Scintillator nanocomposite

Abstract

An improved scintillator nanocomposite having nanoparticles with scintillating properties and diameters of 10 to 50 nanometers and a first matrix material is obtained by adding the nanoparticles to a dispersion medium to form a stable suspension, the dispersion medium being a precursor to the first matrix material, and the precursor being cured to form the first matrix material.

Description

Technical Field

[0001] The present invention generally relates to a method for producing a scintillator nanocomposite, a scintillator nanocomposite, a product having the scintillator nanocomposite, a method for producing a transparent scintillator, a transparent scintillator, a radiation detector, and an imaging system.

Background Art

[0002] Radiation detection materials such as phosphors are used in many applications as scintillator materials in, for example, security or medical scanners (such as X-ray, CT, PET, or SPECT scanners). These materials are typically used in the form of single crystals, and their size is limited due to limitations in the synthesis method.

[0003] Nanoscale composites are an interesting approach for developing radiation detectors that avoid the limitations of single crystals. Composite materials can be produced in various shapes and sizes. Similarly, the cost of scintillator production can be significantly reduced. Furthermore, composites filled with nanosized filler materials have a higher surface-to-volume ratio than conventional composites with micro-sized fillers.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The scintillator nanocomposite 10 generally begins with nanoparticles 12 having scintillation properties in powder form being dispersed in a dispersant or a prepolymer, and is prepared to form a polymer matrix 11 in which the nanoparticles are distributed (see FIG. 1a for the configuration of the scintillator nanocomposite 10 having well-dispersed nanoparticles).

[0005] However, a major limitation to the use of nanocomposite materials in radiation detection is that it is very difficult to achieve uniform dispersion and compatibility in known scintillator nanocomposites (see Fig. 1b). This is due, in part, to the use of dispersants and / or solvents that need to be removed prior to polymerization in order to enable proper dispersion of the nanoparticle powder in the prepolymer. However, this is an extremely difficult process, and any unwanted material remaining in the scintillator causes internal damage 14 to the matrix structure, such as inclusions and / or voids that degrade the transparency and quality of the scintillator nanocomposite. Furthermore, it is difficult to add large amounts of nanoparticles 12 to any matrix material 11. More dispersants and / or solvents may be required, making their removal even more difficult and thereby increasing the problem. Higher nanoparticle content results in increased nanoparticle aggregation in the composite.

[0006] Furthermore, for many optical applications such as radiation detectors, the powder size of the nanoparticles is limited to the range of 10 - 50 nm. Such particles have a small enough light scattering coefficient to (partially) obtain a transparent nanocomposite. However, nanoparticle powders of such small sizes typically strongly aggregate into larger aggregate structures 13, resulting in a lack of the required transparency. In WO 2009 / 054946, the aggregation of nanophosphor scintillators in a matrix material is addressed by surface modification of the nanophosphor particles using ligands that enable separation of the surface charge or direct bonding of chemicals to the matrix material. However, such nanoparticles need to be specifically modified, making their production more complex and making their particles more effective. Furthermore, the ligands can affect the scattering and absorption properties.

[0007] In addition, dopants (e.g., cerium dopants) used in the scintillator material present on the surface of the scintillator material increase the formation of surface defects 15, which reduce luminescence and thus result in a lower quality scintillator.

[0008] One object of the present invention is to obtain a high-quality transparent scintillator composite from nanoparticle powder and a manufacturing process that provides a higher yield of a less complex, high-quality scintillator material. Other objects and advantages are referred to throughout this description.

Means for Solving the Problems

[0009] This object is achieved by a method of producing a scintillator nanocomposite having scintillating properties and nanoparticles having a diameter of 10 to 50 nanometers and a first matrix material, the method comprising adding the nanoparticles to a dispersion medium to form a stable suspension, wherein the dispersion medium is a precursor of the first matrix material, and curing the dispersion medium to form the first matrix material. By using the precursor of the first matrix material as a dispersant, the precursor does not need to be removed, and thus an energy-consuming process step, and more importantly, a processing step that brings defects that reduce the transparency of the scintillator nanocomposite to the final product is eliminated. For this reason, the nanocomposite obtained by the method of the present invention is of higher quality than the nanocomposite obtained from known manufacturing methods.

