RU2711318C2 - Method of producing luminescent ceramics based on complex oxides with garnet structure - Google Patents

Abstract

FIELD: medicine.SUBSTANCE: invention relates to methods of producing ceramic luminescent and scintillation materials. Such materials are used as scintillators for X-ray computed tomography systems, inspection equipment, and so forth, as well as luminophors for solid-state lighting systems. Disclosed method enables to obtain nanostructured powders and luminescent ceramics based thereon, containing simultaneously Gd, Ga, Ce, Al and optionally Y. Method includes the following sequential steps: preparation of aqueous solutions of salts of initial components with accurately known concentrations, combining said solutions in the required amount to provide the required composition of the components, preparing the precipitation solution, adding the solutions of the initial components to the precipitation solution, sediment separation, drying, thermal treatment at temperature 800–1000 °C, compaction and sintering at temperature of not less than 1500 °C. For compliance with stoichiometry, solutions of initial components are divided into 2 or more groups and deposited separately, wherein amount of precipitator is selected so as to ensure most complete deposition of components in group. Gadolinium and gallium enter into different groups. Obtained precipitation is mixed, combined drying is carried out, and then - thermal treatment of obtained product and all subsequent stages.EFFECT: technical result of invention is possibility of obtaining luminescent ceramics based on complex oxides with garnet structure of exactly specified composition.1 cl, 2 ex, 9 dwg

Description

The invention relates to methods for ceramic luminescent and scintillation materials. Such materials are used as scintillators for X-ray computed tomography systems, inspection equipment, etc., as well as phosphors for solid-state lighting systems.

Luminescent ceramics are used as scintillation material for medical imaging systems [GE Gemstone. CWvan Eijk, Nuclear Instr. Meth. Phys. Res. A, 509 (1) (2003), 17-25] and as a phosphor for LED lighting systems [Philips Lumiramics. S. Nishiura, S. Tanabe, K. Fujioka, Y. Fujimoto, Opt. Mater., 2011, 33, 688.]. One of the most promising families of compositions of these materials are complex oxides based on Gd, Ga, Al and other elements, which are considered for use as scintillators [ZM Seeley, NJ Cherepy, SA Payne. J. Cryst. Growth 379 (2013) 79-83. K. Kamada, T. Yanagida, J. Pejchal, M. Nikl, T. Endo, K. Tsutumi, Y. Fujimoto, A. Fukabori, A. Yoshikawa. J. Phys. D 44 (50) (2011), 505104.] and phosphors [S. Nishiura, S. Tanabe, K. Fujioka, Y. Fujimoto. Proc. of SPIE Vol. 7934, 2011, 793404-1-6. J. Ueda, K. Kuroishi, S. Tanabe. Applied Physics Express 7 (2014) 062201-1-3]. The scintillation characteristics of compounds from this family significantly depend on composition variations [K. Kamada, S. Kurosawa, P. Prusa, M. Nikl, VV Kochurikhin, T. Endo, K. Tsutumi, H. Sato, Y. Yokota, K. Sugiyama, A. Yoshikawa. Cz grown 2-in. size Ce: Gd ₃ (Al, Ga) ₅ O ₁₂ single crystal; relationship between Al, Ga site occupancy and scintillation properties. Optical Materials (2014) 36 (12), 1942-1945. Dosovitskiy, G., Fedorov, A., Mechinsky, V., Borisevich, A., Dosovitskiy, A., Tret'jak, E., & Korjik, M. (2017, February). Persistent luminescence in powdered and ceramic polycrystalline Gd ₃ Al ₂ Ga ₃ O ₁₂ : Ce. In IOP Conference Series: Materials Science and Engineering (Vol. 169, No. 1, p. 012014). IOP Publishing]. Thus, to develop and produce scintillation materials based on complex oxides with a garnet structure, a method is needed that allows one to obtain a material with a precisely specified composition.

