Anticounterfeiting marks

Abstract

The present invention relates to an authenticated object and a method to authenticate an object.

Description

ANTICOUNTERFEITING MARKS FIELD OF INVENTION

[0001] The present invention relates to anticounterfeit marks, and particularly anticounterfeit marks comprising luminescent nanoparticles. BACKGROUND OF INVENTION

[0002] The issues of authentication and counterfeit deterrence can be important in many contexts. In the commercial manufacturing world, it is common for unauthorized goods to be manufactured, sold, and distributed in direct competition with authentic goods. Counterfeiting has reached epidemic proportions worldwide, especially in the area of consumer goods such as clothing, luxury watches, handbags and wallets, perfumes, spirits, medical treatments (drugs or devices) among other. Electronics and software products are also particular targets of counterfeiters, who appropriate the value of trademarks or copyrights. Indeed, counterfeit articles can so closely resemble genuine goods that consumers readily confuse the counterfeit articles with the authentic articles.

[0003] Counterfeit deterrence and self-authentication issues are an integral component in the modern world, where information is transmitted with lightening-like speed and fabrication capabilities are broadened with additive manufacturing techniques.

[0004] There are many methods of preventing counterfeiting of goods. Usually, markings are directly put on the goods themselves, by analogy with an artist's signature on his creation. With this methodology however, as soon as the counterfeiter succeeds in reproducing the “signature”, the technique becomes obsolete.

[0005] Otherwise, marking an object with a recognizable mark may hinder its esthetical aspect. Worse, if one of the object’s functions is transparency, for instance glasses or lens, marking the object may deteriorate said object.

[0006] There is thus a great need to develop a marking system in order to prevent reproduction of markings.SUMMARY

[0007] Two axes may be identified for providing a durable and trustworthy marking. First, marking must not be reproducible by any manufacturing technique at a cost much lower than cost of goods to be authenticated. Second, marking should be easily authenticated by consumers and / or provider, for instance while shopping.

[0008] In this disclosure, it is shown how a consumer can be certain that the object he is willing to purchase is genuine.

[0009] The present invention relates to an authenticated object comprising a luminescent mark, said luminescent mark comprising composite particles having a mean size in a range from 100 nm to 1500 nm, said composite particles comprising luminescent nanoparticles dispersed in a metal oxide matrix, said composite particles being distributed throughout the luminescent mark, wherein • Absorbance of the composite particles is less than 0.01 over the UV-visible range of light; • Density of luminescent nanoparticles is greater than 109cm-3.

[0010] Preferably, the density of luminescent nanoparticles is greater than 2.1010cm-3, more preferably 5.1010cm-3, even more preferably 1011cm-3.

[0011] In the present disclosure, the phrase “particles being distributed throughout the luminescent mark” means that, for each convex surface entirely included in the mark and representing at least 10% of the mark’s surface, said convex surface encompasses at least one particle.

[0012] In the present disclosure, density of luminescent nanoparticles is the number of particles per unit of volume.

[0013] In the present disclosure, a convex surface is a surface that verifies the following property: for each pair of points A and B included in the convex surface, the segment AB is also included in said convex surface.

[0014] In the present disclosure, the absorbance of a material over a wavelength range refers to the absorbance of said material for each wavelength of said wavelength range.

[0015] Optionally, the composite particles distribution may be homogenous. In the present disclosure, the phrase “homogenous particles distribution” means that, for each convex surface entirely included in the mark and representing at least 10% of the mark’s surface, the concentration of the composite particles within said convex surface is equal to the concentration of particles within the mark.

[0016] Such an authenticated object allows solving the abovementioned issues. Indeed, the mark of such an authenticated object is transparent and is invisible for a naked human eye. Thus, the authenticated object presents the same aesthetic with or without the mark.

[0017] Conversely, under a predetermined light, the mark is easily seen and may confirm the authenticity of the authenticated object. Moreover, the luminescence signal of the composite particles is intense enough to be imaged individually with the spatial resolution of an optical device already available for the consumer. Preferably, the optical device may be the camera included in a smartphone, or a microscope. Accordingly, verifying if an object is genuine is easy for a consumer.

[0018] The predetermined light may be selected according to the exact nature of the luminescent nanoparticles. For instance, ultraviolet light is especially suitable to trigger luminescence of semi-conductive luminescent nanoparticles or rare-earth doped metal oxide. For rare-earth doped metal oxide, absorption of light is efficient in a limited range of wavelengths – an absorption peak – which may be located in infra-red range. In this case, rare-earth doped metal oxide has no impact on visible light absorbance and infra- red light illumination of the mark leads to luminescent infra-red light that can be measured by usual infra-red sensors.

[0019] Also, providing stable, reliable, and durable luminescent nanoparticles at an industrial scale is hard, and cannot be achieved without the appropriate infrastructure. Moreover, integrating composite particles, and more particularly composite particles comprising luminescent nanoparticles, into an object is a challenge itself. Therefore, the mark cannot be easily counterfeited.

[0020] In some embodiments, the concentration of luminescent nanoparticles in the luminescent mark is in a range from 150 ppm to 5 ppb, preferably from 15 ppm to 15 ppb.

[0021] In the present disclosure, ppm and ppb relate to mass concentration.

[0022] In some embodiments, the luminescent nanoparticles are quantum dots and the concentration of luminescent nanoparticles in the luminescent mark is in a range from 15 ppm to 150 ppb.

[0023] In some embodiments, the luminescent nanoparticles are quantum plates and the concentration of luminescent nanoparticles in the luminescent mark is in a range from 1.5 ppm to 15 ppb.

[0024] In some embodiments, the luminescent nanoparticles are single rare-earth doping elements – i.e., lanthanide elements or Scandium or Yttrium – surrounded by the metal oxide and the concentration of luminescent nanoparticles in the luminescent mark is in a range from 150 ppm to 1.5 ppm.

[0025] In some embodiments, the concentration of composite particles in the luminescent mark is in a range from 500 ppm to 0.5 ppm.

[0026] In some embodiments, the composite particles are distributed randomly throughout the luminescent mark.

[0027] The random distribution of the composite particles inside the mark can be achieved due to manufacturing method (formulation, deposition, drying / curing…). In addition, random distribution allows generating a statistically unique mark that can be registered in a database. Thus, counterfeiting such a mark is extremely difficult.

[0028] Moreover, random distributions allow dispersed particles and strengthen the repartition of the composite particles within the mark. Accordingly, the risk of generating global effect that could be visible for the human eye on the authenticated object becomes particularly low. Thus, the marking is more effective.

[0029] In some embodiments, the average number of luminescent nanoparticles comprised in a composite particle is greater than 10, preferably greater than 20, even more preferably greater than 50.

[0030] In some embodiments, the luminescent nanoparticles comprise at least one of CdSe, CdSeS, ZnSe, ZnSeS, InP, CuInS2spherical quantum dots.

[0031] In some embodiments, the luminescent nanoplatelets comprise at least one of CdSe, CdSeS, ZnSe, ZnSeS, InP, CuInS2 nanoplatelets.

[0032] In some embodiments, the metal oxide matrix is selected from the group consisting of alumina, zirconia, titanium oxide, hafnium oxide, yttrium oxide, gadolinium oxide, or a mixture thereof.

[0033] In some embodiments, the authenticated object is transparent.

[0034] The mark is compatible with transparent objects such as glasses or lens. Thus transparent objects may be marked without hindering their transparency.

[0035] The present invention also relates to an authentication method for acknowledging an object comprising: • Authenticating the object by creating a luminescent mark, said luminescent mark comprising composite particles having an average size in a range from 100 nm to 1500 nm, said composite particles comprising luminescent nanoparticles dispersed in a metal oxide matrix, said composite particles being distributed throughout the luminescent mark, wherein i. Absorbance of the composite particles is less than 0.01 over the UV-visible range of light; ii. Density of luminescent nanoparticles is greater than 109cm-3; • Obtaining an image of reference imaging the luminescence of the luminescent mark, • Storing said image of reference inside a database,• Obtaining a test image of the luminescent mark on the authenticated object; and • Controlling if said test image corresponds to said image of reference in said database.

[0036] The abovementioned method is, for a consumer, a reliable and easy method to verify if an object is genuine.

[0037] In some embodiments, the object is transparent, the image of reference obtained in step b) includes an optical feature of the authenticated object, the test image obtained in step d) of the method includes the same optical feature of the authenticated object; and the matching of step e) includes identification of the optical feature.

[0038] In some embodiments, the object is an ophthalmic lens, such as a unifocal corrective lens, a progressive lens or a plano lens. In other embodiments, the object is a glass container, such as a perfume bottle, a spirit bottle or a cosmetic container. DEFINITIONS

[0039] In the present invention, the following terms have the following meanings:

[0040] “Absorbance” is the decimal logarithm of ratio I0 / I, where I0 is the intensity of light incident on a sample, and I is the intensity of light transmitted through said sample. In this disclosure, absorbance is measured for a 2-millimeter-thick sample. Absorbance is measured for wavelengths in UV and visible range from 350 nm to 780 nm.

[0041] “Core / crown” refers to a heterostructure in which a central nanoparticle: the core, is surrounded by a band of material disposed on the periphery of the core: the crown.

[0042] “Core / shell” refers to a heterostructure in which a central nanoparticle: the core, is embedded by a layer of material disposed on the core: the shell. Two successive shells may be laid, yielding core / shell / shell heterostructure. Core and shell may have the same shape, for instance core is a nanosphere and shell is a layer of essentially constant thickness yielding a spherical core / shell nanoparticle. Core and shell may have different shapes, for instance a dot – a nanosphere or a nanocube or any other nanocluster - isprovided as a core and shell is grown laterally around the core, yielding an heterostructure with shape of a nanoplate but comprising a dot inside the nanoplate: the latter is named dot in plate thereafter. In some embodiments, core and shell have different compositions. In other embodiments composition varies continuously from core to shell: there is no precise boundary between core and shell but properties in centre of the core are different from properties on the outer boundary of shell.

[0043] “Nanometric size” refers to a size of matter in which quantum effects appear due to confinement. For semi-conductive nanoparticles, nanometric size has to be defined with the average Bohr radius of an electron / hole pair. Confinement is effective for size in at least one dimension of the object below 20 nm, preferably below 15 nm, more preferably below 10 nm. The stronger confinements are obtained with a size in at least one dimension below 5 nm.

