Nanocomposite scintillator with ultra-fast emission from multi-exciton states for detecting ionising radiation and relative manufacturing method

Abstract

Ultra- fast nano composite scintillator comprising a matrix in which there are embedded metal halide nanocrystals which emit light from multi-exciton states following an interaction with an ionising and non-ionising radiation. The invention also relates to a method for manufacturing such scintillator.

Description

[0001] NANOCOMPOS ITE SCINTILLATOR WITH ULTRA-FAST EMISS ION FROM MULTI-EXCITON STATES FOR DETECTING IONIS ING RADIATION AND RELATIVE MANUFACTURING METHOD

[0002] Forming an obj ect of the present invention i s a nanocomposite scintillator according to the preamble of the main claim . The present invention also relates to a method for obtaining the aforementioned scintillator, according to the preamble of the corresponding independent claim .

[0003] The obj ect of the invention is generally related to the detection of a radiation .

[0004] As known, the revealing or detection of an ionising radiation ( including high-energy particles such as alphaparticles , beta-particles , electrons , neutrons , etc . and ionising photons , such as X-rays , gamma rays ) is of great importance in several scienti fic and technological fields which range from high-energy and particle physics to medical diagnostics , from monitoring of goods and frontier security, as well as industrial and environmental monitoring .

[0005] Commonly, an ionising radiation is detected using devices called scintillator devices . In these devices , the ionising radiation interacts with the scintillator material through processes which depend on the nature and on the energy of the particles which define such radiation ( for example , through Coulomb scattering, Compton scattering, photoelectric ef fect , creation of electron-lacuna pairs , etc . ) ; such interaction creates a luminescence in the aforementioned material which propagates and is detected by photodiodes or highly ef ficient photomultipliers coupled to the body of the scintillator .

[0006] As known, there are various fundamental parameters for using this type of devices . A first parameter is the probability of interaction with the ionising radiation, determined by the actual atomic weight of the scintillator material Z and by the density according to the power law (proportional to ZD, with n ranging between 1 and 5 depending on the type of speci fic interaction ) . Therefore , there arises the need to include - in the scintillator materials - atoms of heavy elements . In case of detection of neutrons , there arises the need for the presence o f specific ions with which they can interact , such as for example Li , Gd, B for thermal neutrons and H for the fast neutrons .

[0007] A second parameter is the scintillation ef ficiency, which must be high, called " light yield" ( LY) ; it defines the number of photons emitted by a scintillator device for by absorbed ionising radiation energy unit .

[0008] A further parameter is the speed with which the scintillation process occurs , which is typically in the order of si ze a few nanoseconds or higher .

[0009] Lastly, stability under radiations , also referred to as " radiation hardness" , which expres ses the resistance of the scintillator material to high doses of ionising radiation and determines the duration thereo f over time under operating condition, is also important .

[0010] In particular, among the aforementioned parameters , scintillation speed is crucial for the use of scintillators in a manner known as ' time of flight ' ( or TOF) . In high- energy physics , the TOF techniques are for example used in the particle detectors in high-luminosity accelerators where there arises the need to avoid signal pile-up phenomena and precisely locate the origin of the degradation of the particles created by the collis ions . Furthermore , these techniques allow to discriminate between ionised particles and the measuring of the mass of unstable nuclei .

[0011] Likewise , the time of flight positron emis sion tomography ( known as TOF-PET ) , is an imaging technique used in oncology medicine . The latter uses a coincidence time resolution method based on the detection of two photons emitted at 180 ° one with respect to the other following the annihilation of a positron with an electron of the tissue . The time di f ference of their detection is proportional to the length di f ference of the travel of their path and therefore it contains information on the spatial position in which the annihilation process occurred . As a result , the precision with which the annihilation position is determined is determined by the time resolution with which the scintillation time is measured .

[0012] The time for response to the event of interaction with the ionising radiation is therefore critical to a reconstruction of high-quality and precision images . Currently, research aims at obtaining scintillators with response times of a few tens of picoseconds , although this result has not yet been achieved .

[0013] Lastly, it is signi ficant that scintillators with the aforementioned properties can be manufactured with arbitrary shapes and si zes using scalable and cost-ef fective techniques even in terms of energy .

[0014] There are various types of scintillators which di f fer from each other by their composition or by their ef ficiency or by their response time are known . However, each of these types is limited in some characteristic properties and, to date , none is capable meeting all the parameters simultaneously .

[0015] In particular, inorganic crystal scintillators which are particularly used for detecting energetic and penetrating ionising radiations are known; however, they are extremely heavy, expensive and they cannot be produced in arbitrary shapes . Furthermore , their production is extremely energy consuming . On the contrary, plastic scintillators of fer production versatility and lightness , and they can be obtained with di f ferent si zes and shapes with characteristics which can be adapted to the speci fic applications . In the light of the above , plastic scintillators are particularly suitable for providing broad spectrum devices adapted to detect radioactive material , like for monitoring goods at frontiers .

[0016] Typically, these devices consist of plastic or polymeric or glass matrices containing or coated with scintillator material such as organic molecules or polymers . However, organic molecule-based plastic scintillators have low scintillation ef ficiency due to the actual small Z value of the elements forming the organic molecules ( defining the scintillator material ) and low radiation hardness .

[0017] Oxide-based colloidal nanocrystals or semiconductors have recently emerged as possible nanoscintillators due to their optical properties which can be selected through compositional and / or dimensional control , stability against radiations and high actual Z value due to the possible presence of heavy elements in their composition . In particular, the metal halide-based nanocrystals ( including lead) have recently emerged as valid candidates as nanoscintillators for manufacturing nanocomposite scintillators consisting of nanocrystals embedded in plastic or glass matrices . They have a composition containing heavy elements ( e . g . Pb ) , excellent optical properties and particular tolerance to structural defects , which confers high light yield to these scintillators .

[0018] However, similarly to organic molecule-based scintillators , the examples of metal halide nanocrystalbased scintillators reported to date in literature have characteristic emission times ranging from several nanoseconds to hundreds of nanoseconds . This makes them inappropriate for TOF techniques . The reason for these long scintillation times lies in their scintillation mechanism which is typically either due to the recombination of single electron-lacuna pairs ( commonly called single excitons ) or the recombination emissive defect sites or the recombination of excitons trapped in localised reticular distortions ( for example due to the Jahn Teller ef fect ) .

