Technical Field

The invention relates in a first aspect to a solid polymer compositon and in a second aspect to a self- supporting film as well as in a third aspect to a light emitting device.

Background Art

State-of-the-art liquid crystal displays (LCD) or display components comprise luminescent crystal (quan tum dot) based components. In particular, a backlight com ponent of such a LCD might comprise a RGB backlight con sisting of a red, a blue and a green light. Today, typically luminescent crystals (quantum dots) are used to produce the backlight colours of such a backlight component.

The manufacturing of such components faces var ious challenges. One challenge is the embedding of the luminescent crystals into the component. Due to the dif ferent chemical properties of the luminescent crystals, there might be incompatibilities between the various em bedded materials comprising the luminescent crystals or even between luminescent crystals embedded 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.

Document US 2017/0153382 A1 discloses a quantum dot composite material, a manufacturing method and an ap plication thereof. The quantum dot composite material in cludes an all-inorganic perovskite quantum dot and a mod ification protection on a surface of the all-inorganic perovskite quantum dot. Document Tongtong Xuan et al. "Super-Hydropho bic Cesium Lead Halide Perovskite Quantum Dot-Polymer Com posites with High Stability and Luminescent Efficiency for Wide Color Gamut White Light-Emitting Diodes", Chemistry of Materials, vol. 31, no. 3, 12 February 2019, pages 1042- 1047. The document discloses a composite strategy to en hance the stability of water sensitive CsPbBr ₃ quantum dots by embedding the QDs into the super-hydrophobic porous or ganic polymer frameworks.

Document Sijbom H. F. et al. "Luminescent Be havior of the K2S1F6 :Mn ⁴⁺ Red Phosphor at High Fluxes and at the Microscopic Level", ECS Journal of Solid State Sci ence and Technology, 5(1), R3040-R3048 (2016). The document discloses the manufacturing of red non-perovskite phosphor particles.

Disclosure of the Invention

The problem to be solved by the present inven tion is to provide a material composition that overcomes the disadvantages of the prior art.

The present invention will be described in de tail below. 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" is known in the field and relates to materials that exhibits the phenomenon of lumi nescence, specifically fluorescent materials. Accordingly, 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 "phosphor particles" means particles of the phos phor as described above. The particles can be single crys talline or polycrystalline. In the context of the present invention, the term particles refers to primary particles, not secondary particles (e.g. agglomerates or conglomer ates of primary particles)

The term "luminescent crystal" (LC) is known in the field and relates to crystals of 3-100 nm, made of semiconductor 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 "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 synthetic materials comprising repeating 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 silicon based and non-silicon based pol ymers, by way of example: silicon based polymers such as silicone polymers, as well as non-silicon based polymers such as acrylate polymers, carbonate polymers, sulfone pol ymers, epoxy polymers, vinyl polymers, urethane polymers, imide polymers, ester polymers, furane polymers, melamine polymers, styrene polymers, norbornene polymers and cyclic olefin copolymers. Polymers may include, as conventional in the field, other materials such as polymerization ini tiators, stabilizers, solvents, scattering particles.

Polymers may be further characterized by phys ical parameters, such as polarity, glass transition tem perature Tg, Young's modulus and light transmittance.

Polarity (z): The ratio of heteroatoms (i.e. atoms other than carbon and hydrogen) to carbon (n/n) is an indicator for polymer polarity. In the context of this invention, polymers with 0.4 < z < 0.9 are considerd polar, while poymers with z < 0.4 are considered apolar.

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.

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.

According to the present invention, the above described problem is solved by a first aspect of the in vention, a solid polymer composition comprising a first class of luminescent materials, selected from green lumi nescent perovskite crystals, a second class of luminescent materials, selected from non-perovskite red phosphor par ticles and a polymer. Suitable green luminescent perovskite crystals are selected from compounds of formula (I):

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

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

M ¹ represents one or more alkaline metals, in particular Cs,

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

X represents one or more anions selected from the group consisting of halides, pseudohalides and sulfides, in par ticular 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 (I) describes lumines cent crystals where X represents halides or pseudohalides, e.g. Br, Cl, CN, in particular Br.

