Inorganic-organic hybrid nanoparticles with improved energy transfer properties

Abstract

The invention relates to a process for the preparation of inorganic-organic hybrid nanoparticles with down-shifting properties having improved energy transfer properties, the particles obtainable from said process and their use to improve the performance of optoelectronic and photovoltaic devices.

Description

[0001] INORGANIC-ORGANIC HYBRID NANOPARTICLES WITH IMPROVED ENERGY

[0002] TRANSFER PROPERTIES

[0003] DESCRIPTION

[0004] Field of the invention

[0005] The present invention is in the field of luminescent nanoparticles, specifically hybrid inorganic-organic nanoparticles with down-shifting and up-conversion properties for use in optoelectronic and photovoltaic devices.

[0006] Background art

[0007] Down-shifting refers to the phenomenon whereby a material has the ability to absorb light energy at a certain wavelength and re-emit it at longer wavelengths.

[0008] Up-conversion, instead, is a phenomenon whereby energy is absorbed at a longer wavelength and emitted at a shorter wavelength.

[0009] The mechanism underlying these phenomena is the transfer of energy from an absorbing to an emitting species (energy transfer, ET).

[0010] To understand what happens in visible light-emitting materials, three distinct factors are considered: absorption, energy transfer (ET) and Quantum Yield (QY).

[0011] The main objective in the preparation of emitting or luminescent materials is to obtain materials that absorb in the UV and IR and have a large light emission in the visible. Luminescence is nothing other than the emission of light energy by a system, resulting from the absorption of energy, and will be the more intense the greater its absorption. Therefore, there is a need for a material with a high absorption coefficient if a high light emission is desired. The absorption coefficient, or molar absorptivity, represents the specific absorbance of a solution with a unit molar concentration, considering a unit optical path cell, at a given wavelength. The QY, instead, is defined as the percentage of light energy emitted by a system with respect to that absorbed: a system with a QY of 100% will therefore be able to emit in the form of light all the radiation it absorbs.

[0012] It should be noted that, if the absorption of a substance is low, even if the QY is 100%, the light emission will still be low. For this reason, it is not sufficient to consider only the numerical value of QY but rather it is useful to consider the comparison of a QY value obtained with two different systems and with different absorption coefficients.

[0013] In nanoparticles capable of emitting light energy, there is an intermediate step between absorption and light emission, i.e. the transfer of energy between the absorbing species (the matrix and / or antenna) and the emitting one (the dopant): the species that absorbs energy does not emit light radiation, but transfers that absorbed energy to a second species, which is responsible for the light emission. This quantum phenomenon is known in the literature as energy transfer. The efficiency of energy transfer is greater the more absorbed energy is transferred from one species to another.

[0014] There are several quantum phenomena that can interfere with ET and thus decrease its efficiency. Nowadays, there is a need for materials that can maximise ET and thus luminous efficiency.

[0015] As further explained below, a system without an antenna exhibits a QY of less than 0.1 % at a wavelength of 340 nm while this exceeds 10% in the presence of the antenna, for the nanoparticles of the present invention. Thus, in a system with an antenna, in addition to having an increase in light intensity due to the increased absorption of the system, there is also a significant increase in ET efficiency compared to a system without an antenna.

[0016] The luminescent nanomaterials of the present invention comprise, or consist of, three parts: a matrix, understood as the main material that makes up the nanoparticle; a dopant, i.e. atoms of an element that enter the matrix and replace atoms in the matrix; and an antenna, i.e. organic molecules that bind to the nanoparticles. The matrix is responsible for giving structure to the system and is responsible for an initial energy transfer (the matrix absorbs in the UV or I R, transfers its energy to the dopant and this emits in the visible). The dopant is the species responsible for the light emission of nanomaterials. The antenna is responsible for the greatest energy absorption and consequently for the main and most efficient energy transfer phenomenon.

[0017] However, for the same efficient antenna, since there are various quantum phenomena that can interfere with energy transfer (ET), and thus decrease the efficiency of materials, the luminescent materials available today provide a relatively low energy transfer value. The scientific publication Sharma K. Gayatri et al. ('Low temperature synthesis, charachterisation and tunable optical properties of Eu3+and Tb3+doped CaMoC nanoparticles', JOURNAL OF ALLOYS AND COMPOUNDS, Vol. 602, (2014.06.01)) describes a method for the preparation of calcium molybdate (CaMoC ) nanoparticles doped with europium (Eu3+) at low temperatures. However, the procedure is still conducted at rather high temperatures (130°C).

[0018] It is also known in the literature (see, for example, Nehra Kapeesha et al: 'Lanthanides [beta]-diketonate complexes as energy-efficient emissive materials: A review', Journal of Molecular Structure, Elsevier, Vol. 1249 (2021.09.20) or Tang Lu et al: 'Ion exchange YVO4:Eu3+ nanocrystals and their strong luminescence enhanced by energy transfer of thenoyltrifluoroacetone ligands', Journal of Alloys and compounds, Elsevier, (2013.12.21)) that the photoluminescence of common lanthanide salts is weak, in particular due to the very low absorption coefficients of these ions, and that in order to enhance photoluminescence, complexes of Ln3+ions can be synthesised with ligands (antennae) such as beta-diketone compounds with high radiation absorption capacities, which can transfer the absorbed energy to the metal centre. The absorption of radiation by the ligand (antenna) followed by emission by the metal centre is a phenomenon known as the antenna effect.

