Light Emitting Component, a Light Emitting Device and a Sheet-like Material.

Technical Field

The invention relates in a first aspect to a light emitting component and in a second aspect to a light emitting device comprising the light emitting component as well as in a third aspect to a sheetlike material.

Background Art

State-of-the-art liquid crystal displays (LCD) or display components comprise quantum dot based compo nents. In particular, a backlight component of such a LCD might comprise a RGB backlight consisting of a red, a blue and a green light. Today, typically quantum dot particles are used to produce the backlight colours of such a back light component.

The manufacturing of such components faces var ious challenges. One challenge is the embedding of the nanocrystals into the component. Due to the different chem ical properties of the quantum dots, there might be incom patibilities between the various embedded materials com prising the quantum dots or even between quantum dots em bedded within the same material. Such incompatibilities might lead to degradation of the materials in the display components and therefore the lifetime of such a display might be affected.

Luminescent crystal based components often deal with challenges regarding stability and brightness, wherein a good stability and high display brightness of these components is difficult to achieve.

The light conversion factor in that context refers to the ratio between the green light intensity emit ted in perpendicular direction from the self-supporting film and the blue light intensity extincted (e.g. by ab sorption, reflection or scattering) in a direction perpen dicular of the self-supporting.

The crictical value related to display bright ness is transmission haze that refers to the amount of light that is subject to Wide Angle Scattering, normally at an angle greater than 2.5° from normal incident direc tion (measured by ASTM D1003; e.g. with BYK Gardner haze meter) when passing a transparent or partially transparent material (the self-supporting film in this invention).

A technical effect of the low haze is the fact that the lower haze leads to a higher display brightness, measured as "light conversion factor" (LCF)of the self- supporting film.

The document EP 3296 378 A1 discloses a com posite luminescent material. The composite luminescent ma terial comprises: a matrix; and perovskite nanoparticles. The perovskite nanoparticles are dispersed in the matrix, wherein the mass ratio of the perovskite nanoparticles ma trix to the perovskite nanoparticles is 1: (1-50). The evaporation conditions of the organic solvent system can be controlled to manage the crystallization of the polymer matrices used, the arrangement of the additive, and the nucleation and growth of the perovskite nanoparticles. The haze of the material here is mainly defined by the partial crystallization of the polymers used. The haze here is an intrinsic property of the polymers used.

Disclosure of the Invention

The problem to be solved by the present inven tion is therefore to provide a light emitting component that is manufactured in a way to prevent incompatibilities of quantum dot materials in light emitting components, in particular of LCD displays. In addition, the present in vention overcomes the disadvantages of the prior art in terms of stability and brightness. The present invention will be described in de tail below. It is understood that the various embodiments, preferences and ranges as provided / disclosed in this specification may be combined at will. Further, depending of the specific embodiment, selected definitions, embodi ments or ranges may not apply.

Unless otherwise stated, the following defini tions shall apply in this specification:

The terms "a", "an" "the" and similar terms used in the context of the present invention are to be construed to cover both the singular and plural unless otherwise in-dicated herein or clearly contradicted by the context. The term "containing" shall include all, "com prising", "essentially consisting of" and "consisting of". Percentages are given as weight-%, unless otherwise indi cated herein or clearly contradicted by the context. "In dependently" means that one substituent / ion may be se lected from one of the named substituents / ions or may be a combination of more than one of the above.

The term "phosphor" (LC) is known in the field and relates to materials that exhibits the phenomenon of luminescence, specifically fluorescent materials. Accord ingly, a red phosphor is a material showing luminescence in the range of 610 - 650 nm, e.g. centered around 630 nm. Accordingly, a green phosphor is a material showing lumi nescence in the range of 500 - 550 nm, e.g. centered around 530 nm. Typically, phosphors are inorganic particles.

The term "luminescent crystal" (LC) is known in the field and relates to crystals of 3-100 nm, made of sem-iconductor materials. The term comprises quantum dots, typically in the range of 2 - 15 nm and nanocrystals, typically in the range of more than 15 nm and up to 100 nm (preferably up to 50 nm). Preferably, luminescent crystals are approximately isometric (such as spherical or cubic). Particles are considered approximately isometric, in case the aspect ratio (longest : shortest direction) of all 3 orthogonal dimensions is 1 - 2. Accordingly, an assembly of LCs preferably contains 50 - 100 % (n/n), preferably 66 - 100 % (n/n) much preferably 75 - 100 % (n/n) isometric nanocrystals.

LCs show, as the term indicates, luminescence. In the context of the present invention the term lumines cent crystal includes both, single crystals and polycrys talline particles. In the latter case, one particle may be composed of several crystal domains (grains), connected by crystalline or amorphous phase boundaries. A luminescent crystal is a semiconducting material which exhibits a di rect bandgap (typically in the range 1.1 - 3.8 eV, more typically 1.4 - 3.5 eV, even more typically 1.7 - 3.2 eV). Upon illumination with electromagnetic radiation equal or higher than the bandgap, the valence band electron is ex cited to the conduction band leaving an electron hole in the valence band. The formed exciton (electron-electron hole pair) then radiatively recombines in the form of pho toluminescence, with maximum intensity centered around the LC bandgap value and exhibiting photoluminescence quantum yield of at least 1 %. In contact with external electron and electron hole sources LC could exhibit electrolumines cence.

The term "quantum dot" (QD) is known and par ticularly relates to semiconductor nanocrystals, which have a diameter typically between 2 - 15 nm. In this range, the physical radius of the QD is smaller than the bulk ex citation Bohr radius, causing quantum confinement effect to predominate. As a result, the electronic states of the QD, and therefore the bandgap, are a function of the QD composition and physical size, i.e. the color of absorp tion/emission is linked with the QD size. The optical qual ity of the QDs sample is directly linked with their homo geneity (more monodisperse QDs will have smaller FWHM of the emission). When QD reach size bigger than the Bohr radius the quantum confinement effect is hindered and the sample may not be luminescent any-more as nonradiative pathways for exciton recombination may become dominant. Thus, QDs are a specific sub-group of nanocrystals, defined in particular by its size and size distribution.