[0044] “Nanoparticle” refers to a particle having a size in at least one of its dimensions below 100 nm. For a nanosphere, diameter should be below 100 nm. For a nanoplate, thickness should be below 100 nm. For a nanorod, diameter should be below 100 nm.

[0045] “Nanoplate” refers to a 2D shaped nanoparticle, wherein the smallest dimension of said nanoplate is smaller than the largest dimension of said nanoplate by a factor (aspect ratio) of at least 1.5, at least 2, at least 2.5, at least 3, at least 3.5, at least 4, at least 4.5, at least 5, at least 5.5, at least 6, at least 6.5, at least 7, at least 7.5, at least 8, at least 8.5, at least 9, at least 9.5 or at least 10.

[0046] “Visible light / range” visible light or visible range refers to light which wavelength ranges from 380 nm to 780 nm. In other words, visible light or visible range refers to light that can be seen by a human eye. Otherwise, the Ultra Violet (UV)-light ranges from 250 nm to 380 nm.

[0047] “Transparent” refers to a material or object presenting two optical properties. First, light scattering by the transparent material or object should be low, typically below 1% as measured with standard haze measurement according to ASTM D1003- 00, preferably below 0.8%, even preferably below 0.5%, even more preferably below 0.2%. Second, for at least one wavelength in the visible range, the shape of an object seenthroughout a transparent object at said wavelength should be unaltered, in the sense that an observer observing through a transparent object or material can recognize another object when looking through them. In this disclosure, transparency may not necessarily be related to the absorbance of visible light. In other words, transparent material may be transparent and coloured.

[0048] “Mean size”, refers to a size of a population of particles, obtained by a mathematical mean of sizes of each individual particle of the population. Practically, the mean size may be determined by optical microscopy or electron microscopy: size of each particle visible in the microscopy is evaluated by fitting each particle with a circle whose diameter defines the size of the particle – even if particle is not spherical, it may be fitted by a circle - then computing the mean of all individual sizes to obtain the mean size. Other methods, such as light scattering may be used to determine indirectly the mean size of the population of particles. Experimentally, particles are always obtained in the form of population of particles. By extension in this disclosure, the mean size of a particle is the mean size of the population of particles which has been synthesized. For the sake of clarity, a particle having a mean size value comprised between 50 nm and 1000 nm is a particle of a population – or a sub-population – of particles having a mean size between 50 nm and 1000 nm.

[0049] “Doped” refers to a composition of material with a crystalline structure – core or shell – in which a dopant element is substituted to the main element. Such semi- conductive compositions are noted QD:Dopant in the following. For instance, a ZnSe quantum dot may be doped with Manganese (Mn) so that a part of Zn elements are substituted by Mn elements, and noted ZnSe:Mn. For phosphors, compositions are noted according to formula (III).

[0050] “Encapsulated” refers to a state in which a material – or a matrix – coats, surrounds, embeds, contains, comprises, wraps, packs, or encloses a plurality of particles, which may be nanoparticles (1) or composite particles (2).

[0051] “Fluorescent” refers to the property of a material that emits light after being excited by absorption of light. Actually, light absorption drives said material in anenergetically excited state, which eventually relaxes by emission of light of lower energy, i.e., of longer wavelength – red shifted.

[0052] “wt%” refers to the weight percentage of a compound in a formulation or of an element in a compound.

[0053] “Semi-conductive nanoparticles” refers to particles made of a material having an electronic structure corresponding to semi-conductive materials known in electronic industry but having a nanometric size. Due to their specific electronic structure, semi- conductive materials behave as high-pass absorbing materials. Indeed, light having a wavelength more energetic than band gap may be absorbed by the semi-conductive material, yielding an electron / hole pair, an exciton, which later recombine in the material and dissipate heat, or emit light, or both. On the contrary, light having a wavelength less energetic than band gap cannot be absorbed: semi-conductive material is transparent for these wavelengths. In macroscopic semi- conductive materials, visible light is generally absorbed while near / mid infra-red light is not absorbed. When semi-conductive particles have a nanometric size, confinement - i.e., shape and nanometric size - governs electronic structure following the rules of quantum mechanics and light absorption may be limited to UV range or UV and high energy visible light.

[0054] “High-pass filter” refers to optical filters in which absorbance is high, typically higher than 0.5, preferably 1, more preferably 1.5, for wavelength of high energy, i.e. short wavelengths. On the contrary, absorbance for wavelength of low energy, i.e. long wavelengths, is low, typically below 0.1. The transition between both domains of high and low absorbance is defined by the cut-off wavelength. Cut-off wavelength may be in the UV-light range; or in the visible light range; or in the IR-light range.

[0055] “Random distribution” refers to a distribution of objects inside a delimited space that, when said objects are distributed inside said space, the distribution of said objects inside said space does not follow any predictable patent. In other words, each distribution of said objects inside said space are equiprobable.

[0056] “Resolution length” is used to characterize an image and refers to the minimal size of objects that can be distinguished by an imaging means, i.e. imaging device and optionally numerical treatments, yielding said image. An image has a resolution length of 1 µm when objects having a size greater than 1 µm appear individually on the image and when objects separated by a distance larger than 1 µm appear separated on the image.

[0057] “Spatial resolution” is used to characterize an imaging means and refers to the ability of a measurement to separate in an image two marks or particles that are closed together. When spatial resolution is high, marks or particles can be measured and located individually. When spatial resolution is low, marks or particles cannot be measured individually but only in the form of a spatial average to a degree proportional to the resolution length of the image. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 shows fluorescence images obtained by optical microscope for marks comprising different concentrations of composite particles according to a first example.

[0059] Figure 2 shows fluorescence images obtained by optical microscope for marks comprising different concentrations of composite particles according to a second example.

[0060] Figure 3 is a graph representing the absorbance function of the wavelength for different concentration of composite particles according to the first example.

[0061] Figure 4 shows fluorescence images obtained by optical microscope for a mark comprising a mix of composite particles luminescent at different wavelength.

[0062] Figure 5A-5F illustrates various nanoparticles (1) with homostructure (A) or heterostructures: spherical core / shell (B), spherical core / shell / shell (C), dot in plate (D), nanoplate core / shell (E) and nanoplate core / crown (F). DETAILED DESCRIPTION

[0063] This invention relates to an authenticated object comprising a mark. The following descriptions are illustrated through examples that are illustrative rather than restrictive. Authenticated object

[0064] An object to be authenticated is provided. Said object can be any type of solid object, of any material. For instance, the object may be a bag, an electronic device, a book, etc... The object may also be transparent. For instance, the object may be lenses, a glass bottle, a perfume bottle, etc...

[0065] A luminescent mark, as described hereafter, is provided on the object to authenticate. An object comprising a luminescent mark is an authenticated object.

[0066] The mark may be part of the authenticated object and provided while the object is made. For instance, if the object is a lens, composite particles may be injected into the forming lens. After the lens is formed, the composite particles inside the lens may define a mark. More generally, in such a case, the mark is a part of the object.

[0067] In an embodiment, the luminescent mark is located near a surface of the object to be authenticated. Indeed, during the process of formation of the object, the composite particles may sediment under gravity forces – naturally or under centrifugation for instance – and accumulate near a surface of the object. This phenomenon contributes to a local concentration of the luminescent nanoparticles. In addition, the mark is flattened by such a phenomenon, so that imaging of the mark is easier – in terms of optical focusing for instance.

[0068] The mark may also be provided after the object is made. For instance, a transparent patch comprising the mark may be attached to the object to be authenticated. The transparent patch may, for instance, be glued to the object. Luminescent mark

[0069] This disclosure relates to an authentication object comprising at least one mark.

[0070] By mark, it is meant here any material having the following features. • A mark is geometrically limited, and may delimit a convex surface or volume. Nonetheless, the mark may have any shape: squares, straight or curved lines, cylindric… The shape of the mark encompasses all the composite particles as defined hereafter. The mark may be planar – included in a plane – or tridimensional. • The mark comprises composite particles distributed within the mark, the composite particles presenting optical features, allowing the mark to be detected by optical devices, in ultra-violet and / or visible and / or infrared light. The optical features of the composite particles may be absorption of light, reflection of light, polarization of light, fluorescence or emission of light. If optical feature is associated with a spectral peak, the specific Full Width at Half Maximum (FWHM) of said peak may be included in the optical features. If multiple optical peaks are present the ratio between said peak may be included in the optical features.

[0071] The composite particles may have any distribution: spots, squares, straight or curved lines, regular patterns, random pattens, clustering patterns, fractal patterns, splashes… Further, composite particles may comprise luminescent nanoparticles, providing the optical properties.

[0072] The lowest dimension (LD) of the mark is larger than 500 nm, preferably larger than 1 µm, more preferably larger than 2 µm. By “lowest dimension”, it is meant the diameter of the largest circle fully included in the mark (inscribed circle). For instance, for a perfectly discoidal mark, the “lowest dimension” is the diameter. For a rectangular mark, the “lowest dimension” is the length of the small edge. For a curvilinear line, the “lowest dimension” is the narrowest section of the curvilinear line. In this disclosure, an object having a lowest dimension smaller than predetermined LD is not considered as a mark.

[0073] Composite particles may be distributed randomly. Such a distribution ensures that each mark is unique. Random distribution of composite particles includes, amongother, random position of composite particles, random overlap and random orientation of said composite particles.

[0074] Randomly distributed composite particles may be obtained by various methods.

[0075] In a first method, a substrate is first provided, and composite particle is deposited on the substrate.

[0076] In a variant of the first method, a liquid composition comprising composite particles, for instance composite particles comprising luminescent nanoparticles dispersed in a solvent, is provided. Liquid may be sprayed or expelled from capillaries and projected on the substrate under the form of droplets. Depending on speed of ejection, trajectories and impact angle, temperature, type of solvent, surface tension of droplets and wettability of substrate, movement of capillaries, variation of flow rate in capillaries… droplets are distributed randomly and forms randomly distributed composite particles within the mark.

[0077] In a variant of the first method, a liquid composition comprising composite particles, for instance composite particles comprising luminescent nanoparticles dispersed in a solvent, is provided. Droplets are generated (for instance as described in variant above) and flown into a system of rotating blades which modifies trajectories and results in random deposition of droplets on the substrate.

