Lithography-based method for producing a transparent ceramic body having at least two regions of different composition and the transparent ceramic body thus obtained

Abstract

1. A method for producing a transparent ceramic body having at least two regions with different garnet compositions, in particular one of the regions being YAlO 12 The present invention is particularly useful for producing transparent ceramic bodies having a predetermined complex shape and / or a controlled complex distribution of doping ions.

Description

[Technical Field]

[0001] The present invention relates to methods for producing ceramic-based transparent materials with variable three-dimensional (3D) composition and complex shapes, and the present invention also relates to doped transparent ceramics used in laser gain media, scintillators and lighting. [Background technology]

[0002] technical level Materials requiring transparency, particularly but not exclusively in optical applications, have traditionally been based on glass or single crystals. While the former can be easily shaped and produced in large dimensions, their thermal and thermomechanical properties are not sufficient for high performance. While single crystals have favorable properties, they are limited in shape and size, and most require post-processing with significant amounts of scrap. Furthermore, some materials or compositions, such as those with high dopant concentrations, cannot be produced by the melt-growth method used to produce single crystals.

[0003] Transparent ceramics offer the advantages of various forming techniques and possibilities while maintaining the good performance of single crystals. These materials can be more cost-effective compared to their single crystal counterparts because they do not require the slow solidification from the melt required to provide large transparent boules that must be cut to the desired shape. Furthermore, ceramic techniques require lower process temperatures compared to traditional crystal growth methods.

[0004] Applications for transparent ceramics include solid state laser gain media, scintillators, phosphors, lighting, armor, protective windows and domes.

[0005] Among functional transparent ceramics, the most important and most commonly used are the so-called garnets, with the general formula A3B5O xwhere A and B are different metals, or A and / or B represent a mixture of metals. The most widely used garnet is YAlO 12 and is commonly referred to in the art as yttrium aluminum garnet, or its abbreviation YAG. Due to the technical relevance of YAG, the remainder of this specification will primarily refer to this material, although the present invention is generally applicable to any transparent ceramic garnet.

[0006] YAG may be doped with specific transition metal or rare earth ions to adjust and fine-tune its properties in view of the intended application.

[0007] The paper "Fabrication and Optical Properties of High-Performance Polycrystalline Nd:YAG Ceramics for Solid-State Lasers," A. Ikesue et al., Journal of the American Ceramic Society, 78 (1995) 1033-1040, describes the fabrication of a transparent ceramic neodymium-doped YAG of sufficient quality to enable lasing. The fabrication process in this paper uses a mixture of oxide powders as the starting material.

[0008] Another approach to the production of doped YAG is presented in the paper "Co-precipitation synthesis route to yttrium aluminum garnet (YAG) transparent ceramics," J. Li et al., Journal of the European Ceramic Society, 32 (2012) 2971-2979. In this method, YAG powder is prepared by precipitation and then densified into a transparent YAG ceramic, typically by vacuum sintering.

[0009] Sintering additives are preferably used to help eliminate porosity. Sometimes, vacuum sintering is combined with hot isostatic pressing, as reported, for example, in the article "Hot Isostatic Pressing of Transparent Nd:YAG Ceramics," SH. Lee et al., Journal of the American Ceramic Society, 92 (2009) 1456-1463.

[0010] For uniform dopant distribution and simple geometries of the manufactured parts, forming methods such as pressing ("Fabrication and Characterization of Yb-Doped YAG Ceramics", J. Hostasha et al., Optical Materials, 2013, 35, 798-803), tape casting (the paper by Lee et al. cited above), or slip casting ("Aqueous Slip Casting of Transparent Yttrium Aluminum Garnet (YAG) Ceramics", K.A. Appiagyei et al., Ceramics International, 2008, 34, 1309-1313) have been tested and successfully achieved good results for the production of transparent YAG ceramics.

[0011] However, with recent developments in optical and photonic technologies, in addition to the traditional uniformly doped YAG-based components, composite structures with, for example, edge cladding or waveguides are required, where functional modifications of dopant concentration are used for light guiding or thermal management.

[0012] In some cases, such structures may be prepared by using diffusion bonding to bond carefully cut and polished single crystal optical components (technique disclosed in U.S. Pat. No. 5,441,803). However, this technique requires prior preparation of the crystals to be bonded and does not allow the production of optical components with compositions that vary in the micrometer range.

[0013] Alternatively, structures with various dopant profiles are more easily produced by advanced ceramic techniques, where the material structure is shaped in the green stage before full densification, and no further bonding is required after the sintering process.

[0014] A variety of techniques are available for this purpose.

[0015] The first possible technique is tape casting. In this well-known technique, a slurry consisting of powders of the desired inorganic material, a solvent, and a binder (and possibly additional components, such as sintering aids) is deposited on a support, and the solvent is then evaporated to obtain a consolidated tape of binder that embeds the inorganic powder. This tape has sufficient mechanical strength to be removed from the support and handled. Portions of the tape prepared with different compositions can be stacked, pressed, and subjected to a heat treatment to remove the organic components and consolidate the layers of the different inorganic powders. Examples of the application of this technique to the production of ceramic bodies with various dopant concentrations are provided, for example, in the article "Transparent layered YAG ceramics with structured Yb doping produced via tape casting", J. Hostasha et al., Optical Materials, 65 (2017) 21-27, and in the article "Fabrication, microstructure and optical properties of large Nd:YAG and composite Yb:YAG transparent ceramic slabs", S. Yu et al., Ceramics International, 45 (2019) 19340-19344.