A known method of producing ceramics based on a complex oxide of Gd, Ga, Al, activated by Ce, using solid-phase synthesis from the initial nanoscale powders of individual oxides [Chen, X., Qin, H., Zhang, Y., Luo, Z., Jiang, J., Jiang, H. J. Am. Ceram. Soc. 98 (8), 2015, 2352-2356. Chen, X., Qin, H., Wang, X., Yang, C, Jiang, J., Jiang, H. J. Eur. Ceram. Soc. 36 (10), 2016, 2587-2591. US 8,815,122 B2]. For the implementation of this method, initial powders that meet high requirements for microstructure and / or long-term grinding of components for their grinding and homogenization are required. This process, as well as the use of sintering additives, is an undesirable technique, since it can lead to contamination of the initial powder, which, in turn, will cause a deterioration in the luminescent and scintillation characteristics of the materials obtained.

Also known is a method for producing ceramics based on a complex oxide of Gd, Y, Ga, Al, activated by Ce from powders synthesized by aerosol pyrolysis [Z.M. Seeley, N.J. Cherepy, S.A. Payne J. Cryst. Growth 379 (2013) 79-83]. This method allows to obtain powders of a given composition and weakly agglomerated, but uses organometallic precursors and is expensive in industrial implementation.

The method of coprecipitation from aqueous solutions of salts of the components of the obtained material is scalable, uses standard technological equipment and technological processes, and allows one to obtain powders of sufficient quality to obtain transparent ceramics, up to laser.

A known method of producing nanostructured powders of a complex oxide with a garnet structure based on Y, Ga, Al, activated by Ce [RU 2503754, C30B 29/28, 2014], which uses the deposition method, which is carried out by introducing into an aqueous solution of ammonium bicarbonate used in as a precipitant, a mixed aqueous solution of nitric salts of aluminum, yttrium and cerium, with the addition of fluorine in an amount of 1-5%. In this case, the precipitation is carried out with stirring of the reaction mass at a speed of 300-500 rpm./min., The precipitated product is isolated, washed with water, dried and calcined. Precipitation is carried out, preferably, with a 2 molar aqueous solution of ammonium bicarbonate. As the initial solution of a joint aqueous solution of nitric salts of aluminum, yttrium and alloying elements, it is preferable to use a solution with a total concentration of metal ions of 1 mol / L. In this case, a mixed solution of cations is added preferably at a rate of 60 ml / min.

A known method of producing a nanostructured powder of a complex oxide with a garnet structure based on Y, Al, activated by Ce, based on the known precipitation method [G.A. Dosovitsky, D.E. Kuznetsova, P.A. Volkov, K.S. Napolsky, I.V. Roslyakov, Yu.A. Velikodny, S.N. Mudretsova, K. B. Bogatov, A.L. Mikhlin, A.E. Dosovitsky. High Technologies (ISSN 1999-8465), vol. 14, No. 3, 2013, S. 48-52.] This method includes the following successive stages of the process: preparing aqueous solutions of salts of the starting components with predetermined concentrations, mixing these solutions and preparing a general mixed solution, preparation of a precipitating solution, pouring solutions of the starting components into a precipitating solution, separating the precipitate, drying, heat treatment at a temperature of 700-1100 ° C.

However, if this method is used to obtain a nanostructured powder of a complex oxide with a garnet structure based on activated Ce, as shown by mass spectral analysis of the washings and solutions, incomplete precipitation and entry of Ga and / or Gd into the product occurs, and when using a different excess of precipitant incomplete precipitation of these components occurs, due to their chemical nature [B.V. Nekrasov. Fundamentals of General Chemistry. Volume 2, M .: Ed. "Chemistry", 1973].

The closest analogue of the claimed invention in terms of essential features is a method for producing a luminescent ceramic material with a garnet structure, containing Gd, Ga, Ce, Al, D, of the general formula: (Gd _1-z , Ce _z ) _{3 + u} (Ga _1-mn , Al _m , D _n ) _5-u O ₁₂ , which includes the following stages: preparation of aqueous solutions of salts of the starting components, mixing in predetermined proportions, adding a precipitating solution (ammonium carbonate or bicarbonate), separating the precipitate, drying, compacting and sintering to obtain ceramic material (US 9145517, C 09K 11/80, 2015).