[0078] In a variant of the first method, a liquid composition comprising composite particles, for instance composite particles comprising luminescent nanoparticles dispersed in a solvent, is provided. Droplets are generated and allowed to float on a liquid medium. Then, the substrate is dipped in the liquid medium. Depending on speed and angle of dipping, temperature, liquid medium, surface tension of droplets and wettability of substrate… droplets are distributed randomly and forms randomly distributed composite particles on the surface of the substrate.

[0079] The liquid composition disclosed in the three variants above is typically a dispersion of particles in a solvent with a binder and / or polymerizable material, yielding upon polymerization a continuous material in which particles are dispersed – a matrix.The composition of liquid composition defines the total volume of marks, when volatile compounds have been removed and / or polymerizable compounds have been cured.

[0080] In a variant of the first method, a solid composition comprising composite particles, such as composite particles comprising luminescent nanoparticles, is provided. Such solid may be an aggregate of particles, obtained by sintering or mechanical compression or colloidal interactions for instance. The solid material may be prepared in the form of randomly shaped pieces by cutting, milling or other mechanical means. Then, randomly shaped pieces of the solid material are deposited on the substrate and pressed, so as to adhere on the substrate or incorporate in the substrate, yielding a label with randomly distributed marks. In this case, the volume of marks includes the volume of substrate in which particles are incorporated.

[0081] In the first method, the substrate may be the object to be authenticated or an intermediate layer of paper, plastic, metal or any other suitable support, said intermediate layer being later glued or transferred on object to be authenticated. Said intermediate layer may be also linked to the object to be authenticated: any attachment method is suitable, such as sewing, inserting a wire inside the label and making a knot on the article.

[0082] In a second method, the mark is included in the object to be authenticated. In this method, composite particles are included randomly at the surface of the object. Any part of the object in which composite particles may be dispersed may be used as mark. In this case, the volume of the mark includes the volume of object’s part in which composite particles are incorporated. Examples of this second method include outer layer of a multilayered laminate, a coating or a protective film build around an object, for example plastic or glass container, paper boxes, protective plastic film, among others. Another example may include at least one thread within a fabric or a manufactured good or any other parts included in the final object requiring anti-counterfeit protection.

[0083] With both methods, object to be authenticated may be selected from bottles of wine, spirits or other drinks, bottles of perfumes, cosmetic packaging, drug containers, electronic and / or digital devices, fashion accessories, clothes, trunks, boxes, luggage, leather goods, watches, jewels, shoes, food boxes among others.

[0084] Several methods for fabrication of marks comprising randomly distributed composite particles have been disclosed, without limitations, and all lead to marks with a distribution of particles in which particles may be imaged individually.

[0085] Though randomly distributed, composite particles may also be combined to depict an object, a schematic, a logo or more complex prints, a brand name or any other text, symbols or any abstract shape.

[0086] For this disclosure, the mark can be directly printed or deposited by any techniques or embedded in the good. The advantage of such label lies in the material used in the mark (i.e., the difficulty lies in replicating or copying such material) in combination with specific optical features and size distribution allowing for imaging of single particles.

[0087] In some embodiments, each composite particle of the mark comprises particles. However, composite particles may comprise multiple types of particles: their compositions may be different. For the sake of clarity, composition of each composite particle may be defined independently from composition of other composite particle. As will be detailed below, each composite particle may comprise several types of particles, these particles being eventually composite particles comprising several types of nanoparticles.

[0088] Particles have a mean size between 50 nm and 400 nm. These particles may be either high-pass particles or light-reflecting particles or neutral filtering particles.

[0089] Particles are distributed randomly in the marks. Random distribution of particles includes, among other, random position of particles, random overlap of particles and random orientation of particles.

[0090] The composite particles comprised in the mark, i.e., neutral filtering particles and / or high-pass filtering particles and / or light-reflecting particles as the case may be, are present at a concentration in volume below 20%, as compared to the total volume of marks, preferably below 10%, more preferably below 5%.

[0091] This specific combination of particle mean size and volume concentration is advantageous for several reasons. First, particles are separated spatially one from another: each particle may be observed as un individual particle. In other words, marks do not appear homogeneous at the scale of particles and some parts of the marks are devoid of particles. Second, as particles are separated, smaller than the size of marks, they define a random distribution which can be imaged precisely with an image of resolution length better than the particle size. Further, different particles can have different optical property and their distance give access to specific optical features of the label. Last, as particles are separated the local different optical properties could be well measured without interference of other particles. Moreover, a population of different size particles could occupy with more efficacity an empty space respect to identical size particles, without necessarily overlap or be in close contact.

[0092] In an embodiment, marks comprise neutral filtering particles and a second type of particle selected from high-pass particles or light-reflecting particles. The use of neutral filtering particles is useful to enhance contrast and visibility of high-pass filtering particles and / or light-reflecting particles. For instance, if high-pass particles are mixed with neutral filtering particles, they will appear in transmission as white spots in a grey background if irradiated with light above their cut-off wavelength and they will appear in transmission as dark spots in a grey background if irradiated with light below their cut- off wavelength. With neutral filtering particles, images of mark have a better contrast.

[0093] In an embodiment, particles comprised in the mark are composite particles. By composite particles, it is meant particles comprising nanoparticles and a second material, said second material being either a binder yielding aggregates, or a matrix either continuous or porous yielding nanoparticles embedded in a matrix. High-pass nanoparticles aggregated or embedded in a matrix thus define a high-pass particle, provided that binder / matrix material is transparent, or at least with constant absorption, in the range of wavelength where high-pass nanoparticles vary from absorbent to non- absorbent. Similarly, light-reflecting nanoparticles aggregated or embedded in a matrix define a light-reflecting particle, provided that binder / matrix material is transparent, or atleast with constant absorption, in the range of wavelength where light-reflecting nanoparticles do reflect light.

[0094] Particles may be composite particles comprising high-pass nanoparticles and light-reflecting nanoparticles aggregated or embedded in a matrix, thus combining both optical properties in a single particle. This is especially advantageous if range of wavelength reflected by light-reflecting nanoparticles do not overlap with range of wavelength where high-pass nanoparticles vary from absorbent to non-absorbent.

[0095] Particles may be composite particles comprising at least two kinds of high-pass nanoparticles, each kind of high-pass nanoparticles having a different cut-off wavelength as compared to other kinds of high-pass nanoparticles. The composite particle thus obtained may present an absorption spectrum with several ranges of wavelength, each range having a different absorption level. In other words, the composite particle will appear with different levels on a grey scale depending on the wavelength of measure. Below cut-off wavelength, particle appear dark whereas above cut-off wavelength, particle appear bright. Luminescent nanoparticles

[0096] In this disclosure, the luminescent nanoparticles of the composite particles can be any kind of semi-conductive material prepared in the form of nanoparticles or any kind of rare-earth doped metal oxide exhibiting fluorescence properties and known as phosphors. Quantum dots composition / shape / structure

[0097] Suitable luminescent nanoparticles may be selected from fluorescent semi- conductive nanoparticles known as quantum dots, which may have various composition, shape and structure.

[0098] According to an embodiment, the luminescent nanoparticles can be any particles comprising material of formula (I) in the form of nanoparticles, i.e., in the form of domains of nanometric size.MxEy (I) in which M is Zn, Cd or a mixture thereof; and E is S, Se, Te or a mixture thereof. x and y are independently a decimal number from 0 to 5, with the proviso that x and y are not 0 at the same time. Luminescence of such materials is obtained for domains of nanometric size.

[0099] In another embodiment, the quantum dots comprise a material of formula: MxQyEzAw (II) in which M is selected from the group consisting of Zn, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd, Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Cs or a mixture thereof; Q is selected from the group consisting of Zn, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd, Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Cs or a mixture thereof; E is selected from the group consisting of O, S, Se, Te, C, N, P, As, Sb, F, Cl, Br, I, or a mixture thereof; and A is selected from the group consisting of O, S, Se, Te, C, N, P, As, Sb, F, Cl, Br, I, or a mixture thereof. x, y, z and w are independently a decimal number from 0 to 5; x, y, z and w are not simultaneously equal to 0; x and y are not simultaneously equal to 0; z and w are not simultaneously equal to 0.

[0100] Especially, quantum dots may comprise a material of formula MxEy, in which M is Zn, Cd, Hg, Cu, Ag, Al, Ga, In, Si, Ge, Pb, Sb or a mixture thereof; and E is O, S, Se, Te, N, P, As or a mixture thereof. x and y are independently a decimal number from 0 to 5, with the proviso that x and y are not 0 at the same time.

[0101] In a specific embodiment, quantum dots comprise a material selected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, HgO, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbS, PbSe, PbTe, GeS2, GeSe2, SnS2, SnSe2, CuInS2, CuInSe2, CuInZnS, CuInZnSe, AgInS2, AgInSe2, CuS, Cu2S, Ag2S, Ag2Se, Ag2Te, FeS, FeS2, InP, Cd3P2, Zn3P2, CdO, ZnO, FeO, Fe2O3, Fe3O4, Al2O3, TiO2, MgO, MgS, MgSe,MgTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, InAsP, TlN, TlP, TlAs, TlSb, MoS2, PdS, Pd4S, WS2, CsPbCl3, PbBr3, CsPbBr3, CH3NH3PbI3, CH3NH3PbCl3, CH3NH3PbBr3, CsPbI3, FAPbBr3, FAPbI3 (where FA stands for formamidinium), or a mixture thereof.

[0102] In one embodiment, quantum dots are doped with at least one transition metal such as, for example, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Dd, Cr, Mo, W, Sg, Mn, Tc, Re, Bh, Fe, Ru, Os, Hs, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag or Au. Preferably, quantum dots are doped with Mg, Mn, Al, Cu, Te or Ag. In particular, ZnSe quantum dots doped with Mn :ZnSe:Mn, ZnSe quantum dots doped with Al: ZnSe:Al, or ZnSe quantum dots doped with Mg: ZnSe:Mg are suitable. Amount of dopant is preferably less than 10wt%. Dopant amount of 5wt% or 2wt% are suitable. Quantum dots shape

[0103] In one embodiment, quantum dots may have different shapes, provided that they present a nanometric size leading to quantum confinement in the nanoparticle.

[0104] Quantum dots may have nanometric sizes in three dimensions, allowing quantum confinement in all three spatial dimensions. Such quantum dots are for instance nanocubes or nanospheres.

[0105] Quantum dots may have a nanometric sizes in two dimensions, the third dimension being larger: quantum confinement is in two spatial dimensions. Such quantum dots are for instance nanorods, nanowires or nanorings.

