Emissive metasurface for efficient color conversion

Abstract

An emissive metasurface comprising a nanostructured dielectric component and an emissive system comprising at least one emissive component which is at least partially in the near-field proximity to the nanostructured dielectric component, wherein the nanostructured dielectric component comprises a plurality of metaatoms, wherein each of the metaatoms is a void in the dielectric component filled with the emissive component and wherein the emissive system is configured to absorb and emit light in the visible range is disclosed herein.

Description

EMISSIVE METASURFACE FOR EFFICIENT COLOR CONVERSIONTECHNICAL FIELDThe present disclosure relates to the field of nanophotonics, in particular to metasurfaces and semiconductor devices.TECHNICAL BACKGROUNDWith the help of color filters and color conversion elements, for example color displays can be developed that only have a single-color (typically blue) light source. However, it is difficult to achieve efficient color conversion, blocking of the incident blue light, and directional control of the converted light.It has been shown that emissive metasurfaces based elements greatly increase the conversion efficiency and brightness of the emitted light while suppressing the incident light in the emission direction. However, they may not be applicable at lower wavelengths due to strongly increasing absorption of the high refractive index materials such as silicon, that is typically used for such elements.Metamaterials are engineered materials that interact with waves in a desired fashion. With metamaterials, properties of the final product can be realized which are not possible with naturally occurring materials. Building blocks of the metamaterials are so-called meta-atoms, that are smaller than the wavelengths of desire. Metasurfaces are 2D metamaterials with a thickness below the wavelength of interest. They can be any arrangement in between, on the one hand, spatially highly inhomogeneous, with generally non-identical meta-atoms placed on a generally aperiodic lattice, and, on the other, essentially periodic with identical meta-atoms placed in a periodic lattice (including photonic crystal slab geometries). In general, the main distinguishing feature of metasurfaces as opposed to gratings and photonic crystals (both of their functions are defined by their periodic arrangements) is that metasurfaces dominantly inherit properties from their individual meta-atoms and their resonant properties.Light-emitting metasurfaces are metasurfaces with nanoscale emitters such as quantum dots (QDs), dye molecules, or direct-bandgap semiconductors integrated into the metasurface architecture. The meta-atoms can be designed to act as nanoantennas that efficiently couple the emission from the excited metaatoms to the far-field, while imprinting the desired properties onto the emitted light field. To optimize the coupling between the nanoantennas and the emitters, the latter should be localized in optical near fields of the nanoantennas. Light-emitting metasurfaces inherit most of the functionalities provided by optical nanoantennas, such as excitation enhancement and emission enhancement via the Purcell effect, as well as spectral and directional shaping of the emitted light. Emisisve metasurfaces are disclosed e.g., in Vaskin et al., Nanophotonics 2019, 8(7), 1151.US 2019 / 0033683A1 discloses optical elements including a multi-level metasurface stack having two or more metasurface levels.US 2021 / 0063606A1 is directed to metasurface optical coupling elements for a display waveguide.A light emitting diode including a light emission layer and a charge transport layer disposed on the light emission layer are described e.g., in US 2021 / 0050494A1.US 2021 / 0026248A1 is directed to a display device having an integrated metamaterial lens.SUMMARYAccording to a first aspect there is provided an emissive metasurface comprising a nanostructured dielectric component and an emissive system comprising at least one emissive component which is at least partially in the near-field proximity to the nanostructured dielectric component, wherein the nanostructured dielectric component comprises a plurality of metaatoms, wherein each of the metaatoms is a void in the dielectric component filled with the emissive component and wherein the emissive system is configured to absorb and emit light in the visible range. In a further aspect there is provided a semiconductor device comprising the metasurface as described herein, the metasurface being configured for enhancement of absorption of a first color and emission of a second color.Further, there is provided a method for preparing a metasurface as disclosed herein, the method comprising the steps:Providing a nanostructured dielectric component,Coating the dielectric component, Texturing the coating, Etching the dielectric component, and Applying an emissive system on the thus obtained nanostructured surface.BRIEF DESCRIPTION OF THE DRAWINGSEmbodiments are explained by way of example with respect to the accompanying drawings, in which:Fig. 1 shows an exemplary metasurface.Fig. 2 shows the spectrum of the emissive layer electric field energy ratio of amorphous silicon with voids based emissive metasurface.Fig. 3 shows the spectrum of the emissive layer electric field energy ratio of amorphous silicon with voids based emissive metasurface with an ITO layer.Fig. 4 shows the spectrum of the emissive layer electric field energy ratio of amorphous silicon with voids based emissive metasurface.Fig. 5 shows an exemplary meta-atom.Fig. 6a shows the calculated electric field energy in the emissive layer as a function of emission wavelength and angle of incidence theta (0°: incidence normal to the surface). Fig. 6b shows the calculated electric field intensity distribution.Fig. 7 shows the calculated electric field intensity distribution.Fig. 8 shows the calculated electric field energy in the emissive layer as a function of emission wavelength and angle of incidence theta (0°: incidence normal to the