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

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

Suitable non-perovskite red phosphor particles are Mn+4 doped phosphor particules are selected from com pounds of formula (II):

[A] _x [MF _y ]:Mn ⁴⁺ (II), wherein:

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

M represents Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof, in particular Si x represents an absolute value of the charge of the [MFy] ion, in particular 2; and Y represents 5, 6 or 7, in particular 6.

The polymer has a molar ratio of the sum of (oxygen + nitrogen) to carbon z, wherein z < 0.9, z < 0.75 in particular z < 0.4, in particular z < 0.3, in partic ular z < 0.25.

A solid polymer composition comprising spe cific green luminescent crystals, specific non-perovskite red Mn4+-doped phosphors and specific polymer matrices, enables high stability of the luminescent crystals and the non-perovskite red phosphors when used in light emitting devices, in particular in LCD displays. In particular, formula (I) describes perov- skite luminescent crystals which, upon absoprption of blue light emit light of a wavelength in the green light spec trum between 500 nm and 550 nm, in particular centred around 527 nm.

In an advantageous embodiment, the green lu minescent perovskite crystals are in particular green lu minescent perovskite crystals of the formula (I'):

FAPbBrs (I').

In a further advantageous embodiment of the invention, the non-perovskite red phosphor particles are non-perovskite red phosphor Mn+4 doped phosphor particles of formula (11 ):

K2SiF6:Mn4+ (II'').

In an advantageous embodiment of the solid pol ymer composition, the green luminescent perovskite crys tals and the non-perovskite red phosphor particles are em bedded into the polymer.

In a further advantageous embodiment of the solid polymer composition, the green luminescent perov skite crystals and the non-perovksite red phosphor parti cles are embedded in the polymer without an encapsulation

This means in particular that the perovskite crystals and the non-perovksite red phosphor particles do not need any encapsulation (such as particle surface pro tection or shelling) to be embedded into the polymer.

In particular, the green luminescent perov skite crystals and the non-perovskite red phosphor parti cles are both distributed within the polymer and in par ticular are essentially distributed within the polymer such that they do not exceed a surface of the polymer.

In a further advantageous embodiment of the invention, the polymer has a molar ratio of the sum of (oxygen + nitrogen + sulphur + phosphorous + fluorine + chlorine + bromine + iodine) to carbon z < 0.9, preferably z < 0.4, preferably z < 0.3, most preferably z < 0.25.

In a further advantageous embodiment of the solid polymer composition, the difference in concentration DO _MP of Mn between the center of each non-perovskite red phosphor particle and an area 100 nm below the particle surface is Ac _Mn £ 50%, in particular Ac _Mn £ 20%.

In particular, such concentration differ ences Ac _Mn can be determined by using scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) on a cross-section of a single phosphor particle. Such cross-section of a single phosphor particle can be prepared by focused ion beam (FIB).

In particular, non-perovskite red phosphor particles with said concentration difference Ac _Mn do not exhibit a protection layer or shell, in particular do not require a inorganic protection layer or shell on the sur face for stabilization.

In particular, since no protection layer or shell is necessary, the processing steps for the manufac turing of the non-perovskite red phosphor particles can be reduced.

The center of the particle refers in partic ular to a center area of the particle, in particular a core or core region of the particle.

In contrast to known red phosphor particles, the non-perovskite red phosphor particles as introduced in this invention do advantageously not comprise an inorganic protection layer on the surface. In particular, the non- perovskite red phosphor particles do not comprise a meta- loxide or K2S1F6 protection layer.

For an advantageous embodiment, the omission of the inorganic protection layer might be implemented as following, wherein the suggested embodiments might be in dependent from each other or might be combined: Advantageously, the non-perovskite red phosphor par ticles are free of an inorganic surface coating. In particular, the particles are free of inorganic sur face coating with a composition that differes from the composition of a core of each non-perovskite red phosphor particle. Free of an inorganice surface coat ing means in particular that there is essentially no such coating present on the respective surface. Advantageously, each non-perovskite red phosphor par- ticicles exhibits a homogenous distribution of Mn+4 from the particle center to the particle surface. Therefore, in particular, each non-perovskite red phosphor particular has an essentially homogenous concentration C _Mn of Mn over the whole volume of the respective particle.