The aim of the creation of the claimed invention is the possibility of obtaining luminescent ceramics of a given composition based on complex oxides with a garnet structure containing simultaneously Gd, Ga, Ce, Al, as well as one or more additional elements.

To this end, a method is proposed for producing luminescent ceramics based on complex oxides with a garnet structure containing Gd, Ga, Ce, Al, carried out in a multi-stage method, including the initial stage of preparing aqueous solutions of salts of the starting elements, mixing them in predetermined proportions, and then adding them to the solution ammonium bicarbonate, separation of precipitated precipitate, drying, heat treatment, compaction and sintering to obtain ceramic material, and precipitation is obtained by infusion of solutions of the starting components nentes into the precipitator solution, and solutions containing various components are poured in different groups, not less than two, selecting the amount of precipitant in such a way as to ensure the most complete precipitation of the components included in the group, while Gd and Ga enter into different groups, then spend mixing all the precipitates, their joint drying, and then heat treatment at a temperature of 800-1000 ° C and sintering at a temperature above 1500 ° C.

The combination of the above essential features makes it possible to obtain a nanostructured powder by the method of deposition from an aqueous solution of a precisely specified composition from which a high-density luminescent ceramic can be obtained.

It is important that precipitates are formed by an extremely close production method - the method of co-precipitation with ammonium hydrogen carbonate, and only the conditions for the deposition are different, namely, the excess precipitant used to carry out the deposition; this ensures their similar chemical nature of precipitation. The precipitation mixes in the wet state, thus, already at the drying stage, the precipitation forms mixed aggregates, all of whose components are in the form of reactive salts, which facilitates the interaction of the components.

Brief Description of the Drawings

In FIG. Figure 1 shows the dependences of the residual content of gallium and gadolinium salts in the mother liquor on the excess of ammonium bicarbonate used in the deposition.

In FIG. 2 shows an image of a powder of the composition Gd _2.97 Ce _0.03 Al ₂ Ga ₃ O ₁₂ obtained in accordance with Example 1, obtained by scanning electron microscopy.

In FIG. 3 shows an image of a ceramic composition Gd _2.97 Ce _0.03 Al ₂ Ga ₃ O ₁₂ obtained in accordance with Example 1, obtained by scanning electron microscopy.

In FIG. 4 shows the photoluminescence spectrum of ceramics of the composition Gd _2.97 Ce _0.03 Al ₂ Ga ₃ O ₁₂ obtained in accordance with Example 1.

In FIG. 5 shows the amplitude spectra recorded upon excitation by an alpha-particle source of a reference sample — a single crystal of yttrium aluminum garnet activated by cerium (1) and ceramics of the composition Gd _2.97 Ce _0.03 Al ₂ Ga ₃ O ₁₂ obtained in accordance with Example 1 (2) .

In FIG. 6 presents the images of precipitation of compounds Gd + Ce, Y, Ga, Al obtained in accordance with Example 2, obtained by scanning electron microscopy. 1 - precipitate obtained from nitric solution of aluminum; 2 - precipitate obtained from a nitric acid solution of yttrium; 3 - precipitate obtained from gallium nitrate solution; 4 - precipitate obtained from a nitric acid solution of gadolinium and cerium.

In FIG. 7 shows an image of a ceramic composition Gd _1.485 Y _1.485 Ce _0.03 Al _2.5 Ga _2.5 O ₁₂ obtained in accordance with Example 2, obtained by scanning electron microscopy.

In FIG. 8 shows the photoluminescence spectrum of ceramics of the composition Gd _1.485 Y _1.485 Ce _0.03 Al _2.5 Ga _2.5 O ₁₂ obtained in accordance with Example 2.