[0106] Quantum dots may have a nanometric size in one dimension, the other dimensions being larger: quantum confinement is in one spatial dimension only. Such quantum dots are for instance nanoplates, nanosheets, nanoribbons or nanodisks. Nanoplates are especially interesting in this disclosure because absorption cross section – i.e., efficiency to capture a photon of incident light on the quantum dot – is ten times higher than a nanosphere having the same composition and structure emitting at the same wavelength. This higher cross section improves significantly sensitivity of assays. In addition, nanoplates have narrower FWHM emission spectra – typically below 40 nm –and shorter photoluminescence decay time – by one order of magnitude - as compared to spherical quantum dots.

[0107] The exact shape of quantum dots defines confinement properties, then electronic and optical properties. Quantum dots structure

[0108] In an embodiment, quantum dots are homostructures. By homostructure, it is meant that the quantum dot is homogenous and has the same local composition in all its volume. A homogeneous spherical quantum dot is illustrated in figure 5A.

[0109] In an alternative embodiment, quantum dots are heterostructures. By heterostructure, it is meant that the quantum dot is comprised of several sub-volumes, each sub-volume having a different composition from neighbouring sub-volumes. In a particular embodiment, all sub-volumes have a composition defined by formula (II) disclosed above, with different parameters, i.e., elemental composition and stoichiometry.

[0110] Example of heterostructure are core / shell nanoparticles, the core (11) having any shape disclosed above. A shell (12) is a layer covering totally or partially the core. A particular example of core / shell heterostructure is a multi-layered structure comprising a core (11) and several successive shells (12, 13). For convenience, these multi-layered heterostructures are named core / shell hereafter. Core (11) and shell (12,13) may have the same shape – sphere in sphere for example – or not – sphere in plate for instance. A core / shell spherical nanoparticle is illustrated in figure 5B. A core / shell / shell spherical nanoparticle is illustrated in figure 5C. A sphere in plate nanoparticle is illustrated in figure 5D – also named a dot in plate. A core / shell nanoplate is illustrated in figure 5E.

[0111] Another example of heterostructure are core / crown nanoparticles, the core having any shape disclosed above. A crown is a band of material disposed on the periphery of the core. This heterostructure is particularly useful with cores being nanoplates and crown disposed on the edges of the nanoplate. A core / crown nanoplate is illustrated in figure 5F.

[0112] These heterostructure may have a gradient of composition from the core to the outside of the shell so that there is no precise boundary between core and shell but properties in centre of the core are different from properties on the outer boundary of shell.

[0113] In a configuration, nanoparticles (1) are formula (II) type semi-conductive nanoparticles and comprise a core based on cadmium, sulfur and selenium and are selected from: • CdSe / CdS, CdSe / CdS / ZnS, CdSe / CdS / ZnSe, CdSe / CdS / ZnSeyS(1-y), CdSe / ZnSe / ZnS, CdSe / Zn SexS(1-x) / ZnS, • CdSexS(1-x) / ZnS, Cd SexS(1-x) / ZnSe, Cd SexS(1-x) / Zn SeyS(1-y), CdSexS(1-x) / ZnS, Cd SexS(1-x) / ZnSe, • CdSe / CdyZn(1-y)S, CdSe / CdyZn(1-y)S / ZnS, CdSe / CdyZn(1-y)S / ZnSe, CdSe / CdyZn(1-y)S / ZnSezS(1-z) • CdSe / CdyZn(1-y)Se, CdSe / CdyZn(1-y)Se / ZnS, CdSe / CdyZn(1-y)Se / ZnSe, CdSe / CdyZn(1-y)Se / ZnSezS(1-z), • CdSexS(1-x) / CdS, CdSexS(1-x) / CdS / ZnS, Cd SexS(1-x) / CdS / ZnSe, CdSexS(1-x) / CdS / ZnSeyS(1-y), • CdSexS(1-x) / CdyZn(1-y)S, CdSexS(1-x) / CdyZn(1-y)S / ZnS, CdSexS(1-x) / CdyZn(1-y)S / ZnSe, CdSexS(1-x) / CdyZn(1-y)S / ZnSezS(1-z), • CdSexS(1-x) / CdyZn(1-y)Se, CdSexS(1-x) / CdyZn(1-y)Se / ZnS, CdSexS(1-x) / CdyZn(1-y)Se / ZnSe, CdSexS(1-x) / CdyZn(1-y)Se / ZnSezS(1-z), where x, y and z are rational numbers between 0 (excluded) and 1 (excluded), and emit light by fluorescence. Emitted light is typically a band centered on a wavelength in the visible range from 380 nm to 780 nm. Emitted light is typically a band having a FWHM less than 50 nm, preferably less than 30 nm, more preferably less than 20 nm.

[0114] In a configuration, nanoparticles (1) are formula (II) type semi-conductive nanoparticles and comprise a core based on cadmium, selenium and tellure and are selected from: • CdTe / CdSe, CdTe / CdSe / ZnS, CdTe / CdSe / ZnTe, CdTe / CdSe / ZnSeyS(1-y), CdTe / ZnSe / ZnS, CdTe / ZnSexS(1-x) / ZnS,• CdTexSe(1-x) / ZnS, Cd TexSe(1-x) / ZnSe, CdTexSe(1-x) / ZnSeyS(1-y), CdTexSe(1-x) / ZnS, CdTexSe(1-x) / ZnSe, • CdTe / CdyZn(1-y)S, CdTe / CdyZn(1-y)S / ZnS, CdTe / CdyZn(1-y)S / ZnSe, CdTe / CdyZn(1-y)S / ZnSezS(1-z)• CdTe / CdyZn(1-y)Se, CdTe / CdyZn(1-y)Se / ZnS, CdTe / CdyZn(1-y)Se / ZnSe, CdTe / CdyZn(1-y)Se / ZnSezS(1-z), • CdTexSe(1-x) / CdS, CdTexSe(1-x) / CdS / ZnS, CdTexSe(1-x) / CdS / ZnSe, CdTexSe(1-x) / CdS / ZnSeyS(1-y), • CdTexSe(1-x) / CdyZn(1-y)S, CdTexSe(1-x) / CdyZn(1-y)S / ZnS, CdTexSe(1-x) / CdyZn(1-y)S / ZnSe, CdTexSe(1-x) / CdyZn(1-y)S / ZnSezS(1-z), • CdTexSe(1-x) / CdyZn(1-y)Se, CdTexSe(1-x) / CdyZn(1-y)Se / ZnS, CdTexSe(1-x) / CdyZn(1-y)Se / ZnSe, CdTexSe(1-x) / CdyZn(1-y)Se / ZnSezS(1-z), where x, y and z are rational numbers between 0 (excluded) and 1 (excluded), and emit light by fluorescence. Emitted light is typically a band centered on a wavelength in the visible range from 380 nm to 780 nm. Emitted light is typically a band having a FWHM less than 50 nm, preferably less than 30 nm, more preferably less than 20 nm.

[0115] In a configuration, nanoparticles (1) are formula (II) type semi-conductive nanoparticles and comprise a core based on zinc, sulfur and selenium and are selected from: • ZnSe / ZnS, ZnSe / ZnSeyS(1-y), ZnTe / ZnSeyS(1-y) • ZnSexS(1-x) / ZnS, ZnSexS(1-x) / ZnSe, ZnSexS(1-x) / ZnSeyS(1-y), ZnSexTe(1-x) / ZnS, ZnSexTe(1-x) / ZnSe, ZnSexTe(1-x) / ZnSexS(1-x), • ZnSe / CdyZn(1-y)S, ZnSe / CdyZn(1-y)S / ZnS, ZnSe / CdyZn(1-y)S / ZnSe, ZnSe / CdyZn(1-y)S / ZnSezS(1-z) • ZnSe / CdyZn(1-y)Se, ZnSe / CdyZn(1-y)Se / ZnS, ZnSe / CdyZn(1-y)Se / ZnSe, ZnSe / CdyZn(1-y)Se / ZnSezS(1-z), • ZnSexS(1-x) / ZnS, ZnSexS(1-x) / ZnS / ZnSe, ZnSexS(1-x) / ZnS / ZnSeyS(1-y), • ZnSexS(1-x) / CdyZn(1-y)S, ZnSexS(1-x) / CdyZn(1-y)S / ZnS, ZnSexS(1-x) / CdyZn(1-y)S / ZnSe, ZnSexS(1-x) / CdyZn(1-y)S / ZnSezS(1-z),• ZnSexS(1-x) / CdyZn(1-y)Se, ZnSexS(1-x) / CdyZn(1-y)Se / ZnS, ZnSexS(1-x) / CdyZn(1-y)Se / ZnSe, ZnSexS(1-x) / CdyZn(1-y)Se / ZnSezS(1-z), where x, y and z are rational numbers between 0 (excluded) and 1 (excluded), and emit light by fluorescence. Emitted light is typically a band centered on a wavelength in the visible range from 380 nm to 780 nm. Emitted light is typically a band having a FWHM less than 50 nm, preferably less than 30 nm, more preferably less than 20 nm.