The term "perovskite crystals" is known and particularly includes crystalline compounds of the perov skite structure. Such perovskite structures are known per se and described as cubic, pseudocubic, tetragonal or or thorhombic crystals of general formula M1M2X3, where Ml are cations of coordination number 12 (cuboctaeder) and M2 are cations of coordination number 6 (octaeder) and X are anions in cubic, pseudocubic, tetragonal or orthorhombic positions of the lattice. In these structures, selected cations or anions may be replaced by other ions (stochastic or regularly up to 30 atom-%), thereby resulting in doped perovskites or nonstochiometric perovskites, still main taining its original crystalline structure. The manufac turing of such luminescent crystals is known, e.g. from WO2018 028869.

The term "polymer" is known and includes or ganic and inorganic synthetic materials comprising repeat ing units ("monomers"). The term polymers includes homo polymers and co-polymers. Further, cross-linked polymers and non-cross-linked polymers are included. Depending on the context, the term polymer shall include its monomers and oligomers. Polymers include, by way of example, acry late polymers, carbonate polymers, sulfone polymers, epoxy polymers, vinyl polymers, urethane polymers, imide poly mers, ester polymers, furane polymers, melamine polymers, styrene polymers, norbornene polymers, silicone polymers and cyclic olefin copolymers. Polymers may include, as conventional in the field, other materials such as polymer ization initiators, stabilizers, fillers, solvents.

Polymers may be further characterized by phys ical parameters, such as polarity, glass transition tem perature Tg, Young's modulus and light transmittance. Transmittance: Typically, polymers used in the context of this invention are light transmissive for vis ible light, i.e. non-opaque for allowing light emitted by the luminescent crystals, and possible light of a light source used for exciting the luminescent crystals to pass. Light transmittance may be determinded by white light in terferometry or UV-Vis spectrometry.

Glass transition temperature: (Tg) is a well- established parameter in the field of polymers; it de scribes the temperature where an amorphous or semi-crys talline polymer changes from a glassy (hard) state to a more pliable, compliant or rubbery state. Polymers with high Tg are considered "hard", while polymers with low Tg are considered "soft". On a molecular level, Tg is not a discrete thermodynamic transition, but a temperature range over which the mobility of the polymer chains increase significantly. The convention, however, is to report a single temperature defined as the mid-point of the temper ature range, bounded by the tangents to the two flat re gions of the heat flow curve of the DSC measurement. Tg may be determined according to DIN EN ISO 11357-2 or ASTM E1356 using DSC. This method is particularly suitable if the polymer is present in the form of bulk material. Al ternatively, Tg may be deter-mined by measuring tempera ture-dependent micro- or nanohardness with micro- or nanoindentation according to ISO 14577-1 or ASTM E2546-15. This method is suited for luminescent components and light ing devices as disclosed herein. Suitable analytical equip ment is available as MHT (Anton Paar), Hysitron TI Premier (Bruker) or Nano Indenter G200 (Keysight Technologies). Data obtained by temperature controlled micro- and nanoindentation can be converted to Tg. Typically, the plastic deformation work or Young's modulus or hardness is measured as a function of temperature and Tg is the tem perature where these parameters change significantly. Young's modulus or Young modulus or Elasticity modulus is a mechanical property that measures the stiff ness of a solid material. It defines the relationship be tween stress (force per unit area) and strain (proportional deformation) in a material in the linear elasticity re gime of a uniaxial deformation.

The term "scattering particles" is known and includes organic or inorganic particles having a refractive index different to the matrix where the scatter particles are incorporated. Due to this refractive index difference, light passing the matrix will be scattered or diffracted at the location of each scatter particle. Typical sizes of scatter particles are in the range of 20 - 20'000 nm, preferably 50 - lO ^' OOOnm, much preferably 100 - 5 ^' 000 nm. As the the term particle implies, networks are excluded. Typically, the difference in refractive index Ah! scatter ing particles - solid polymer is at least 0.02, preferably 0.1, much preferably 0.2. Typically, the amount of such scattering particles may vary over a broad range, suitable minimum concentrations are, for example, more than 0.01 wt%, preferably more than 0.1 wt%, most preferably 1 wt%. Suitable maximum concentrations are less than 30 wt%, pref erably less than 15wt%, much preferably less than 8 wt%. In case of self supporting films 50 - 5000 mg/m2, prefer ably 100 - 1000 mg/m2, such as 500 mg/m2.

According to the present invention, the above described problem is solved by a first aspect of the in vention, a light emitting component comprising a light source, a first layer comprising red phosphor and a second layer comprising luminescent crystals.

The first layer is arranged adjacent to the light source. The term "layer" refers to all possible types how the red phosphor could be applied to the light source. In particular, if the red phosphor is applied as a film or as droplets or individual particles, this types of appli cation of the red phosphor are covered by the term "layer". In particular, the layer does not need to be a continuous layer and does not need to be uniform.

In particular, the first layer can further be an assembly of quantum dots that are distributed adjacent to the light source.

The adjacent arrangement of the first layer to the light source means that the first layer is in close contact to a surface of the light source. Upon absorption of the blue light of the light source, the red phosphor of the first layer emits light in the red light spectrum. In particular, the red phosphor of the first layer emits light with a longer wavelength than the excitation wavelength of the light source.

The second layer comprises luminescent crys tals of perovskite structure. Upon absorption of the light emitted by the light source, the luminescent crystals emit light of a wavelength in the green light spectrum. In par ticular, the luminescent crystals of the second layer emit light with a longer wavelength than the excitation wave length of the light source.

The second layer has a haze h2 of 20 < h2 £ 70%.

Advantageously, the second layer has a haze h2 of h ₂ of 10%< h ₂ < 100%.

Haze in the context of the present invention means transmission haze. Transmission haze is the amount of light that is subject to Wide Angle Scattering (At an angle greater than 2.5° from normal incident direction (measured by ASTM D1003; e.g. with Byk gardner haze me ter)when passing a transparent material (the second layer in this invention).