In FIG. 9 shows the amplitude spectra recorded upon excitation by an alpha-particle source of a reference sample — a yttrium aluminum garnet single crystal activated by cerium (1) and ceramics of the composition Gd _1.485 Y _1.485 Ce _0.03 Al _2.5 Ga _2.5 O ₁₂ obtained in accordance with Example 2 (2).

The implementation and examples of the invention

A method for producing luminescent ceramics based on it of complex oxides with a garnet structure of a precisely defined composition includes the following operations:

1) Preparation of aqueous solutions of salts of the starting components with precisely known concentrations. The starting components include Gd, Ga, Ce, as well as one or more elements, such as lanthanides (La-Lu), Sc, Al, etc. Solutions can be prepared by dissolving salts with water, preferably nitrates, or oxides in acid, preferably in nitric acid. The concentration of solutions can be determined by any known method, for example, gravimetry, titration, dissolution of a known sample.

2) Taking these solutions in the required amount to ensure the required composition of the components when combining these solutions.

3) Preparation of a precipitant solution, preferably ammonium bicarbonate NH ₄ HCO ₃ with a concentration of at least 10%.

4) Pouring solutions of the starting components into the precipitator solution, and solutions containing various components are poured in different groups, not less than two, so that for each group conditions are realized that provide the most complete precipitation of the components included in the group.

5) Separation of precipitates by any suitable method, for example, filtration, and their washing.

6) Mixing precipitation in any suitable way, for example, in a ball mill.

7) Drying the resulting mixture.

8) Heat treatment at a temperature of 800-100 ° C.

9) Optionally - grinding the powder in any suitable way, for example, in a ball, planetary ball or bead mill.

10) Compaction by any known method, for example, uniaxial pressing, isostatic pressing, slip casting, filter pressing, injection casting, tape casting, gel casting, robocasting, stereolithography.

11) Sintering of compacts at a temperature of at least 1500 ° C.

The inventive method is illustrated by the following examples:

Example 1

Nitric acid solutions of aluminum, gallium, gadolinium, cerium are prepared with concentrations of 1 mol / L according to the cation content. The concentration of the solutions is specified by gravimetric analysis. Then, the necessary quantities of solutions of the components are selected, in amounts that ensure the total composition corresponding to the formula Gd _2.97 Ce _0.03 Al ₂ Ga ₃ O ₁₂ , and with a calculated product weight of 20 g. The required amounts of elements are: Gd - 10.08 g , Ce - 0.09 g, Al - 1.17 g, Ga - 4.52 g (calculated amount of elements in grams per element). The required quantities of solutions are selected based on their actual concentration. Then a mixed solution is prepared by mixing the nitric acid solutions of Gd, Ce, Al and the nitric solution of Ga is left separately.

In a glass beaker placed an aqueous solution of ammonium bicarbonate with a concentration of 15 wt. % in the amount corresponding to an excess of 15% in excess of the stoichiometric amount (185 ml). With constant stirring, a mixed solution containing Gd, Ce, Al is poured into it with a thin stream. The precipitate is filtered off and washed on the filter with water and isopropanol. Then in a glass beaker placed an aqueous solution of ammonium bicarbonate with a concentration of 15 weight. % in the amount corresponding to an excess of 30% in excess of the stoichiometric amount (125 ml). With constant stirring, a solution containing Ga is poured into it with a thin stream. The precipitate was also filtered off and washed on the filter with water and isopropanol.

Filtered and washed precipitates are placed in a ball mill drum and ground for 30 minutes. The resulting pulp is loaded into a quartz crucible and placed in an oven. Drying is carried out at a temperature of 100 ° C for 8 hours, mixing the contents of the crucible every hour. The dried product is ground in an agate mortar and sieved through a mesh of polyamide yarns with a mesh size of 100 μm. The crucible with the product is loaded into the furnace and heat treatment is carried out at 850 ° C for 2 hours after the furnace enters the mode. In FIG. 2 shows an image of the obtained powder.