Advantageously, the non-perovskite red phosphor par ticles have a Manganese (Mn)-concentration C _Mn of C _Mn ³ 6 mol%, in particular of C _Mn ³ 9 mol%, in particular of C _Mn ³ 11 mo1%.

Without being bound to theory, it is believed that, in contrast to known non-perovskite red phosphor particles that need an inorganic layer for stabilization, the polymer matrix here provides the stability.

In a further advantageous embodiment of the invention, the green luminescent perovskite crystals are of size between 3nm and lOOnm. In particular, the size of perovskite crystals can be determined by transmission elec tron microscopy.

In a further advantageous embodiment of the invention, the non-perovskite red phosphor particles have a Mn-concentration C _M of 6 < C _M £ 15 mol%, preferably 10 £ C _M £ 14 mol%, most preferably 11 £ C _M £ 13 mol%.

Advantageously, the non-perovskite red phos phor particles have a particle size (volume-weighted av erage) s _p of s _p £ 10 pm, advantageously of s _p £ 5 pm, ad vantageously of s _p £ 2 pm, advantageously of s _p £ 1 pm, advantageously of s _p ³ 50 nm, advantageously of s _p ³ 100 nm, advantageously of s _p ³ 200nm.

Further advantageously, the non-perovskite red phosphor particles have a particle size (volume- weighted average) of 200 nm < s _p £ 10 pm, very particular 200 nm < s _p £ 5 pm.

Particle sizes are measured by means of standard characterization methods, e.g. scanning electron microscopy (SEM).

In particular, the combination of the spe cific size of the green luminescent perovskite crystals of 3nm to 100 and the non-perovskite red phosphor parti cles of s _p £ 10 pm, advantageously of s _p £ 5 pm, might re sult in an advantageous embodiment. If particles with these respective sizes are embedded in the polymer, the amount of particles in the polymer can be optimized due to the advantageous light particle interaction in this size range.

In an advantageous embodiment, the solid poly mer composition comprises an acrylate, very advantageously the polymer comprises a cyclic aliphatic acrylate. I

In another advantageous embodiment, the solid polymer comprises a multi-functional acrylate.

In another advantageous embodiment, the solid polymer is cross-linked. Cross linking may be achieved as known in the field, e.g. by adding cross-linking agents or multivalent monomers.

An advantageous solid polymer composition has a glass transition temperature T _g of T _g < 120°C, advanta geously of T _g < 100°C, advantageously of T _g < 80°C, advan tageously of 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 of the invention, the solid polymer composition comprises scat tering particles selected from the group consisting of metal oxide particles and polymer particles. Advanta geously, the particles are metal oxide particles, prefer ably selected from the group consisiting of TiCh, ZrCh, AI2O3 and organopolysiloxanes.

In a further advantageous embodiment the solid polymer is semicrystalline.

In a further advantageous embodiment the solid polymer has a melting temperature T _p of T _p < 140°C, pref erably T _p < 120°C, most preferably T _p < 100°C.

The inventive solid polymer compositions may be obtained in analogy to known methods using the starting materials of formula (I), formula (II) and monomers / ol igomers of the respective polymer. The invention thus pro vides for a method of manufacturing a solid polymer compo sition comprising the steps of

(a) combining compound of formula (I), compound of formula (II), monomer and/or oligomer of the polymer, optionally diluent, optionally scattering particles, op tionally catalyst or other additives, to thereby obtain a first dispersion;

(b) optionally removing the diluent to thereby obtain an ink;

(d) curing said ink to thereby obtain the in ventive solid polymer composition.

A second aspect of the invention refers to a self-supporting film that comprises a solid polymer com position according to the first aspecet of the invention.

Advantageously, the self-supporting film emits green and red light in response to excitation by light of a wavelength shorter than the emitted green light.