[0019] However, there is still a strong need to develop processes for the preparation of luminescent nanoparticles that are more efficient and result in (nano)materials or (nano)particles with high luminescence.

[0020] Brief description of the figures

[0021] Figure 1 : XRD spectrum of a sample of CaMoC doped with 10% Eu3+versus Ca ion2+. Figure 2: TEM image of a sample of CaMoC doped with 10% Eu3+vs. Ca ion2+.

[0022] Figure 3: Emission spectra of samples functionalised with antenna in different solvents. Figure 4: Absorption spectrum of the sample CaMoC>4:Eu15%@TTA (i.e. CaMoC doped with 15% Eu3+with TTA as the antenna) in acetonitrile. The broad absorption band centred at about 340 nm is observed.

[0023] Figure 5: Exploded schematic representation of a photovoltaic cell.

[0024] Figures 5A to 5E: Exploded schematic representations of a nanoparticle-functionalised photovoltaic cell according to any one of the embodiments of the invention, for example, with nanoparticles deposited on the photovoltaic material layer i.e. silicon (5A), with nanoparticles deposited on the polymeric encapsulant layer on the photovoltaic material side (5B) or on the glass side (5C), with nanoparticles deposited on the glass layer on the side facing the polymeric encapsulant layer (5D) or on the side facing outward (5E)). Figure 6: Photovoltaic window in which the nanoparticles of the invention are embedded within the polymer constituting the window itself.

[0025] Figure 7: Current vs. voltage curve of a commercial cell functionalised with the nanoparticles of the invention. Figure 7 shows that the functionalised commercial cell (upper curve) is more efficient than the non-functionalised commercial cell (lower curve).

[0026] Summary

[0027] The present invention relates to a process for the preparation of luminescent nanoparticles, in particular hybrid inorganic-organic nanoparticles with improved energy transfer properties, the main features of which are listed in the first of the appended claims.

[0028] Further objects of the invention are the particles obtained or obtainable by said process and the optoelectronic or photovoltaic device or polymer film comprising such nanoparticles.

[0029] The appended claims summarising the invention form an integral part of this description. Detailed description of the invention

[0030] An object of the present invention is therefore a process for the preparation of particles having increased luminescence compared to those known in the art.

[0031] In particular, the present invention relates to a process for the preparation of nanoparticles comprising a matrix, wherein said matrix comprises one or more chemical species selected from the group of molybdates, vanadates, aluminates, tungstates, silicates, oxides of alkali, alkaline-earth metals or transition elements; and wherein said matrix is doped with a lanthanide element or a transition element, and wherein said nanoparticles are functionalised with a beta diketone compound, and wherein said nanoparticles have an average diameter of between 2 and 20 nm; comprising the following steps: a) dissolving a salt or oxide of calcium or strontium and at least one salt or oxide of a lanthanide and / or transition element in nitric acid (HNO3) and removing the excess nitric acid by evaporation, b) adding molybdate, vanadate, tungstate, aluminate, silicate or oxide of an alkali or alkaline earth metal or a transition element or ammonium, and adding glycol, c) adding NaOH to bring the pH into a range from 2 to 14, d) heating the mixture from step c), e) cooling and separating the solid from the liquid fraction, f) washing the solid obtained in step e), g) drying the nanoparticles obtained in step f), h) adding the nanoparticles from step g) to a solution of a beta diketonic compound in an organic solvent, i) the suspension is left under agitation for 10 hours at room temperature, j) cooling and separating the solid from the liquid fraction, k) washing the solid obtained in step j), l) optionally, the nanoparticles from step k) are stored as an acetonitrile suspension, characterised by the fact that step d) is conducted at a temperature of 80°C to 120°C for between 6 hours and 2 hours respectively.

[0032] In fact, it was surprisingly found that carrying out the reaction of step d) at a temperature of 80°C to 120°C for a time of 6 hours to 2 hours, respectively, enables the preparation of nanoparticles with a high / improved luminous efficiency of more than 10.

[0033] This high / improved luminous efficiency effect is scientifically explained by the fact that operating in such a narrow set of process variables allows preparing nanoparticles with an average diameter between 2 nm and 20 nm. This particle size enables the improved interaction between the dopant element, e.g. Europium, and the antenna, e.g. Tenoyltrifluoroacetone (TTA), since the energy transfer (ET) phenomenon occurs over distances of 10 nm.

[0034] Thus, the combination of the temperature and reaction time conditions is responsible for the effect of providing particles with an average diameter between 2 nm and 20 nm, and thus particles with a high / improved luminous efficiency of more than 10.

[0035] Since energy transfer was found to occur at distances of 10 nm, reaction parameters were also found that would allow particle sizes of less than 20 nm to be achieved, in order to ensure efficient energy transfer to the internal dopant atoms as well.

[0036] Such an improvement in energy transfer was made possible by optimising the nanomaterial synthesis process, in particular the process of synthesising the matrix, which was then functionalised with antennae comprising a diketone function, preferably Tenoyltrifluoroacetone (TTA).

[0037] The nanoparticles, in particular the matrix, are synthesised using the polyol process in glycol at temperatures between 80°C and 120°C, preferably 105°C to 120°C, more preferably 115°C, according to step d) of this procedure.

[0038] In step b), glycol is added. The glycol can be, for example, ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol. Preferably, the glycol is ethylene glycol.