[0019] Furthermore , the metal halide nanocrystals with adequate optical quality are typically synthesised with techniques called "hot inj ection" in which a precursor solution is inj ected in a high-temperature heated solution in which other known reagents required for the synthesis are dissolved at low concentration . Although this technique provides nanocrystals that are uni form and with ef ficient emission, it is not industrially scalable .

[0020] Furthermore , metal halide nanocrystals can be synthesi zed with techniques carried out at room temperature , such as the Ligand Assisted Reprecipitation ( LARP ) technique . In this case , the productivity scalability is higher than the hot inj ection synthesis , but still limited by concentration gradient in the reaction environment . This entails that the large-scale room-temperature syntheses generate inhomogeneous products with less ef ficient emission of the counterparties produced by hot inj ection .

[0021] Furthermore , due to their ionic nature and ease of undergoing phase transition towards non-emissive forms , metal halide nanocrystals are chemically fragile and the embedding thereof in high optical quality matrices is very di f ficult and it typically entail s the deterioration of the emissive properties thereof . This is particularly dramatic in the production of plastic nanocomposites for in-situ radical polymerisation, wherein the nanocrystals are dispersed in organic monomer solutions in the presence of polymerisation initiators ( exempli fied by but not limited to radical or cation or anion initiators ) which are activated for example thermally or optically or in another manner . In these cases , however, the monomer species or the polymerisation initiators commonly result in damaging surfaces and even dissolving nanocrystals and promote the aggregation thereof in large domains which entail decrease in the emission ef ficiency and light di f fusion optical loss .

[0022] The patent text W02021 / 090167 on behal f of the Applicant in question discloses a nanocomposite scintillator comprising a body made of polymeric material or silica-based glass containing colloidal nanocrystals where the latter are metal halide perovskite semiconductor nanocrystals which act as an 'antenna' for the ionising radiation and they sensiti ze the emission by low Z value secondary organic emitters which, considered individually, have an almost insigni ficant interaction with the ionising radiation .

[0023] Despite operating in an acceptable manner, the nanocomposite scintillators subj ect of the aforementioned patent text reveal some drawbacks common to conventional scintillators . First and foremost , the nanocrystals are inserted into polymer matrices produced starting from polymer chains dissolved in a solvent and solidi fied by evaporating it . The need for this rudimental technique arose from the need to avoid damaging nanocrystals . However, it is not adapted for manufacturing high-quality massive nanocomposites but only for producing small prototypes used for study purposes .

[0024] Furthermore , j ust like conventional scintillators , the scintillators described in the aforementioned prior art text have an emission scintillation mechanism due to the recombination of single excitons which confer scintillation times of tens of nanoseconds , inappropriate for high- performance TOF applications . In order to accelerate the scintillation time of the nanocrystals , the patent text W02021 / 090167 proposes the coupl ing of nanocrystals with organic emitters with shorter luminescence time , but still much higher than a nanosecond . The use of organic emitters , even together with semiconductor nanocrystals , further entails low stability against radiations which hinder the use of nanocrystal composite scintillators / organic emitter described in the aforementioned prior art document at high- radioactivity contexts or for long operating times .

[0025] CN113621368 discloses an ultra- fast scintillator with metal organic structure and caesium lead halide perovskite quantum dot , and a relative preparation method . This prior art document considers that , being an important raw material for the preparation of an ultra- fast scintillator, perovskite quantum dots have the advantages of high light ef ficiency, a short fluorescence transient and the like ; however, the instability of perovskite quantum dots makes these quantum dot agglomerate easi ly, grow and become large nanocrystals . According to the invention, a metal organic structure is introduced to adj ust and control the si ze of the quantum dots and improve their stability so as to obtain an ultra- fast scintillation with a short transient duration .

[0026] Herein described is a scintillator with an at least a few nanoseconds response .

[0027] Therefore , to date there are not known scintillators with satis factory scintillation times for high-resolution TOF applications ( rimes less than 100 ps ) and which can be obtained through reproducible , scalable and cost-ef fective manufacturing techniques . Further, none of the scintillators of the prior art solutions allows to obtain ultra- fast responses (within times shorter than 100 ps ) using metal halide nanocrystals as a single active component .

[0028] Therefore , an obj ect of the present invention i s to provide an improved nanocomposite scintillator with respect to the prior art solutions and those already disclosed in scienti fic publications , but still in the study stage , which allows to obtain ultra- fast scinti llation times , high light yield and high radiation hardness .

[0029] In particular, an obj ect of the present invention is to provide a nanocomposite scintillator which can have an ultrafast scintillation time that is less than 500 picoseconds .

[0030] A further obj ect of the invention is to provide a scintillator having a high ef ficiency, that is a nanocomposite scintillator which has a high probability of interaction with the ionising radiation or with neutrons .

[0031] A further obj ect of the present invention is to provide a nanocomposite scintillator which has a high resistance to radiations , that is stable scintillation properties following prolonged exposure to ionising radiation .

[0032] Another obj ect o f the present invention is to provide a method for obtaining a scintillator of the type indicated above which uses a highly scalable and cost-ef fective manufacturing technique using a single active component di f ferent from the matrix .

[0033] A further obj ect of the invention is to provide a method for manufacturing ultra- fast scintillation nanocomposite scintillators which can be implemented in a highly scalable and cost-ef fective manner by growing highly ef ficient nanoparticles directly in a monomer mixture during the polymerisation process .

[0034] A further obj ect of the present invention is to provide multicomponent systems wherein nanocomposite scintillators according to the present invention are combined with other scintillator devices , such as for example inorganic scintillator crystals , particularly for improving the performance thereof in terms of scintillation rapidity .

[0035] These and other obj ects which shall be apparent to the person skilled in the art are attained by a nanocomposite scintillator according to the attached claims .