Advantageously, the the solid polymer compo sition is sandwiched between two barrier layers.

In a further advantageous embodiment, such a self-supporting film can have a thickness t _ssf of 0.001 < t _ssf £ 10 mm, preferably of 0.01 < t _SSf £ 0.5 mm. 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 an advantageous embodiment, the barrier film may be permeable for oxygen. In another advantageous em bodiment, the barrier 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 pres sure, 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 for 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.

Advantageously, a polymer oxygen barrier mate rial 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.

The inventive self-supporting films may be ob tained in analogy to known methods using the starting ma terials of formula (I), formula (ii) and monomers / oligo mers of the respective polymer. The invention thus provides for a method of manufacturing a self-supporting film, com prising the steps of

(a) combining compound of formula (I), compound of formula (II), monomer and/or oligomer of the polymer, optionally diluent, optionally scattering particles, optinally catalyst or other additives, to thereby obtain a first dispersion;

(b) optionally removing the diluent to thereby obtain an ink; c) coating said ink on a barrier film to thereby obtain a coated barrier film;

(d) laminating said coated barrier film with a second barrier film

(e) curing said laminated barrier films to thereby obtain the inventive self-supproting film; The inventive manufacturing is simple and can be easily applied to existing production lines.

A third aspect refers to a light emitting de vice which is preferably a liquid crystal display. The light emitting device comprises a solid polymer composi tion according to the first aspect of the invention or a self-supporting film according to the second aspect of the invention.

An advantageous embodiment of the light emit ting devive comprises an array of more than one blue LED, wherein the array of LEDs covers essentially the full liquid crystal display area. In addition, a diffusor plate is arranged between the array of more than one blue LED and the self-supporting film.

In a further advantageous embodiment of the invention, the one or more blue LEDs 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 > 600 Hz.

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. 1 shows a schematic of a solid polymer composition according to an embodiment of the invention;

Fig. 2 shows a schematic of a sheet-like mate rial according to an embodiment of the invention; and

Fig. 3 shows a light emitting device according to an embodiment of the invention.

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. 1 shows a schematic of a solid polymer composition 100 according to an embodiment of the first aspect, wherein the solid polymer composition comprieses green luminescent perovskite crystals 1 of formula (I), non-perovskite red phosphor crystals 2 of formula (II), and a polymer 3. The polymer has a molar ratio of the sum of (oxygen + nitrogen) to carbon z, wherein z < 0.9, z < 0.75 in particular z < 0.4, in particular z < 0.3, in particular z < 0.25.

Further embodiments of the solid polymer com position in Fig. 1 might comprise further features accord ing to the first aspect of the invention.

Fig. 2 shows a schematic of an embodiment of a self-supporting film according to the second aspect of the invention. In an advantageous embodiment as demon strated in the figure, the self-supporting film might comprise barrier layers 4 that sandwich the solid polymer composition 100.

Fig. 3 shows a schematic of an embodiment of a light emitting device, in particular a liquid crystal display (LCD) according to the third aspect of the inven tion. Advantageously, the light emitting device comprises a solid polymer composition 100 as shown in Fig. 1 or a self-supporting film as shown in Fig. 2. Advantageously, the light emitting device comprises more than one blue LED 6, wherein the LEDs covers essentially the full liq uid crystal display area 5. In particular, a diffusor plate is arranged between the array of more than one blue LED and the self-supporting film (the diffusor plate is not shown in the figure). Experimental Section

Example 1: Preparation of a self-supporting film comprising a solid polymer composition as described herein:

Green perovskite QDs (FAPbBrs): 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 zir- conia beads (5 mm diameter) 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 FAPbBr3:Oleylamine = 100:15) and toluene (>99.5 %, puriss, Sigma Aldrich). The final concentration of FAPbBr ₃ was lwt%. The mixture was then dispersed by ball milling using yttrium stabilized zirconia beads with a di ameter size of 200 pm at ambient conditions (if not other wise defined, the atmospheric conditions for all experi ments are: 35°C, 1 atm, in air) for a period of lh 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) and 10 wt% non-perov- skite red phosphor particles ("KSF", K2S1F6:Mn ⁴⁺ ), commer cially available in solid form, in a speed mixer and the toluene was evaporated by vacuum (<0.01 mbar) at room tem perature .