[0039] In step c), the pH is raised by addition of NaOH in a range from 2 to 14, preferably 7 to 14, more preferably 8 to 10, and even more preferably 9 to 10, or 9 to 9.5.

[0040] Particularly, step d) is conducted at a temperature of 115°C for 3 hours. More preferably, step d) is conducted at a temperature of 115°C for 3 hours in ethylene glycol.

[0041] To a person skilled in the art, it is evident that with the synthesis procedure according to any embodiments described here, it is possible to obtain nanoparticles (NPs) comprising or consisting of different matrices, doped with different lanthanides or transition elements, and functionalised with different beta-diketonic antennae.

[0042] For example, nanoparticles comprising one or more chemical species chosen from the group of molybdates, vanadates, aluminates, tungstates, silicates, oxides of alkaline, alkaline-earth metals or transition elements can be synthesised using the above procedure.

[0043] Preferably, by said process, nanoparticles comprising one or more chemical species chosen from calcium molybdate, strontium molybdate, calcium vanadate, strontium vanadate, calcium tungstate, strontium tungstate, aluminates can be synthesised. According to a preferred aspect of the invention, the chemical species is calcium molybdate.

[0044] In such cases, these materials are included in the nanoparticle matrix. The antenna used is a beta diketone compound, preferably one chosen from the group consisting of: Hacac acetylacetone (2,4-pentanedione), Hacac-F7 perfluoroacetylacetone (heptafluoroacetylacetone), Hbfa benzoyl-2-furanoylmethane, Hbpp 1 ,3-bis(3-pyridyl)-1 ,3-propanedione, Hbtfac benzoyltrifluoroacetone, Hbzac benzoylacetone (1-phenyl-1 ,3-butanedione), Hdbbm di(4-bromo)benzoylmethane, Hdcm d,d-dicampholylmethane, Hdmbm 4,4_-dimethoxydibenzoylmethane, Hdmh 2,6- dimethyl-3,5-heptanedione, Hdnm dinaphthoylmethane, Hdpm dipivaloylmethane (2,2,6,6-tetramethyl-3,5-heptanedione) Hdppm di(perfluoro-2- propoxypropionyl)methane, Hdtp 1 ,3-di(2-thienyl)-1 ,3-propanedione, Hfacam 3- (trifluoroacetyl)-d-camphor, Hfdh 6,6-trifluoro-2,2-dimethyl-3,5-hexanedione (pivaloyltrifluoroacetone), Hfhd 1 ,1 ,2,6,7,7-decafluoro-3,5-heptanedione Hfod 6, 6, 7,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione, Hftac 2-furyltrifluoroacetone (4,4,4-trifluoro- 1 - (2-furyl)-1 ,3-butanedione), Hhfac hexafluoroacetylacetone (1 ,1 ,5,5-hexafluoro-2,4- pentanedione), Hhfbc 3-(heptafluorobutyryl)-d-camphor Hhfth 4,4,5,6,6-heptafluoro-1- (2-thienyl)-1 ,3-hexanedione, Hmfa 4-methylbenzoyl-2-furanoylmethane, Hmhd 6- methyl-2,4-heptanedione, Hntac 2-naphthoyltrifluoroacetone (4,4,4-trifluoro-1-(2- naphtyl)-1 ,3-butanedione), Hpop 3-(5-phenyl-1 ,3,4-oxadiazol-2-yl)-2,4-pentanedione, Hppa 3-phenyl-2,4-pentanedione, Hpta (= Htpm) pivaloyltrifluoroacetone (5,5-dimethyl- 1 ,1 ,1-trifluoro-2,4-hexanedione), Hptp 1-phenyl-3-(2-thienyl)-1 ,3-propanedione, H(t- cam) 3-(tert-butylhydroxymethylene)-d-camphor, Htfac trifluoroacetylacetone (1 ,1 ,1- trifluoro-2,4-pentanedione), Htfn 1 , 1 ,2,3,7,7,8,9,9,9-tetradecafluoro-4,6-nonanedione, Hthd (= Hdpm, Htmhd) 2,2,6,6-tetramethyl-3,5-heptanedione (dipivaloylmethane), Htnb 4, 4, 4, -trifluoro- 1 -(2-naphtyl)- 1 ,3-butanedione, Htmod 2,2,6,6-tetramethyl-3,5- octanedione, Htrimh 2,2,6-trimethyl-3,5-heptanedione, Htod 2,2,7-trimethyl-3,5- octanedione and mixtures of these, most preferably Tenoyltrifluoroacetone (TTA). A beta-diketone compound is defined as a compound having at least one beta-diketone function, i.e. two ketone groups in beta with each other.

[0045] Each of these matrices can be doped with a lanthanide or a transition element. Of particular interest are Europium, Thulium, Ytterbium, Neodymium, Yttrium, Manganese, Cerium, Terbium, Samarium, and Dysprosium.

[0046] According to a preferred aspect, the lanthanide element or the transition element is chosen from Europium, Thulium, Ytterbium, Neodymium, Yttrium, Manganese, Cerium, Terbium, Samarium, Dysprosium. According to a more preferred aspect, the lanthanide element is Europium. Particularly suitable for the purpose of the present invention are species with intense light emission in the visible such as Terbium, Samarium and Dysprosium, or species that emit in the infrared, including Thulium, Neodymium, Erbium, Holmium and Ytterbium.