[0036] For a better understanding of the present invention, the following drawings are attached hereto , purely by way of non-limiting example , wherein : figure 1 shows , by way of example , the processes for the radiative emission of single excitons , single excitons charged with an additional carrier ( known as positive or negative trions depending on whether the additional carrier is a lacuna or an electron) , and double excitons or biexcitons ; in this figure , the electrons being indicated as solid beads and the lacunae as void beads ; figure 2 shows , by way of non- limiting example , the processes for the non-radiative ionisation - of the Auger type - of double excitons or bi-excitons which lead to an acceleration of the emission processes ; in this figure the electrons still being indicated as solid beads and the lacunae as void beads ; figure 3 shows a schematic representation of a nanocomposite scintillator which consists of a matrix containing nanocrystals ( shown as cubes ) grown therein; figure 4 shows a chart showing the development o f the multi-exciton scintillation processes ( curve R) over time for nanocrystals of CsPbBr3 in a nanocomposite scintillator according to the invention . Furthermore , the figure shows the development over time of the variation of the photoinduced optical absorption for neutral single excitons ( curve S ) , single charged excitons or trions ( curve T ) and double excitons ( curve D) of the second composite in a scintillator according to the invention, such curves indicate that the scintillation dynamics are very similar to the recombination dynamics from multiple excitons ; figure 5 shows a chart showing the development over time of the photoluminescence ( curve F) due to the recombination of single excitons o f nanocrystals of CsPbBrS in a nanocomposite scintillator according to the invention; figure 6a shows a photograph of a prototype of a nanocomposite scintillator made of polyacrylate containing nanocrystals of CsPbBrS under environmental lighting; figure 6b shows a radioluminescence ( curve K) and photoluminescence ( curve L ) ef ficiency chart for identical prototypes irradiated with increasing doses of gamma radiations from cobalt decay 60 up to IMGy of total dose , this showing the stability of the scintillation properties of the scintillator following a high exposure to radiation; figure 7 shows an image under the scanning transmission electron microscopy ( STEM) of metastable nanoparticles produced as nanocrystal synthesis intermediate o f CsPbBrS according to the invention; figure 8 shows the evolution of the optical absorption spectrum of the metastable nanoparticles ( curve M) like in figure 7 during the polyacrylate matrix polymerisation process whose end product is the nanocrystals of CsPbBrS with the typical optical absorption spectrum ( curve J) ; figure 9a shows the evolution of the photoluminescence quantum yield ( curva W) of nanoparticles of CsPbBrS during the polymerisation of an acrylic-based nanocomposite ; figure 9b shows the single exciton luminescence time dynamics of the synthesis intermediate metastable nanoparticles ( curve U) and of the final nanocrystals of CsPbBrS ( curve B ) , to indicate the suppression of non- radiative de-excitation channels ; figure 10a shows a perspective view of a speci fic embodiment of a nanocomposite scintillator in form of rigid panel made of polymethylmethacrylate ( PMMA) ; figure 10b shows a perspective view of a speci fic embodiment of a nanocomposite scintillator in the form of a flexible panel made of acrylic mixture ; figure 10c shows a perspective view of a speci fic embodiment of a nanocomposite scintillator in form of a thin film made of PMMA; figure I la and l lbl and l lb2 , show a schematic view and photographs under environmental and ultraviolet lighting, respectively , of a possible embodiment of a multi-component device for the ultra- fast and ef ficient detection of ionising radiation by coupling ultra- fast nanocomposite scintillators according to the invention with other scintillator materials with slow scintillation but with density and yield in greater light ; and figure 11c shows the diagram of a multi-layer scintillator according to the invention .

[0037] The present invention relates to the field of nanocomposite scintillators in the initial part of the present document , described, but it di f fers from the prior art for two fundamental reasons :

[0038] 1 ) for the nature of the physical process which leads to the emission of scintillation, which occurs following the radiative recombination of multiple excitons in the in the band edge states of the nanostructures . This drastically changes the kinematics of the scintillation process allowing to obtain scintillation times up to a few tens of picoseconds ; and

[0039] 2 ) for the use of a particular embodiment carried out at room temperature , cost-ef fective and widely scalable which allows to prepare nanocomposite scintillators with the aforementioned unprecedented properties and resistance to radiations .

[0040] More particularly, the invention relates to a nanocomposite scintillator in which there is used a colloidal nanocrystal-based scintillator element , scintillators such as for example nanocrystals , nanocubes , nanowires , nanosheets of lead halides or, metal chalcogenides , oxides or other systems which can easily interact with the ionising radiation or with neutrons . The optical properties of such nanocrystals can be adj usted by controlling their dimension, their shape and their composition which can be easily varied through suitable synthetic choices and through postsynthesis treatments ; this al lows to obtain emission spectra, which can be varied at will , from ultraviolet to almost infrared .

[0041] For example , with reference to the Figures I la, b and c, they show forms of nanocrystals given by way of nonlimiting example .

[0042] In particular, figure I la shows a high-density scintillator crystal 11 , such as for example a bismuth germanate (Bi4Ge3012 ) , sodium iodide , lanthanum bromide , lutetium, cadmium tungstate , caesium iodide , in which there is infiltrated a nanocrystal-based scintillator nanocomposite with ultra- fast multi-exciton scintillation polymerised directly in the holes 13 .

[0043] Figure 11c shows a nanocrystal-based scintillator nanocomposite with multi-exciton scintillation ( indicated with 14 ) interposed between a thin layer ( 15 ) and a massive crystal ( 16 ) of high-density scintillator material like the ones described above . In all the cases of figures 11 , the high-density material is responsible for the generation of electrons and secondary photons ( electromagnetic shower ) following interaction with ionising radiation . The electromagnetic shower excites the nanocomposite scintillator, which emits multi-exciton scintillator light with ultra- fast times . The component 16 of figure 11c is also made of a high-density scintillator material like the ones described above and it is responsible for absorbing the ionising beam possibly transmitted by the components 14 and 15 . In this composite " system" , the scintillation signal possibly produced in the portion 16 is time-correlated with the one derived from the ultra- fast nanocomposite scintillator 14 therefore providing an overall scintillation signal of greater intensity while simultaneously maintaining the high time resolution .