[0116] In a configuration, nanoparticles (1) are formula (II) type semi-conductive nanoparticles and comprise a core based on zinc, cadmium, sulfur and selenium and are selected from: • CdwZn(1-w)Se / CdS, CdwZn(1-w)Se / CdS / ZnS, CdwZn(1-w)Se / ZnSe / ZnS, CdwZn(1-w)Se / CdS / ZnSe, CdwZn(1-w)Se / CdS / ZnSeyS(1-y), • CdwZn(1-w)SexS(1-x) / ZnS, CdwZn(1-w)SexS(1-x) / ZnSe, CdwZn(1-w)SexS(1-x) / ZnSeyS(1-y), CdwZn(1-w)SexTe(1-x) / ZnS, CdwZn(1-w)SexTe(1-x) / ZnSe, • CdwZn(1-w)Se / CdyZn(1-y)S, CdwZn(1-w)Se / CdyZn(1-y)S / ZnS, CdwZn(1-w)Se / CdyZn(1-y)S / ZnSe, CdwZn(1-w)Se / CdyZn(1-y)S / ZnSezS(1-z) • CdwZn(1-w)Se / CdyZn(1-y)Se, CdwZn(1-w)Se / CdyZn(1-y)Se / ZnS, CdwZn(1-w)Se / CdyZn(1-y)Se / ZnSe, CdwZn(1-w)Se / CdyZn(1-y)Se / ZnSezS(1-z), • CdwZn(1-w)SexS(1-x) / CdS, CdwZn(1-w)SexS(1-x) / CdS / ZnS, CdwZn(1-w)SexS(1-x) / CdS / ZnSe, CdwZn(1-w)SexS(1-x) / CdS / ZnSeyS(1-y), • CdwZn(1-w)SexS(1-x) / CdyZn(1-y)S, CdwZn(1-w)SexS(1-x) / CdyZn(1-y)S / ZnS, CdwZn(1-w)SexS(1-x) / CdyZn(1-y)S / ZnSe, CdwZn(1-w)SexS(1-x) / CdyZn(1-y)S / ZnSezS(1-z), • CdwZn(1-w)SexS(1-x) / CdyZn(1-y)Se, CdwZn(1-w)SexS(1-x) / CdyZn(1-y)Se / ZnS, CdwZn(1-w)SexS(1-x) / CdyZn(1-y)Se / ZnSe, CdwZn(1-w)SexS(1-x) / CdyZn(1-y)Se / ZnSezS(1-z), where w, x, y and z are rational numbers between 0 (excluded) and 1 (excluded), and emit light by fluorescence. Emitted light is typically a band centered on a wavelength in the visible range from 380 nm to 780 nm. Emitted light is typically a band having a FWHM less than 50 nm, preferably less than 30 nm, more preferably less than 20 nm.

[0117] Most preferred formula (II) nanoparticles (1) are CdSe / CdS / ZnS, CdSexS(1-x) / CdS / ZnS, CdSe / ZnSe / ZnS, CdSe / ZnSexS(1-x) / ZnS, CdSexS(1-x) / ZnSe / ZnS, CdxZn(1-x)Se / ZnSe / ZnS. Phosphors – rare-earth doped metal oxides

[0118] Suitable luminescent nanoparticles may be selected from rare-earth doped metal oxides exhibiting fluorescence properties and known as phosphors. The properties of fluorescence of such rare-earth doped metal oxides are strongly governed by the crystalline structure of the oxide and the concentration of doping element.

[0119] In this disclosure, a single rare-earth doping element surrounded by the metal oxide structure is considered as a luminescent nanoparticle. Indeed, luminescent light is emitted by the rare-earth element alone, though influenced by its surrounding.

[0120] According to an embodiment, the rare-earth doped metal oxides can be any compound of formula (III). (A(1-x)REx)a(MpOq) (III) wherein: M represents one or more elements capable of associating with oxygen (O) to form a crystalline compound; RE corresponds to one or more luminescent rare-earth ion(s); A corresponds to one or more constituent ion(s) of the crystalline matrix whose electronic levels are not involved in the luminescence process; 0<x<1, in particular 0.1≤x≤0.9, in particular 0.2≤x≤0.6, in particular 0.2≤x≤0.4 and more particularly x is 0.4; and the values of p, q and a are such that the electroneutrality of (A(1-x)REx)a(MpOq) is respected.

[0121] A can be more particularly selected from yttrium (Y), gadolinium (Gd), lanthanum (La), bismuth (Bi), lutetium (Lu), erbium (Er), terbium (Tb) and mixtures thereof, in particular A can be selected from Y, Gd, La and mixtures thereof; in particular A represents Y or Gd, preferably A represents Y.

[0122] In particular, M in the above-mentioned formula (III) can represent one or more elements selected from V, P, W, Mo, As, Al, Hf, Zr, Ge, Ti, Sn, Mn and Si. Preferably, M represents one or more elements selected from V, P, Al, Hf, Zr, Ge, Ti, Sn, Mn and Si, and in particular selected from V, P, W, Mo, As and Al. The crystalline metal oxide matrix of the luminescent nanoparticles used according to the invention may incorporate one or more types of MpOq anions, In particular, M may represent V(1-y)Py with y ranging from 0 to 1.

[0123] According to a particular embodiment, p in the above-mentioned formula (III) is different from zero.

[0124] By way of example, a composite particle of the invention may be of formula (III) wherein M represents V and / or P, p is 1, so that the metal oxide matrix of said composite particle comprises VO43-and / or PO43-anions.

[0125] In another example embodiment, M represents Al, A represents Y or Lu, p is 5 and q is 12, so that the Aa(MpOq) matrix of said composite particle is the garnet Y3Al5O12 (YAG) or Lu3Al5O12(LuAG).

[0126] According to another particular embodiment, a composite particle of the invention may be of formula (III) wherein M represents Hf or Zr, Ge, Ti, Sn, Mn, p is 2 and q is 7, so that the metal oxide matrix of said composite particle is AaHf2O7, AaZr2O7, AaGe2O7, AaTi2O7, AaSn2O7or AaMn2O7. In particular, A may represent La, Y, Gd or Lu, in which case a=2.

[0127] In another example embodiment, p is zero and A is Y or Gd, so that the Aa(MpOq) matrix of said nanoparticle is of the type Y2O3or Gd2O3.

[0128] Examples of phosphors include, but are not limited to Y2O3:Gd, Y2O3:Dy, Y2O3:Tb, Y2O3:Ho, Y2O3:Er, Y2O3:Tm, Gd2O3:Eu, Y2O2S:Pr, Y2O2S:Sm, Y2O2S:Eu, Y2O2S:Tb, Y2O2S:Ho, Y2O2S:Er, Y2O2S:Dy, Y2O2S:Tm, Y2O2S:Eu, Y2O3:Eu,YVC:Eu, and NaGdF4:Tb, wherein the Tb can be replaced with Eu, Dy, Pr, Ce or other rare-earths. Additional luminescent material – organic fluorophores

[0129] Besides semi-conductive nanoparticles and phosphors, additional luminescent material may be used, with the proviso that they are associated – either aggregated with semi-conductive nanoparticles or included as doping compound in the metal oxide matrix – to form the luminescent nanoparticles.

[0130] Suitable additional luminescent materials are the following organic fluorophores : Fluorescein (green luminescent light), Rhodamine B (red luminescent light), 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (known as BODIPY) and derivatives (known as BODIPY dyes), Diketopyrrolopyrroles (known as DPP) and derivatives (known as DPP dyes), coumarins and derivatives (green to blue luminescent light), Perylene diimides (bright red luminescent light), Spiropyrans, Diarylethenes ; and mixtures thereof.

[0131] In an embodiment, a phosphor is comprising a plurality of luminescent nanoparticle – i.e., single rare-earth element – dispersed in a metal oxide matrix, yielding a composite particle. It must be noted that the concentration of rare-earth elements in the metal oxide matrix must be low. Indeed, if rare-earth elements are too close, the luminescent effect may be quenched. Therefore, the distance between neighbouring rare- earth elements is of nanometric size, and the composite particle definition is appropriate: the composite particle is a metal oxide matrix in which single rare-earth elements are dispersed, each single rare-earth element behaving as a luminescent nano-source, noted luminescent nanoparticle herein. The weight fraction of rare-earths in the composite particle may be in a range from 1000 ppm to 100000 ppm, preferably from 1000 ppm to 20000 ppm. For instance, in YAG metal oxide matrix, the weight fraction of Cerium may be from 1000 ppm to 10000 ppm; the weight fraction of Neodymium may be from 5000 ppm to 15000 ppm; the weight fraction of Ytterbium may be from 50000 ppm to 100000 ppm; the weight fraction of Erbium may be from 1000 ppm to 10000 ppm; the weight fraction of Thullium may be from 1000 ppm to 5000 ppm;

[0132] In another embodiment, composite particles comprise luminescent nanoparticles of formula (I) dispersed in a metal oxide matrix.

[0133] Luminescent composite particles comprise nanoparticles of formula (I) disclosed hereabove, said nanoparticles being embedded in an encapsulating material. By encapsulating material, it is meant a material that covers all surface of nanoparticles. In other words, encapsulating material forms a barrier around the nanoparticles. Such a barrier as several advantages. In particular, said nanoparticles may be protected against chemicals, e.g., moisture, oxidants, during preparation of curable powder coating, during cure, or after cure. Besides, nanoparticles that are not dispersible in a binder may be encapsulated in an encapsulating material whose compatibility with said binder is good: the barrier behaves as a compatibilization agent. Last, the encapsulating material may have a role of refractive index matching, in order to lower diffusion or haze: indeed, when core-shell nanoparticles are dispersed in a matrix, haze is proportional to the difference of refractive index between the matrix and the dispersed nanoparticles. Adding an encapsulating material with an intermediate refractive index mitigates this effect and lowers haze.

[0134] In this disclosure, the encapsulating material is a metal oxide material. Suitable metal oxides are SiO2, Al2O3, TiO2, ZrO2, FeO, ZnO, MgO, SnO2, Nb2O5, CeO2, BeO, IrO2, CaO, Sc2O3, Na2O, BaO, K2O, TeO2, MnO, B2O3, GeO2, As2O3, Ta2O5, Li2O, SrO, Y2O3, HfO2, MoO2, Tc2O7, ReO2, Co3O4, OsO, RhO2, Rh2O3, CdO, HgO, Tl2O, Ga2O3, In2O3, Bi2O3, Sb2O3, PoO2, SeO2, Cs2O, La2O3, Pr6O11, Nd2O3, La2O3, Sm2O3, Eu2O3, Tb4O7, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, Gd2O3, or a mixture thereof. Preferred metal oxides are SiO2, Al2O3, TiO2, ZrO2, HfO2, GeO2, SnO2, or a mixture thereof.

[0135] In another embodiment, composite particles comprise luminescent nanoparticles of formula (I) and organic fluorophores dispersed in a metal oxide matrix as described hereabove.

[0136] In another embodiment, composite particles comprise rare-earth elements and organic fluorophores enclosed in a metal oxide matrix as described hereabove – as dopant or organic inclusion.

[0137] In an embodiment, the loading charge of the nanoparticles in the composite particle is at least 1%, preferably at least 2.5%, more preferably at least 5%, said loading charge being the mass ratio between the mass of nanoparticles comprised in a composite particle and the mass of said composite particle. Indeed, the performance of composite particles is proportional to the concentration of nanoparticles they contain. Therefore, a high concentration of core-shell nanoparticles is advantageous. It has to be noted however that increasing concentration of core-shell nanoparticles without degrading their properties – as a consequence of aggregation or manufacturing process for instance – is not easy.