[0047] For the preparation of the luminescent nanoparticles of the present invention, more than one lanthanide and / or more than one transition element may also be used as a dopant, e.g. two or three lanthanides and / or two or three transition elements, even in combination with each other.

[0048] By way of example, one or more pairs of lanthanides working synergistically can be employed to enhance luminescence properties, such as the terbium-itterbium or ytterbium-erbium pair. In addition, pairs of a lanthanide with a transition element can be used to increase light emission intensities, such as the manganese-europium pair.

[0049] The lanthanides mentioned can all enjoy the antenna effect from different beta-dichotonic molecules as described here. The same applies to the transition metals in the case of co-doping with at least one lanthanide (or rather, the transition metals can also enjoy the antenna effect but would not be able to emit light radiation without the presence of at least one lanthanide).

[0050] At least one lanthanide and / or transition element is present in an amount of 1% to 20% (w / w %) by weight of the alkali or alkaline earth metal.

[0051] Preferably, the at least one lanthanide or transition element is present in an amount of 1 % to 20% (w / w %) by weight of the calcium or strontium weight.

[0052] According to a preferred aspect, in which the matrix can further include other ions, preferably it includes sodium ions.

[0053] According to a preferred embodiment of the process, the matrix comprises sodium ions and the chemical species is calcium molybdate, the lanthanide element is europium and this element is present in an amount of 1% to 20% (w / w %) by weight relative to calcium. According to a more preferred embodiment of the process, the nanoparticle matrix has the following chemical formula

[0054] Cai-XMoO4 :Eu(x / 2), where x is between 0.01 and 0.99.

[0055] According to a preferred embodiment of the process, in step a) the calcium salt is calcium nitrate (Ca(NOs)2), the oxide of a lanthanide element is europium (III) oxide (EU2O3), and / or in step b) ammonium molybdate is added.

[0056] According to a preferred embodiment of the process, the organic solvent in step h) is acetonitrile.

[0057] In the experimental part, a form of realisation of the synthesis process of europium-doped calcium molybdate nanoparticles (Cai.xMoO4 :Eu(x / 2)) is exemplified, in which these nanoparticles are synthesised by a process in ethylene glycol and subsequently functionalised with thenoyltrifluoroacetone (TTA) (the antenna) by mixing at room temperature in acetonitrile.

[0058] The synthesis of Cai.xMoO4 :Eu(x / 2) takes place at a temperature of 115°C, which allows nanoparticles to be synthesised between 2 and 20 nm, i.e. the desired size range to have a good energy transfer (ET) between antenna and lanthanide, since the ET phenomenon occurs at distances of 10 nm. Antenna-functionalised nanoparticles, compared to nonfunctionalised ones, show an increase in quantum yield (QY) from 0.1% to 10.4%, indicating a very efficient ET mechanism. To the applicant's knowledge, the nanoparticles obtainable by the process of the invention are the most efficient, under the same measurement conditions (solvent and temperature), in terms of ET both compared with complexes and with other antenna-functionalised nanoparticles known in the state of the art.

[0059] In addition, the functionalisation of the above-mentioned materials, i.e. the bonding with the antenna, takes place through the use of a solvent, acetonitrile, which significantly increases the luminescence of the material obtained, reducing the quenching phenomena (Example 2). Visually, a great difference in terms of emission was observed between particles prepared in a standard solvent such as, for example, dimethylformamide and those prepared in acetonitrile. Therefore, functionalisation of the nanoparticles when carried out in acetonitrile enables the preparation of nanoparticles that are even more efficient in terms of the luminescence of the material obtained (Figure 3).

[0060] Therefore, a process for functionalising luminescent nanoparticles with an antenna binder, or simply antenna, is also an object of the present invention.

[0061] In other words, the present invention also relates to a process for functionalising particles, specifically luminescent particles, with a beta-diketonic compound comprising the following steps: h) adding to a solution of a beta-dike tonic compound in an organic solvent, preferably acetonitrile, particles comprising a matrix comprising molybdates, vanadates, aluminates, tungstates, silicates or oxides of alkali metals, alkaline earth metals or transition elements and which are doped with at least one lanthanide element and / or one transition element; i) leaving the suspension obtained from step h) under agitation for 10 hours at room temperature; j) cooling and separating the precipitated solid by cooling and including the functionalised particles from the liquid fraction, k) washing the functionalised particles separated in step j), I) optionally store the functionalised particles from step k) as a suspension in acetonitrile.

[0062] The process according to any of the embodiments described here has also proved suitable for the preparation of luminescent nanoparticles other than those exemplified, to name but a few:

[0063] - nanoparticles with a matrix comprising SrWCU doped with Eu(lll) using benzoyltrifluoroacetone (btfac) as an antenna;

[0064] - YVO matrix nanoparticles4 doped with Dy(lll) with TTA as the antenna;

[0065] - nanoparticles with a matrix comprising Y2O3 doped with the pair Tb(lll)- Yb(lll) with 4,4,- trifluoro-1-(2-naphtyl)-1 ,3-butanedione (tnb) as an antenna .

[0066] Another object of the invention, are nanoparticles obtained or obtainable by the process according to any of the embodiments described herein.

[0067] According to a preferred aspect, these nanoparticles have an average diameter between 2 and 20 nm and a light efficiency value of more than 10.