The second layer is arranged remotely from the first layer. Remotely in this context means in particular that the second layer is arranged such that it does not get in contact with the first layer, or it does essentially not get in contact with the first layer. Remotely can fur ther mean that the second layer is arranged in parallel to the first layer with a distance between the two.

In an advantageous embodiment of the invention, the second layer might comprise luminescent crystals, a polymer and scattering particles.

In this case, the haze in the second layer is generated by means of the scattering particles distributed in the polymer.

Advantageously, luminescent crystals are em bedded in a cross-linked polymer, in particular a solid cross-linked polymer. Typically, such crosslinked-polymers are transparent with a low haze of < 10%.

The haze of the cross-linked polymer might be increased by incorporating scattering particles into such polymers.

Advantageously, the light emitting component comprises luminescent crystals, wherein the luminescent crystals are selected from compounds of formula (II):

[M ¹ A ¹ ] _a M ² _b X _c (II), wherein:

A ¹ represents one or more organic cations, preferably formamidinium,

M ¹ represents one or more alkaline metals,

M ² represents one or more metals other than

M ¹ , in particular Pb,

X represents one or more anions selected from the group consisting of halides, pseudo halides and sulfides, in particular Br, a represents 1-4, b represents 1-2, c represents 3-9, and wherein either M ¹ , or A ¹ , or M ¹ and A ¹ being present. Further advantageously, a concentration of Pb is of 5 - 200 mg/m ² , in particular 10 - 100 mg/m ² , very particular 20 - 80 mg/m ² ,

In particular, the first layer is arranged be tween the light source and the second layer.

In particular, there is an air gap between the second layer and the first layer or the red phosphor re spectively. The gap might also be a vacuum gap or a gap filled with another gas.

In particular, the second layer is arranged in parallel to the first layer.

In particular, the second layer is arranged such that there is an air gap between the first layer and the second layer, but such that there are supporting points between the first layer and the second layer to keep the second layer in a specific distance to the first layer.

In particular, the second layer is arranged such that there is essentially an air gap between the first layer and the second layer but there might still be touch ing points between the first and the second layer.

The particular arrangement of the one or more light sources, the first layer and the second layer impede incompatibilities between the individual materials thereof, in particular between the materials of the first and the second layer.

For an advantageous embodiment, the light source, the first layer and the second layer are arranged in said order in a vertical alignment.

In particular, the second layer might be ar ranged remotely to more than one light source and/or to more than one first layer.

In particular, the second layer might be ar ranged remotely to more than one light source, wherein each light source comprises its respective first layer adjacent to the respective light source. In an advantageous embodiment of the invention, the second layer has a haze h2 of h2 £ 80%, preferably £ 70%, most preferably £ 60%.

In another advantageous embodiment of the in vention, the second layer has a haze h2 of 10 < h2 £ 80%, preferably 20 < h2 £ 70%, most preferably 30 < h2 £ 60%.

The low haze of the second layer has the tech nical effect that the luminescent perovskite crystals in the second layer are more stable, in particular if they are exposed to a blue light source. The stability is a result of the reduced multiplex scattering of the blue light in the second layer due to the lower haze.

In addition, a further technical effect of the low haze is the fact that the lower haze leads to a higher display brightness, measured as "light conversion factor" (LCF)of the second layer. The light conversion factor of the second layer refers to the ratio between the green light intensity emitted in perpendicular direction from the second layer and the blue light intensity extincted (e.g. by absorption, reflection or scattering) in perpen dicular direction from the second layer.

In a further advantageous embodiment of the invention, the red phosphor is selected from one or more of core-shell quantum dots and/or is based on In or Cd, preferably on InP or CdSe respectively. The shell typically comprises ZnS or ZnSeS.

In a further advantageous embodiment of the invention, the core-shell quantum dots have a platelet structure. Preferably, such platelet structured dots are based on CdSe.

In a further adavtageous embodiment of the in vention, the core-shell quantum dots comprise a CdSe core which is doped with Zn. Such doping, sometimes also re- ferred-to as allyoing, reduces the amount of Cd per quantum dot.

Advantageously, the red phosphor is a Mn+4 doped phosphor of formula (I): A _x [MF _y ]:Mn ⁴⁺ (I), wherein:

A represents Li, Na, K, Rb, Cs or a combination thereof,

M represents Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y,

La, Nb, Ta, Bi, Gd, or a combination thereof, x represents an absolute value of the charge of the [MF _y ] ion; and Y represents 5, 6 or 7, in particular, wherein the red phosphor is of formula (I):

K ₂ SiF ₆ :Mn ⁴⁺ .

In a further advantageous embodiment of the light emitting component, the perovskite luminescent crys tals are selected from compounds of formula (II):

[M ¹ A ¹ ] _a M ² _b X _c (II), wherein:

A ¹ represents one or more organic cations, preferably formamidinium (FA),

M ¹ represents one or more alkaline metals,

M ² represents one or more metals other than

Ml, in particular Pb,

X represents one or more anions selected from the group consisting of halides, pseudohalides and sulfide, in particular Br, a represents 1-4, b represents 1-2, c represents 3-9, and wherein either M ¹ , or A ¹ , or M ¹ and A ¹ being present .

In particular, formula (II) describes perov skite luminescent crystals which, upon absorption of the light emitted by the light source, emit light of a wave length in the green light spectrum between 500 nm and 550 nm, in particular centred around 527 nm.

In particular, formula (II) describes lumines cent crystals where X represents halides or pseudohalides, e.g. Br, Cl, CN, in particular Br.

In particular, formula (II) describes lumines cent crystals wherein M ² represents Pb.

In particular, formula (II) describes lumines cent crystals, wherein A ¹ represents FA (formamidinium) and M ¹ is not present.