[0010] According to another preferred embodiment of the present invention, the scintillator nanoparticles are garnet nanoparticles, preferably cerium-doped nanoparticles, most preferably Y 3 Al 5 O 12 :Ce (YAG:Ce) nanoparticles, (Lu,Gd) 3 Al 5 O 12 :Ce (LGAG:Ce) nanoparticles, or (Lu,Gd) 3 (Al,Ga) 5O 12 : Nanoparticles selected from the group of Ce (LGGAG:Ce) nanoparticles. These are garnets which are known to be very suitable, for example, in medical imaging or security imaging.

[0011] In a preferred embodiment of the present invention, the dispersion medium is glycol, preferably 1,4 - butanediol. This is a particularly suitable precursor for the polyurethane matrix material.

[0012] In a preferred embodiment of the present invention, the second dispersion medium is mixed with the first dispersion medium before adding the nanoparticles or before stable suspension. The second dispersion medium is a precursor of the second matrix material. In one example, the second matrix material can be used to achieve other improved properties, such as optical or mechanical properties. The first and second matrix materials can be cured into a single matrix material (e.g., copolymer). Here too, it is advantageous to use a dispersant that reacts to become the matrix material instead of something that needs to be removed.

[0013] In a preferred embodiment of the present invention, the first or second matrix material is a polymer material, preferably a polymer material selected from the group of polyurethanes, polybutylene terephthalates, unsaturated polyester resins, aromatic polyamides, aromatic polyimides, polyesters such as polystyrene, or polysulfones.

[0014] Polymers are often very suitable for processing, are compatible with the nanoparticles, and there are sufficient options for precursors or precursor synthesis that endow them with optical properties suitable for various optical applications (e.g., radiation imaging).

[0015] According to another preferred embodiment of the present invention, curing is preferably carried out at a high temperature between 220 and 250 degrees Celsius, more preferably at about 225 degrees Celsius, and / or at a high pressure, preferably at a pressure higher than 20 bar, most preferably at a pressure of about 40 bar, and / or for at least 24 hours. These are good reaction conditions especially in the case of polymer matrix materials such as polyurethanes.

[0016] In a preferred embodiment of the present invention, the resulting nanocomposite has a polyurethane gel matrix material. Polyurethane can be relatively easily molded into many different shapes in many applications.

[0017] The present invention further aims to produce and obtain a transparent scintillator that has improved quality and can be used, for example, in a radiation detector applicable in an imaging system.

[0018] Other aspects and embodiments of the present invention will be understood by those skilled in the art by reading and understanding the following detailed description. Many additional benefits and advantages will become apparent to those skilled in the art by reading the following detailed description of the preferred embodiments.

[0019] The present invention is illustrated by the accompanying drawings.

Brief Description of the Drawings

[0020]

Figure 1a

Figure 1b

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0021] The present invention can take the form of various components and combinations of components, as well as various process operations and combinations of process operations. The drawings are for illustrative purposes only of preferred embodiments and should not be construed as limiting the present invention. For better visualization, certain features may be omitted or not drawn to scale.

[0022] Some types of scintillator nanoparticles (e.g., garnet-based nanoparticles) are known. Although the present invention is described with respect to some specific scintillating nanoparticles by way of example, it is not limited thereto, and those skilled in the art will know how to prepare and use other types of scintillator nanoparticles as well.

[0023] To obtain the scintillator nanocomposite 10, the scintillator nanoparticles 12 need to be embedded in a matrix 11, which is here described using a polymer matrix. As described above, known scintillator nanocomposites are prepared by dispersing nanoparticles in a precursor material that is formed into a matrix, such as a monomer that can be (co)polymerized in a polymer matrix for example. Non-polymer precursors are possible, such as inorganic precursors that can be cured in an inorganic matrix material having a glass-like structure.

[0024] The refractive indices of the scintillator nanoparticles and the matrix must be adapted to be suitable in optical applications, for example in a radiation detector. However, this is not trivial since nanoparticles usually have a higher refractive index than most polymers. For example, Y 3 Al5 O 12 : The refractive index of Ce nanoparticles is 1.8, and usually, the polymer has a refractive index of 1.7 or less (for example, polyurethane has a refractive index of about 1.5). High refractive index polymers are rare and expensive. The refractive index of the polymer matrix can be increased by adding inorganic particles such as TiO 2 or ZrO 2 etc., but it is necessary to use a very large amount of inorganic materials, which will cause even more defects in the nanocomposite, thus affecting the problem to be solved by the present invention. A better solution is to use scintillator nanoparticles with a very small diameter. Since the scattering intensity depends on the sixth power of the particle diameter (Rayleigh equation), only particles with a size smaller than the wavelength of visible light do not interfere with the incident light, and ultimately, the composite does not seem turbid. In particular, nanoparticles smaller than 50 nm in the matrix seem transparent to the human eye.