surface).Fig. 9 shows a method for preparing a metasurface.Fig. 10 shows an exemplary LED color conversion filter.Fig. 11 shows an exemplary semiconductor device.Fig. 12 shows the emission spectrum of a planar emissive film on an unstructured substrate.DETAILED DESCRIPTION OF EMBODIMENTSBefore a detailed description of the embodiments under reference of the figures is given, general explanations are made.The embodiments disclose an emissive metasurface comprising a nanostructured dielectric component and an emissive system comprising at least one emissive component which is at least partially in the near-field proximity to the nanostructured dielectric component, wherein the nanostructured dielectric component comprises a plurality of metaatoms, wherein each of the metaatoms is a void in the dielectric component filled with the emissive component and wherein the emissive system is configured to absorb and emit light in the visible range.The metaatoms may be configured so that they resonantly match with the frequency of the light absorbed and / or with the light emitted by the emissive system.The nanostructured dielectric component may be configured so that a localized resonance mode of the metaatoms and a lattice resonance mode of the nanostructured dielectric component are either matched to the emission frequency of the emissive system, or to the absorption frequency of the emissive system.The plurality of metaatoms may be arranged such that they support at least one lattice resonance mode and wherein the metaatoms may have a size and shape such that they support at least one Mie resonance mode.The metaatoms may for example be arranged in a lattice. The lattice may for example be a square lattice, a hexagonal lattice, or the like.In an embodiment, the nanostructured dielectric component in the metasurface is configured so that a first localized (e.g., Mie) resonance mode of the metaatoms and a lattice resonance mode of the nanostructured dielectric component are matched to the emission frequency of the emissive system, and so that a second localized (e.g., Mie) resonance mode of the metaatoms is matched to the absorption frequency of the emissive system.A matching of lattice mode to Mie-type resonance was derived by iterative lattice mode matching with the following lattice modes equations:The iterative matching of lattice mode to Mie-type resonances may be done according to ACS Photonics 2018 (5), 1359 with the following steps:1. Choose angles of incidence 0 and <P2. Choose diffraction orders (p, j, I, and m) (for chosen 0 and <P with initial lattice period a) for close match of either one of the two equations.3. Tune period a to satisfy the lattice mode equation completely.4. Retune disc geometries using new a to have simulated Mie-resonance at chosen emission wavelength.The metasurface comprises voids. The voids substantially concentrate the electric field inside the emissive system in the recesses of the nanostructured dielectric component.In an embodiment, the void has an irregular or regular shape. Having a regular shape, the void may have a certain geometry. The void may have a shape selected from cuboid, rhombic prism, truncated pyramid; with or without rounded edges, and from cylinders and truncated cones.The emission frequency may for example relate to output light emitted by the emissive system and the absorption frequency may for example relate to input light absorbed by the emissive system.The voids may have a diameter of 100 nm to 500 nm, more preferably of 150 nm to 450 nm, most preferably of 200 nm to 400 nm.The nanostructured dielectric component and the emissive system layer may be configured to resonantly enhance the absorption of the emissive system, e.g., at low wavelengths.The nanostructured dielectric component and the emissive system may be configured to resonantly enhance the emission of the emissive system.The geometry and dimensions of the nanostructured dielectric surface (and other additional layers) are configured so that it is possible to resonantly enhance the absorption of the emissive system at low wavelengths as well as its emission at longer wavelengths with overall low absorption losses.In an embodiment, the nanostructured dielectric component and the emissive system layer are configured to perform emission at longer wavelengths with overall low absorption losses.The emissive metasurface may be configured for color conversion in the visible spectrum. In this way, the metasurface may for example be applied as a LED color conversion filter. For example, the emissive system may be configured to provide a ternary or higher order emissive energy transfer system for efficient metasurface based color conversion. The metasurface may in particular provide an efficient wide wavelength gap color conversion. The emissive metasurface may for example be configured for up-conversion and / or down-conversion.There are embodiments, wherein the emissive metasurface is configured for directional intensity control of incident and emitted light.The emissive system is typically chosen to emit light of a desired wavelength.In an embodiment, the emissive system is located on top of the nanostructured dielectric component. This may for example be achieved by conformal coating of the nanostructured dielectric component.The nanostructured dielectric component may have different materials. In an embodiment, the nanostructured dielectric component is selected from a-Si (amorphous silicon), Si, ZnTe, GaP, GaAs, GaSb, Ge, GeTe, InP, InAs, InSb, PbS, Te, PbSe, PbTe, M0S2, MoTe2, AlSb, AlAs, and SiC, III-V semiconductor, such as GaP, etc. The nanostructured dielectric component may have a thickness of less than 200 nm at the thickest part. Preferably, the nanostructured dielectric component a thickness of less than 100 nm at the thickest part, and most preferably, the nanostructured dielectric component has a thickness of less than 50 nm at the thickest part.The individual shape, i.e., the meta-atom, may be in nanometer size. For periodic metasurfaces, the size of the repeating unit may be between about 100 nm