The resulting powder is compacted by uniaxial pressing into tablets with a diameter of 30 mm and a thickness of 2 mm at a pressure of 4 tons. Then, these tablets are sintered at a temperature of 1600 ° C in air. The result is a ceramic sample with a density of 98%, a photoluminescence band with a maximum of 530 nm and a scintillation optical output of more than 35,000 photons / MeV. In FIG. 3 shows the image of the chips obtained ceramics. In FIG. Figure 4 shows the photoluminescence spectrum of the resulting ceramic. In FIG. 5 shows the amplitude spectrum of the obtained ceramics. The light output of ceramics can be estimated at 38,000 photons / MeV.

Example 2

Prepare nitric acid solutions of aluminum, gallium, gadolinium, yttrium, cerium with concentrations of 1 mol / l according to the cation content. The concentration of the solutions is specified by gravimetric analysis. Then, the necessary quantities of solutions of the components are selected, in amounts that provide a total composition corresponding to the formula Gd _1.485 Y _1.485 Ce _0.03 Al _2.5 Ga _2.5 O ₁₂ , and with a calculated product weight of 24 g. The required amounts of elements are: Gd - 7.08 g, Y - 4.0 g, Ce - 0.13 g, Al - 2.05 g, Ga - 5.29 g. The required quantities of solutions are selected based on their actual concentration.

In a glass beaker placed an aqueous solution of ammonium bicarbonate with a concentration of 15 wt. % With constant stirring, a nitric acid solution of one of the components, Gd + Ce, Y, Ga, Al, is poured into it with a thin stream. The precipitate is filtered off and washed on the filter with water and isopropanol. The following amounts and excesses of precipitant are used for precipitation: Gd + Ce - 78 ml, excess 15%; Y - 90 ml, excess 30%; Ga - 144 ml, an excess of 30%; Al - 128 ml, excess 15%. In FIG. 6 shows images of precipitation.

Filtered and washed precipitates are placed in a ball mill drum and ground for 30 minutes. The resulting pulp is loaded into a quartz crucible and placed in an oven. Drying is carried out at a temperature of 100 ° C for 8 hours, mixing the contents of the crucible every hour. The dried product is ground in an agate mortar and sieved through a mesh of polyamide yarns with a mesh size of 100 μm. The crucible with the product is loaded into the furnace and heat treatment is carried out at 850 ° C for 2 hours after the furnace enters the mode.

The resulting powder is compacted by uniaxial pressing into tablets with a diameter of 30 mm and a thickness of 2 mm at a pressure of 4 tons. Then, these tablets are sintered at a temperature of 1600 ° C in air. The result is a ceramic sample with a density of 98%, a photoluminescence band with a maximum of 530 nm and a scintillation optical output of more than 40,000 photons / MeV. In FIG. 7 shows the image of the chips obtained ceramics. In FIG. Figure 8 shows the photoluminescence spectrum of the resulting ceramic. In FIG. 9 shows the amplitude spectrum of the obtained ceramics. The light output of ceramics can be estimated at 63,000 photons / MeV.

Thus, the inventive method allows to obtain luminescent ceramics containing simultaneously Gd, Ga, Ce and other elements, avoiding the loss of one or more of these elements, leading to a violation of the composition.

Claims (1)

A method for producing luminescent ceramics based on complex oxides with a garnet structure containing Gd, Ga, Ce, Al, carried out by a multistage method, including the initial stage of the preparation of aqueous solutions of salts of the starting elements, mixing them in predetermined proportions, and then adding them to a solution of ammonium bicarbonate, separation of the precipitate, drying, heat treatment, compacting and sintering to obtain a ceramic material, characterized in that precipitates are obtained by pouring solutions of the starting components in the precipitator solution, and solutions containing various components are poured into various groups of not less than two, selecting the amount of precipitant in such a way as to ensure the most complete precipitation of the components included in the group, while Gd and Ga enter into different groups, then mix all precipitation, their joint drying, and then heat treatment at a temperature of 800-1000 ° C and sintering at a temperature above 1500 ° C.

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