[0044] According to a fundamental characteristic of the present invention, the colloidal nanocrystals used as nanoscintillators have a scintillation following transients from multi-excitons created following the interaction with the ionising radiation . The key di f ference with respect to the conventional mechanism based on emission from single excitons is the co-presence of several electron-lacuna pairs in the nanocrystal ( therefore , said multi-excitons indicating the simultaneous presence of several excitons at the same time ) under irradiation from ionising radiation which activates additional recombination channels with respect to the case from single exciton, resulting in a strongly accelerated scintillation, with characteristic times even lower than 100 picoseconds .

[0045] These processes are both of the radiative type ( as schematised in Figure 1 ) and due to the increase in the inherent probability of recombination of multiple exciton states (which increase the radiative emission rate , commonly referred to as radiative ' rate ' , corresponding to the inverse of the scintillation radiative decay time ) , and non- radiative ( as schematised in Figure 2 ) , associated with competitive processes which accelerate the decay time further .

[0046] Speci fically, as schematised in Figure 1 , with respect to the radiative li fetime of single excitons , the single charged excitons ( trions ) show a halved radiative time , and double excitons ( or bi-excitons ) show an acceleration of the radiative time that is four times higher than that of the single excitons .

[0047] The increase in the probability of radiative emission of multi-excitons therefore entails an increase in the overall light yield given that it allows radiative processes to time-overcome the non-radiative loss channels present in the material ( such as for example , phononic processes ) which reduce the yield thereof operating as a single exciton .

[0048] On the contrary, the non-radiative multi-exciton processes , such as for example the Auger recombination ( see diagram in Figure 2 ) , accelerate the time dynamics but they can lead to reductions in the light yield i f their probability exceeds that of the radiative decay . In particular, the Auger recombination schematised in Figure 2 for the bi-exciton case consists in the non-radiative annihilation of one of the two excitons ( 4 ) whose energy is trans ferred to a carrier of the second exciton ( in the case schematised in Figure 2 , to the electron 1 ) , causing the emission thereof from the nanoparticle ( 5 ) which is therefore ionised .

[0049] It should be observed that the multi-exciton Auger non- radiative recombination can be suppressed through widely acknowledged nanocrystal engineering strategies . The latter comprise the dimensional control , the hetero-structuring and he engineering of the quantum confinement potential .

[0050] The key dif ference in the scintillation mechanism with respect to the cases commonly known lies in the reason of the strongly accelerated scintillation times of the present invention which makes it particularly suitable for TOF techniques .

[0051] A key aspect of the invention lies in the fact that the obtainment of scintillation from multi-exciton states requires nanocrystals that are speci fically engineered so that they do not have structural defects , such as for example , vacancies or interstices in or on the surfaces thereof . This is due to the fact that such structural defects act as traps for the carriers ( electrons and lacunae ) generated in the nanocrystals from the interaction with the ionising radiation on faster time scales ( typically smaller than 10 picoseconds ) of the exciton and multi-exciton recombination, time scales which are respectively characterised by scintillation times ranging from a few nanoseconds ( for neutral single excitons ) to tens of picoseconds (multi-excitons ) . In the presence of the aforementioned defects , this allows the conventional nanocrystals not to show scintillation from multiple excitons under ionising radiation excitation, a key requirement to obtain an ultra- fast scintillation .

[0052] With reference to Figure 3 , the nanocomposite scintillator subj ect of the present invention comprising nanocrystals with multi-exciton scintillation 7 ; following irradiation from ionising radiation or from neutrons ( indicated in figure 3 with number 8 ) , there is ef f iciently produced light radiation from multi-exciton states 9 , radiation which is guided by a body of the scintillator C, as shown by the arrow 10 in said figure 3 . At the edges of the body C there are present high ef ficiency detectors , indicated with 11 ( only one shown in figure 3 ) , adapted to receive and convert the guided light radiation into electricity .

[0053] The body of the nanocomposite scintillator comprises a "matrix" 6 which can be obtained with various materials . By way of non-limiting example , the latter may be : polyacrylates and polymethylmethacrylates , Polyolefins , Polyvinyls , Epoxy resins , Polycarbonates , Polyacetates , Polyamides , Polyurethanes , Polyketones , Polyesters , Polycyanoacrylates , Silicones , Polyglycols , Polyimides , fluorinated polymers , Polycellulose and derivatives such as methyl cellulose , hydroxymethyl cellulose , Poly oxazine , silica-based glasses . The matrix 6 o f the nanocomposite scintillator may be obtained through co-polymers of the polymers mentioned above .

[0054] A non-limiting example of a nanocomposite scintillator with emission from multi-exciton states produced according to the invention is defined by a polyacrylate nanocomposite scintillator comprising scintillator nanocrystals of CsPbBrS grown directly in the polymer matrix starting from metastable nanoparticles obtained by ef ficient stirring using a turbo emulsi fier as described hereinafter . In a demonstrative but non-limiting example , said turbo emulsi fier may be f the rotor-stator type .

[0055] According to a key aspect of the invention, these nanocrystals have a substantial suppression of surface defects with respect to the conventional materials , resulting in an extensive ultra- fast contribution ( about 20% of the total ) to the scintillation dynamics due to the multiexciton radiative recombination as shown by the curve R in Figure 4 . This contribution, less than 100 picoseconds , is about 50 times faster than the normal exciton luminescence with characteristic time of about 10 nanoseconds as shown in Figure 5 .

[0056] It should be observed that transient absorption measurements at growing values of the power of excitation, corresponding to the activation multi-exciton processes in the nanocrystals in question, show transient absorption dynamics in bi-exciton regimen ( curve D in figure 4 ) in the same ultra- fast time scintillation regimen ( curve R in figure 4 ) . In particular, the curve S in Figure 4 show the typical single-exciton dynamics , substantially slower than the scintillation dynamics ( curve R) , while curve D shows the transient absorption dynamics due to bi-excitons which equals - in its short time component - the radioluminescence dynamics ( curve R in Figure 4 ) .

[0057] Furthermore , as shown in Figure 6b these nanocompos ites show a high resistance to radiations which allows the use thereof in high radiation-dose environments without being subj ected to structural damages or without damaging their optical properties .

[0058] Another key characteristic of the invention lies in the fact that these nanocomposite scintillators are produced through a simple synthesis whose yield scales linearly with the amount of precursors used .