to 500 nm, more preferably between 150 nm to 450 nm, most preferably between 200 nm to 400 nm. The size typically defines thebroadest extension of the shape, i.e., the meta-atom. The voids may have larger lateral extension than the meta-atoms so that the dielectric component is laterally non-connected.The dimensions of the metaatoms may be smaller than half of the freespace wavelength. Preferably, Ax, Ay, Az < A) / 2, where Xo is the freespace wavelength, and where Ax, Ay, Az are the dimensions of a metaatom. This may apply to emission and absorption.In an embodiment, the refractive index (n=n+ik) of the dielectric nanostructured layer is in the range 7>n>2.5, with k>0.05 at absorption or emission wavelength, or in the range 5>n>3, with k > 0.1 at absorption or emission wavelength.There are embodiments of the metasurface, wherein the emissive system comprises a ternary or higher order emissive system.The emissive system may comprise at least one emissive component selected from an organic dye, chromophores, fluorophores, inorganic materials, and quantum dots.In an embodiment, the emissive system is an organic dye layer. The dye may be a mixture of a chemical substance that chemically bonds to the substrate to which it is applied. Typical dyes are chemical substances that are solved in a solvent, such as water, or organic solvents. The day may be responsible for converting light of a certain first wavelength to light of a certain second wavelength.Alternatively, the emissive system may comprise an inorganic material. In other words, the emissive system may comprise at least one inorganic molecule, or might consist of at least one inorganic molecule. The at least one inorganic molecule preferably converts light of a certain first wavelength to light of a certain second wavelength. Exemplary inorganic molecules might be quantum dots. An inorganic layer might comprise one type of quantum dots or might comprise a mixture of different quantum dots.In a preferred embodiment, the at least one emissive system is a chromophore layer. A chromophore layer is a layer that comprises at least one chromophore, or consists of a chromophore. The at least one chromophore preferably converts light of a certain first wavelength to light of a certain second wavelength. A chromophore is the part of a molecule, or the molecule itself that is responsible for the color. The chromophore(s) may be present as pure substances, or may be present in a suitable matrix.Exemplary chromophores comprise a conjugated pi-system, such as fluorenes, spirofluorenes, spirobifluorenes, quinolines, naphthalines, anthracenes, etc.A chromophore might be selected from the group consisting of (Ir-ATP), (Z)-6-Mesityl-N-(6- mesitylquinolin-2(lH)-ylidene)quinolin-2-amine-BF2 complex (MQAB), BDP24, 2,7-Bis(carba- zol-9-yl)-9,9-spirobifluorene (Spiro-2CBP), etc..The emissive system may be configured for up-conversion and down-conversion.In an embodiment, the emissive system comprises an emitter and an acceptor mixed together in a matrix material.The absorber and the emitter may be two different molecules. The acceptor may for example be acceptor chromophores and the emitter may for example be donor chromophores.The emitter and the acceptor may be selected so that the absorption and emission peaks of the emissive system are tuned to the resonances of the nanostructure.By tuning of the concentrations of the emitter and acceptor in the emissive system, the efficiency of the energy transfer, the field distribution inside the emissive system, and the loss by reabsorption may be optimized. For example, donor chromophores may get excited at low wavelength and transfer energy to acceptor chromophores through non-radiative dipole-dipole coupling and the acceptor chromophore may emit at higher wavelength. The non-radiative dipole-dipole coupling may for example be caused by Forster or fluorescence resonance energy transfer (FRET). This may enhance the overall color conversion efficiency.There are embodiments provided, wherein the effective refractive index of the emissive system is matched to the resonant nanostructure.The refractive index n=n+ik of the emissive system at absorption wavelength may be n = 2.0 at k = 0.2, and the refractive index n=n+ik of the emissive system at emission wavelength may be n = 1.8 at k = 0.01.The metasurface might be placed on a substrate. Typical substrates are glass, SiCh, sapphire, etc. The substrate might be relevant as support for the metasurface. Additionally, or alternatively, the substrate might have a technical function, such as stabilizing the metasurface, emitting light, etc.. A preferred substrate is glass.The metasurface is typically placed on the substrate in that way, that the dielectric component is in direct contact with, or in close proximity to the substrate. The dielectric component might be connected with an adhesive to the substrate.The emissive system might be separated by the dielectric component from the substrate.In cases, wherein the dielectric component is a continuous layer, the emissive system is not in contact with the substrate.In cases, wherein the dielectric component is a noncontinuous layer, the emissive system is in contact with the substrate. In these cases, the substrate might be the support for individual geometric patterns.Further, there is provided a semiconductor device comprising the metasurface as disclosed herein, the metasurface being configured for enhancement of absorption of a first color and emission of a second color. The semiconductor device may for example be a light-emitting diode (LED).In the semiconductor device the first color may be blue and second color may be red or green. Furthermore, there is provided a method for preparing a metasurface as disclosed herein, the method comprising the steps:Providing a nanostructured dielectric component,Coating the dielectric component,Texturing the coating,Etching the dielectric component, andApplying an emissive layer on the thus obtained nanostructured surface.The method may further comprise the step of sputtering a metal layer on the dielectric