[0016] Possible variations of the tape casting technique are "co-casting", as described, for example, in WO 2009 / 038674 A2, in which slurries of different composition are deposited in parallel on a support, and "co-sintering" of ceramic green bodies, as described, for example, in the article "Composite laser ceramics by advanced bonding techniques", A. Ikesue et al., Materials, 11 (2018) 271.

[0017] These ceramic forming methods allow the introduction of layered and gradient doping profiles, but they suffer in part from the low precision of compositional and structural features, and the forming techniques mentioned above still limit the forming possibilities to fairly simple structures, making it extremely difficult to produce even radially graded objects, for example.

[0018] Another possible approach for the production of transparent ceramic bodies is based on 3D printing (also known as additive manufacturing) of slurries of ceramic powders.

[0019] This approach has been followed, for example, in the article "First 3D-printed composite inorganic polycrystalline scintillator," G.A. Dosovitskiy et al., CrystEngComm, vol. 19, 30 (2017) 4260-4264, in the article "3D-printed ceramic phosphors and their photoluminescence properties under blue laser excitation," S. Hu et al., Journal of the European Ceramic Society, vol. 39, 8 (2019) 2731-2738, and in Chinese Patent Application Publication No. 108530070 A. In these documents, 3D printing is used to produce doped ceramic objects with a uniform composition, i.e., the distribution of dopants does not vary in any direction within the object.

[0020] In WO 2017 / 218895 A1, 3D printing is used to produce YAG-based transparent ceramics for the fabrication of laser gain media. The method described here uses synthesized YAG powder and is tested to produce components with doped and undoped one-dimensional profiles.

[0021] Finally, CN109761608A describes a 3D printing method for producing composite (doped) transparent cylindrical ceramic bodies with a two-dimensional concentration gradient distribution of doping ion concentration in the radial direction of the body. The method involves preparing two slurries of ceramic powder with different compositions (e.g., a rare-earth-doped ceramic slurry and an undoped ceramic slurry) and loading them into two separate reservoirs; connecting the two reservoirs to a pressure control device and a nozzle placed in the cavity of a direct-write rapid prototyping machine; adjusting the pressure in the two reservoirs using computer-aided software to control the ratio of the two different slurries entering the nozzle cavity, and then layer-by-layer stacking, printing, and molding the different slurries in the radial direction to obtain a rod-shaped intermediate; cold isostatic pressing this intermediate at a pressure in the range of 100–200 MPa (holding time 1–2 min), followed by heat treatment at a temperature in the range of 700–800 °C in an oxygen atmosphere (this heat treatment is referred to in the art as debinding); and finally, subjecting the debinding body to high-temperature vacuum sintering (10 -3 This method involves annealing the sintered body at high temperature (1300 to 1600°C) in an oxygen-containing atmosphere and then precision polishing the sintered body after sintering at 1600 to 1900°C under a pressure of less than 100 Pa to obtain a dense ceramic sintered body.

[0022] However, in our experience, when two slurries of different compositions are deposited simultaneously, cross-contamination of the slurries may occur, which is not a problem in the case of CN109761608A, since the objective of this document is to obtain a graded structure. However, it should be noted that this approach does not allow for the production of components formed by two or more different chemical compositions with a highly defined dopant distribution. Furthermore, contamination between the slurries can also result in the creation of optical defects (the presence of undesirable ions - impurities) that reduce the performance of the material.

[0023] Other problems that may be encountered using prior art methods in preparing transparent ceramic bodies having complex shapes and / or complex dopant distribution profiles are: - partial sintering, which is associated with the presence of starting powders that are not fully reacted or that have reacted but form transitional phases, preventing the achievement of high transparency. Partial sintering also leads to diffuse porosity; - residual pores that act as scattering centers and therefore reduce transparency; - the presence of secondary phases which may act as scattering and / or absorption centers and thus reduce transparency and introduce undesired absorption; - defects at and around interfaces or layers that also act as scattering centers; - selective segregation of ceramic powders in each slurry, which prevents the formation of chemical phases required to obtain the required transparency; - deformation during sintering, which prevents the formation of an object of the required shape and dimensions;

[0024] The commercial exploitation of next-generation optically transparent ceramics is delayed by the lack of industrially suitable manufacturing processes for 3D transparencies.

[0025] The object of the present invention is to provide a method for producing a transparent ceramic body, which method allows full 3D control of the shape and composition of the transparent body, and, in the case of doped materials, the doping ion distribution. Another object of the present invention is to provide a transparent ceramic body obtained by this method. Summary of the Invention