[0059] A further advantage of the synthesis used lies in its ef fectiveness when carried out at a temperature preferably comprised between 15 and 40 ° C and even more preferably, between 20 and 30 ° C .

[0060] The aforementioned multicomponent scintillator devices may also consist of di f ferent materials such as heterostructured materials .

[0061] According to a key characteristic of the present invention, the nanocrystals used as multi-exciton nanoscintillators in the nanocomposite scintillator described are , purely by way of non-limiting example , nanocrystals of generic compositions of the type :

[0062] A) M1M2Xs, which may or may not be doped with heteroatoms where :

[0063] M1=Cs or other elements of group IA or 1 in the IUPAC nomenclature ;

[0064] M2=Pb, Sn or other elements of group IV or 14 in the IUPAC nomenclature ;

[0065] X= element of group VIIA or 17 in the IUPAC nomenclature) ;

[0066] B) RMX3, which may or may not be doped with heteroatoms, where :

[0067] R= [CH3NH3]+, [CH(NH2)2]+, [CH6N3]+or other variously constituted organic molecules;

[0068] M=Pb, Sn or other elements of group IV or 14 in the IUPAC nomenclature ;

[0069] X= element of group VIIA or 17 in the IUPAC nomenclature) ;

[0070] C) M22M2X6, both not doped and doped with heteroatoms, where:

[0071] M1=Cs or other elements of group IA or 1 in the IUPAC nomenclature ;

[0072] M2= element of group IV or 14 in the IUPAC nomenclature;

[0073] X= element of group VIIA or 17 in the IUPAC nomenclature) ;

[0074] D) M13M22X9or RsM22X9not doped or doped with heteroatoms, where

[0075] M1=Cs or other elements of group IA or 1 in the IUPAC nomenclature ;

[0076] R= [CH3NH3]+, [CH(NH2)2]+, [CH6N3]+or other variously constituted organic molecules;

[0077] M2=Bi or other element of group VA or 15 in the IUPAC nomenclature,

[0078] X= element of group VIIA or 17 in the IUPAC nomenclature.

[0079] E) M12M2M3X6, where:

[0080] M1=element of group IA or 1 in the IUPAC nomenclature;

[0081] M2= elements of group IB or 11 in the IUPAC nomenclature or of group IIIA or 13 in the IUPAC nomenclature;

[0082] M3= element of group VA O 15 in the IUPAC nomenclature;

[0083] X= element of group VIIA or 17 in the IUPAC nomenclature.

[0084] Such compounds are for example: Cs2CuSbC16, Cs2CuSbBr6,

[0085] Cs2CuBiBr6, Cs2AgSbBr6, Cs2AgSbI6, Cs2AgBiI6, Cs2AuSbCl6, Cs2AuBiCl6, Cs2AuBiBr6, Cs2InSbCl6, Cs2InBiCl6, Cs2TlSbBr6, Cs2TlSbl6, and Cs2TlBiBr6. Such compounds may be not doped or doped with heteroatoms that is other atomic species (as will be defined below) .

[0086] F) Further possible generic compositions M12M2M3X6' not doped or doped with heteroatoms, where:

[0087] M1=element of group IA or 1 in the IUPAC nomenclature;

[0088] M2= monovalent cations of chemical elements or species;

[0089] M3= trivalent cations of chemical elements or species;

[0090] X= element of group VIIA or 17 in the IUPAC nomenclature) . Such compounds may be not doped or doped with heteroatoms.

[0091] G) M2M3X6, where:

[0092] M1=element of group IA or 1 in the IUPAC nomenclature;

[0093] M3= trivalent cations of chemical elements or species which are balanced by the presence of ion vacancies;

[0094] X= element of group VIIA or 17 in the IUPAC nomenclature. Such compounds may be not doped or doped with heteroatoms.

[0095] H) ABX3 where:

[0096] A= divalent cation of chemical elements or species;

[0097] B= trivalent cation of chemical elements or species;

[0098] X= chalcogenide ion such as for example Se, S, Te, 0. Such compounds may be not doped or doped with heteroatoms.

[0099] I) A2M3M5X6, where:

[0100] A= divalent cation of chemical elements or species;

[0101] M3= trivalent cation of chemical elements or species;

[0102] M5= pentavalent cation pf chemical elements or species and X= chalcogenide ion. Such compounds may be not doped or doped with heteroatoms.

[0103] L) M22M2X4, where:

[0104] M1=Cs or other elements of group IA or 1 in the IUPAC nomenclature ;

[0105] M2= divalent cation of chemical elements or other species; X= element of group VIIA or 17 in the IUPAC nomenclature. Such composites may or may not be doped with other atomic species ( or heteroatoms ) such as for example alkaline earth metals , alkaline metals , lanthanides , actinides , transition or post-transition metals which improve or change the optical or structural properties thereof .

[0106] The nanocrystals are alternatively in form of nanocubes , nanospheres , nanowires and nanosheets . The dimensions are comprised between 1 nanometre and 200 nanometres . Such crystals constitute from 0 . 0001 % to 99% by weight of the body of the scintillator .

[0107] The metal halide nanocrystals are distributed with controlled orientation that is dispersed in the nanocomposite , in a controlled manner in their position which ranges from 0% to 100% ; furthermore , such metal halide nanocrystals are distributed with controlled orientation with degree ranging from 0% to 100% .

[0108] Described below is the invention in greater detail , with reference to the synthesis of the nanocrystals and polymerisation of the matrix of a nanocomposite scintillator with emission from multi-excitons according to an example shown solely by way of non-limiting example , of the scope of protection of the invention .

[0109] In an embodiment of the invention, there has been provided and tested an ultra- fast multi-exciton nanocomposite scintillator ( according to figure 3 ) consisting, as described, of a polyacrylate matrix 6 ( in particular a PMMA copolymer and polymethylmethacrylate ( PLMA) ) which embeds nanocrystals 7 of CsPbBr3 .