[0025] Unfortunately, such small nanoparticles tend to form aggregates 13 due to the van der Waals forces resulting from their relatively large surface area. The aggregates 13 usually increase in size to several hundred nanometers and behave like submicron particles that scatter incident light, reducing the transparency of the nanocomposite, which is very disadvantageous for the transparency and quality of the scintillator nanocomposite.

[0026] The present invention presents a manufacturing method that results in a transparent scintillator nanocomposite that more homogeneously distributes nanoparticles smaller than 50 nm in the matrix and simultaneously reduces the defects caused by dispersants or solvents used in known methods for manufacturing the nanoparticle dispersion used in the production of the scintillator nanocomposite.

[0027] First, prepare scintillator nanoparticles using any of many known scintillator nanoparticle synthesis methods (101).

[0028] Next, the nanoparticles are dispersed in an organic medium (102). This organic medium is a precursor material for forming (at least a part of) the matrix material, and it is an insight of the present invention that it can be, for example, a monomer that can be (co)polymerized into a polymer matrix. There are many requirements for the organic material and the resulting matrix material, which makes it not easy to select a suitable organic medium. First, the organic medium disperses the scintillator nanoparticles to form a stable suspension up to a solids content of 50%. Second, the resulting matrix material (e.g., a polymer) needs to be radiation-curable, compatible with any other material present in the nanocomposite (e.g., a polymer that can or cannot form a copolymer), and have a refractive index compatible with such materials, and preferably, it is not too expensive or difficult to obtain. Surprisingly, it has been found that glycols and especially 1,4-butylene glycol [HO-(CH 2 ) 4 -OH] have the properties necessary to be used as an organic medium that can be (co)polymerized into a suitable polymer matrix material such as polyurethane or polyester. 1,4-Butanediol further has a stabilizing effect on Ce 3+ and the nanoparticles, so it is very attractive to use 1,4-butanediol in a cerium-doped scintillator material. This reduces surface defects 15 in the nanocomposite 10 caused by the migration of cerium later.

[0029] For example, examples of alternative precursor materials are precursors of aromatic polyamides or aromatic polyimides such as dianhydrides, diamines, N,N-dimethylacetamide (DMAc) or N-methylpyrrolidinone (NMP), precursors of polystyrene such as 4,4'-azobis(4-cyanovaleric acid) (ACVA), polyvinylpyrrolidone (PVP), or precursors of polysulfones such as diphenols (bisphenol-A or 1,4-dihydroxybenzene) and bis(4-chlorophenyl)sulfone. As described above, inorganic precursors are also conceivable.

[0030] The suspension of the precursor material and the nanoparticles is cured into the matrix material (103). To polymerize the glycol, for example, to form polyurethane or polyester, another monomer (e.g., isocyanate or dicarboxylic acid) needs to be added. This polymerization mechanism is generally known. Other reagents such as comonomers can be used to form copolymers and catalysts. It is preferred to use dibutyltin dilaurate (DBTDL) as the catalyst because this catalyst is known to shorten the reaction time. Using 1,6 - diisocyanatohexane (HDI) as the isocyanate source is preferred because it can enhance transparency and increase the amount of nanoparticles in the matrix. After polymerization, the nanoparticles 12 are embedded in the polymer matrix 11 in a homogeneous manner with fewer or at least smaller aggregates 13, and less disintegration 14 and fewer surface defects 15 of the matrix (as schematically shown in Figure 1a). Except for this, the presence of the nanoparticles does not have a significant impact on the reaction conditions or the resulting polymer.