Advantageously, the luminescent crystals are further embedded in a solid polymer. Suitable are partic ularly polymers, where the repeating units of said polymer comply with the following: [0 atoms + N atoms] / [C atoms] < 0.9. Preferably, this value is < 0.4, more preferably < 0.3, most preferably < 0.25.

In a further advantageous embodiment, such a solid polymer comprises an acrylate. Very preferably, the polymer comprises or consists of repeating units selected from the group of cyclic aliphatic acrylates (monofunc tional acrylates).

In another advantageous embodiment, the solid polymer is cross-linked and comprises a multi-functional acrylate. In addition to the monofunctional acrylates.

In a further advantageous embodiment, the solid polymer has a glass transition temperature T _g of T _g < 120°C (preferably T _g < 100°C, very preferably T _g < 80°C, very preferably T _g < 70°C). Each T _g is measured according to DIN EN ISO 11357-2:2014-07 during the second heating cycle and applying a heating rate of 20K/min, starting at -90°C up to 250°C.

In a further advantageous embodiment, such a solid polymer is configured as a sheet-like polymer. The sheet-like polymer can have the shape of a polymer film with a film thickness of typically 0.001 - 10 mm, most typically 0.01 - 0.5 mm. The sheet-like polymer can either be continuous and flat or discontinuous with e.g. a micro- structure (e.g. with prism-shape).

In a further advantageous embodiment, the solid polymer is sandwiched between two barrier layers. In par ticular, such sandwich arrangement refers to an arrangement in a horizontal direction with a barrier layer, the polymer and another barrier layer. The two barrier layers of the sandwich structure can be made of the same barrier layer material or of different barrier layer materials.

The technical effect of the barrier layers is to improve the stability of the luminescent perovskite crystals, in particular against oxygen or humidity.

In particular, such barrier layers are known in the field; typically comprising a material / a com bination of materials with low water vapour transmission rate (WVTR) and / or low oxygen transmission rate (OTR). By selecting such materials, the degradation of the LCs in the component in response to being exposed to water vapor and / or oxygen is reduced or even avoided. Barrier layers or films preferably have a WVTR < 10 (g)/(m ^A 2*day) at a temperature of 40°C / 90% r.h. and atmospheric pressure, more preferably less than 1 (g)/(m ^A 2*day), and most pref erably less than 0.1 (g)/(m ^A 2*day).

In one embodiment, the barrier film may be per meable for oxygen. In an alternative embodiment, the bar rier film is impermeable for oxygen and has an OTR (oxygen transmission rate) < 10 (mL)/(m ^A 2*day) at a temperature of 23°C / 90% r.h. and atmospheric pressure, more preferably < 1 (mL)/(m ^A 2*day), most preferably < 0.1 (mL)/(m ^A 2*day).

In one embodiment, the barrier film is trans missive for light, i.e. transmittance visible light > 80%, preferably > 85%, most preferably > 90%.

Suitable barrier films may be present in the form of a single layer. Such barrier films are known in the field and contain glass, ceramics, metal oxides and polymers. Suitable polymers may be selected from the group consisting of polyvinylidene chlorides (PVdC), cyclic ole fin copolymer (COC), ethylene vinyl alcohol (EVOH), high- density polyethylene (HDPE), and polypropylene (PP); suit able inorganic materials may be selected from the group consisting of metal oxides, SiOx, SixNy, AlOx. Most pref erably, a polymer humidity barrier material contains a ma terial selected from the group of PVdC and COC.

Most advantageously, a polymer oxygen barrier material contains a material selected from EVOH polymers.

Suitable barrier films may be present in the form of multilayers. Such barrier films are known in the field and generally comprise a substrate, such as PET with a thickness in the range of 10 - 200 pm, and a thin inor ganic layer comprising materials from the group of SiOx and AlOx or an organic layer based on liquid crystals which are embedded in a polymer matrix or an organic layer with a polymer having the desired barrier properties. Possible polymers for such organic layers com-prise for example PVdC, COC, EVOH.

In a further advantageous embodiment of the invention, a diffusor film or diffusor plate is arranged in between the first layer and the second layer.

In a further advantageous embodiment of the invention, a light guide plate and a diffusor film are arranged between the first layer and the second layer of the invention. Advantageously, the light emitted from the light source and the first layer enters the light guide plate in an angle of 90° in respect of the light that is emitted by the light guide plate to the diffusor film and finally excites the luminescent crystals in the second layer.

In a further advantageous embodiment of the invention, a diffusor sheet is arranged between the first layer and the second layer of the invention. Advanta geously, the light emitted from the light source and the first layer enters the diffusor plate in an angle of 0° in respect of the light that is emitted by the light guide plate to the diffusor sheet and finally excites the lumi nescent crystals in the second layer.

A second aspect of the invention refers to a light emitting device comprising the light emitting compo nent according to the first aspect. In particular, such a light emitting device is a liquid crystal display (LCD).

In an advantageous embodiment of the invention, the light emitting component of the light emitting device comprises an array of more than one light source, wherein each light source has a respective adjacent first layer arranged adjacent to the particular light source, such that an array of light sources with their respective first lay ers forms. A second layer is arranged remotely to the ar ray. The second layer is arranged such that an air gap forms between the first layers of the array and the second layer. The array covers essentially the full liquid crystal display area.

In an advantageous embodiment, each light source of the array of the one or more light sources is covered with the respective adjacent first layer, therefore building an array with individual light sources and their respective adjacent first layer.

Advantageously, the second layer can be formed in one piece to cover at least part of the array or the full array of individual light sources of the array of one or more light sources and their respective adjacent first layer, wherein the second layer is arranged remotely from the array of individual light sources and their respective first layers.

In another advantageous embodiment, the second layer can be formed by multiple layer pieces that cover at least a part of the array or the full array of light sources with their respective first layers, wherein all multiple layer pieces of the second layer are arranged remotely from the array of light sources with their respective first layers.

In a further advantageous embodiment of the invention, the one or more of the light sources of the array are each adapted to switch between on and off with a frequency f of f ³ 150 Hz, preferably of f ³ 300 Hz, very preferably of f ³ 600 Hz.