component.In a first step of the method described herein, a nanostructured dielectric component is provided. Preferably, the dielectric component corresponds to the dielectric components described herein. The dielectric component comprises voids.The dielectric lay component er is preferably provided on a substrate. The substrate preferably corresponds to the substrates described herein. The dielectric component may be connected to the substrate via bonding. The bonding may be a chemical bonding, covalent bonding, ionic bonding, or it may be through an adhesive.As described, the dielectric component may completely cover at least one side of the optional substrate. Alternatively, the dielectric component may not completely cover the substrate on one side.In a further step, the thickness of the dielectric component may be reduced by applying an appropriate method. The thickness of the component may be reduced by etching, e.g., chemical etching, or physical etching. Preferably, the etching may be carried out with ion beam etching (IBE). The reduced thickness of the dielectric component may be about 20 to 50%, about 20 to 40%, or about 20 to 30% of the thickness of the provided dielectric component.Further a metal layer may be applied on the dielectric component. The metal layer may be applied on the provided dielectric component, or on the dielectric component reduced in thickness. The metal applied may be a transition metal. An examples of a suitable transition metal is chromium. The method for applying the metal layer may be sputtering. Thus, in an exemplary embodiment, a chromium layer is sputtered on the dielectric component, either on the provided dielectric component, or on the dielectric component reduced in thickness.In an embodiment, a metal layer is sputtered on the dielectric component, either reduced in thickness, or as provided.The metal layer may completely cover the provided dielectric component, or the dielectric component reduced in thickness.The metal layer may be about 1 to 50%, about 5 to 30%, or about 10 to 20% of the thickness of the provided dielectric component.In a further step, the dielectric component is coated. In embodiments, wherein a metal layer is present on the dielectric component, the metal layer is coated.The coating may be a coating that is resistant at least to moisture, oxygen, etc., to avoid the chemical reaction (e.g., oxidation) of the dielectric component, or, if present, of the metal layer. Thus, preferably, the coating completely covers the dielectric component, or, if present, the metal layer.The coating may have a thickness of about 10 to 50%, about 15 to 30%, or about 20 to 25% with respect to the thickness of the provided dielectric component.In a further step, the coating is textured. Texturing in the present case may be defined as introducing a pattern at least in the outermost layer, i.e., the coating. The pattern may be in that way, that there are voids and the layer below the coating is in direct contact with the atmosphere. It is also possible that not only the outermost layer is textured, but also the further layers and thus, layers below the outermost layers are textured. In the latter case also further layers may be in direct contact with the atmosphere.The texturing may be carried out by appropriate methods. Exemplary methods may be ultraviolet (UV), far ultraviolet (FUV), and extreme ultraviolet (EUV) light exposure using masks, electron beam (EB) exposure, ion beam etching (IBE), reactive ion etching (RIE), etc. The texturing may also be carried out by combining at least two different methods.The method further comprises the step of etching the dielectric component. In this step, the applied further layers, such as the coating, the optional metal layer, or optional further layers are removed from the dielectric component. Preferably, the substrate is then in direct contact with the atmosphere.A further embodiment is a metasurface prepared by a method as described herein.The metasurface disclosed herein may allow a strong enhancement of the light emission and a direction control of the emitted light.As used herein the term ’’organic” is used in its generally understood meaning, i.e. it refers to compounds which are carbon-containing compounds. As it is used here, it also includes elemental carbon, at least in the form of fullerenes. The term ’’organic” is further meant to exclude specific carbon-containing compounds such as: hydrogen-free chalkogenides of carbon, e.g. CO, CO2, CS2, and derivatives thereof, e.g. H2CO3, KSCN; further excluded are salt-like carbides which are binary compounds of elements with carbon, which decompose to hydrocarbons under the influence of water or dilute acids. Salt-like carbides have the general formula MkCb or MnC2, wherein M1or Mndenotes a metal ion with one or two valences. Salt-like carbides of calcium, silver and copper decompose to acetylene, the salt-like carbide of aluminium (AI4C3) decomposes to methane. Further excluded carbon-containing compound which do not form part of the term ’’organic” are metallic carbides, which are non-stoichiometric compounds having the character of an alloy. They are resistant to acids and are electrically conducting.As used here a chromophore is the part of a molecule responsible for its color.A fluorophore (or fluorochrome, similarly to a chromophore) is a fluorescent chemical compound that can re-emit light upon light excitation.A phosphor is an emitter emitting phosphorescence. In phosphorescence the emitter does not reemit the radiation it absorbs withion ps- to ns but in ps to s after the absorption of photon. Here organic or inorganic phosphors can be part of the emissive system.Organic dye is a molecule which contains one or more chromophores / fluorophores or phosphors.The organic dye can be a small molecule (up to lOOODa) or a polymer.Further the emitters can be inorganic phosphors or QDs.QD as used here are also called (semiconductor) nanocrystals, are semiconductor particles a few nanometers in size, having optical and electronic properties that differ from those of larger