[0031] The polymerization reaction is carried out in a pressurized oven such as an autoclave. The temperature must be near or above the boiling point of the organic medium. The temperature must be near or higher than the boiling point of the organic medium. In the case of 1,4 - butylene glycol, this provides a temperature window of 220 to 250 degrees Celsius, and a suitable working temperature is 225 degrees Celsius. A high pressure of at least 20 bar or more, preferably about 40 bar or more, must be applied. Furthermore, the reaction must be maintained under these conditions for at least 24 hours to obtain a well - cured and well - dispersed scintillator nanocomposite.

[0032] To be able to obtain a high-quality nanocomposite, all starting materials need to be dehydrated and degassed (preferably at a temperature of 100 to 150 °C) in order to avoid inclusions or defects in the nanocomposite. In particular, the presence of water makes it very difficult or even impossible to obtain a scintillator nanocomposite because the polymerization reaction is too fast to enable easy control of the nanoparticles.

[0033] Defects are not caused by insufficient or ineffective solvent removal, so a nanoparticle composite with improved transparency and quality can be obtained. This can be further improved by melting the obtained nanocomposite (104) and injection molding the molten composite (105). This process with fast dissolution and rapid cooling can reduce further defects. This is particularly effective when the nanocomposite contains a polymer having a block structure in which harder segments and softer segments are joined together, for example in the case of polyurethane.

[0034] Since the segments have a high polarity and thus a strong tendency to aggregate, a (pseudo)crystalline structure that reduces transparency is formed, so the transparency before injection molding is still not optimal. Cross-linking between the segments disappears in response to heating and injection, preventing the development of crystallites, and as a result, a very much improved transparency of the nanocomposite is obtained.

[0035] The improved nanocomposites of the present invention can be further processed for use in various applications such as radiation detectors. Figure 4 shows a highly simplified view of a radiation detector in which a scintillator 31 is optically attached to a photodiode 32 mounted on an integrated circuit 33. Vertical configurations, other layers, pixelated detectors, and other configurations are further contemplated in the context of the present invention.

[0036] Next, the radiation detector 30 can be incorporated into an imaging system 40 such as an X-ray imaging system, a CT imaging system 40 (schematically shown as an example in FIG. 5), a PET imaging system, or a SPECT imaging system. The improved nanocomposite can be further processed like a known nanocomposite, and the structure 106 of the radiation detector can be generated using known techniques.

[0037] Example 1.Y 3 Al 5 O 12 : 1% Ce nanoparticles (~20 vol.%) 11.498 g of aluminum isopropoxide, 11.336 g of yttrium acetate hydrate, and 0.111 g of cerium acetate hydrate is were mixed with a solvent mixture of 1,4-butylene glycol and diethylene glycol in a mass ratio of 9:1.

[0038] The colloidal solution was stirred on a hot plate for 3 hours by gentle heating at 50 degrees Celsius. After the mixture was homogenized, it was poured into a high-pressure autoclave container. After washing the air present in the autoclave with argon, the mixture was heated to 225 degrees Celsius at a heating rate of 1.5 °C / min for 60 hours. After the process was completed, the mixture was cooled to obtain a translucent yellowish suspension.

[0039] Next, 9 g of the obtained dehydrated suspension was quickly mixed with 16 g of dehydrated 1,6-diisocyanatohexane and 1 drop of dibutyltin dilaurate. The viscous material was poured into a Teflon mold and held in an oven at 60 °C for 8 hours to obtain nanocomposite microparticles.

[0040] The nanocomposite microparticles were introduced into an injection mold, melted at 210 degrees Celsius, and immediately cooled in the mold.

[0041] Figure 3(a) shows the transmittance T, reflectance R, and absorptance A of the resulting transparent YAGCe - polyurethane nanocomposite. Figure 3(b) shows the luminescence of the obtained nanocomposite under 450 and 360 nm excitation. The scintillators in this example are transparent at visible wavelengths but absorb wavelengths in X - rays, thereby making them suitable for use in CT and other X - ray radiation detectors. In the case of PET, the absorption should be at 511 keV. For other purposes, absorption of ultraviolet or other wavelengths may be required. By selecting the correct scintillating nanoparticles, the absorption and emission wavelengths can be set, for example, using nanoparticles based on Eu or Tb.

[0042] Taking into account the stoichiometric differences in amounts, LGAG:Ce (confirmed with at least Lu 2 Gd 1 Al 5 O 12 : 1% Ce) and LGGAG:CE (confirmed with at least Lu 2 Gd 1 Al 4 Ga 1 O 12 : 1% Ce) gave similar results. In particular, garnet scintillators such as LGGAG:Ce are difficult to obtain with sufficient transparency and quality. The method of the present invention also gives nanocomposite scintillators with high transparency and high quality for these types.