A third aspect of the invention refers to a self-supporting film comprising luminescent crystals. The luminescent crystals are of perovskite structure and emit green and/or red light in response to excitation by light of a wavelength shorter than the emitted light. The self- supporting film has a haze h2 of h2 of 20 < h2 £ 70%, preferably h2 < 80%, preferably < 70%, most preferably < 60%.

In another advantageous embodiment of the in vention , the self-supporting film has a haze (measured with BYK gardner haze meter) h2 of 10 < h2 £ 80%, most preferably 30 < h2 £ 60%.

In another advantageous embodiment of the in vention , the self-supporting film has a transmittance (measured with BYK gardner haze meter) of > 75%, preferably > 85%, most preferably > 90%.

In an advantageous embodiment of the invention, the luminescent crystals are characterized in that the lu minescent crystals are embedded in a cross-linked polymer, in particular a solid cross-linked polymer.

In a further advantageous embodiment of the invention, the the luminescent crystals (20) are selected from compounds of formula (II):

[M ¹ A ¹ ] _a M ² _b X _c (II), wherein:

A ¹ represents one or more organic cations, preferably formamidinium (FA),

M ¹ represents one or more alkaline metals, M ² represents one or more metals other than M ¹ , in par ticular Pb,

X represents one or more anions selected from the group consisting of halides, pseudohalides and sul fides, in particular Br, a represents 1-4, b represents 1-2, c represents 3-9, and wherein either M ¹ , or A ¹ , or M ¹ and A ¹ being present .

Further advantageously, M ² represents Pb, and the concentration of Pb is of 5 - 200 mg/m2, in particu lar 10 - 100 mg/m2, very particular 20 - 80 mg/m2.

In another advantageous embodiment of the in vention , the self-supporting film is comprising scattering particles, preferably selected from polymeric composi tions, most preferably from organopolysiloxane.

Typical sizes of scatter particles are in the range of 20 - 20'000 nm, preferably 50 - lO ^' OOOnm, much preferably 100 - 5 ^' 000 nm. Typically, the amount of such scattering particles may vary over a broad range, suitable minimum concentrations are, for example, more than 0.01 wt%, preferably more than 0.1 wt%, most preferably 1 wt%. Suitable maximum concentrations are less than 30 wt%, pref erably less than 15wt%, much preferably less than 8 wt%. In case of self supporting films 50 - 5000 mg/m2, prefer ably 100 - 1000 mg/m2, such as 500 mg/m2.

In a further advantageous embodiment of the self-supporting film, the solid polymer is a polymer as referred to in the first aspect of the present invention.

Advantageously, such polymer comprises an acrylate, in particular comprises or consists of repeating units selected from the group of cyclic aliphatic acry lates, in particular, and/or wherein the acrylate comprises repeating units selected from monofunctional acrylate mon omers and multifunctional acrylate monomers. In a further advantageous embodiment, the solid polymer is characterized by a molar ratio of the sum of (oxygen + nitrogen) to carbon < 0.9, preferably < 0.4, preferably < 0.3, most preferably < 0.25.

In a further advantageous embodiment, the solid polymer has a glass transition T _g of T _g < 120°C (preferably T _g < 100°C, very preferably T _g < 80°C, very preferably T _g < 70°C); whereby each T _g is measured according to DIN EN ISO 11357-2:2014-07 during the second heating cycle and applying a heating rate of 20K/min, starting at -90°C up to 250°C.

In addition, an in an advantageous embodiment, the polymer might be a sheet-like polymer.

In a further advantageous embodiment, the pol ymer is sandwiched between two barrier layers.

Advantageously, the self-supporting film com prises luminescent crystals that emit red light in response to the excitation by light of a wavelength shorter than the emitted light.

A fourth aspect of the invention refers to a light emitting device, in particular a liquid crystal dis play (LCD), comprising the self-supporting film according to the third aspect.

Other advantageous embodiments are listed in the dependent claims as well as in the description below.

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become ap parent from the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:

Fig. la shows a schematic figure of a light source for emitting blue light with a first layer compris ing red phosphor; Fig. lb shows a schematic figure of a light emitting component according to an advantageous embodiment of the invention;

Fig. lc shows a schematic figure of a self- supporting film according to an embodiment of the inven tion;

Fig. 2 shows a schematic figure of a light emitting component according to a further advantageous em bodiment of the invention;

Fig. 3 shows a schematic of a light emitting component according to a further advantageous embodiment of the invention;

Fig. 4 shows a schematic of a light emitting component according to a further advantageous embodiment of the invention;

Fig. 5 shows a light emitting device according to an advantageous embodiment of the invention;

Fig. 6a shows an emission spectrum of the de vice schematically shown in Fig. 6b; and

Fig 7a shows an emission spectrum of the device schematically shown in Fig. 7b.

Modes for Carrying Out the Invention

Embodiments, examples, experiments represent ing or leading to embodiments, aspects and advantages of the invention will be better understood from the following detailed description thereof. Such description makes ref erence to the annexed drawings, wherein:

Fig. la shows a schematic of a component com prising comprises a light source 10 for emitting blue light aa and a first layer 1 comprising red phosphor emitting red light bb. Advantageously, the red phosphor particles of the red layer 1 are selected from core-shell CdSe QDs, core-shell InP QDs, KSF phosphor (K2S1F6:Mn ⁴⁺ ). Upon absorp tion of the blue light aa, the red phosphor emits light in the red light spectrum bb.

In particular, the component shown in Fig. lb shows the arrangement of the light source 10 and the first layer 1 that is adjacent to the light source 10. In this schematic, the first layer 1 comprises red phosphor parti cles that are distributed adjacent to the light source 10.