[0110] Advantageously, the polyacrylate matrix has a high optical quality, a low coef ficient of absorption in the entire spectrum o f the visible (with ensuing minimal losses by absorption by the matrix 1 of the scintillator even for large devices ) and a good resistance to radiations . The nanocrystals of composition CsPbBrS were synthesised through a technique based on the efficient stirring using a turbo emulsifier of a precursor solution, generating a colloidal dispersion of precursor nanocrystals which evolve to scintillator nanocrystals directly in a polymer matrix. The Applicant could not find evidence that such technique has previously been used for the synthesis of the aforementioned nanocrystals (and equivalent colloidal nanocrystals) .

[0111] The synthesis of colloidal nanocrystals is typically afflicted by concentration profiles in the reaction environment, which progressively become significant as the volume increases. The experimental procedures reported in literature relating to the mixing of large volumes (especially in the field of formulation) invariably mention the high-speed stirring specifically to address such problem. On a large scale, neither the stirring obtained using a magnetic bar nor obtained using a rod (overhead stirring) offer satisfactory results and the use of homogenisers of the turbo emulsifier type is preferred.

[0112] The present invention uses turbo emulsifiers which is unknown in the synthesis of colloidal nanocrystals. For the purposes of the present invention, the turbo emulsifier may be - by way of non-limiting example - of the rotor-stator type .

[0113] In the embodiment of the invention, reported by way of example, a solution A is prepared by dissolving Cs2CO3 at a concentration comprised between 1.5 and 0.5 M, preferably between 1.25 and 0.70 M in propionic acid. The solution is therefore diluted up to a concentration comprised between 5 mM and 0.5 mM, preferably between 2mM and ImM with a heptane / isopropanol mixture whose composition in volume ratio ranges between 3:1 and 1:1 and it is preferably 2:1. There is prepared a solution called B, by dissolving PbBr2 at a concentration comprised between 1 and 0 . 1 M and tetrabutyl ammonium bromide at a concentration comprised between 1 and 0 . 1 M, under magnetic stirring in a propionic acid and isopropanol mixture in a volume ratio comprised between 3 : 1 and 1 : 1 , containing an amount of oleylamine in a volume ratio comprised between 6 : 1 and 3 : 1 with respect to isopropanol . Said solution is stirred for a period of time comprised between 30 and 60 minutes at a temperature comprised between 60 and 90 ° C .

[0114] The solution A is stirred using a turbo emulsi fier, for example but not limited to the type of rotor-stator ; then, the solution B is added within a period of time comprised between 10 seconds and 1 second, preferably between 5 and 2 s .

[0115] The mixture is left to evolve under turbo-emulsion for a period of time comprised between 60 s and 10 s , preferably between 40 s and 20 s leading to the formation of metastable nanoparticles of composition CsPbBr3 which is rectangularshaped ( see image under scanning transmission electron microscopy in Figure 7 ) which act as growth intermediates for the scintillator nanocrystals responsible for the scintillation properties of the nanocomposite scintillator .

[0116] The metastable particles are isolated, after diluting the reaction mixture with isopropanol in a volume ratio comprised between 0 . 1 and 0 . 8 with respect to the reaction mixture , by centri fuging at a rate comprised between 6000 rpm and 1500 rpm . The metastable particles are therefore dissolved in an organic monomer solution ( for example , acrylics such as methyl methacrylate and lauryl methacrylate ; in amounts ranging from 0 . 001 % to 95% by weight ) in the presence of polymerisation activators which are subsequently activated for example optically or thermally .

[0117] According to a key aspect of the invention, the scintillator nanocrystals CsPbBrS are formed during the polymerisation of the plastic matrix, reaching the final shape thereof at the end of the solidi fication process thereof . This is highlighted by the evolution of the optical absorption spectrum during the solidi fication process shown in Figure 8 ( line M shows the optical absorption spectrum of the metastable nanoparticles and curve J the optical absorption spectrum o f the final nanocrystals ) . The intermediate curves show the spectra during the process .

[0118] This unique characteristic of the invention avoids nanocrystal decay processes common to the techniques known in literature and it allows to produce high optical quality nanocomposites .

[0119] Furthermore , as shown in Figure 9a, the polymerisation of the plastic matrix entails a gradual increase in the photoluminescence quantum yield of the nanocrystals up to 90% ( curve W) accompanied by a slowing down of the emission dynamics from single exciton thereof ( see Figure 9b, where the curve U shows the decay kinematics of the metastable precursor nanoparticles ; and the curve B shows the decay kinematics of the final nanocrystals ) .

[0120] This indicates that the manufacturing method produces nanocomposites containing nanocrystals of CsPbBrs wherein the non-radiative defects are removed ef fectively . This aspect is of key importance towards obtaining the multiexciton scintillation whose time kinematics is shown in figure 4 .

[0121] In all embodiments of the present invention, the nanocomposite scintillator may be tri- , bi- or monodimensional and with an arbitrary shape . The lateral dimensions of a nanocomposite scintillator may vary from 10 micrometres to 300 centimetres , with thicknesses ranging between 50 nanometres and 200 centimetres .

[0122] Figure 10a shows a speci fic solution of a nanocomposite scintillator in form of a rigid panel made of PMMA; figure 10b shows a speci fic solution of a nanocomposite scintillator in form of a flexible panel made o f acrylic mixture ; figure 10c shows a speci fic solution of a nanocomposite scintillator in form of a thin film made of PMMA.

[0123] As described above relating to figure 11 , in an embodiment of the present invention, the nanocomposite scintillator is optically coupled to other scintillator systems to accelerate the scintillation time thereof or generally to improve the performance thereof .

[0124] In an embodiment of the present invention, at least one of the faces of the scintillator is connected to at least one light detector 15 ( e . g . photodiode or photomultipliers ) .

[0125] To summarise, the present invention relates to a nanocomposite scintillator comprising high atomic number metal halide nanocrystals which emit a radiation scintillation light through a multi-exciton recombination process when struck by a radiation for example ionising . This is obtained thanks to the simultaneous presence - in each nanocrystal - of several electron-lacuna pairs which allow a strongly accelerated scintillation process even with times less than 100 ps .

[0126] Thanks to the radiative recombination of multiple excitons in the band edge states o f the nanocrystal s , there is a scintillation within very rapid times , up to a few tens of picoseconds .