[0026] These objects are achieved by the present invention, which in a first aspect provides a method for producing a transparent ceramic body, comprising the steps of: (a) preparing a first suspension comprising: (1) solvent, (2) Oxide phase A3BO 12+xa mixture of powders of oxides, hydroxides, nitrates or chlorides of metals in the stoichiometric ratio required to produce: (3) a sintering aid selected from powdered silicon oxide, tetraalkyl orthosilicate, calcium oxide powder, calcium oxide precursor, magnesium oxide powder, magnesium oxide precursor, and mixtures thereof; and (4) a dispersant selected from polyethylene glycol, menhaden fish oil, phosphate esters, dicarboxylic acids, stearic acid, and silanes; (b) removing the solvent from the suspension of step (a) to obtain a mixture; (c) preparing a homogeneous slurry comprising the mixture of step (b) and a photocurable resin; (d) preparing a second suspension comprising at least: (1') a solvent, (2') Oxide phase A3BO 12+x a mixture of powders of oxides, hydroxides, nitrates or chlorides of metals in the stoichiometric ratio required to produce: (3') a sintering aid selected from powdered silicon oxide, tetraalkyl orthosilicate, calcium oxide powder, calcium oxide precursor, magnesium oxide powder, magnesium oxide precursor, and mixtures thereof; and (4') a dispersant selected from polyethylene glycol, menhaden fish oil, phosphate esters, dicarboxylic acids, stearic acid, and silanes; wherein at least one second suspension has a different composition than the first suspension; (e) removing the solvent from the suspension of step (d) to obtain a mixture; (f) preparing a homogeneous slurry comprising the mixture of step (e) and a photocurable resin; (g) forming a deposit comprising layers of the slurries of steps (c) and (f) by a layer-by-layer 3D printing technique, operating at a temperature between 20 and 30°C, to obtain a consolidated body, wherein after the deposition of each layer of slurry, a photopolymerization operation of a photocurable resin is carried out, and a washing operation is carried out to remove the non-polymerized slurry of the first composition after the successive photopolymerized layers of the first composition before depositing a layer of slurry of a second composition thereon or adjacent thereto; (h) heat treating the solidified body of step (g) in air or an oxygen-rich atmosphere at a temperature in the range of 100 to 1000°C to remove organic and volatile components of the solidified body, thereby obtaining a degreased body; and (i) sintering the degreased body of step (h) in a vacuum at a temperature ranging from 1600°C to 1900°C for a time ranging from 6 hours to 32 hours to obtain a sintered body; or (i') sintering heat treatment of the degreased body of step (h) in vacuum at a temperature in the range of 1400°C to 1800°C for a time in the range of 2 hours to 20 hours, followed by hot isostatic pressing at a temperature in the range of 1400°C to 1800°C under an applied pressure in the range of 100 to 300 bar for a time in the range of 1 hour to 4 hours to obtain a sintered body.

[0027] The method of the present invention may further include an optional step (j) of annealing the sintered body obtained in step (i) or step (i') in an oxidizing or reducing atmosphere to adjust the oxidation state of the dopant.

[0028] In a second aspect, the present invention relates to transparent ceramic materials obtained by the above method, and to optical devices based on these materials. [Brief explanation of the drawings]

[0029] [Figure 1]FIG. 1 shows a schematic representation of a first possible ceramic transparent body of the invention, which is made up of two parts of materials of different chemical composition. [Figure 2] FIG. 2 shows a second possible ceramic transparent body of the present invention, which is composed of a region of a first chemical composition partially embedded in a region of a second chemical composition. [Figure 3-6] 3-6 show further possible ceramic transparent bodies of the present invention having complex 3D structures. DETAILED DESCRIPTION OF THE INVENTION

[0030] The inventors have confirmed that although methods for producing transparent ceramic bodies are generally known in the art, but are also based on 3D printing techniques, only the combination of conditions and steps of the method of the present invention makes it possible to obtain complete control of the composition profile of the final transparent ceramic body in three spatial directions, and in particular the deposition of the layers at temperatures between 20 and 30 °C, the use of dispersants, and the washing of any layers after photopolymerization are essential to obtain the desired result.

[0031] The present invention will now be described with reference to the drawings.

[0032] In a first aspect, the present invention relates to a method for producing a transparent ceramic body having a predetermined complex shape and / or a controlled complex distribution of doping ions.

[0033] For purposes of the present invention, the compounds used in the method must be highly pure, for example, the oxides, hydroxides or nitrates described below must have a purity of at least 99%, preferably greater than 99.99%.

[0034] For simplicity, the method is described below with respect to the preparation and use of two different slurries, although it will be apparent to one skilled in the art that the steps of the method can also be carried out using three or more slurries to obtain transparent ceramic bodies with more complex compositional profiles.

[0035] The method comprises steps (a) through (i) or (i'), or steps (a) through (j), as described in detail below.

[0036] The first step of the method, step (a), consists of preparing a homogeneous slurry of (1) a solvent, (2) a mixture of powders of precursors of the desired garnet phase, (3) one or more sintering aids, and (4) a dispersing agent.

[0037] The solvent (1) can be selected from alcohols such as ethanol or isopropanol, and the weight of the solvent is usually 1.5 to 2.5 times, preferably about 2 times, the weight of the powder mixture (2).

[0038] Component (2) is the desired oxide phase A3B5O 12+x The powders consist of a mixture of metal oxides, hydroxides, nitrates, or chlorides in the exact stoichiometric ratio required to produce ##STR1## where A, B, and x have the meanings given above. These powders must have an average particle size of less than 10 μm, preferably less than 5 μm, and the shape of the powder particles must be essentially or nearly spherical with an aspect ratio of 0.8 to 1.0.

[0039] These powders are generally commercially available from a number of suppliers; for example, rare earth oxides are sold by Alfa-Aesar (USA) and Merck (Germany).