[0068] In particular, the nanoparticles obtainable from the process described above have any of the characteristics listed above with reference to the process of their preparation. More particularly, they are nanoparticles having an average diameter of between 2 and 20 nm, comprising (or consisting of) a matrix based on molybdates, vanadates, aluminates, tungstates, silicates, oxides of alkali metals, alkaline-earth metals or transition elements, one or more dopants chosen from among lanthanides and transition metals, and functionalized with at least one antenna ligand, e.g., a beta-diketonic compound. For example, nanoparticles with a CaMoC matrix doped with Eu(lll) with TTA as the antenna, nanoparticles with a matrix comprising SrWCU doped with Eu(lll) using benzoyltrifluoroacetone (btfac) as the antenna; nanoparticles with matrix comprising Y O4 doped with Dy(lll) using TTA as antenna; nanoparticles with matrix comprising Y2O3 doped with the pair Tb(l 11)- Yb(lll) using 4,4,-trifluoro-1-(2-naphtyl)-1 ,3-butanedione (tnb) as antenna.

[0069] Another object of the invention is an optoelectronic device, i.e. an electro-optical or optoelectrical transducer system, such as LEDs, sensors and photovoltaic devices, or a polymeric film comprising the aforementioned nanoparticles according to any of the embodiments described herein.

[0070] In fact, the nanoparticles obtainable with the process of the invention can be incorporated within polymeric matrices such as polymethyl methacrylate (PM MA) and ethylene vinyl acetate (EVA) and / or polyvinyl chloride (PVC) while maintaining luminescence properties. Thus, polymer films with energy transfer properties can be produced to protect optoelectronic devices, or to increase the performance of photovoltaic devices of different nature (c-Si, a-Si, pc-Si, GaAs, CIGS and in general all photovoltaic devices in which there is no good conversion of UV and / or IR energy into electrical energy).

[0071] According to an embodiment, the polymer film comprising the aforementioned nanoparticles comprises, or consists of, PMMA and / or EVA and / or PVC.

[0072] In photovoltaics, the advantage lies not only in the recovery of energy from an unexploitable portion of the solar spectrum to generate electricity and its conversion into exploitable (i.e. visible) energy, but also in the increase of the overall solar energy absorbed by the system. For example, lanthanides possess a low absorption coefficient and, consequently, low light emission. Both calcium molybdate and TTA have high absorption coefficients and together cover a large portion of the UV spectrum (200-400 nm).

[0073] More specifically, the present invention also relates to an opto-electronic device, which as a whole is indicated in the figures by the number 100.

[0074] Such an opto-electronic device 100 is preferably of the photovoltaic type.

[0075] Such an opto-electronic device 100 comprises nanoparticles according to any of the described embodiments and / or nanoparticles obtainable by the process according to any of the described embodiments.

[0076] In particular, the invention also relates to an opto-electronic device 100, preferably photovoltaic, comprising nanoparticles having an average diameter between 2 and 20 nm comprising a matrix, wherein said matrix comprises one or more chemical species selected from the group of molybdates, vanadates, aluminates, tungstates, silicates, oxides, of alkali metals, alkaline-earth metals or transition elements; wherein said matrix is doped with one or more lanthanide elements and / or one or more transition elements, and wherein said nanoparticles are functionalised with at least one di-ketone compound. As an example, the opto-electronic device 100 can be additivated with:

[0077] - CaMoO4 nanoparticles doped with Eu(lll) and functionalised with TTA as antenna

[0078] - nanoparticles with a matrix comprising SrWO4 doped with Eu(lll) using benzoyltrifluoroacetone (btfac) as an antenna;

[0079] - YVO4 matrix nanoparticles doped with Dy(lll) with TTA as the antenna; and / or

[0080] - nanoparticles with a matrix comprising Y2O3 doped with the pair Tb(lll)- Yb(lll) with 4,4,- trifluoro-1-(2-naphtyl)-1 ,3-butanedione (tnb) as antenna.

[0081] The luminescent nanoparticles of the invention can be added to the opto-electronic device according to techniques known to be suitable for the purpose.

[0082] A person skilled in the art is able to choose the most suitable technique depending on the material on which the luminescent nanoparticles are to be deposited, be it a glass or a thermoplastic or thermosetting polymer (including resin), or depending on the portion of the device most suitable for performance enhancement.

[0083] Some examples of deposition techniques are: sputtering, drop casting, spin coating, sputtering, Physica Vapour Deposition (PVD), Chemical Vapour Deposition (CVD).

[0084] Alternatively, it is also possible to embed the nanomaterials directly into the polymer matrix during the manufacturing phase of the matrix itself.

[0085] A conventional photovoltaic cell generally comprises three main layers (excluding the electronic parts): the bottom layer, which consists of the material responsible for the photovoltaic effect (e.g. silicon, germanium, ...), an intermediate layer of encapsulating material (typically a polymeric material, preferably a thermoplastic polymer) that covers the layer of photovoltaic material, and finally a layer of protective glassy material.

[0086] In particular, as shown in Figures 5 to 5E, an opto-electronic device 100 according to the invention may comprise a photovoltaic cell comprising in turn: a first, internal, layer 101 , which consists of the material responsible for the photovoltaic effect (e.g. Silicon, Germanium, ...), a second, intermediate layer 102 of encapsulating material (typically a polymeric material, preferably a thermoplastic polymer) covering / coating the photovoltaic material layer, and finally a third, outer layer 103 of protective glassy material.