[0127] As indicated in the present document , in order to have the ef fect indicated above , it is also crucial that the nanocrystals be without non-radiative defects that is be free of structural defects , for example vacancies or interstices , within them or on their surfaces . This so as to avoid "traps" for the electrons generated in the nanocrystals by the interaction with the ionising radiation on time scales smaller than those of the multi-excitation recombination .

[0128] The absence of defects in the or on the nanocrystals is obtained thanks to the method for producing the scintillator material and this thanks to the fact that the scintillator nanocrystals evolve to scintillator nanocrystals directly in the (polymer ) matrix : which receives them .

[0129] The above could neither be found in nor deduced from the prior art texts W02021 / 090167 and CN113621368 .

[0130] With regard to W02021 / 090167 , it discloses a multicomponent composite scintillator of the sensitised type that is a scintillator having a body made of polymeric or glass material per se having low scintillation ef ficiency given that the constituents thereof have a low atomic number ; in said material there are dispersed sensitiser elements and a high atomic number adapted to increase the probability of interaction with the ionising radiation which strikes the scintillator and sensitising the light emission of second elements , said emitters , through secondary processes including the trans fer of energy, charge , emission of photons and / or electrons or anything else .

[0131] This , with the aim of obtaining a fast scintil lator with scintillation time less than 5 nanoseconds .

[0132] To this end, W02021 / 090167 discloses the use of high atomic weight perovskite nanostructures which interact with the ionising radiation or neutrons and which, as described in the introductory part of the present document , act as "antennas" which, after interaction with the radiation, sensitise the emission by organic emitters present in the matrix, with low atomic number .

[0133] Therefore , in the prior art document in question, herein described is the use of perovskite nanostructures which " sensitise" the emitters (nanoparticles of semiconductors or metals or other elements or molecules with low atomic number ) , both present in a matrix which receives them (made of glass or polymeric ) .

[0134] Therefore , while this prior art document discloses a fast scintillator, with emission times of nanoseconds , where there are present perovskite elements which easily interact with the incident radiation and which emit a radiation thereof adapted to be absorbed by the emitters which in turn emit a luminescence thereof , the present invention discloses a scintillator which uses a matrix in which there are present nanocrystals which, struck by a radiation, emit a light radiation through an " internal" multi-exciton recombination process .

[0135] The content of W02021 / 090167 is not disclosed in the present document where the invention provides for that the scintillation be directly obtained from nanostructures with multi-exciton scintillation which emit light with ultra- fast times , in the order of picoseconds . As mentioned, the scintillator of the present invention uses high atomic number metal halide nanocrystals which emit a radiation scintillation light through ultra- fast multi-exciton recombination processes , said light radiation being directly detected by detectors arranged adj acent to the body of the scintillator . There is no use of such radiation to generate a scintillation emission in other elements or molecules arranged in the body of the scintillator ( as described in this document ) .

[0136] These characteristics , which of fer the advantages described in the description above , are neither described in nor deducible from W02021 / 090167 .

[0137] The aforementioned characteristics are neither described in nor deducible from CN113621368 either, relating to a scintillator material and to a preparation method thereof which uses a plastic body in which there are present a metal organic structure and perovskite quantum dots . Therefore , the Chinese prior art document nears the contents of W02021 / 090167 , but it does not disclose the characteristics mentioned above of the invention subj ect of the present document in any manner whatsoever .

[0138] In addition, although indicating that the scintillator is of the "ultra- fast" type , CN113621368 does not state that the response thereof is still of a few nanoseconds ; therefore , the present invention, obtained using methods di f ferent from those of the scintillator described in the Chinese prior art document of fers a much faster response such to allow the use thereof in machines where there is required an ultra- fast response , such as time of flight positron emission tomography machines where the response of the detector is key to a reconstruction of high-quality and precision images ( as described in the introductory part of the present document ) .

[0139] In the light of the above , it is not deemed that W02021 / 090167 and CN113621368 disclose or suggest a scintillator and a method for carrying it out like the one subj ect of the present patent application .

[0140] All embodiments described in the present document may be combined or used for providing devices in tandem and / or multicomponent configuration, wherein di f ferent nanoscintillators (both or only a few types of ultra- fast multi-exciton type ) are engineered so as to generate scintillation light with speci fic wavelength following interaction with di f ferent radiations ( ionised and nonionised) .

[0141] The scintillator may also be in form of optical fibre . The invention has allowed to demonstrate the suitability of nanocrystals with ultra- fast multi-exciton emission such as nano-scintillators with ultra- fast response times for obtaining nanocomposite scintillators that are ef ficient , fast and with high resistance to radiations .

Claims

CLAIMS1. Ultra-fast composite scintillator comprising a body (C) comprising nanocrystals (7) of metal halides with high atomic number capable of emitting a radiation scintillation light through ultra-fast multi-exciton recombination processes, the nanocrystals being devoid of structural defects both internally and on the outer surface thereof.

2. Ultra-fast composite scintillator according to claim 1, characterised in that the body of the scintillator (C) is associated with a detector (11) arranged at at least one edge thereof, said detector collecting and converting the light radiation produced by said nanocrystals (7) into electricity, the emission of scintillation by the nanocrystals being due to the recombination of charged excitons, double excitons, triple excitons or exciton complexes of order higher than three.