[0043] It is also possible to obtain gels, such as polyurethane gels, as matrix materials for scintillator materials. In particular, when the nanoparticles have luminescent properties, several interesting applications can be created using gel-based nanocomposites: for example, flexible luminescent sheets (e.g., for safety applications, fabrics, etc.) or health applications (e.g., for treating skin diseases with light. In this case, the luminescence is optically excited). They can also be applied to certain toys. Furthermore, they can have a luminescent function and be used in the same fields as known (polyurethane or other) gels: luminescent computer mouse pads / keyboard wrist rests, luminescent bicycle parts, luminescent motorcycle seats, luminescent shoe insoles, luminescent padding parts for medical devices, luminescent adhesive pads for holding cell phones and tablet computers, any conformal luminescent layer for covering products, and others.

[0044] Example 2. Lu 2 Gd 1 Al 5 O 12 : Polyurethane gel (PU gel) filled with 1% Ce nanoparticles (~35 vol.%) 6.008 g of aluminum isopropoxide, 7.529 g of lutetium acetate hydrate, 3.350 g of gadolinium acetate hydrate, and 0.104 g of cerium acetate hydrate were mixed with a solvent mixture of 1,4-butylene glycol and diethylene glycol in a mass ratio of 9:1. The colloidal solvent was stirred on a hot plate for 3 hours with gentle heating at 50 °C.

[0045] After the mixture was homogenized, it was poured into a high-pressure autoclave container. The air present in the autoclave was purged with argon. The mixture was heated to 225 °C at a heating rate of 1.5 degrees / min for 60 hours. After the process was completed, the mixture was cooled to obtain a translucent yellowish suspension.

[0046] 5 g of the resulting dehydrated suspension was rapidly mixed with 6.5 g of a mixture of polymeric MDI (a mixture of oligomeric polyisocyanates) and an MDI isomer (isocyanate (1-isocyanato-4-[(4-isocyanatophenyl)methyl]benzene)). The resulting viscous polyurethane gel was poured into a Teflon mold.

[0047] The nanocomposite can be made in any shape or form (e.g., sheet, powder, molded article, foil, etc.) using the method of the present invention as long as the precursor material is (co)polymerized into an optically compatible matrix material for the scintillating nanoparticles with the nanoparticles sufficiently dispersed. Curing is not limited to curing by heating. For example, ultraviolet polymerization and other curing reactions known to those skilled in the art are also contemplated.

[0048] The nanoparticle composite of the present invention can be applied in various ways known to those skilled in the art, such as deposition, coating, printing, etc.

[0049] The nanoparticle composite of the present invention can be molded by injection or other molding techniques, 3D printing, and other techniques known to those skilled in the art.

[0050] Although the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description should be considered as illustrative or explanatory and not restrictive. The present invention is not limited to the disclosed embodiments.

[0051] The term "about" in this application is considered to mean including values that are 10% lower or higher than a given value.

[0052] Other modifications to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the term "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, and can also be distributed in other forms, such as via the Internet or other wired or wireless electrical communication systems.

[0053] Any reference signs in the claims should not be construed as limiting the scope of the claims.

Claims

1. A method for manufacturing a scintillator nanocomposite having scintillation characteristics and nanoparticles with a diameter of 10 to 50 nanometers and a first matrix material, A step of adding the nanoparticles to 1,4-butanediol to form a stable suspension, wherein the 1,4-butanediol is used as a precursor of the first matrix material and the 1,4-butanediol is used as a dispersion medium for the nanoparticles, A step of curing the dispersion medium without removing the dispersion medium to form the first matrix material, The method having.

2. The method according to claim 1, wherein the nanoparticles are garnet nanoparticles.

3. The method according to claim 1 or 2, wherein the first matrix material is a polymer material.

4. The method according to any one of claims 1 to 3, wherein the curing is at high temperature and / or high pressure.

5. A method for producing a transparent scintillator, A step of dissolving the nanocomposite obtained by the method according to any one of claims 1 to 4, A step of injection molding the dissolved nanocomposite, The method having.

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