[0138] The composite particles may be in the form of a monodisperse population. Monodisperse composite particles are advantageous for various reasons, especially when used in transparent curable powder coatings: a homogeneous size distribution avoids uncontrolled light diffusion and ensures spatial homogeneity of the coating.

[0139] The mean size of the composite particles is preferably in a range from 50 nm to 500 nm, more preferably from 50 nm to 250 nm. Composite particles having a mean size from 50 nm to 250 nm, preferably from 50 nm to 100 nm are especially suitable for curable powder coatings with high transparency and low haze.

[0140] The composite particles may be chemically modified on their surface. Chemical modification may be obtained by grafting, by adsorption of molecules or by physical processes – heat, vacuum or gaseous treatment. Chemical modification may use compatibilization agents, allowing to mix composite particles in complex formulations – such as resins, varnishes, paints, colloidal dispersion… - without aggregation or phase separation of the composite particles.

[0141] With composite particles comprising luminescent nanoparticles of formula (I) dispersed in a metal oxide matrix, the weight fraction of luminescent nanoparticles in the curable powder coating composition is higher than for non-encapsulated nanoparticles of formula (I), as the encapsulating material of the luminescent nanoparticles does not contribute to luminescence. Luminescent nanoparticles concentration

[0142] The concentration of luminescent nanoparticles in the luminescent mark is preferably in a range from 150 ppm to 150 ppb.

[0143] In this disclosure, the concentration of luminescent nanoparticles in phosphors is defined as follow: the luminescent nanoparticle comprises the single rare-earth element and the unit cell of the metal oxide matrix in which the dopant is included. For instance, for a YAG:Ce – yttrium aluminium garnet doped with cerium, a yellow phosphor – one cerium element is included in a unit cell of Y3Al5O12 and define the luminescent nanoparticle, hence its mass. Monomers and catalysts

[0144] For some applications, a mark according to the invention is created on ophthalmic lens. Monomers suitable for ophthalmic lenses may be classified in various chemical classes.

[0145] Allyl monomers or allyl oligomers are suitable for manufacture of ophthalmic lenses having a refractive index about 1.5-1.56. In this disclosure, an allyl monomer or allyl oligomer is a compound comprising an allyl group. Examples of suitable allyl compounds include diethylene glycol bis(allyl carbonate), ethylene glycol bis(allyl carbonate), oligomers of diethylene glycol bis(allyl carbonate), oligomers of ethylene glycol bis(allyl carbonate), bisphenol A bis(allyl carbonate), diallylphthalates such as diallyl phthalate, diallyl isophthalate and diallyl terephthalate, and mixtures thereof.

[0146] In an embodiment, the amount of said allyl monomers or allyl oligomers in the polymerizable composition may be from 20 to 99% by weight, in particular from 50 to 99% by weight, more particularly from 80 to 98% by weight, even more particularly from 90 to 97% by weight, based on the total weight of the composition. In particular, the polymerizable composition used for generating the matrix may comprise from 20 to 99% by weight, in particular 50 to 99% by weight, more particularly from 80 to 98% by weight, even more particularly from 90 to 97% by weight, based on the total weight of the composition, of diethylene glycol bis(allyl carbonate), oligomers of diethylene glycol bis(allyl carbonate) or mixtures thereof.

[0147] (Meth)acrylic monomers or (meth)acrylic oligomers are also suitable for manufacture of ophthalmic lenses having a refractive index about 1.5-1.56. In this disclosure, a (meth)acrylic monomer or (meth)acrylic oligomer is a compound comprising having acrylic or methacrylic groups. (Meth)acrylates may be monofunctional (meth)acrylates or multifunctional (meth)acrylates.

[0148] In an embodiment especially adapted for polymerization of allyl or (meth)acrylic monomers or oligomers, the catalyst meant for initiating polymerization is a free radical initiator. In a particular embodiment, catalyst is selected in the group consisting of a peroxodicarbonate, a peroxyester, a perketal, and mixtures thereof. Particularly suitable catalysts are selected in the group consisting of benzoyl peroxide, methyl ethyl peroxide, methyl ethyl ketone peroxide, di-t-butyl peroxide, lauroyl peroxide, acetyl peroxide, diisopropyl peroxydicarbonate, bis(4-t-butylcyclohexyl) peroxydicarbonate, t-butyl peroxy-2-ethylhexanoate, t-hexyl peroxy-2-ethylhexanoate, and mixtures thereof. In an alternative particular embodiment, catalyst is an azo compound selected from the group consisting of 2,2'-azobisisobutyronitrile, dimethyl 2,2'-azobis(2-methylpropionate), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 4,4'-azobis(4- cyanopentanoic acid), and mixtures thereof.

[0149] Other examples of monomers or oligomers include compounds used to prepare polyurethane or polythiourethane materials. Thus, mixture of monomers or oligomers having at least two isocyanate functions with monomers or oligomers having at least two alcohol, thiol or epithio functions are suitable polymerizable compositions for manufacture of ophthalmic lenses. Generally, refractive index of such materials is in the range 1.6-1.74.

[0150] Monomer or oligomer having at least two isocyanate functions may be selected from symmetric aromatic diisocyanate such as 2,2' Methylene diphenyl diisocyanate (2,2' MD I), 4,4' dibenzyl diisocyanate (4,4' DBDI), 2,6 toluene diisocyanate (2,6 TDI), xylylene diisocyanate (XDI), 4,4' Methylene diphenyl diisocyanate (4,4' MDI) or asymmetric aromatic diisocyanate such as 2,4' Methylene diphenyl diisocyanate (2,4' MDI), 2,4' dibenzyl diisocyanate (2,4' DBDI), 2,4 toluene diisocyanate (2,4 TDI) or alicyclic diisocyanates such as Isophorone diisocyanate (IPDI), 2, 5(or 2, 6)-bis(iso-cyanatomethyl)-Bicyclo[2.2.1 ]heptane (NDI) or 4,4' Diisocyanato- methylenedicyclohexane (H12MD I) or aliphatic diisocyanates such as hexamethylene diisocyanate (HDI) or mixtures thereof.

[0151] Monomer or oligomer having thiol function may be selected from Pentaerythritol tetrakis mercaptopropionate, Pentaerythritol tetrakis mercaptoacetate, 4-Mercaptomethyl-3,6-dithia-1,8-octanedithiol, 4-mercaptomethyl-1,8-dimercapto-3,6- dithiaoctane, 2,5-dimercaptomethyl-1 ,4-dithiane, 2,5-bis[(2-mercaptoethyl)thiomethyl]- 1,4-dithiane, 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,7- dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 5,7-dimercaptomethyl-1,11- dimercapto-3,6,9-trithiaundecane and mixture thereof.

[0152] Monomer or oligomer having epithio function may be selected from bis(2,3- epithiopropyl)sulfide, bis(2,3-epithiopropyl)disulfide and bis[4-(beta epithiopropylthio)phenyl]sulfide, bis[4-(beta -epithiopropyloxy)cyclohexyl]sulfide.

[0153] In an embodiment, the composition of the polymerizable composition yielding polyurethane or polythiourethane materials is stoichiometric, i.e. the number of isocyanate functions on monomers is substantially equal to the number of alcohol, thiol or epithio functions on monomers, so as to obtain a fully reticulated polymer.

[0154] In an embodiment especially adapted to compositions yielding polyurethane or polythiourethane materials, the catalyst meant for initiating polymerization is an organotin compound, and may be selected from dimethyltin chloride, dibutyltin chloride, and mixtures thereof.

[0155] Other examples of monomers or oligomers include compounds used to prepare materials usually known as Sol-Gels. Such monomers or oligomers may be selected from alkoxysilanes, alkylalkoxysilanes, epoxysilanes, epoxyalkoxysilanes, and mixtures thereof. These monomers or oligomers may be prepared in a solvent to form the polymerizable composition. Suitable solvents are polar solvents, such as water / alcohol mixtures.

[0156] Alkoxysilanes may be selected among compounds having the formula: RpSi(Z)4-p in which the R groups, identical or different, represent monovalent organic groups linked to the silicon atom through a carbon atom, the Z groups are identical or different and represent hydrolyzable groups or hydrogen atoms, p is an integer ranging from 0 to 2. Suitable alkoxysilanes may be selected in the group consisting of tetraethoxysilane Si(OC2H5)4 (TEOS), tetramethoxysilane Si(OCH3)4 (TMOS), tetra(n- propoxy)silane, tetra(i-propoxy)silane, tetra(n-butoxy)silane, tetra(sec-butoxy)silane or tetra(t-butoxy)silane.

[0157] Alkylalkoxysilanes may be selected among compounds having the formula: RnYmSi(Z1)4-n-m in which the R groups, identical or different, represent monovalent organic groups linked to the silicon atom through a carbon atom, the Y groups, identical or different, represent monovalent organic groups linked to the silicon atom through a carbon atom, the Z groups are identical or different and represent hydrolyzable groups or hydrogen atoms, m and n are integers such that m is equal to 1 or 2 and n + m= 1 or 2.

[0158] Epoxyalkoxysilanes may be selected among compounds having the formula: RnYmSi(Z1)4-n-min which the R groups, identical or different, represent monovalent organic groups linked to the silicon atom through a carbon atom, the Y groups, identical or different, represent monovalent organic groups linked to the silicon atom through a carbon atom and containing at least one epoxy function, the Z groups are identical or different and represent hydrolyzable groups or hydrogen atoms, m and n are integers such that m is equal to 1 or 2 and n + m= 1 or 2.

[0159] Suitable epoxysilanes may be selected from the group consisting of glycidoxy methyl trimethoxysilane, glycidoxy methyl triethoxysilane, glycidoxy methyl tripropoxysilane, α-glycidoxy ethyl trimethoxysilane, α-glycidoxy ethyl triethoxysilane, β-glycidoxy ethyl trimethoxysilane, β-glycidoxy ethyl triethoxysilane, β-glycidoxy ethyl tripropoxysilane, α-glycidoxy propyl trimethoxysilane, α-glycidoxy propyl triethoxysilane, α-glycidoxy propyl tripropoxysilane, β-glycidoxy propyl trimethoxysilane, β-glycidoxy propyl triethoxysilane, β-glycidoxy propyl tripropoxysilane, γ-glycidoxy propyl trimethoxysilane, γ-glycidoxy propyltriethoxysilane, γ-glycidoxy propyl tripropoxysilane, 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl) ethyltriethoxysilane.