[0087] The peculiarity of the opto-electronic device 100 according to the invention lies in the fact that said nanoparticles can, for example, be deposited to form a layer with nanoparticles 110 on at least one of the following surfaces:

[0088] - on the first layer 101 , of photovoltaic material (Figure 5A), in particular on surface 101a facing the second layer 102,

[0089] - on the second layer 102, of polymer encapsulant, either on a first surface 102a facing the first layer 101 (bottom side, Figure 5B), or on the second opposite surface 102b facing the third layer 103 (top side, Figure 5C),

[0090] - on the third layer 103 of glassy material, either on a first surface 103a facing the second layer 102 (bottom side, Figure 5D) or on the second opposite surface 103b facing outwards (top side, Figure 5E).

[0091] Obviously, nanoparticles can be deposited either on a single surface of the surfaces 101a, 102a, 102b, 103a, 103b listed above, or even on several surfaces of those listed above, i.e. on one or more of the first 101 , second 102 and third 103 layers.

[0092] For example, nanoparticles can be deposited either on the first layer, of photovoltaic material, or on the third layer, of glassy material. Again, for illustrative purpose, in the case of a photovoltaic window 200, nanomaterials can also be embedded within the polymer constituting the window itself (Figure 6). Finally, a further object is the use of the nanoparticles obtained or obtainable by the above-mentioned process according to any of the embodiments described herein, for the preparation of an optoelectronic or photovoltaic device or polymeric film comprising the aforementioned nanoparticles.

[0093] Experimental section

[0094] EXAMPLE 1 : synthesis of CaMoO4 nanoparticles :Eu functionalised with TTA

[0095] The reagents used for the synthesis of the nanoparticles (NPs) of the invention are listed below: calcium nitrate tetrahydrate, >99.0% (Sigma-Aldrich®); ammonium molybdate tetrahydrate (Sigma-Aldrich®); ethylene glycol (Thermo Scientific™); Europium (III) oxide, 99.996% (REacton®, REO, AlfaAesar); nitric acid, 70% (Alfa Aesar), NaOH >99.0% (Sigma-Aldrich®), Thenoyltrifluoroacetone (Sigma-Aldrich®), acetonitrile (Sigma- Aldrich®).

[0096] Calcium molybdate nanoparticles doped with europium (CaMoC :Eu) are synthesised in a polyol process in ethylene glycol at 115°C in order to prepare nanoparticles with an average diameter of less than 20 nm.

[0097] Europium (III) oxide (EU2O3) is used as a precursor, ammonium molybdate and the synthesis is conducted at 115°C. The internal charge of the system is counterbalanced by sodium ions introduced via NaOH. Samples were prepared with different percentages of Eu(lll) dopant compared to calcium ions.

[0098] The summary procedure is outlined below: a. 0.2368 g calcium nitrate tetrahydrate (Ca(NOs)2 4H2O) and 0.0352 g europium (III) oxide (EU2O3) are dissolved in 70 % nitric acid under stirring and the excess acid is evaporated. b. When the fumes stop coming out, 1.2360 g of ammonium molybdate tetrahydrate and 15 mL of ethylene glycol are added. c. NaOH is added until a pH of 9-9.5 is reached. d. Everything is brought under reflux for 3 hours at 115°C. e. The resulting suspension is cooled and centrifuged at 8000 rpm for 8 minutes. f. The liquid fraction is removed and the solid is washed with 4 acetone washes (8000 rpm for 8 minutes). g. The resulting nanoparticles are dried in an oven at 40°C until a dry powder is obtained. h. The powdered nanoparticles are added to a solution of TTA in acetonitrile while maintaining a nanoparticle / antenna mass ratio of 1 / 5. i. The suspension is left under agitation for 10 hours at room temperature. j. The suspension is cooled and centrifuged to separate the solid from the liquid fraction. k. The solid is washed with 4 washes in acetonitrile (8000 rpm for 8 minutes) to remove excess TTA. l. The nanoparticles are dispersed again in acetonitrile.

[0099] Characterisation of nanoparticles

[0100] Determination of particle size

[0101] To determine the size of nanoparticles, the techniques used were X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM).

[0102] Sample preparation

[0103] Data on a sample of CaMoC doped with 10% Eu3+versus Ca2+ion are reported.

[0104] XRD measurements are performed on the powder sample dried in an oven at 40°C for 4 hours. For TEM, 10 uL of sample solution in water (concentration 10 mg / mL) is deposited on a copper screen.

[0105] Instrumentation

[0106] The XRD instrument is equipped with an X-ray source with a copper anode (Ka, A =1.5418 A) and a solid-state detector equipped with a 'Peltier' capable of cooling the Si(Li) crystal of which it is made down to -100°C, allowing the internal noise to be reduced to extremely low values.

[0107] A Hitachi Regulus 8220® instrument equipped with the Oxford energy dispersive spectroscopy system was used for TEM image acquisition.

[0108] Results

[0109] The XRD spectrum (Figure 1) reflects the tetragonal structure with point group 141 / a of calcium molybdate, as expected from the comparison with data found in the literature. The experimental parameters are shown in Table 1 and an average crystallite size of 11.92 nm is observed. From the TEM images (Figure 2), nanoparticles ranging in size from 5 nm to 20 nm are observed. For the sample considered, there is an average size distribution of 12.9 nm.