Fig. lb shows a schematic of a light emitting component according to an advantageous embodiment of the invention. The light emitting component comprises a light source 10 for emitting blue light, a first layer 1 com prising red phosphor and a second layer 2 comprising lumi nescent crystals 20. The red phosphor of the first layer 1, upon absorption of the blue light aa, emits light in the red light spectrum bb. The first layer 1 is arranged adjacent to the light source 10. The luminescent crystals 20 of the second layer 2 are of perovskite structure. Upon absorption of the light emitted by the light source 10, the luminescent crystals 20 emit light of a wavelength in the green light spectrum cc. The second layer 2 has a haze h2 of 10% < h2 £ 100%. The second layer 2 is arranged remotely from the first layer 1. In particular, there is an air gap between the second layer 2 and the first layer 1.

In a further advantageous embodiment, the light emitting component in Fig. lb might have a haze h2 of 20 < h2 £ 70%, preferably h2 £ 80%, preferably h2 £ 70%, very preferably h2 £ 60%.

Advantageously for this embodiment, the red phosphor is selected from one or more of core-shell quantum dots based on In or Cd; in particular based on InP (III) or CdSe (IV) respectively.

Further advantageously, the red phosphor is a Mn+4 doped phosphor of formula (I) as described above. An example of such an embodiment is disclosed in the experi mental section (experiment 1).

In a further advantageous embodiment of Fig. 2, the luminescent crystals 20 are selected from compounds of formula (II) as disclosed above. An example of such an embodiment is disclosed in the experimental section (ex periment 2).

In a further advantageous embodiment, the lu minescent crystals 20 are selected from the coumpounds of formula (II), wherein M ² is Pb and wherein the concentration of Pb is 5 - 200 mg/m ² , in particular 10 - 100 mg/m ² , very particular 20 - 80 mg/m ² .

Advantageously, the luminescent crystals 20 are embedded in a solid polymer, in particular wherein the polymer comprises an acrylate, very particular wherein the polymer comprises a cyclic aliphatic acrylate (monofunc tional acrylates).

In another advantageous embodiment, the solid polymer is cross-linked and comprises a multi-functional acrylate. In addition to the monofunctional acrylates.

Such a polymer might further be configured as a sheet-like polymer.

In a further advantageous embodiment, the pol ymer can be sandwiched between barrier layers 21. An exam ple of such barrier layers 21 are shown in Fig. lc.

In a further advantageous embodiment the solid polymer has a glass transition temperature T _g of T _g < 120°C (preferably T _g < 100°C, very preferably T _g < 80°C, very preferably T _g < 70°C).

In a further advantageous embodiment, the sec ond layer might scattering particles embedded in the solid polymer, in particular for generating said haze (scattering particles are not shown in the figures).

Fig. lc shows a schematic of an embodiment of the self-supporting film 200. The self-supporting film com prises luminescent crystals 20 embedded in a polymer, wherein the luminescent crystals 20 are of perovskite structure and emit green cc and/or red light bb in response to excitation by light of a wavelength shorter than the emitted light, and wherein the self-supporting film has a haze h2 of 20 < h2 £ 70%, preferably h2 < 80%, in particular of h2 < 70%, very particular of h2 < 60%.

Advantageously, the self-supporting film 200 comprises scattering particles embedded in the polymer (scattering particles are not shown in the figure).

In a further embodiment, the luminescent crys tals 20 of the self-supporting film 200 are embedded in a cross-linked solid polymer.

In a further advantageous embodiment, the lum inescent crystals 20 are selected from the compounds of formula (II).

In a further advantageous embodiment, the lu minescent crystals 20 are selected from the coumpounds of formula (II), wherein M ² is Pb and wherein the concentration of Pb is 5 - 200 mg/m ² , in particular 10 - 100 mg/m ² , very particular 20 - 80 mg/m ² .

In a further advantageous embodiment, the solid polymer comprises an acrylate, in particular com prises or consists of repeating units selected from the group of cyclic aliphatic acrylates, in particular, and/or wherein the acrylate comprises repeating units se lected from monofunctional acrylate monomers and multi functional acrylate monomers.

In a further advantageous embodiment of the self-supporting film 200, the solid polymer is character ized by a molar ratio of the sum of (oxygen + nitrogen) to carbon < 0.9, preferably < 0.4, preferably < 0.3, most preferably < 0.25.

In a further advantageous embodiment, the solid polymer has a glass transition temperature T _g of T _g < 120°C, in particular of T _g < 100°C, in particular of T _g < 80°C, in particular of T _g < 70°. In a further advantageous embodiment, the solid polymer is configured as a sheet-like polymer and/or wherein the solid polymer is sandwiched between two barrier layers 21.

Fig . 2 shows a schematic of a further embodi ment of the light emitting component. The light emitting component comprises a light source 10 for emitting blue light, a first layer 1 comprising red phosphor and a second layer 2 comprising luminescent crystals 20. The red phos phor of the first layer 1, upon absorption of the blue light aa, emits light in the red light spectrum bb. The first layer 1 is arranged adjacent to the light source 10. The luminescent crystals 20 of the second layer 2 are of perovskite structure. Upon absorption of the light emitted by the light source 10, the luminescent crystals 20 emit light of a wavelength in the green light spectrum cc. The second layer 2 has a haze h2 of 40% < h2 £ 90%. The second layer 2 is arranged remotely from the first layer 1. In particular, there is an air gap between the second layer 2 and the first layer 1.

In this embodiment, not only one but multiple light sources 10 and their respective first layers 1 are arranged in an array, wherein the second layer 2 that serves as the second layer 2 for all light sources 10 and their respective first layer 1, is formed in one piece.

All advantageous features as disclosed in Fig. lb can also be combined with the embodiment in Fig. lc.

Fig . 3 shows a schematic of a light emitting component for a specific backlight architecture, in par ticular for LCD displays. In addition to the schematic in Fig. 2, there is a diffusor plate 3 arranged between the first layer 1 and the second layer 2. Fig . 4 shows a further schematic of a further light emitting device for a specific backlight architec ture, in particular for LCD displays. The device comprises a light emitting component with a light source 10 for emit ting blue light aa, a first layer 1 comprising red phos phor, and a second layer 2 comprising luminescent crystals 20. The first layer 1 is arranged adjacent to the light source 10. The second layer 2 is arranged remotely from the first layer 1. A diffusor film 3 and a light guide plate (LGP) 4 are arranged in between the first layer 1 and the second layer 2. In particular, the light source 10 and the first layer 1 are arranged such that blue aa and the red bb light enter the LGP 4 in an angle of 90° in regard of the light emitted by the LGP 4 that excites the luminescent crystals 20 of the second layer 2. Anyway, the light source 20 might in another advantageous embodiment be arranged such that the light enters the LGP in an angle of 0°.