particles as a result of quantum mechanics. The nanocrystals can also be phophors (or phosphorescent QDs).The matrix as used herein could consist of organic molecules / polymers or could be inorganic. Its main function is to ensure good distribution of the absorbing and the emitting components in the (at least) tri-components or ternary emissive systems.The emissive system may contain a matrix, at least one chromophore, inorganic or hybrid absorber absorber and at least one emitter (fluorophore or phosphor). The absorbing and the emitting chromophore can be combined in one organic dye / molecule.In the context of the application, the near-field proximity of a component describes the region of space which is closer to the component than the free-space wavelength of the interacting light fields.Fig. 1 shows a top view of an exemplary metasurface comprising an array of 5x4 meta-atoms. The dashed area corresponds to the dielectric layer and the circle reflects the voids in the dielectric layer. “D” is the diameter of each void. “P” is the size of the repeating unit in the metasurface (and that of the metaatom). “D” and “P” may have a size of between 100 nm to 500 nm, preferably of 150 nm to 450 nm and more preferably of 200 nm to 400 nm. “D” may also be larger than “P”, so that the dielectric nanostructure consists of non-connected parts.Fig. 2 shows the simulation of the spectrum of the electric field energy ratio in the emissive system of an emissive metasurface comprising an amorphous silicon layer with voids and a top organic emissive layer filling the voids. The energy ratio was determined by calculation of the electric field energy inside the emissive layer normalized to the electric field energy inside the same volume of the emissive layer for a plane emissive layer of the same height and absent a-Si nanostructure. The field energies inside the emissive system are enhanced by a factor of up to ~6 for the metasurface as compared to an unstructured reference. The period was matched for a lattice mode in the glass substrate.The simulation parameters were as follows: infinite periodic cylindrical void structure with a square period P = 377 nm and void diameter of D = 290 nm; height of the a-Si layer: 35 nm; emissive system layer (filling the voids and on top of a-Si layer) height: 255 nm; emissive layer refractive index: n = 1.8 and no absorption; and glass (Borofloat 33) substrate.Fig. 3 shows the emissive layer energy ratio spectrum of a similar system as described in Fig. 2 with an additional ITO layer between the substrate and the a-Si layer. The simulation parameters different to those of Fig. 2 are: P = 360 nm and D = 320 nm; emissive system layer height: 280 nm;100 nm ITO layer thickness.Fig. 4 shows the spectrum of the emissive layer electric field energy ratio of a very thin amorphous silicon layer with cylindrical voids filled with the emissive system layer. The field energies inside the emissive layer are enhanced by a factor of up to ~17 for the metasurface as compared to an unstructured reference (which is the emissive system onto a flat dielectric layer of the same dielectric). The simulation parameters were as follows: infinite periodic void structure with a square period P = 335 nm and void diameter of D = 320 nm; height of the a-Si layer: 8 nm; emissive system layer height (filling the voids and on top of a-Si layer): 260 nm. Very strong electric field enhancement is observed at 550 nm.Fig. 5 shows a crosscut along one of the period axes of an exemplary meta-atom 100. The metaatom 100 comprises a substrate 101, a dielectric layer of amorphous silicon 104 and an emissive layer 103. 105 depicts the air. As can be seen there is a void in the amorphous silicon layer 104 that is filled with the emissive system layer 103. At least two meta-atoms 100 may form a metasurface.Fig. 6a shows the calculated electric field energy in the emissive layer as a function of emission wavelength and angle of incidence theta (0°: incidence normal to the surface). Due to reciprocity, the angle of incidence in the calculation corresponds to the angle of the outgoing emission. The top pair of a rising and a falling straight line at approx. 560 nm wavelength indicates a lattice modes for n = 1.47 (glass substrate). It can be seen in the simulated grayscale map that a lattice mode, strongly depending on 9, is observed close to the lines. The simulation parameters are those of Fig. 2 (the crosscut of the calculated gray scale map at 9 = 0 corresponds to the graph ofFig. 2). Fig. 6b shows a crosscut of the calculated electric field intensity distribution the periodic repeat unit of the emissive metasurface for wavelength of 560 nm. The main resonance is located in the emissive layer in the center of the void structure.Fig. 7 shows a crosscut of the calculated electric field intensity distribution (of the system described in Fig. 3) inside the periodic repeat unit of the emissive metasurface for wavelength 560. The main resonance is located in the emissive layer in the center of the void structure.Fig. 8 shows the calculated electric field energy in the emissive layer as a function of emission wavelength and angle of incidence theta (0°: incidence normal to the surface). The emissive metasurface system is the one described in Fig. 4 (the crosscut of the calculated gray scale map at 0 = 0 corresponds to the graph of Fig. 4). The top pair of a rising and a falling straight line at approx. 600 nm wavelength indicates a lattice mode inside the emissive layer for n = 1.80. It can be seen in the simulated grayscale map that a lattice mode, strongly depending on 9, is observed close to the lines starting at approx. 570 nm. The sharp resonance starting at 550 nm is less dependent on 9.Fig. 9 shows an exemplary meta-atom 100. The meta-atom 100 comprises a substrate 101, a dielectric layer of amorphous silicon 104 and an emissive layer 103. 105 depicts the air. As can be seen there is a void in the amorphous silicon layer 104 that is filled with the emissive layer 103. At least two meta-atoms 100 may form a metasurface.Fig. 8 shows the Calculated Electric field distribution for a wavelength of 550 nm of an emissive metasurface comprising an amorphous silicon layer with voids and a top organic emissive layer. The voids are filled cylindrical voids, filled with the emissive layer. The resonance is located in the emissive layer in the center of the void structure. Fig. 2 shows the corresponding emissive layer energy ratio.Fig. 9 shows a general method for preparing a metasurface 900. Provided was a dielectric layer 904, that was optionally placed on a substrate 901. In step A, the dielectric layer 904 was covered with a coating 902. In step B, the coating 902 was textured. In step C, the dielectric layer 904 was etched. The coating 902 may also be removed in a previous intermediate step, or in this step C. In step D, an emissive layer 903 was applied on the thus obtained structured surface. The emissive layer 903 may be applied by evaporation.Fig. 10 shows an exemplary LED color conversion filter 1011. The LED color conversion filter 1011 comprises a substrate 1001 and a blue emission layer 1007 placed on the substrate 1004. The light emitted from the blue emission layer 1007 passes through the emissive layer 1003 comprising the metasurface 1000. The emission 1008 is in the desired wavelength and the desired direction, as the metasurface 1000 may convert the light and direct the emitted light. Furthermore, the emission 1008 might be enhanced.Fig. 11 shows an exemplary semiconductor device 1112. The semiconductor device 1112 comprises a substrate 1101, such as a TFT substrate. The semiconductor device 1112 further comprises charge transport layers 1109 and electrodes 1110. The semiconductor device 1112 also comprises a blue emission layer 1107. The semiconductor device (1112 further comprises metasurfaces 1100, 1100’ . The metasurfaces might convert the light emitted from the blue emission layer to different wavelengths. Thus, the semiconductor device 1112 might emit light ofconverted wavelengths and of light of the blue emission layer 1107. The combination of the blue light and of the converted light corresponds to light of the desired color.Fig. 12 shows the measured optical density and emission spectrum of planar and unstructured organic emissive system film on an unstructured glass substrate. The glass substrate, covered with a 50 nm layer of LiF, a 220 nm thick emissive layer of Ir-ATP (emitter) + MQAB (absorber) + TSBF (matrix), vacuum vapor evaporated simultaneous with a volume ratio of 1 to 3 to 96, of BDP24, MQAB, and TSBF, respectively, covered with a 10 nm thick layer of LiF. Efficient energy transfer from the donor (MQAB) to the acceptor (Ir-ATP) is achieved for excitation at 450 nm with peak emission at 567 nm. Thus, a large wavelength gap is achieved with this exemplary ternary energy transfer system, with the emission peak close to peak resonances shoen in the previous figures. Whereas the left y-axis refers to the optical density (OD), the right y-axis refers to the emission, calculated in counts per second. The thinner line shows the optical density, and the thicker line refers to the emission.The embodiments may also comprise:[1] An emissive metasurface (1000, 1100, 1100’) comprising a nanostructured dielectric component (101, 101’, 201, 601, 901) and an emissive system (103, 603, 903, 1003) comprising at least one emissive component which is at least partially in the near-field proximity to the nanostructured dielectric component (104, 904), wherein the nanostructured dielectric component (104, 904) comprises a plurality of metaatoms (100), wherein each of the metaatoms is a void in the dielectric component filled with the emissive component and wherein the emissive system (103, 603, 903, 1003) is configured to absorb and emit light in the visible range.[2] The metasurface (1000, 1100, 1100’) according to [1], wherein the metaatoms (100) are configured so that they resonantly match with the frequency of the light absorbed and emitted by the emissive system (103, 603, 903, 1003).[3] The metasurface (1000, 1100, 1100’) according to [1] or [2], wherein the nanostructured dielectric component (104, 904) is configured so that a localized resonance mode of the metaatoms (100) and a lattice resonance mode of the nanostructured dielectric component (104, 904) are either matched to the emission frequency of the emissive system, or to the absorption frequency of the emissive system (103, 603, 903, 1003).[4] The metasurface (1000, 1100, 1100’) according to any of [1] to [3], wherein the nanostructured dielectric component (104, 904) is configured so that a first localized resonance mode of the metaatoms (100) and a lattice resonance mode of the nanostructured dielectric component (104, 904) are matched to the emission frequency of the emissive system (103, 603, 903, 1003), and so that a second localized resonance mode of the metaatoms (100) is matched to the absorption frequency of the emissive system (103, 603, 903, 1003).[5] The metasurface (1000, 1100, 1100’) according to any of [1] to [4], wherein the void has an irregular or regular shape.[6] The metasurface (1000, 1100, 1100’) according to any of [1] to [5], wherein the void has a shape selected from cuboids, rhombic prisms, truncated pyramids, cylinders, truncated cones, truncated balls and other 3D shapes are produced by design, all with or without rounded edges.[7] The metasurface (1000, 1100, 1100’) according to any of [1] to [6], wherein the nanostructured dielectric component (104, 904) and the emissive system (103, 603, 903, 1003)are configured to resonantly enhance the absorption of the emissive system (103, 603, 903, 1003).[8] The metasurface (1000, 1100, 1100’) according to any of [1] to [7], wherein the nanostructured dielectric component (104, 904) and the emissive system (103, 603, 903, 1003) are configured to resonantly enhance the emission of the emissive system (103, 603, 903, 1003).[9] The metasurface (1000, 1100, 1100’) according to any of [1] to [8], wherein the emissive metasurface (1000, 1100, 1100’) is configured for color conversion in the visible spectrum.

[0010] The metasurface (1000, 1100, 1100’) according to any of [1] to [9], wherein the emissive metasurface (1000, 1100, 1100’) is configured for directional intensity control of incident and emitted light.

[0011] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0010] , wherein the emissive system (103, 603, 903, 1003) is located on top of the nanostructured dielectric component (104, 904).

[0012] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0011] , wherein the nanostructured dielectric component (104, 904) is selected from a-Si, Si, ZnTe, GaP, GaAs, GaSb, Ge, GeTe, InP, InAs, InSb, PbS, Te, PbSe, PbTe, MoS2, MoTe2, Al Sb, Al As, and SiC, III- V semiconductor, such as GaP.

[0013] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0012] , wherein the nanostructured dielectric component (104, 904) has a thickness of <100 nm, or <50nm.

[0014] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0013] , wherein the dimensions of the metaatoms (100) are smaller than half of the freespace wavelength.

[0015] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0014] , wherein the refractive index (n=n+ik) of the dielectric nanostructured component (104, 904) is in the range 7>n>2.5, with k>0.05, or in the range 5>n>3, with k >0.1 at absorption or emission wavelength.

[0016] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0015] , wherein the emissive system (103, 603, 903, 1003) comprises a ternary or higher number of components emissive system (103, 603, 903, 1003).

[0017] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0016] , wherein the emissive component comprises at least one of the following: organic dyes (chromophores as absorbers and fluorophores or phosphors as emitters) as well as inorganic absorbers and emitters including quantum dots.

[0018] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0017] , wherein the emissive component comprises a combination of organic matrix and inorganic absorbers and / or emitters and other way around - inorganic matrix with organic absorbers / emitters.

[0019] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0018] , wherein the emissive system (103, 603, 903, 1003) comprises at least one component as an emitter and at least one component as an acceptor mixed together in a matrix material.

[0020] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0019] , wherein the absorber and the emitter are two different organic dyes / molecules.

[0021] The metasurface (1000, 1100, 1100’) according to

[0020] , wherein the emitter and the absorber are selected so that the absorption and emission peaks of the emissive system (103, 603, 903, 1003) are tuned to the resonances of the emissive metasurface.

[0022] The metasurface (1000, 1100, 1100’) according to

[0020] or

[0021] , wherein by tuning of the concentrations of the emitter and absorber in the emissive system (103, 603, 903, 1003), the efficiency of the energy transfer, the field distribution inside the emissive system is optimized (103, 603, 903, 1003), and the loss by reabsorption is minimized.

[0023] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0022] , wherein the absorption coefficient of the emissive system (103, 603, 903, 1003) is optimized for efficient performance of the emissive metasurface.

[0024] The metasurface (1000, 1100, 1100’) according to any of [1] to

[0023] , wherein the refractive index n=n+ik of the emissive system (103, 603, 903, 1003) at absorption wavelength is n = 2.0 at k = 0.2, and the refractive index n=n+ik of the emissive system (103, 603, 903, 1003) at emission wavelength is n = 1.8 at k = 0.01.

[0025] A semiconductor device comprising the metasurface (1000, 1100, 1100’) according to any of [1] to

[0024] , the metasurface (1000, 1100, 1100’) being configured for enhancement of absorption of a first color and emission of a second color.

[0026] The semiconductor device (1112) of

[0025] , wherein the first color is blue and second color is red or green.

[0027] A method for preparing a metasurface (900) according to any of [1] to

[0024] , the method comprising the steps:Providing a nanostructured dielectric component (104, 904),Coating the dielectric component (104, 904),Texturing the coating,Etching the dielectric component (104, 904), andApplying an emissive system (103, 603, 903, 1003) on the thus obtained nanostructured surface.

[0028] The method (900) according to

[0025] , further comprising the step of sputtering a metal layer on the dielectric component (104, 904).LIST OF REFERNCE SIGNS100 metaatom1500, 1100, 1100’ metasurface101, 901, 1001, 1101 substrate902 coating103, 603, 903, 1003 emissive system104, 904 dielectric component105 air900 method for preparing a metasurface1007, 1107 blue emission layer1008 emission1011 LED color conversion filter1109 charge transport layers1110 electrode1112 semiconductor device

Claims

CLAIMS1. An emissive metasurface comprising a nanostructured dielectric component and an emissive system comprising at least one emissive component which is at least partially in the near- field proximity to the nanostructured dielectric component, wherein the nanostructured dielectric component comprises a plurality of metaatoms, wherein each of the metaatoms is a void in the dielectric component filled with the emissive component and wherein the emissive system is configured to absorb and emit light in the visible range.

2. The metasurface according to claim 1, wherein the metaatoms are configured so that they resonantly match with the frequency of the light absorbed and / or with the light emitted by the emissive system.

3. The metasurface according to claim 1, wherein the nanostructured dielectric component is configured so that a localized resonance mode of the metaatoms and a lattice resonance mode of the nanostructured dielectric component are either matched to the emission frequency of the emissive system, or to the absorption frequency of the emissive system.

4. The metasurface according to claim 1, wherein the nanostructured dielectric component is configured so that a first localized resonance mode of the metaatoms and a lattice resonance mode of the nanostructured dielectric component are matched to the emission frequency of the emissive system, and so that a second localized resonance mode of the metaatoms is matched to the absorption frequency of the emissive system.

5. The metasurface according to claim 1, wherein the void has an irregular or regular shape.

6. The metasurface according to claim 1, wherein the void has a shape selected from cuboids, rhombic prisms, truncated pyramids, cylinders and truncated cones, all of them with or without rounded edges.

7. The metasurface according to claim 1, wherein the nanostructured dielectric component and the emissive system are configured to resonantly enhance the absorption of the emissive system.

8. The metasurface according to claim 1, wherein the nanostructured dielectric component and the emissive system are configured to resonantly enhance the emission of the emissive system.

9. The metasurface according to claim 1, wherein the emissive metasurface is configured for color conversion in the visible spectrum.

10. The metasurface according to claim 1, wherein the emissive metasurface is configured for directional intensity control of incident and emitted light.

11. The metasurface according to claim 1, wherein the emissive system is located on top of the nanostructured dielectric component.

12. The metasurface according to claim 1, wherein the nanostructured dielectric component is selected from a-Si, Si, ZnTe, GaP, GaAs, GaSb, Ge, GeTe, InP, InAs, InSb, PbS, Te, PbSe, PbTe, M0S2, MoTe2, AlSb, AlAs, and SiC, III-V semiconductor, such as GaP.

13. The metasurface according to claim 1, wherein the nanostructured dielectric component has a thickness of <100 nm, or <50nm.

14. The metasurface according to claim 1, wherein the dimensions of the metaatoms are smaller than half of the freespace wavelength.

15. The metasurface according to claim 1, wherein the refractive index (n=n+ik) of the dielectric nanostructured component is in the range 7>n>2.5, with k>0.05, or in the range 5>n>3, with k >0.1 at absorption or emission wavelength.

16. The metasurface according to claim 1, wherein the emissive system comprises a ternary or higher order emissive system.

17. The metasurface according to claim 1, wherein the emissive component comprises at least one of an organic dye, chromophores, fluorophores, inorganic materials, and quantum dots.

18. The metasurface according to claim 1, wherein the emissive system comprises an emitter and an absorber mixed together in a matrix material.

19. The metasurface according to claim 18 wherein the absorber and the emitter are two different molecules.

20. The metasurface according to claim 18, wherein the emitter and the absorber are selected so that the absorption and emission peaks of the emissive system are tuned to the resonances of the nanostructure.

21. The metasurface according to claim 17, wherein, by tuning of the concentrations of the emitter and absorber in the emissive system, the efficiency of the energy transfer, the field distribution inside the emissive system, and the loss by reabsorption are optimized.

22. The metasurface according to claim 1, wherein the effective refractive index of the emissive system is matched to the resonant nanostructure.

23. The metasurface according to claim 1, wherein the refractive index n=n+ik of the emissive system at absorption wavelength is n = 2.0 at k = 0.2, and the refractive index n=n+ik of the emissive system at emission wavelength is n = 1.8 at k = 0.01.

24. A semiconductor device comprising the metasurface of claim 1, the metasurface being configured for enhancement of absorption of a first color and emission of a second color.

25. The semiconductor device of claim 24, wherein the first color is blue and second color is red or green.

26. A method for preparing a metasurface according to claim 1, the method comprising the steps:Providing a nanostructured dielectric component,Coating the dielectric component,Texturing the coating,Etching the dielectric component, andApplying an emissive system on the thus obtained nanostructured surface.

27. The method according to claim 26, further comprising the step of sputtering a metal layer on the dielectric component.

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