Zn(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt%) diluted with water, and 30 g of silver nitrate (AgNO3, manufactured by Fujifilm Wako Pure Chemical Industries). Then, an acidic solution was added dropwise to the above suspension so that Ba(NO3)2, Ca(NO3)2, Zn(NO3)2, AgNO3, and silica sol were present in amounts of 5 wt%, 5 wt%, 5 wt%, 3 wt%, and 10 wt% relative to the substrate particles, respectively (third step). Next, steps 4 to 6 of Example 1 are carried out, and the resulting particles are designated as Example 3.

[0057] Figure 5a shows an SEM image of the particles from Example 3. Figure 5b is a magnified view of a part of it. This SEM image shows that the particles in Example 3 are porous. This is thought to be because the crystals of the strontium aluminate compound are granulated (crosslinked) via silver.

[0058] "Example 4" Porous wet particles (Sasol's AS3 aggregate-improved product) consisting of a mixed oxide of strontium aluminate with an average particle size D50 of 2.5 μm were prepared and added to pure water to a solid content concentration of 35%. Then, the mixture was wet-milled with 50 μm zirconia beads, and the beads were separated to prepare porous core base particles with an average particle size D50 of 0.3 μm (Step 1-1). Porous wet particles (Sasol AS2UF) made of a mixed oxide of strontium aluminate with an average particle size D50 of 2.5 μm were prepared and added to pure water to a solid content concentration of 35%. Then, the mixture was wet-milled with 50 μm zirconia beads, and the beads were separated to prepare porous shell base particles with an average particle size D50 of 0.3 μm (Steps 1-2). Next, the substrate particles for the core and the substrate particles for the shell were mixed in a weight ratio of 1:2, and these substrate particles were added to an ammonium nitrate buffer solution at pH 8.8 to prepare a suspension (second step). An acidic solution was prepared by mixing 12 g of aluminum phosphate, 85 g of colloidal silica sol from EVERGREEN (Al2O3 / SiO2 molar ratio 0.0010), 20 g of pure water, 30 g of barium nitrate (Ba(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt%) diluted with water, 30 g of calcium nitrate (Ca(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt%) diluted with water, 30 g of zinc nitrate (Zn(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries) (10 wt%) diluted with water, 3 g of yttrium nitrate (Y(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries), 3 g of cerium nitrate (Ce(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries), and 1 g of terbium nitrate (Tb(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries). Then, an acidic solution was added dropwise to the above suspension so that Ba(NO3)2, Ca(NO3)2, Zn(NO3)2, Y(NO3)3, Ce(NO3)3, and silica sol were present in amounts of 30 wt%, 30 wt%, 30 wt%, 30 wt%, 3 wt%, and 3 wt%, respectively, relative to the substrate particles (third step). Furthermore, we prepared europium nitrate solution (Eu(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries) (5 wt% diluted with water), dysprosium nitrate solution (Dy(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries) (5 wt% diluted with water), and terbium nitrate solution (Tb(NO3)3, manufactured by Fujifilm Wako Pure Chemical Industries) (5 wt% diluted with water). Then, Eu(NO3)3 solution, Dy(NO3)3 solution, and Tb(NO3)3 solution were added dropwise to the suspension at concentrations of 0.5 wt%, 2.0 wt%, and 0.5 wt% relative to the substrate particles, respectively (Step 4). Next, the mixed solution was sprayed to dry the ammonia in an environment below 70°C (step 5). Then, the water was evaporated in that environment (step 6). The particles produced by this process will be designated as Example 4.

[0059] Figure 6a shows an SEM image of the particles from Example 4. This SEM image shows that the particles in Example 4 are even more porous than those in Example 3. This is thought to be because the crystals of the strontium aluminate compound were granulated (crosslinked) via cerulium and terbium. As demonstrated in Examples 3 and 4, it was found that by maintaining the overall afterglow luminescence and making the material porous, it is possible to maintain high particle quality while also reducing weight. [Industrial applicability]

[0060] The strontium compound of the present invention is a novel compound with afterglow emission properties, and can be used as afterglow emission particles in lighting, displays, sensors, photoelectric elements, stress emission materials, etc., and can also be applied to biomedical fields.

Claims

1. A strontium aluminate compound having residual luminescence, doped with at least europium, silicon, and nitrogen, In the XPS spectrum, The maximum peak of the 2p electron bonding energy of aluminum is in the range of 70 eV to 75 eV. It has two peaks in the range of 130 eV to 137 eV, including the peak with the maximum binding energy of strontium's 3d electrons. The silicon has a maximum peak bond energy of 2p electrons in the range of 10¹ eV to 10⁵ eV. Strontium aluminumate compound.

2. It is doped with dysprosium. The maximum binding energy peak attributed to the 4d electrons of the dysprosium is in the range of 150 eV to 155 eV. The strontium aluminate compound according to claim 1.

3. The silicon has a maximum peak bond energy of 2p electrons in the range of 101.5 eV to 102.5 eV. The strontium aluminate compound according to claim 1.

4. The nitrogen atom has a bond energy peak of 395 eV to 398 eV. The strontium aluminate compound according to claim 1.

5. Afterglow-emitting luminescent particles comprising crystals of the strontium aluminate compound according to claims 1 to 4.

6. The afterglow-emitting particle according to claim 5, which is porous.

7. A step of preparing substrate particles containing strontium aluminate, A step of preparing a suspension by adding the base particles to an alkaline solution containing ammonium ions, The step of adding an acidic solution containing aluminum ions, silicate ions, and nitrate ions to the suspension, The step of adding europium nitrate to the suspension, The process of evaporating ammonia, Furthermore, the process includes a step of evaporating the moisture. A method for producing afterglow-emitting particles.

8. The acidic solution contains at least one selected from barium nitrate, calcium nitrate, and zinc nitrate. A method for producing afterglow-emitting particles according to claim 7.

9. A method for producing afterglow-emitting particles according to claim 8, wherein the acidic solution comprises at least one selected from silver nitrate, cerium nitrate, yttrium nitrate, and terbium nitrate.

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