[0110] Example 2: Comparative luminescence testing

[0111] Sample preparation: Comparison among functionalisation methods

[0112] The emission spectra of samples of nanoparticles of CaMoC>4:Eu15%@TTA obtained according to Example 1 but varying the functionalization solvent were recorded. Specifically, 20 mg of powdered nanoparticles of CaMoC , doped with 15% Eu ions3+with respect to Ca ions2+, were mixed with 2 g TTA in 5 mL of solvent (cone. 4 mg / mL of nanoparticles):

[0113] - acetonitrile (AcN), according to Example 1 ;

[0114] - ethanol (EtOH), according to the earlier publication by Tang Lu et al. and

[0115] - acetic acid (CH3 COOH).

[0116] The solutions were left under agitation for 8 hours, after which they were centrifuged at 12000 rpm for 10 minutes. The supernatants were drained off and the precipitate was redispersed in the initial solvent, again at a concentration of 4 mg / mL, using an ultrasonic bath for 10 minutes. Prior to redispersing the precipitate of the sample functionalised in AcN, a portion of the precipitate was taken and dried, weighed and then dispersed in water (H2 O), again at a concentration of 4 mg / mL.

[0117] Finally, each solution was diluted 10-fold in the respective solvent and the respective luminescence emission spectra were recorded.

[0118] Instruments

[0119] Luminescence spectra were aeguired through a modular spectrofluorometer (model Nanolog / Fluorolog-3-2iHR20, Horiba-Jobin Yvon®) with a 450 W Xenon lamp and a photomultiplier as detector.

[0120] The parameters used for the measurements were kept identical for the collection of each spectrum and are given below: Integration Time: 0.050000s EX1 : Excitation 1 Excitation: 333.00 nm

[0121] Side Entrance Slit: 5.00 nm Bandpass

[0122] Side Exit Slit: 5.00 nm Bandpass

[0123] First Intermediate Slit: 5.00 nm Bandpass

[0124] Grating: Density 1200 (Blaze: 500)

[0125] Emission range: 575650 -nm

[0126] Side Entrance Slit: 2.00 nm Bandpass Side Exit Slit: 2.00 nm Bandpass

[0127] Grating: Density 1200 (Blaze: 500)

[0128] Results

[0129] Figures 3 and 4 show the emission spectra of the samples at the same concentration and measurement conditions. Table 2 shows the emission intensity percentages, assuming 100% intensity for the sample with the highest intensity, i.e. the acetonitrile (AcN) sample.

[0130] Table 2 It can be seen that the intensity is significantly higher for particles where functionalisation has taken place in acetonitrile than for other solvents.

Claims

CLAIMS1) Process for the preparation of nanoparticles comprising a matrix, wherein said matrix comprises one or more chemical species chosen from the group of molybdates, vanadates, aluminates, tungstates, silicates, oxides of alkali metals, alkaline-earth metals or transition elements; and wherein said matrix is doped with a lanthanide element or a transition element, and wherein said nanoparticles are functionalised with a beta diketone compound, and where said nanoparticles have an average diameter of between 2 and 20 nm; the procedure comprising the following steps: a) dissolving a salt or oxide of calcium or strontium and at least one salt or oxide of a lanthanide and / or transition element in nitric acid (HNO3) and removing the excess nitric acid by evaporation, b) adding molybdate, vanadate, tungstate, aluminate, silicate or oxide, of an alkali or alkaline earth metal or a transition element or ammonium, and adding glycol, c) adding NaOH to bring the pH into a range from 2 to 14, d) heating the mixture of step c) to a temperature of 80°C to 120°C for 6 hours to 2 hours respectively, preferably to a temperature of 115°C for 3 hours, e) cooling and separating the solid from the liquid fraction, f) washing the solid obtained in step (e), g) drying the nanoparticles obtained in step f), h) adding the nanoparticles from step g) to a solution of a beta diketonic compound in an organic solvent, i) the suspension is left to stir for 10 hours at room temperature j) cooling and separating the solid from the liquid fraction, k) washing the solid obtained in step j), l) optionally, the nanoparticles from step k) are stored as an acetonitrile suspension.2) Process according to claim 1 , wherein the chemical species is chosen from calcium molybdate, strontium molybdate, calcium vanadate, strontium vanadate, calcium tungstate, strontium tungstate, calcium aluminate, strontium aluminate, and is preferably calcium molybdate.3) Process according to claim 1 or 2, wherein the beta diketone compound is chosen from Hacac acetylacetone (2,4-pentanedione), Hacac-F7 perfluoroacetylacetone (heptafluoroacetylacetone), Hbfa benzoyl-2-furanoylmethane, Hbpp 1 ,3-bis(3-pyridyl)- 13-propanedione, Hbtfac benzoyltrifluoroacetone, Hbzac benzoylacetone (1-phenyl-1 ,3- butanedione), Hdbbm di(4-bromo)benzoylmethane Hdcm d,d-dicampholylmethane,Hdmbm 4,4_-dimethoxydibenzoylmethane, Hdmh 2,6-dimethyl-3,5-heptanedione, Hdnm dinaphthoylmethane Hdpm dipivaloylmethane (2,2,6,6-tetramethyl-3,5- heptanedione), Hdppm di(perfluoro-2-propoxypropionyl)methane, Hdtp 1 ,3-di(2-thienyl)-1.3-propanedione, Hfacam 3-(trifluoroacetyl)-d-camphor, Hfdh 6,6,6-trifluoro-2,2- dimethyl-3,5-hexanedione (pivaloyltrifluoroacetone) Hfhd 1 ,1 ,2,6,7,7-decafluoro-3,5- heptanedione, Hfod 6,6,7,7,8,8-heptafluoro-2,2-dimethyl-3,5-hexanedione Hftac 2- furyltrifluoroacetone (4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione), Hhfac hexafluoroacetylacetone (1 ,1 ,1 ,5,5-hexafluoro-2,4-pentanedione), Hhfbc 3- (heptafluorobutyryl)-d-camphor, Hhfth 4,4,5,6,6-heptafluoro-1-(2-thienyl)-13- hexanedione, Hmfa 4-methylbenzoyl-2-furanoylmethane, Hmhd 6-methyl-2,4- heptanedione, Hntac 2-naphthoyltrifluoroacetone (4,4,4-trifluoro-1-(2-naphtyl)-1 ,3- butanedione), Hpop 3-(5-phenyl-1 ,3,4-oxadiazol-2-yl)-2,4-pentanedione, Hppa 3- phenyl-2,4-pentanedione, Hpta (= Htpm) pivaloyltrifluoroacetone (5,5-dimethyl-1 , 1 , 1 - trifluoro-2,4-hexanedione), Hptp 1-phenyl-3-(2-thienyl)-1 ,3-propanedione, H(t-cam) 3- (tert-butylhydroxymethylene)-d-camphor, Htfac trifluoroacetylacetone (1 ,1 ,1-trifluoro-2.4-pentanedione), Htfn 1 ,1 ,2,3,7,8,9,9,9-tetradecafluoro-4,6-nonanedione, Hthd (= Hdpm, Htmhd) 2,2,6,6-tetramethyl-3,5-heptanedione (dipivaloylmethane), Htnb 4,4,- trifluoro- 1 -(2-naphtyl)- 1 ,3-butanedione, Htmod 2,2,6,6-tetramethyl-3,5-octanedione Htrimh 2,2,6-trimethyl-3,5-heptanedione, Htod 2,2,7-trimethyl-3,5-octanedione and preferably tenoyltrifluoroacetone (TTA).4) Process according to any one of claims 1 to 3, wherein the lanthanide element and / or the transition element is chosen from Europium, Thulium, Ytterbium, Erbium, Neodymium, Yttrium, Manganese, Cerium, Terbium, Samarium, Dysprosium and is preferably Europium or pairs thereof, preferably wherein said pairs are chosen from: Terbium-ltterbium, Yttrium-Erbium, Manganese-Europium.5) Process according to any one of claims 1 to 4, wherein the at least one lanthanide element and / or the at least one transition element is present in an amount of from 1 % to 20% (w / w %) by weight of the alkali or alkaline earth metal.6) Process according to any of claims 1 to 5, where the matrix further comprises sodium ions.7) Process according to any one of claims 1 to 6, wherein the matrix comprises sodium ions and the chemical species is calcium molybdate, the lanthanide element is europium and wherein said element is present in an amount of from 1 % to 20 % (w / w %) by weight with respect to calcium.8) Process according to any one of claims 1 to 7, wherein in step a) the calcium salt is calcium nitrate (Ca(NOs)2), the oxide of a lanthanide element is europium (III) oxide (EU2O3), and / or in step b) ammonium molybdate is added.9) Process for functionalising luminescent particles with a beta-diketonic compound comprising the following steps: h) adding particles comprising a matrix comprising molybdates, vanadates, aluminates, tungstates, silicates or oxides of alkali metals, alkaline earth metals or transition elements to a solution of a beta-diketonic compound in an organic solvent and which are doped with at least one lanthanide element and / or transition element; i) leaving the suspension obtained from step h) under agitation for 10 hours at room temperature; j) cooling and separating the precipitated solid by cooling and including the functionalised particles from the liquid fraction, k) washing the functionalised particles separated in step j), l) optionally store the functionalised particles from step k) as a suspension in acetonitrile.10) Process according to any one of claims 1 to 8 or process for functionalisation according to claim 9, wherein the organic solvent of step h) is acetonitrile.11) Nanoparticles obtainable by the process according to claim 10.12) Nanoparticles according to claim 11 , having an average diameter between 2 and 20 nm and a luminous efficiency value greater than 10.13) Optoelectronic or photovoltaic device or polymer film comprising nanoparticles according to claim 11 or 12 .14) Opto-electronic device according to claim 13 comprising a photovoltaic cell comprising in turn a first, inner layer (101) comprising material responsible for the photovoltaic effect, a second, intermediate layer (102) of encapsulating material that covers said first layer (101), a third, outer layer (103) of protective glassy material, wherein said nanoparticles are deposited to form a nanoparticle layer (110) on at least one of the following surfaces:- on said first layer (101), in particular on its surface (101a) facing said second layer (102),- on said second layer (102), or on a first surface (102a) facing the first layer (101), or on the opposite second surface (102b) facing the third layer (103),- on said third layer (103) of glassy material, either on a first surface (103a) facing the second layer (102), or on the second opposite surface (103b) facing outwards.15) Use of nanoparticles according to claim 11 or 12 for the preparation of an optoelectronic or photovoltaic device or a polymer film.

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