[0040] The more common oxidation state for rare earth elements is +3, but +2 (e.g., Sm 2+ ,EU 2+ or Yb 2+ ) or +4 (e.g., Ce 4+) oxidation states are possible; similarly, the metals Sc, Fe, and Cr can exist in the +3 oxidation state, but may also exist in other oxidation states. The parameter x, which can vary between -0.1 and 0.1, accounts for variability in oxygen stoichiometry due to the presence of ionic materials with oxidation states different from +3; x is positive if the oxidation states of the ions of metals A and B are, on average, >3 and negative if the oxidation states of the metals are, on average, <3. Given the formula for a particular desired composition, calculating the amounts of different oxides, hydroxides, nitrates, or chlorides to be used in preparing the mixture of step (a) is straightforward for the average chemist.

[0041] The sintering aid (3) is selected from silicon oxide (SiO2, commonly referred to as silica) powder, tetraalkyl orthosilicate (general formula Si(OR)4, where R is typically a C1-C4 alkyl), calcium oxide powder, calcium oxide precursor, magnesium oxide powder, magnesium oxide precursor, or mixtures thereof. This component makes sintering in step (i) or (i') easier and more efficient. If the component used as a sintering aid is or contains a powdered compound, it must have a particle size of less than 2 μm, preferably less than 1 μm. A useful form of silicon oxide is colloidal silica, a suspension of silica powder consisting of aggregates of nanometer-sized silica particles. When used as an oxide, the sintering aid component is added in a weight range of 0.0005 to 0.003 g per gram of the garnet phase precursor mixture (2).

[0042] Finally, the dispersant (4) is selected from polyethylene glycol, menhaden fish oil, phosphate esters, dicarboxylic acids, stearic acid, and silanes. Polyethylene glycol is commonly referred to as PEG. Menhaden fish oil, hereinafter also referred to by the abbreviation MFO, is preferably blown (i.e., treated by blowing air through it to cause partial oxidation of its unsaturated bonds).

[0043] All of these materials are commercially available. The molecular weight of PEG useful for the purposes of the present invention is 200-600 Da. The amount of dispersing agent is 0.5-5 wt. % of the suspension in step (a), preferably 1.5-2.5 wt. %.

[0044] Components (1), (2), (3) and (4) can be homogenized by any mixing method to obtain a homogenous suspension.

[0045] Step (b) of the process of the present invention consists in removing the solvent from the suspension prepared in step (a), which may be carried out by any method to obtain a wet mixture.

[0046] Step (c) of the method of the present invention comprises preparing a homogeneous slurry of the mixture obtained in step (b) with a photocurable resin.

[0047] Photocurable resins are widely known and extremely common, particularly in the fields of semiconductor and microelectromechanical system (MEMS) manufacturing, and are sold by many suppliers. A suitable photocurable resin useful for the purposes of the present invention is, for example, a mixture of 1,6-hexanediol diacrylate, acrylated oligoamine, benzyl alcohol, camphorquinone, and ethyl 4-(dimethylamino)benzoate. The slurry can be homogenized using any mixing method. The total amount of photocurable resin is 50-60% by volume of the slurry.

[0048] Steps (d)-(f) of the method of the present invention involve preparing a second homogeneous slurry. The components of this slurry, as well as their weight or volume ratios, are the same as those of the slurries prepared in steps (a)-(c), except that the specific compositions of the first and second slurries used to produce the ceramic body must differ. The total amounts of photocurable resin in the two slurries must not differ by more than 3% by volume, so that the difference in linear shrinkage between printed parts using them is less than 3%.

[0049] If more than two slurries are prepared and used, these last conditions must be observed for all slurries, i.e., they all have different compositions and the total amount of resin should not differ by more than 3% by volume between any pair of resins used.

[0050] In step (g), the slurries prepared in steps (c) and (f) are used to deposit first and second layers of slurry according to a pre-determined deposition and pattern time sequence, followed by washing before any change in the slurry, to form a deposit of the desired configuration by 3D printing. Each step of the layer deposition must be performed at a temperature in the range of 20-30°C; the inventors have confirmed that temperatures higher than 30°C result in selective precipitation of oxides in the printed layer, while temperatures below 20°C make it difficult to distribute and spread the slurry.

[0051] For the purposes of this invention, the preferred technique is lithography-based ceramic manufacturing (LCM), a variant of stereolithography. In this technique, thin layers of the first and second slurries prepared in steps (c) and (f) are first deposited on a substrate (a sample holder) and then on top of an already consolidated layer in a subsequent step. Each deposited layer typically has a thickness of approximately 10–100 μm and is deposited according to a predefined geometric shape defined by a CAD design. The layers are then consolidated by light irradiation using an appropriate physical or digital mask.

[0052] The LCM method can be described as follows: A strong LED with a defined light spectrum exposes a mirror array (Digital Mirror Device - DMD). The DMD either partially transmits the light (individual mirrors in position 1) or transmits it to an absorbing field (individual mirrors in position 0). The transmitted light is projected through a lens in a pixel pattern (exposure field) onto a vat containing a slurry. This selective exposure of the photosensitive material causes the material to harden in the exposed areas by photopolymerization. In this method, a photocurable organic binder with uniformly dispersed ceramic particles is applied in layers and then cured in regions according to the method described above. The photopolymerization light wavelength depends on the resin used and is generally specified by the manufacturer. For the preferred resins of this invention, the photopolymerization wavelength is 375-460 nm.

[0053] Thus, the construction of the consolidated body is achieved layer by layer in cycles comprising an operation of slurry deposition followed by an operation of photopolymerization of the resin of the layer. Whenever the construction of the desired final body requires the deposition of a slurry in contact with (i.e., on top of and / or adjacent to) an already consolidated layer, and having a composition different from that of the slurry that formed the consolidated layer, the intermediate product obtained after the last photopolymerization operation must be washed, for example with a solvent, to remove any unconsolidated residues of the previous slurry.

[0054] In the resulting compact, particles of the various oxides are embedded in a matrix of hardened polymer obtained by photopolymerization of the resin ("photocuring"), which already possesses the shape and desired composition profile in three spatial directions of the final transparent ceramic body.

[0055] The next step (h) of the method involves removing the polymer, dispersant, and other possible volatile components of the compact produced by photocuring of the resin. This operation, called "debinding," is preferably carried out in air or an oxygen-rich atmosphere. In this step, the compact is subjected to a heat treatment for up to 72 hours at temperatures ranging from room temperature to 100-1000°C, preferably 550-800°C. Heating in this stage must not be too rapid to avoid localized accumulation of gases generated by polymer decomposition or evaporation of light compounds, which could cause deformation or even pressure bursts that could destroy the object. In particular, the heating rate should be between 0.05°C / min and 2°C / min, preferably less than 0.25°C / min in the range of 115-250°C. The resulting product of this step is a debounded body with a density of 40-60% of full density.

[0056] The next step in the process is to sinter the debindered body in a vacuum to obtain the final ceramic body. -1 This means a pressure of less than 1 Pa.

[0057] Sintering can be carried out in two possible alternative ways: by a purely thermal sintering step (i) or by a thermal sintering step followed by hot isostatic pressing in step (i'). During either of these steps, the garnet phase is formed from the oxides in mixtures (2) and (2') and the material is densified, i.e. the pores of the debindered body are eliminated.

[0058] Step (i) is carried out by subjecting the debindered body of step (h) to a heat treatment in a vacuum at a temperature in the range of 1600°C to 1900°C for a time in the range of 6 hours to 32 hours, thereby obtaining the transparent ceramic body desired by the present invention.

[0059] Step (i') is carried out by subjecting the debindered body from step (h) to a sintering heat treatment in a vacuum at a temperature ranging from 1400°C to 1800°C for a time ranging from 2 hours to 20 hours, followed by hot isostatic pressing (HIP) at a temperature ranging from 1400°C to 1800°C under an applied pressure ranging from 100 to 300 bar for a time ranging from 1 hour to 4 hours, thereby obtaining the desired transparent ceramic body of the present invention. HIP can be carried out by using a gas and a compressor to set the desired sintering temperature. Generally, higher pressures allow for operation at lower temperatures, which slows grain growth and therefore provides advantages in terms of transparency.

[0060] In both steps (i) and (i'), the heating rate in the temperature range of 1200-1600°C must be less than 100°C / h.

[0061] A vacuum furnace with a clean atmosphere (graphite-free) is preferably used for the sintering process in either step (i) or (i').

[0062] The method may further comprise an optional step (j) of annealing the transparent ceramic body obtained in step (i) or (i') in an oxidizing or reducing atmosphere to bring the dopant ions to the desired oxidation state, which may be necessary, for example, if the dopant ions are oxidized during the debinding step (h) or reduced during the sintering step (i) or (i') carried out in vacuum.

[0063] In a second aspect, the present invention provides a transparent ceramic body that can be used as a component of an optical system in generating, amplifying, shaping or directing laser beams, as a scintillator and other similar applications.

[0064] Preferred articles of the invention are based on two YAG compositions modified with doping ions, or on one pure YAG composition and one YAG composition modified with doping ions.

[0065] The method of the present invention is useful and advantageous for producing transparent ceramic bodies having a non-uniform and controlled spatial distribution of doping ions in three spatial directions, in the case of both simple and complex shaped objects.

[0066] Some examples of possible transparent ceramic bodies that can be produced by the method of the present invention are described below.

[0067] For simplicity, most of the transparent ceramic bodies are shown as disk-shaped in the figures described below, although other shapes can clearly be produced using the methods of the present invention. Objects similar to those shown in the figures below (i.e., layered bodies or objects with gradient dopant concentration profiles, even in complex configurations) can have any shape, such as square, rectangular, or other polygonal or irregular shapes. Both 2D and 3D structures are depicted in the figures, and complex 3D shapes and 3D distributions of dopants can be produced, as can the methods of the present invention.

[0068] FIG. 1 shows a top view and a side view of a transparent ceramic body 10 having two portions (11 and 12) of different compositions (e.g., doped and undoped YAG) printed side by side, which can be fabricated as described in Example 3.

[0069] 2 shows, in top and side views, an object 20 made of two sections (21 and 22) of different uniform compositions (e.g., doped and undoped YAG). The concentric inset 22 has the doped YAG composition, and the outer zone 21 has the undoped YAG composition; this object can be fabricated as described in Example 7.

[0070] Figure 3 shows, in top and side views, an object 30 consisting of two layers 31 and 32 of different compositions (e.g., a doped YAG layer and an undoped YAG layer). The object can be fabricated in step (g) of the method of the present invention by printing first a series of layers of the slurry produced in step (c), followed by a second series of layers of the slurry produced in step (f). During the subsequent sintering step (i) or (i'), a limited amount of ions typically diffuses between the doped and undoped YAG layers, forming a thin, graded intermediate layer (up to 150 μm) that does not affect the graded nature of the overall object.

[0071] FIG. 4 shows top and side views of another possible ceramic transparent body 40 of the present invention. The body is formed as a single piece with layers of a graded chemical composition profile (graded dopant concentration) across the body's thickness. This body can be fabricated by preparing several slurries with different dopant concentrations in multiple steps of the type (c) and (f), and then repeating step (g) by depositing different slurries with decreasing (or increasing) dopant concentrations. A consolidated body prepared by repeating step (g) with different slurries will have a graded profile of doping ions across its thickness, but during the subsequent sintering step (i) or (i')), the doping ions will diffuse from regions of higher concentration to regions of lower concentration, resulting in an essentially continuous gradient concentration profile.

[0072] 5 and 6 show, in top and side views, further possible ceramic transparent bodies of the present invention with complex 3D structures. These structures can also be fabricated by appropriately preparing different slurries and printing them in multiple steps (g), as described above with reference to FIG.

[0073] In particular, Figure 5 shows an object 50 made from three concentric regions of different composition (51, 52, and 53, respectively, from the outermost region to the central region), where the outer region 51 and the middle region 52 have a uniform composition, while the central region 53 has a gradient composition across its thickness. This type of object can also be fabricated in the shape of an elongated rod with a circular or polygonal cross-section. This object can be fabricated by preparing several slurries with different concentrations of dopant in multiple steps of type (c) or (f), and then repeating step (g) with printing different slurries with decreasing (or increasing) dopant concentrations. A consolidated body prepared by repeating step (g) with different slurries has a graded profile of doping ions across the thickness of the object, but during the subsequent sintering step (i) or (i'), the doping ions diffuse from the higher concentration regions to the lower concentration regions, resulting in an essentially continuous gradient concentration profile.

[0074] FIG. 6 shows another possible transparent body 60 of the present invention consisting of concentric regions of different composition, where the outer region (61) has a radially graded composition profile and the central region (62) has a hemispherically graded composition profile; this configuration can also be obtained in an object having the shape of an elongated rod with a circular or polygonal cross section.

[0075] The present invention is further illustrated by the following examples. [Example]

[0076] Example 1 In this example, Yb 0.3 Y 2.7 AlO 12 The preparation of a Yb-doped YAG sample with the composition is described.

[0077] Commercially available raw materials were used for the preparation: Al2O3™-DAR from Taimei Chemical Industry Co., Ltd., Y2O3 REacton® from Alfa-Aesar, and Yb2O3 from Sigma-Aldrich. All powders had purity levels of 99.9% or higher.

[0078] The oxide powders were prepared with a stoichiometry of 10% atomic substitution of Y by Yb (Yb 0.3 Y 2.7 AlO 12 The oxide powder mixture was mixed for 48 hours by ball milling in a plastic container using 300 g of Al2O3 milling media with diameters ranging from 0.5 to 2 cm, along with 200 g of ethanol and 0.5 g of tetraethyl orthosilicate (Sigma-Aldrich) as a sintering agent. The ethanol was then extracted by rotary evaporation. The resulting powder was then mixed with 1,6-hexanediol diacrylate, acrylated oligoamine (Genomer 100), and 1,6-hexanediol diacrylate. * The mixture was mixed with 5695 (RAHN, Switzerland) and benzyl alcohol using a planetary mill at 300 rpm for 30 minutes. Camphorquinone and ethyl 4-(dimethylamino)benzoate were then added as photoinitiators, and the slurry was ball-milled for 24 hours to obtain a photocurable suspension. The solid loading was 42% by volume.

[0079] 25°C, layer thickness 20 μm, exposure energy 170 mJ / cm 2 The printed body was then washed and dried at 120°C.

[0080] The printed sample size was 13.5 mm × 13 mm and the thickness was 1.75 mm. Debinding was performed in air at a temperature of 600 °C. Sintering was performed in a vacuum furnace equipped with a tungsten heating element at a temperature of 1750 °C with a soaking time of 16 hours. The sintered body was mirror-polished to reveal the Yb formed during vacuum sintering. 2+ The ion is Yb 3+Finally, the samples were polished with diamond pastes with grain sizes ranging from 30 μm to 0.25 μm using a standard optical polisher.

[0081] Example 2 This example describes the optical characterization of the doped YAG sample prepared in Example 1.

[0082] Yb in Example 1 0.3 Y 2.7 AlO 12 The sample was tested in a laser cavity longitudinally pumped by a fiber-coupled semiconductor laser, a typical testbed for evaluating the laser emission performance of potential laser materials. Under quasi-continuous pumping conditions, laser emission was obtained from the sample at a wavelength of 1030 nm, with a maximum slope efficiency of 17%, a maximum output power of 2.2 W, and an absorbed pump power of 13.6 W (conversion efficiency of 15.5%).

[0083] Example 3 This example describes the preparation of a YAG / Yb-doped YAG sample in a parallel configuration with the geometry shown in FIG. 1 (where YAG is YAlO 12 and the doped YAG has a composition of Yb 0.3 Y 2.7 AlO 12 (having a composition of

[0084] Commercially available raw materials were used for the preparation: Al2O3™-DAR from Taimei Chemical Industry Co., Ltd., Y2O3 REacton® from Alfa-Aesar Corporation, and Yb2O3 from Sigma-Aldrich. All powders had purity levels of 99.9% or higher. Two mixtures were prepared.

[0085] For the first mixture, the oxide powder was prepared with a stoichiometry of 10% atomic substitution of Y by Yb (Yb 0.3 Y 2.7 AlO 12The oxide powder mixture was mixed for 48 hours by ball milling in a plastic container using 300 g of Al2O3 milling media with diameters ranging from 0.5 to 2 cm, along with 200 g of ethanol, 0.5 g of tetraethyl orthosilicate (Sigma-Aldrich) as a sintering agent, and 2.0 g of MFO (Blown Menhaden Z3 / Defloc Z3, Warner G. Smith). The ethanol was then extracted by rotary evaporation. The resulting powder was then mixed with 1,6-hexanediol diacrylate, acrylated oligoamine (Genomer 100), and 1,6-hexanediol diacrylate. * The mixture was mixed with 5695 (RAHN, Switzerland) and benzyl alcohol using a planetary mill at 300 rpm for 30 minutes. Camphorquinone and ethyl 4-(dimethylamino)benzoate were then added as photoinitiators, and the slurry was ball-milled for 24 hours to obtain a photocurable suspension. The solid loading was 42% by volume.

[0086] For the second mixture, the oxide powder was replaced with YAG (YAlO 12 The oxide powder mixture was mixed for 48 hours by ball milling in a plastic container using 300 g of Al2O3 milling media with diameters ranging from 0.5 to 2 cm, along with 200 g of ethanol, 0.5 g of tetraethyl orthosilicate (Sigma-Aldrich) as a sintering agent, and 2.0 g of MFO (Blown Menhaden Z3 / Defloc Z3, Warner G. Smith). The ethanol was then extracted by rotary evaporation. The resulting powder was then mixed with 1,6-hexanediol diacrylate, Genomer 4, and 2.0 g of methyl methacrylate (MMF). *The mixture was mixed with 5695 and benzyl alcohol using a planetary mill at 300 rpm for 30 minutes. Camphorquinone and ethyl 4-(dimethylamino)benzoate were then added as photoinitiators, and the slurry was ball-milled for 24 hours to obtain a photocurable suspension. The solids loading was 42% by volume.

[0087] 25°C, layer thickness 20 μm, exposure energy 170 mJ / cm 2 Printed in.

[0088] Half of each 20 μm layer was printed with mixture 1 and half with mixture 2. A cleaning operation was performed after each change of mixture to completely remove unpolymerized slurry from the print.

[0089] The print was then washed and dried at 120°C.

[0090] The printed sample size was 13.5 mm × 13 mm and the thickness was 1.75 mm. Debinding was performed in air at 600 °C. Sintering was performed in a vacuum furnace equipped with a tungsten heating element at a temperature of 1750 °C with a soaking time of 16 hours. The sintered body was mirror-polished to reveal the Yb formed during vacuum sintering. 2+ The ion is Yb 3+ Finally, the samples were polished with diamond pastes with grain sizes ranging from 30 μm to 0.25 μm using a standard optical polisher.

[0091] The desired structure was obtained.

[0092] Example 4 (comparison) The procedure of Example 3 was repeated in the same manner, with the only difference being that no washing operation was carried out after each change of mixture during the printing stage.

[0093] The desired structure could not be obtained due to cross-contamination of the slurries resulting in mixed compositions on both parts of the object.

[0094] Example 5 (comparison) The procedure of Example 3 was repeated in the same manner, except that the printing step was carried out at 40°C.

[0095] Due to the rheological properties of the slurry at this temperature, the desired parallel structure could not be obtained.

[0096] Example 6 (comparison) The procedure of Example 3 was repeated in the same manner, except that 2.0 g of the commercial dispersant Tego® Dispers 652 (Evonik Industries, Essen, Germany) was used instead of 2.0 g of MFO to prepare two slurries of the ceramic phase precursor.

[0097] The viscosity of the slurry was too high to allow printing, so the desired results could not be achieved.

[0098] Example 7 This example describes the preparation of the 3D structure of the complex shown in FIG.

[0099] Two slurries were prepared as described in Example 3.

[0100] Printing was performed according to Figure 2 at 25°C, with a layer thickness of 20 μm and an exposure energy of 170 mJ / cm 2 A washing operation was carried out after each change of slurry in order to completely remove unpolymerized slurry from the print.

[0101] The print was then washed and dried at 120°C.

[0102] The printed sample size was 13 mm x 13 mm and the thickness was 2 mm. The circular inset had a thickness of 1 mm and a diameter of 6 mm. Debinding was performed in air at a temperature of 600 °C. Sintering was performed in a vacuum furnace equipped with a tungsten heating element at a temperature of 1750 °C with a soaking time of 16 hours. The sintered body was mirror-polished to reveal the Yb produced during vacuum sintering. 2+ The ion is Yb3+ Finally, the samples were polished with diamond pastes with grain sizes ranging from 30 μm to 0.25 μm using a standard optical polisher.

[0103] The desired structure was obtained. [Explanation of symbols]

[0104] 10, 20, 30, 40, 50, 60 Transparent ceramic body 11, 12 Two layers of different composition 21, 22 Two layers of different composition 31, 32 Two layers of different composition 51, 52 outer area 53 Central area 61 Outer area 62 Central area

Claims

1. A method for producing a transparent ceramic body, comprising the steps of: (a) preparing a first suspension comprising: (1) a solvent, (2) Oxide Phase A ３ B ５ O １２＋ｘ a mixture of powders of oxides, hydroxides, nitrates or chlorides of metals in the stoichiometric ratio required to produce: (3) a sintering aid selected from powdered silicon oxide, tetraalkyl orthosilicate, calcium oxide powder, calcium oxide precursor, magnesium oxide powder, magnesium oxide precursor, and mixtures thereof; and (4) a dispersant selected from polyethylene glycol, menhaden fish oil, phosphate esters, dicarboxylic acids, stearic acid, and silanes; (b) removing the solvent from the suspension of step (a) to obtain a mixture; (c) preparing a homogeneous slurry comprising the mixture of step (b) and a photocurable resin; (d) preparing at least one second suspension comprising: (1') a solvent, (2') Oxide Phase A ３ B ５ O １２＋ｘ a mixture of powders of oxides, hydroxides, nitrates or chlorides of metals in the stoichiometric ratio required to produce: (3') a sintering aid selected from powdered silicon oxide, tetraalkyl orthosilicate, calcium oxide powder, calcium oxide precursor, magnesium oxide powder, magnesium oxide precursor, and mixtures thereof; and (4') a dispersant selected from polyethylene glycol, menhaden fish oil, phosphate esters, dicarboxylic acids, stearic acid, and silanes; (e) removing the solvent from the suspension of step (d) to obtain a mixture; (f) preparing a homogeneous slurry comprising the mixture of step (e) and a photocurable resin; (g) forming a stack comprising layers of the slurries of steps (c) and (f) by a layer-by-layer 3D printing technique, operating at a temperature between 20 and 30°C, to obtain a consolidated body, wherein after the deposition of each layer of slurry, an operation of photopolymerization of a photocurable resin is carried out, and a washing operation of the successive photopolymerized layers of a first composition is carried out to remove unpolymerized slurry of the first composition before depositing a layer of slurry of a second composition thereon or adjacent thereto; (h) heat treating the solidified body of step (g) in air or an oxygen-rich atmosphere at a temperature in the range of 100 to 1000°C to remove organic and volatile components of the solidified body, to obtain a degreased body; and (i) sintering the degreased body of step (h) in vacuum at a temperature ranging from 1600°C to 1900°C for a time ranging from 6 hours to 32 hours to obtain a sintered body; or (i') sintering heat treatment of the degreased body of step (h) in vacuum at a temperature ranging from 1400°C to 1800°C for a time ranging from 2 hours to 20 hours, followed by hot isostatic pressing at a temperature ranging from 1400°C to 1800°C with an applied pressure ranging from 100 to 300 bar for a time ranging from 1 hour to 4 hours to obtain a sintered body; wherein said first suspension and said at least one second suspension have different compositions.

2. 2. The method according to claim 1, further comprising a step (j) of annealing the sintered body obtained in step (i) or step (i') in an oxidizing or reducing atmosphere to adjust the oxidation state of possible dopants.

3. 3. The method according to claim 1 or 2, wherein the metal oxide, hydroxide, nitrate or chloride powder of mixtures (2) and (2') has an average particle size of less than 10 μm, an aspect ratio of 0.8 to 1.0, and a purity of at least 99%.

4. The method according to any one of claims 1 to 3, wherein the sintering aids (3) and (3'), when they are or contain compounds in powder form, have a particle size of less than 2 μm.

5. 5. The method according to claim 1, wherein the solvent (1) or (1') is an alcohol, the weight of which is 1.5 to 2.5 times the weight of the powder mixture of (2) or (2').

6. 6. The method according to any one of claims 1 to 5, wherein the sintering aids (3) and (3') are used in a weight range of 0.0005 to 0.003 g per gram of the mixtures (2) and (2') of metal oxides, hydroxides, nitrates or chlorides, respectively.

7. The method of any one of claims 1 to 6, wherein the photocurable resin is used in an amount of 50 to 60% by volume of the slurry of step (c) or (f).

8. 8. The method according to any one of claims 1 to 7, wherein the amount of dispersant (4) is from 1.5 to 2.5% by weight of the suspension prepared in step (a) and the amount of dispersant (4') is from 1.5 to 2.5% by weight of the suspension prepared in step (d).

9. The method of any one of claims 1 to 8, wherein step (g) is performed by lithography-based ceramic manufacturing (LCM).

10. 10. The method of any one of claims 1 to 9, wherein step (h) is carried out at a temperature in the range of 550 to 800°C for a maximum of 72 hours at a heating rate of 0.05°C / min to 2°C / min, and below 0.25°C / min at temperatures in the range of 115 to 250°C.

11. A transparent ceramic body (50) having a non-uniform and controlled spatial distribution of chemical composition, wherein different regions have different compositions of the general formula A3B5O12+x, where -0.1≦x≦0.1, A is selected from Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof, and B is selected from Al, Fe, Cr, Sc, Ga and mixtures thereof; A transparent ceramic body (50) consisting of concentric regions, outer regions (51, 52) having different, uniform compositions, and a central region (53) having a gradient profile of composition across its thickness.

12. A transparent ceramic body (60) having a non-uniform and controlled spatial distribution of chemical composition, wherein different regions have different compositions of the general formula A3B5O12+x, where -0.1≦x≦0.1, A is selected from Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof, and B is selected from Al, Fe, Cr, Sc, Ga and mixtures thereof; A transparent ceramic body consisting of concentric regions of different composition, with an outer region (61) having a radially graded composition profile and a central region (62) having a hemispherically graded composition profile.

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