Fig . 5 discloses a schematic of an advantageous light emitting device according to an embodiment of the invention. The light emitting device, in particular an liquid crystal display comprises the light emitting compo nent, e.g. as shown in one of the embodiments in Fig. 1 to 4.

An advantageous light emitting device com prises a light emitting component comprising an array of one or more, in particular more than one, light sources 10. Each light source 10 comprises its respective first layer 1 arranged adjacent to the light source 10. In addi tion, such an embodiment comprises one second layer 2 ar ranged remotely to the array. In particular, the array covers essentially the full liquid crystal display area 5.

A further advantageous light emitting device comprises the one or more of the light sources 10 of the array, wherein each light source 10 is adapted to switch between on and off with a frequency f of f ³ 150 Hz, in particular of f ³ 300 Hz, very particular of f ³ 600 Hz.

Fig. 6a shows an emission spectrum of an em bodiment of a light emitting component according to the invention as shown schematically in Fig. 6b. The light emitting component comprises multiple light sources 10 for emitting blue light aa, each light source comprises a re spective first layer 1 comprising red phosphor and upon absorption of the blue light aa, the red phosphor emits light in the red light spectrum bb. The red phosphors are arranged adjacent to the respective light source 10.

As shown in Fig. 7b, a second layer 2 compris ing luminescent crystals 20 is arranged remotely to the multiple light sources 10 and their respective first layers 1. Upon absorption of the light emitted by the light sources 10, the luminescent crystals 20 emit light of a wavelength in the green light spectrum cc. The second layer 2 has a haze of 10%< h2 < 100%.

Accordingly, the emission spectrum shown in Fig. 7a of the light emitting device shows peaks in the range of the blue, green and red visible light.

Experimental Section

Example 1: Preparation of a backlight unit for a LCD display by using a component as described herein Fig. 6b shows the schematic of a component of an array for which the emission spectrum was measured as is shown in Fig. 6a. The component in Fig. 6b comprises a light source 10 for emitting blue light aa and a first layer 1 comprising red phosphor emitting red light bb. Advantageously, the red phosphor particles of the red layer 1 are selected from core-shell CdSe QDs, core-shell InP QDs, KSF phosphor (K2S1F6:Mn ⁴⁺ ). Upon absorption of the blue light aa, the red phosphor emits light in the red light spectrum bb. The emission spectrum of the component shows peaks in the visible blue and red range of the spectrum.

In particular, the component shown in Fig. lb shows the arrangement of the light source 10 and the first layer 1 that is adjacent to the light source 10. In this schematic, the first layer 1 comprises red phosphor parti cles that are distributed adjacent to the light source 10.

To measure the data, a 2D-array of 200 indi vidual LEDs was used whereby the LEDs comprised a blue emitting gallium nitride chip and red emitting core-shell cadmium selenide quantum dots which were deposited directly on the blue LED chip (on-chip). The emission spectrum of this LED array is shown in Fig. 6a.

Example 2: The array from Example 1 was taken and additionally, a diffuser plate 3 is placed on top of the array of light sources with their respective first layer adjacent to the respective light source. The diffusor plate serves to homogeneously distribute the generated light of the LEDs, similar to the light emitting component as shown in Fig. 3.

In addition, a green remote perovskite QD film (self-supporting film in accordance with example 3) is placed on top of the diffusor plate (only loose placement; no glueing or similar). Then two crossed prism films (crossed BEFs) and a brightness enhancement film (DBEF) are placed on top of the green perovskite film (not shown in the Figure). The emission spectrum of the complete back light structure is measured with a spectrometer (Konica Minolta CS-2000) showing blue, red and green emission peaks, as shown in Figure 7a.

Example 3: Preparation of a green remote per ovskite QD film as a self-supporting film, in accordance with the 3 ^rd aspect of the invention, with low haze h2 and low T _g : Green perovskite QDs with composition forma- midinium lead tribromide (FAPbBrs) are synthesized in tol uene as follows: Formamidinium lead tribromide (FAPbBrs) was synthesized by milling PbBr2 and FABr. Namely, 16 mmol PbBr2 (5.87 g, 98% ABCR, Karlsruhe (DE)) and 16 mmol FABr (2.00 g, Greatcell Solar Materials, Queanbeyan, (AU)) were milled with Yttrium stabilized zirconia beads (5 mm diam eter) for 6 h to obtain pure cubic FAPbBr ₃ , confirmed by XRD. The orange FAPbBr ₃ powder was added to Oleylamine (80— 90, Acros Organics, Geel (BE)) (weight ratio FAP- bBr3:Oleylamine = 100:15) and toluene (>99.5 %, puriss, Sigma Aldrich). The final concentration of FAPbBr ₃ was 1 wt%. The mixture was then dispersed by ball milling using yttrium stabilized zirconia beads with a diameter size of 200 pm at ambient conditions (if not otherwise defined, the atmospheric conditions for all experiments are: 35°C, 1 atm, in air) for a period of 1 h yielding an ink with green luminescence.