[0160] In an embodiment especially adapted to compositions yielding Sol-Gel materials, the catalyst meant for initiating polymerization is a Lewis Acid. Carboxylates of metals such as zinc, titanium, zirconium, tin or magnesium; aluminum acetylacetonate Al(AcAc)3are suitable catalysts.

[0161] In an embodiment, the amount of alkoxysilanes is 0 to 90% by weight based on the theoretical dry extract of the polymerizable composition; the amount of alkyl alkoxysilanes is 20 to 90% by weight based on the theoretical dry extract of the polymerizable composition, the amount of catalyst is 0.1 to 5% by weight based on the on the theoretical dry extract of the polymerizable composition. Authentication method

[0162] This disclosure also relates to a method of verifying that an object is genuine.

[0163] In a first step, a mark is created. This mark comprises particles distributed randomly, wherein particles independently comprise high-pass filtering nanoparticles or light-reflective nanoparticles or neutral filtering nanoparticles. In addition, concentration in volume of high-pass filtering nanoparticles, light-reflective nanoparticles and neutral filtering nanoparticles is less than 10 %, as compared to the total volume of particles. All embodiments disclosed above may apply for the mark.

[0164] In a second step, an image of reference of the mark is obtained. The resolution length of the image of reference is lower than the lowest dimension of particles comprised in the mark. The image of reference is preferably obtained by fabricant during or immediately after creation of the mark. In an embodiment, the image of reference is a combination of several images obtained under different conditions, such as wavelength of illumination, wavelength of imaging, intensity of illumination, magnification, polarizing filter, position and orientation of camera… The combination of images may include image analysis and treatments.

[0165] Then, in a third step, image of reference is stored in a database, so that image of reference may be retrieved later to authenticate an object comprising a mark. In an embodiment, the image of reference is stored with supporting metadata, such as features on the object to be authenticated, dates… Database is preferably accessible remotely, through servers or through a user-shared information system for some metadata of database. This is particularly useful because the information is always accessible and longtime recorded, thus not depending from the state of the server.

[0166] These three steps are usually performed by a fabricant who wishes to protect objects against counterfeiting with an authentication kit comprising a mark and an image of reference of said mark.

[0167] In an embodiment, the method of verifying that an object is genuine comprises further fourth and fifth steps, typically performed by a potential customer willing to purchase an object. These steps may also be performed by the provider of said object.

[0168] In a fourth step, a test image of the mark is obtained. Preferably, the test image is obtained with an optical device already available for the consumer, such as the camera included in a smartphone for instance – optionally with optical add-ons.

[0169] Then, in a fifth step, a search is run in the database to retrieve the test image. An algorithm of matching, such as those used for facial recognition, may be used. Alternatively, a direct comparison of test image in database may be used. If the test image corresponds to an image of reference, then the control is positive, and authentication of object is established. If metadata were stored with image of reference, they may be displayed on the customer smartphone.

[0170] It is worth noting that the spatial resolution of the imaging device used to obtain test image in step four is critical. Indeed, if test image of mark has a large resolution length – i.e., a bad separation of individual objects - it may be not retrieved in the database, leading to an incorrect assessment of authenticity. In a variant, fifth step includes a control of test image resolution length to enable or disable control with the database.

[0171] In an embodiment, a plurality of images is obtained, then combined to obtain the test image. The plurality of images may be obtained under different conditions, such as wavelength of illumination, wavelength of imaging, intensity of illumination, magnification, position and orientation of the camera… The combination of images may include image analysis and treatments.

[0172] In another embodiment, the test image obtained in the fourth step is an image of a part of the mark and matching of fifth step is run to identify if the test image corresponds to a part of an image of reference.

[0173] While various embodiments have been described and illustrated, the detailed description is not to be construed as being limited hereto. Various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the disclosure as defined by the claims. Authentication method for transparent objects

[0174] This disclosure also relates to a method of verifying that a transparent object is genuine, in particular an ophthalmic lens.

[0175] Indeed, in the last step of the authentication method, i.e., matching the two images – reference and test – of the luminescent mark, the same part of the object has to be imaged. As images have a high resolution, the field of the images is limited and matching can be achieved only if both images have been made on the same part of the object.

[0176] Therefore, in an embodiment, the image of references includes an optical feature of the authenticated object, different from the luminescent mark. This is especially interesting with transparent objects: the image of reference may include a geometric limit of the object or an optical reference of the object.

[0177] In this embodiment, the image of reference obtained in second step includes an optical feature of the authenticated object. This optical feature thus defines a spatial reference in the image of reference. And the test image obtained in the fourth step of the method also includes the same optical feature of the authenticated object. Then, thematching of the fifth step includes identification of the optical feature of the test image to define the spatial reference of the test image, then matching images based on a first match of spatial references of both images.

[0178] For instance, for ophthalmic lenses, the optical feature may be the optical centre of unifocal corrective lenses. Localization of the optical centre of the lens is very easy and defines the spatial reference. Last, the luminescent mark may be located within this spatial reference, for the image of reference and the test image, allowing easier matching.

[0179] For instance, for ophthalmic lenses, the optical feature may be the permanent markings of progressive lenses, in accordance with the ANSI Z80.1 and ISO 8980-2 standards. The alignment reference markings; the indication of the manufacturer, tradename, trademark or supplier – such as nasal or temporal engravings – can be used as optical feature. In an embodiment, the luminescent mark is located near, above or below a permanent marking, so that the part of the ophthalmic lens to be imaged is defined unambiguously.

[0180] For instance, for plano ophthalmic lenses, i.e., devoid of any corrective effect – frequently encountered for solar lenses – thus without optical centre nor progressive markings, a trademark or a fitting marking located on the lens can be used as optical feature.

[0181] For instance, for glass containers especially designed for a specific product – like perfume bottles, spirit bottles or cosmetic containers – the optical feature may be a specific reflection obtained in the edge of the glass container. The optical feature may be a pseudo-optical centre if the glass container behaves locally like a focal lens. The optical feature may be an engraving or a marking on the glass container, like the name of the product, name of supplier or regulatory markings. EXAMPLES

[0182] The present invention is further illustrated by the following examples. Protocol 1: Optical imaging.

[0183] In the following examples, the luminescent mark of the examples is observed and photographed under a microscope. The mark is illuminated with UV light at a wavelength of 375 nm. The photo is acquired with 150 ms acquisition time, and the incoming light is filtered at 520 nm and 650 nm. The microscope is adjusted to provide a x10 magnification with a numerical aperture of 0.25. Example 1: CdSe / ZnSe / ZnS quantum dots (Green) in an aluminum oxide matrix.

[0184] Figure 1 shows the luminescence of composite particles of a mark according to a first example. The mark of example 1 has been obtained as follows.

[0185] A stock solution of Allyl Diglycol Carbonate (ADC) is prepared, comprising 5 mg / mL of 30 wt% CdSe core, ZnSe first shell, ZnS second shell quantum dots in an alumina matrix. The composite particles, being the quantum dots embeded in the alumina matrix, have a mean diameter of 840 nm.

[0186] Three diluted solutions are independently prepared from the stock solution, the three solutions having respective concentrations of 50 µg / mL [C1], 5 µg / mL [C2] and 0.5 µg / mL [C3] of composite particles. Considering that the average density of the polymer is 1, these concentrations respectively correspond to 50 ppm, 5 ppm and 0.5 ppm. Also, these concentrations respectively correspond to 2.1013luminescent nanoparticles per cm3, 2.1012luminescent nanoparticles per cm3and 2.1011luminescent nanoparticles per cm3.

[0187] Then, samples are prepared by mixing each diluted solutions to a 30% isopentenyl pyrophosphate (IPP) solution. For each 1mL of diluted solution, 150 µL of 30% IPP solution is added.

[0188] Each sample is sonicated, vortexed and injected into a mold. Then, each sample is polymerized over 19 hours. The polymerization is as follows: 5 hours ramping from ambient temperature to 60°C, 3 hours ramping from 60°C to 78°C, 10 hours at 78°C.

[0189] Another witness sample, not comprising any quantum dots, is prepared.

[0190] The upper left image of figure 1 corresponds to the luminescence of the sample comprising 50 µg / mL of particles. The upper right image of figure 1 corresponds to theluminescence of the sample comprising 5 µg / mL of particles. The lower left image of figure 1 corresponds to the luminescence of the sample comprising 0.5 µg / mL of particles. The lower right image of figure 1 corresponds to the luminescence of the witness.

[0191] On figure 1, luminescence is identified by black areas. It is noted that the luminescence of the quantum dots is green.

[0192] First, it is noted that the witness sample fails to provide any luminescence. Second, it is also noted that the distribution of the luminescent nanoparticles of all the samples comprising particles is random. This is a direct consequence of the preparation method for the sample, that does not favor any distribution for the composite particles.

[0193] For all the samples, luminescence may be observed, and the resolution is sufficient to identify luminescent dots, corresponding to luminescent nanoparticles or aggregates of luminescent nanoparticles.

[0194] Figure 3 is a graph representing the absorbance function of the wavelength for different concentration of composite particles according to the first example. It shows that sample of concentration [C1] presents some absorbance in the visible range, while samples of concentration [C2] and [C3] presents an absorbance inferior to 0.01 for all the visible range. Example 2: CdSeS(4MLs) / CdS with ZnS shell quantum plates (Red) in a zirconium oxide matrix.

[0195] Figure 2 shows the luminescence of composite particles of a mark according to a second example. The mark of example 2 has been obtained as follows.

[0196] A stock solution of Allyl Diglycol Carbonate (ADC) is prepared, comprising 5 mg / mL of 0,3 wt% CdSeS(4MLs) / CdS with ZnS shell quantum plates in a zirconia matrix. The luminescent nanoparticles, being the quantum plates embeded in the zirconia matrix, have a mean diameter of 1050 nm.

[0197] Two diluted solutions are independently prepared from the stock solution, thetwo solutions having respective concentrations of 50 µg / mL and 5 µg / mL of particles. Considering that the average density of the polymer is 1, these concentrations respectively correspond to 0.5 ppm and 0.05 ppm and to 2.1012luminescent nanoparticles per cm3, and 2.1011luminescent nanoparticles per cm3.

[0198] Then, samples are prepared by mixing each diluted solutions to a 30% isopentenyl pyrophosphate (IPP) solution. For each 1mL of diluted solution, 150 µL of 30% IPP solution is added.

[0199] Each sample is sonicated, vortexed and injected into a mold. Then, each sample is polymerized over 19 hours. The polymerization is as follows: 5 hours ramping from ambient temperature to 60°C, 3 hours ramping from 60°C to 78°C, 10 hours at 78°C.

[0200] The left image of figure 2 corresponds to the luminescence of the sample comprising 50 µg / mL of particles. The right image of figure 1 corresponds to the luminescence of the sample comprising 5 µg / mL of particles.

[0201] On figure 2, luminescence is identified by black areas. It is noted that the luminescence of the quantum plates is red.

[0202] It is also noted that the distribution of the luminescent nanoparticles of all the samples comprising particles is random. This is a direct consequence of the preparation method for the sample, that does not favor any distribution for the composite particles.

[0203] For both samples, luminescence may be observed, and the resolution is sufficient to identify luminescent dots, corresponding to luminescent nanoparticles or aggregates of luminescent nanoparticles. Accordingly, these samples define marks according to the invention, that may be uniquely identified. Example 3: mix of CdSe / ZnSe / ZnS quantum dots (Green) and CdSeS(4MLs) / CdS with ZnS shell quantum plates(Red) in a zirconium oxide matrix.

[0204] Figure 3 shows the luminescence of composite particles of a mark according to a third example. The mark of the third example has been obtained by mixing CdSe / ZnSe / ZnS quantum dots and CdSeS(4MLs) / CdS with ZnS shell quantum plates.Then, a sample obtained in the same way as in examples 1 and 2 has been prepared and observed.

[0205] In figure 3, the top image corresponds to the luminescence in all the visible range. The bottom left image corresponds to the luminescence filtered at 650 nm (red), while the bottom right image corresponds to the luminescence filtered at 520 nm (green). It is observed that each of the quantum dots and the quantum plates presents a luminescence at their respective wavelengths. Thus, a mix of luminescent nanoparticles is suitable to create a mark according to the invention. Besides, such marks are more robust, since it can be analyzed as a superposition of two luminescent marks at two different wavelengths. Other examples for quantum dots, that can be prepared as examples 1 and 2 Matrix Loading Nanoparticles (AlxZryMzO) charge x y z (M) Core / shell / shell nanoplatelets A 6 / 17 4 / 17 1.5% Core / shell / shell nanoplatelets B 1 / 20 9 / 20 0.017 (Hf) 2% Core / shell / shell nanospheres C 6 / 17 4 / 17 0 1% Core / shell / shell nanospheres D 2 / 5 1 / 5 0 15% Core / shell / shell nanoplatelets E 6 / 17 4 / 17 0 3% Core / shell / shell nanospheres F 2 / 5 1 / 5 0 1% Core / shell nanospheres G 6 / 17 4 / 17 0 2% Core / shell nanospheres H 1 / 10 17 / 40 0 15% Core / shell / shell nanoparticles I 8 / 15 1 / 10 0 15% Core / shell / shell nanoplatelets J 1 / 40 77 / 60 0 10% Core / shell nanospheres K 1 / 20 9 / 20 0.017 (Si) 15% Core / shell nanoparticles L 2 / 9 1 / 3 0 15% Core / shell nanoparticles M 2 / 5 1 / 5 0 12% Core / shell / shell nanoparticles N 1 / 20 9 / 20 0.017 (Ti) 15% Core / shell / shell nanoparticles O 1 / 40 9 / 20 0.031 (Ti) 15%

[0206] Core / shell / shell nanoplatelets A: CdSe0.45S0.55 / Cd0.30Zn0.70S / ZnS, with a core of thickness 1.2 nm and a lateral dimension, i.e., length or width, greater than 8 nm and shells of thicknesses 2.5 nm and 2 nm, emitting red fluorescent light.

[0207] Core / shell / shell nanoplatelets B: CdSe0.72S0.28 / CdS / ZnS, with a core of thickness 1.2 nm and a lateral dimension, i.e., length or width, greater than 8 nm and shells of thicknesses 3.5 nm and 0.5 nm, emitting red fluorescent light.

[0208] Core / shell / shell nanospheres C: CdSe / CdS / ZnS, with a core of diameter 4.5 nm and shell thicknesses of 1.5 nm and 1 nm, emitting red fluorescent light.

[0209] Core / shell / shell nanospheres D: CdSe / ZnSe / ZnS, with a core of diameter 4.5 nm and shell thicknesses of 1.5 nm and 1 nm, emitting green fluorescent light.

[0210] Core / shell / shell nanoplatelets E: CdSe0.72S0.28 / ZnSe / ZnS, with a core of thickness 1.2 nm and a lateral dimension, i.e., length or width, greater than 8 nm and shells of thicknesses 3.5 nm and 0.5 nm, emitting red fluorescent light.

[0211] Core / shell / shell nanoparticles F: InP / ZnSe / ZnS with a core of diameter 4.0 nm and shell thicknesses of 2 nm and 1 nm, emitting red fluorescent light.

[0212] Core / shell / shell nanoparticles G: InP / ZnSe / ZnS with a core of diameter 3.0 nm and shell thicknesses of 2 nm and 1 nm, emitting red fluorescent light.

[0213] Core / shell / shell nanoparticles H: InP / ZnSe / ZnS with a core of diameter 2.5 nm and shell thicknesses of 1.5 nm and 1.25 nm, emitting green fluorescent light.

[0214] Core / shell / shell nanoparticles I: InP / ZnSe / ZnS with a core of diameter 2.5 nm and shell thicknesses of 2.75 nm and 2.50 nm, emitting green fluorescent light.

[0215] Core / shell / shell nanoplatelets J: CdSe0.10S0.90 / ZnS / Cd0.20Zn0.80S, with a core of thickness 1.5 nm and a lateral dimension, i.e., length or width, greater than 10 nm and shells of thicknesses 1 nm and 2.5 nm, emitting green fluorescent light.

[0216] Core / shell nanospheres K: CdSe0.10S0.90 / ZnS, with a core of diameter 4 nm and shell thickness of 1 nm, emitting green fluorescent light.

[0217] Core / shell nanoparticles L: InP / ZnS, having a diameter of 3.5 nm, emitting green fluorescent light.

[0218] Core / shell nanoparticles M: InP / ZnSe, having a diameter of 4.4 nm, emitting green fluorescent light.

[0219] Core / shell / shell nanoparticles N: InP / GaP / ZnS, having a diameter of 7.2 nm, emitting green fluorescent light.

[0220] Core / shell / shell nanoparticles O: InP / ZnSe / ZnS, having a diameter of 7.4 nm, emitting green fluorescent light.

Claims

CLAIMS 1. An authenticated object comprising a luminescent mark, said luminescent mark comprising composite particles having a mean size in a range from 100 nm to 1500 nm, said composite particles comprising luminescent nanoparticles dispersed in a metal oxide matrix, said composite particles being distributed throughout the luminescent mark, wherein • Absorbance of the composite particles is less than 0.01 over the UV-visible range of light; • Density of luminescent nanoparticles is greater than 109cm-3.

2. The authenticated object according to claim 1, wherein the concentration of luminescent nanoparticles in the luminescent mark is in a range from 150 ppm to 5 ppb.

3. The authenticated object according to claim 1 or 2, wherein the luminescent nanoparticles are quantum dots and the concentration of luminescent nanoparticles in the luminescent mark is in a range from 15 ppm to 150 ppb.

4. The authenticated object according to claim 1 or 2, wherein the luminescent nanoparticles are quantum plates and the concentration of luminescent nanoparticles in the luminescent mark is in a range from 1.5 ppm to 15 ppb.

5. The authenticated object according to claim 1 or 2, wherein the luminescent nanoparticles are single rare-earth doping element surrounded by the metal oxide and the concentration of luminescent nanoparticles in the luminescent mark is in a range from 150 ppm to 1.5 ppm.

6. The authenticated object according to claim 1 or 2, wherein the concentration of composite particles in the luminescent mark is in a range from 500 ppm to 0.5 ppm.

7. The authenticated object according to claim 1 to 6, wherein the composite particles are distributed randomly throughout the luminescent mark.

8. The authenticated object according to claim 1 to 7, wherein the average number of luminescent nanoparticles comprised in a composite particle is greater than 10, preferably greater than 20, even more preferably greater than 50.

9. The authenticated object according to claim 1 to 8, wherein the luminescent nanoparticles comprise at least one of CdSe, CdSeS, ZnSe, ZnSeS, InP, CuInS2spherical quantum dots.

10. The authenticated object according to claim 1 to 9, wherein the luminescent nanoplatelets comprise at least one of CdSe, CdSeS, ZnSe, ZnSeS, InP, CuInS2nanoplatelets.

11. The authenticated object according to claim 1 to 10, wherein the metal oxide matrix is selected from the group consisting of alumina, zirconia, titanium oxide, hafnium oxide, yttrium oxide, gadolinium oxide, or a mixture thereof.

12. The authenticated object according to claim 1 to 11, wherein the authenticated object is transparent.

13. Authentication method for acknowledging an object comprising: a. Authenticating the object by creating a luminescent mark, said luminescent mark comprising composite particles having a mean size in a range from 100 nm to 1500 nm, said composite particles comprising luminescent nanoparticles dispersed in a metal oxide matrix, said composite particles being distributed throughout the luminescent mark, wherein i. Absorbance of the composite particles is less than 0.01 over the UV-visible range of light; ii. Density of luminescent nanoparticles is greater than 109cm-3; b. Obtaining an image of reference imaging the luminescence of the luminescent mark, c. Storing said image of reference inside a database,d. Obtaining a test image of the luminescent mark on the authenticated object; and e. Controlling if said test image corresponds to said image of reference in said database.

14. The authentication method according to claim 13, wherein the object is transparent, wherein the image of reference obtained in step b) includes an optical feature of the authenticated object, wherein the test image obtained in step d) of the method includes the same optical feature of the authenticated object; and wherein the matching of step e) includes identification of the optical feature.

15. The authentication method according to claim 13 or 14, wherein the object is an ophthalmic lens, such as a unifocal corrective lens, a progressive lens or a plano lens.

16. The authentication method according to claim 13 or 14, wherein the object is a glass container, such as a perfume bottle, a spirit bottle or a cosmetic container.

Images