3. Ultra-fast composite scintillator according to claim 1, characterised in that the metal halide nanocrystals have one of the following compositions:A) M1M2Xs, which may or may not be doped with heteroatoms where :M1=Cs or other elements of group IA or 1 in the IUPAC nomenclature ;M2=Pb, Sn or other elements of group IV or 14 in the IUPAC nomenclature,X= element of group VIIA or 17 in the IUPAC nomenclature) ;B) RMX3 which may or may not be doped with heteroatoms, whereR= [CH3NH3P, [CH(NH2)2]+, [CH6N3]+or other variously constituted organic molecules;M=Pb, Sn or other elements of group IV or 14 in the IUPAC nomenclature ;X= element of group VIIA or 17 in the IUPAC nomenclature) ;C) M22M2X6 not doped and doped with heteroatoms, where:M1=Cs or other elements of group IA or 1 in the IUPAC nomenclature ;M2= element of group IV or 14 in the IUPAC nomenclature;X= element of group VIIA or 17 in the IUPAC nomenclature;D) M13M22X9O R3M22X9not doped or doped with heteroatoms, where :M1=Cs or other elements of group IA or 1 in the IUPAC nomenclature ;R= [CH3NH3]+, [CH(NH2)2]+, [CH6N3]+ or other variously constituted organic molecules;M2= Bi or other element of group VA or 15 in the IUPAC nomenclature,X= element of group VIIA or 17 in the IUPAC nomenclature.E) M22M2M3X6 doped or not doped with heteroatoms, where: Ml= element of group IA or 1 in the IUPAC nomenclature;M2= elements of group IB or 11 in the IUPAC nomenclature or of group IIIA or 13 in the IUPAC nomenclature;M3= element of group VA O 15 in the IUPAC nomenclature;X= element of group VIIA or 17 in the IUPAC nomenclature, such as: Cs2CuSbC16, Cs2CuSbBr6, Cs2CuBiBr6, Cs2AgSbBr6, Cs2AgSbl6, Cs2AgBil6, Cs2AuSbC16, Cs2AuBiC16, Cs2AuBiBr6, Cs2InSbCl6, Cs2InBiCl6, Cs2TlSbBr6, Cs2TlSbI6, and Cs2TlBiBr6.F) M22M2M3X6, doped or not doped with heteroatoms, where M1=element of group IA or 1 in the IUPAC nomenclature; M2= monovalent cations of chemical elements or species, M3= trivalent cations of chemical elements or species,X= element of group VIIA or 17 in the IUPAC nomenclature.G) M2M3X6, not doped or doped with heteroatoms, where: M1=element of group IA or 1 in the IUPAC nomenclature;M3= trivalent cations of chemical elements or species which are balanced by the presence of ion vacancies;X= element of group VIIA or 17 in the IUPAC nomenclature.H) ABX3not doped or doped with heteroatoms where:A= monovalent or divalent cation of chemical elements or species ;B= trivalent or tetravalent or pentavalent cation oof chemical elements or species; andX= chalcogenide ion such as for example Se, S, Te, 0 (group VI or 16 in the IUPAC nomenclature) .I) A2M3M5X6doped or not doped with heteroatoms, where: A= divalent cation of chemical elements or species;M3= trivalent cation of chemical elements or species;M5= pentavalent cation pf chemical elements or species and X= ion of an element of group VI or 16 in the IUPAC nomenclature .L) M32M2X4 doped or not doped with heteroatoms, where:M1=Cs or other elements of group IA or 1 in the IUPAC nomenclature ;M2= divalent cation of chemical elements or other species; X= element of group VIIA or 17 in the IUPAC nomenclature.M) AM2M2X4 doped or not doped with heteroatoms where:A= monovalent cation of chemical elements or species of group 1 in the IUPAC nomenclature;M= monovalent cation of chemical elements or species of group 1 in the IUPAC nomenclature different from A;M2= pentavalent cation of chemical elements or species;X= ion of an element of group VI or 16 in the IUPAC nomenclature .

4. Ultra-fast composite scintillator according to claim 1, characterised in that the metal halide nanocrystals are alternatively in form of nanocubes, nanospheres, nanowires and nanosheets.

5. Ultra-fast composite scintillator according to claim 1, characterised in that the metal halide nanocrystals have dimensions comprised between 1 nanometre and 200 nanometres.

6. Ultra-fast composite scintillator according to claim1, characterised in that the metal halide nanocrystals constitute from 0.0001% to 99% by weight of the body of the scintillator .

7. Ultra-fast composite scintillator according to claim 1, characterised in that the metal halide nanocrystals are distributed, in a controlled manner in their position, with degree ranging from 0% to 100%.

8. Ultra-fast composite scintillator according to claim 1, characterised in that the metal halide nanocrystals are distributed with controlled orientation with degree ranging from 0% to 100%.

9. Ultra-fast composite scintillator according to claim 1, characterised in that the body of the scintillator (C) has a matrix (6) comprising at least one of the following polymers or respective copolymers: Polyacrylates and Polymethylmethacrylates, Polyolefins, Polyvinyls, Epoxy resins, Polycarbonates, Polyacetates, Polyamides, Polyurethanes, Polyketones, Polyesters, Polycyanoacrylates, Silicones, Polyglycols, Polyimides, fluorinated polymers, Polycellulose and derivatives such as methyl cellulose, hydroxymethyl cellulose, Poly oxazine, silica-based glasses.

10. Ultra-fast composite scintillator according to claim 1, characterised in that the metal halide nanocrystals are alternatively dispersed in a plastic matrix or deposited in form of film on at least one surface of the body (C) of the scintillator.

11. Ultra-fast composite scintillator according to claim 1, characterised in that sensitized composite scintillator is optically coupled to other scintillator systems to accelerate the scintillation time thereof.

12. Ultra-fast composite scintillator according to claim 1, characterised in that the composite scintillator is in form of optical fibre.

13. Ultra-fast composite scintillator according to claim 1, characterised in that the composite scintillator is a component of multi-component scintillator devices also consisting of different materials such as metamaterials.

14. Ultra-fast composite scintillator according to claim 1, characterised in that it is alternatively tri-, bi- or mono-dimensional shaped, lateral dimensions comprised between 10 micrometres and 300 centimetres and a thickness comprised between 50 nanometres and 200 centimetres.

15. Ultra-fast composite scintillator according to claim 1, characterised in that the body (C) of the scintillator is coupled, in tandem and / or multicomponent configuration, to at least another scintillator so that the ultra-fast scintillator acts as an ultra-rapid timekeeping device to increase the time resolution of the device.

16. Method for providing an ultra-fast scintillator according to claim 1, said scintillator having a body (C) made of polymeric material comprising nanocrystals (7) , characterised in that the nanocrystals are metal halide nanocrystals produced through the turbo-emulsion of a precursor solution generating a colloidal dispersion of precursor nanocrystals which evolve in the scintillator nanocrystals directly in the polymeric material of the scintillator body (C) .

17. Method according to claim 16, characterised in that the precursor nanocrystals are dissolved in the polymeric material in the presence of polymerisation activators and at an amount comprised between 0.001% and 99% by weight, the scintillator nanocrystals forming during the polymerisation of the plastic matrix.

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