The non-perovksite red phosphor particles K2SiF6:Mn ⁴⁺ were manufactured by state of the art methods. Such particles are known to have sizes with a diameter of typically 2-50 pm.

The particles are e.g. manufactured by the method disclosed in Sijbom H. F. et al. ICP-MS showed that the resulting KSF particles had a Mn-concentration of 1.5 mol%. SEM analysis with EDX-mapping of Mn further showed that the Mn is distributed homonegenously within the KSF particles from particle core to particle surface proving that the KSF particles are free of an inorganic shell or any other encapsulation.

The volume-weighted average KSF particle size was 3 pm as determined by SEM.

The resulting mixture was then coated with 50 micron layer thickness on a 100 micron barrier film (sup plier: I-components (Korea); Product: TBF-1007), then lam inated with a second barrier film of the same type. After wards the laminate structure was UV-cured for 60 s (UVAcubelOO equipped with a mercury lamp and quartz filter, Hoenle, Germany) to thereby obtain a self-supporting film wherein the inventive solid polymer composition is sand wiched between two barrier layers. The resulting KSF quan tity per film area was around 6g/m2.

Performance Tests: The initial performance of the as obtained film showed a green emission wavelength of 526 nm with a FWHM of 22 nm and a red emission wavelength characteristic for K ₂ SiF ₆ :Mn ₄₊ . The color coordinates (CIE1931) of the film were x = 0.23 and y = 0.20 when placed on a blue LED light source (450 nm emission wave length) 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 glass transition temperature Tg of the UV- cured solid polymer composition was determined by DSC ac cording to DIN EN ISO 11357-2:2014-07 with a starting tem perature 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 be sides the glass transition). For the DSC measurement the solid polymer composition was removed from the film by delaminating the barrier films. The measured Tg of the UV- cured resin composition was 75°C.

The stability of the film was tested for 150 hours under blue LED light irradiation by placing the film into a light box with high blue intensity (supplier: Hoenle; model: LED CUBE 100 IC) with a blue flux on the film of 410 mW/cm ² at a film temperature of 50°C. Further more the film was also tested for 150 hours in a climate chamber with 60°C and 90% relative humidity. The change of optical parameters after stability testing of the film for was measured with the same procedure as for measuring the initial performance (described above). The change of opti cal parameters were as following:

Example 2: Preparation of a self-supporting film comprising a solid polymer composition with a large KSF particle size.

KSF particles with a volume-weighted average particle size of 20 pm(measured by SEM) were synthesized similar to the procedure in experiment 1. ICP-MS showed that the resulting KSF particles had a Mn-concentration of 1.6 mol%. SEM analysis with EDX-mapping of Mn further showed that the Mn is distributed homonegenously within the KSF particles from particle core to particle surface indicating that the KSF particles are free of an inorganic shell or any other encapsulation. These KSF particles were used to prepare a film with the same materials (perovskite crystals, monomer/crosslinker mixture, photoinitiator, scattering particles) and the same color coordinates as in example 1. In order to achieve the same film color coordi nates as in example 1, the KSF concentration had to be increased from 10 wt% (as in example 1) to 25 wt%. This resulted in a KSF quantity per film area of around 15g/m ² . This shows that a KSF particle size of 3 pm is preferred compared to 20 pmbecause the KSF quantity per film area is 2.5 times lower, therefore less KSF particles are needed per film area and ultimately less KSF particles are needed e.g. for a display comprising the film.

Conclusion: These results show that a self- supporting luminescent film could be obtained whereby the green provskite crystals and non-perovskite red phosphor particles (K2S1F6:Mn ₄₊₎ both show a good chemical compati bility and high stability when tested under high blue flux and high temperature/humidity. Furthermore these results also show that a small KSF particle size is preferred.