Film formation: 0.1 g of the green ink was mixed with an UV curable monomer/crosslinker mixture (0.7 g FA-513AS, Hitachi Chemical, Japan / 0.3 g Miramer M240, Miwon, Korea) containing lwt% photoinitiator Diphe nyl (2,4,6-trimethylbenzoyl) phosphine oxide (TCI Europe, Netherlands) and 2 wt% polymeric scattering particles (Or- ganopolysiloxane, ShinEtsu, KMP-590) in a speed mixer and the toluene was evaporated by vacuum (<0.01 mbar) at room temperature. The resulting mixture contained 500 ppm Pb as measured with inductively coupled optical emission spec troscopy (ICP-OES) and was then coated with 50 micron layer thickness on a 100 micron barrier film (supplier: I-compo- nents (Korea); Product: TBF-1007), then laminated with a second barrier film of the same type. Afterwards the lam inate structure was UV-cured for 60 s (UVAcubelOO equipped with a mercury lamp and quartz filter, Hoenle, Germany). The initial performance of the as obtained green perovskite QD film shows an emission wavelength of 526 nm, a FWHM of 22 nm and a color coordinate in Y-direction ("y-value", CIE1931) of y = 0.15 when placed on a blue LED light source (450 nm emission wavelength) with two crossed prism sheets (X-BEF) and one brightness enhancement film (DBEF) on top of the QD film (optical properties measured with a Konica Minolta CS-2000). The haze of the obtained QD film is 50% and the transmittance is 85% (measured with Byk Gardner haze meter). The light conversion factor (LCF; LCF = emit ted green intensity (integrated emission peak) divided by the reduction of the blue intensity (integrated emission peak); measured with perpendicular emission of green and blue from the QD film by using a Konica Minolta CS-2000).

The glass transition temperature Tg of the UV- cured resin composition was determined by DSC according to DIN EN ISO 11357-2:2014-07 with a starting temperature of -90°C and an end temperature of 250°C and a heating rate of 20 K/min in nitrogen atmosphere (20 ml/min). The purging gas was nitrogen (5.0) at 20 ml/min. The DSC system DSC 204 FI Phoenix (Netzsch) was used. The T _g was determined on the second heating cycle (the first heating from -90°C to 250°C showed overlaying effects besides the glass tran sition) . For the DSC measurement the UV-cured resin compo sition was removed from the QD film by delaminating the barrier films. The measured Tg of the UV-cured resin com position was 75°C.

The stability of the QD film was tested for l'OOO hours under blue LED light irradiation by placing the QD film into a light box with high blue intensity (supplier: Hoenle; model: LED CUBE 100 IC) with a blue flux on the QD film of 220 mW/cm2 at a QD film temperature of 50°C. The change of optical parameters of the QD film after flux testing for l'OOO hours was measured with the same procedure as for measuring the initial performance (de scribed above). The change of optical parameters were as following :

• Change of y-value: from 0.15 to 0.119 (- 0.031)

• Change of LCF: from 50% to 40% (- 10%)

• Change of green emission wavelength: from 526 nm to 525 nm (- 1 nm) • Change of green FWHM: 0 nm

Similar results are obtained when replacing FAPbBr3 by [CsFA]PbBr3. Such perovskites are described in Document WO2018/028869 Al, e.g. example 10.

Comparative example 1 for example 3: Prepara tion of a green remote perovskite QD film with high haze and low T _g .

The procedure was the same as in the previous procedure for the QD film with low haze, except the fol lowing parameters were changed:

• Pb amount of the whole UV curable acrylate mixture is 200 ppm

• 12 wt% scattering particles KMP-590 were mixed into the UV curable acrylate mixture to increase the haze of the final QD film.

The as obtained green perovskite QD film showed an emission wavelength of 525 nm, a FWHM of 22 nm ands a y-value of 0.149 (almost identical to the low-haze QD film in experiment 3). The LCF of the QD film is 43%. The haze of the QD film was 98% and the transmittance is 81%. The measured Tg of the UV-cured resin composition was 77°C. It can be seen that the LCF is lower than in experiment 3. A higher haze leads to a lower LCF and a lower haze leads to a higher LCF. Therefore, a lower haze of the QD film is beneficial to have a higher LCF and in turn a higher display efficiency (at specific comparable white point colour co ordinates) .

The change of optical parameters of the QD film after flux testing for l'OOO hours were as following:

• Change of y-value: from 0.149 to 0.058 (- 0.091)

• Change of LCF: from 43% to 14% (- 29%)

• Change of green emission wavelength: from 525 nm to

521 nm (- 4 nm)

• Change of green FWHM: 0 nm

These results show that a higher haze of the QD film leads to lower QD film stability under high blue flux compared to example 3 (specifically, the y-value, LCF and emission wavelength are all less stable). Therefore, it is advantageous to have a low haze of the QD film which leads to improved QD film stability under high blue flux in order to have stable colour coordinates and a stable white point during the operating life-time of the display device.

Comparative example 2 for example 3: Prepara tion of a green remote perovskite QD film with low haze and high T _g .

The procedure was the same as in the procedure of example 3, except the acrylate monomer mixture (0.7 g FA-513AS, Hitachi Chemical, Japan / 0.3 g Miramer M240,

Miwon, Korea) was replaced by the following acrylate mon omer mixture:

• 0.7 g FA-DCPA, Hitachi Chemical, Japan / 0.3 g FA-

320M, Hitachi Chemical, Japan.

The as obtained green perovskite QD film showed an emission wavelength of 526 nm, a FWHM of 22 nm and a y-value of 0.153 (almost identical to the low-haze QD film in experiment 3). The LCF of the QD film is 49%. The haze of the QD film was 51% and the transmittance is 85%. The measured Tg of the UV-cured resin composition was 144°C.

The change of optical parameters of the QD film after flux testing for l'OOO hours were as following:

• Change of y-value: from 0.153 to 0.068 (- 0.085)

• Change of LCF: from 49% to 21% (- 28%)

• Change of green emission wavelength: from 526 nm to

525 nm (- 1 nm)

• Change of green FWHM: 0 nm

These results show that a high T _g of the solid polymer of the QD film (self-supporting film) leads to lower QD film stability under high blue flux. Therefore it is advantageous to have a low T _g of the QD film which leads to improved QD film stability under high blue flux in order to have stable colour coordinates and a stable white point during the operating life-time of the display device. Table 1 . Summary of the parameter changes after high-flux testing for experiment 3 and comparative examples 1 and 2: