LIGHT EMITTING COMPONENT, A LIGHT EMITTING DEVICE AND A SHEET-LIKE MATERIAL

Abstract

A light emitting component comprising a light source (10) for emitting blue light (aa), a first layer (1) comprising a red phosphor, and a second layer (2) comprising luminescent crystals (20). 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 first layer (1) is arranged adjacent to the light source (10). The second layer (2) is arranged remotely from the first layer (1).

Claims

1. A light emitting component comprising a light source for emitting blue light, a first layer comprising a red phosphor, wherein upon absorption of the blue light, the red phosphor emits light in the red light spectrum, and wherein the first layer is arranged adjacent to the light source, a second layer, said second layer comprising luminescent crystals, a solid polymer and scattering particles, wherein the luminescent crystals are of perovskite structure, wherein upon absorption of the light emitted by the light source, the luminescent crystals emit light of a wavelength in the green light spectrum, wherein the luminescent crystals and the scattering particles are embedded in the solid polymer, wherein the second layer has a haze h.sub.2 of 20≤h.sub.2≤70%, and wherein the second layer is arranged remotely from the first layer.

2. The light emitting component according to claim 1, wherein the luminescent crystals are embedded in a cross-linked solid polymer.

3. A light emitting component comprising a light source for emitting blue light, a first layer comprising a red phosphor, wherein upon absorption of the blue light, the red phosphor emits light in the red light spectrum, and wherein the first layer is arranged adjacent to the light source, a second layer, said second layer comprising luminescent crystals and a cross-linked solid polymer, wherein the luminescent crystals are of perovskite structure, wherein upon absorption of the light emitted by the light source, the luminescent crystals emit light of a wavelength in the green light spectrum, wherein the luminescent crystals are embedded in the cross-linked solid polymer, wherein the second layer has a haze h.sub.2 of 20≤h.sub.2≤70%, wherein the second is arranged remotely from the first layer.

4. The light emitting component according to claim 1, wherein the luminescent crystals are selected from compounds of formula (II):
[M.sup.1A.sup.1].sub.aM.sup.2.sub.bX.sub.c   (II), wherein: A.sup.1 represents one or more organic cations, preferably formamidinium, M.sup.1 represents one or more alkaline metals, M.sup.2 represents one or more metals other than M.sup.1, in particular Pb, X represents one or more anions selected from the group consisting of halides, pseudohalides and sulfides, in particular Br, a represents 1-4, b represents 1-2, c represents 3-9, and wherein either M.sup.1, or A.sup.1, or M.sup.1 and A.sup.1 being present.

5. The light emitting component according to claim 4, wherein M.sup.2 represents Pb, wherein a concentration of Pb is of 5-200 mg/m.sup.2, in particular 10-100 mg/m.sup.2, very particular 20-80 mg/m.sup.2.

8. The light emitting component according to claim 1, wherein 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.

9. The light emitting component according to claim 1, wherein the red phosphor is a Mn+4 doped phosphor of formula (I):
[A].sub.x[MF.sub.y]:Mn.sup.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 [MFy] ion; and Y represents 5, 6 or 7, preferably (I″)
K.sub.2SiF.sub.6:Mn.sup.4+  (I″).

8. The light emitting component according to claim 1, wherein the solid polymer comprises an acrylate, in particular comprises or consists of repeating units selected from the group of cyclic aliphatic acrylates, in particular, and/or wherein the acrylate comprises repeating units selected from monofunctional acrylate monomers and multifunctional acrylate monomers.

9. The light emitting component according to claim 1, wherein 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.

10. The light emitting component according to claim 1, wherein the solid polymer has a glass transition temperature T.sub.g of T.sub.g≤120° C., in particular of T.sub.g≤100° C., in particular of T.sub.g≤80° C., in particular of T.sub.g≤70° C.

11. The light emitting component according to claim 1, wherein the solid polymer is configured as a sheet-like polymer and/or wherein the solid polymer is sandwiched between two barrier layers.

12. A light emitting device, in particular a liquid crystal display (LCD), comprising the light emitting component according to claim 1.

13. The light emitting device according to claim 12, wherein the light emitting component comprises an array of more than one light sources with a respective adjacent first layer, one second layer arranged remotely to the array, and a diffusor plate arranged between the first layers and the second layer, in particular, wherein the array covers essentially the full liquid crystal display area.

14. The light emitting device according to claim 12, wherein 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≥150 Hz, in particular of f≥300 Hz, very particular of f≥600 Hz.

15. A self-supporting film, comprising luminescent crystals embedded in a polymer, wherein 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, and wherein the self-supporting film has a haze h.sub.2 of 20≤h.sub.2≤70%, in particular h.sub.2<80%, in particular of h.sub.2<70%, very particular of h.sub.2<60%.

16. The self-supporting film according to claim 15, wherein the polymer comprises scattering particles.

17. The self-supporting film according to claim 15, wherein the luminescent crystals are embedded in a cross-linked solid polymer.

18. The self-supporting film according to claim 15, wherein the luminescent crystals are selected from compounds of formula (II):
[M.sup.1A.sup.1].sub.aM.sup.2.sub.bX.sub.c   (II), wherein: A.sup.1 represents one or more organic cations, preferably formamidinium, M.sup.1 represents one or more alkaline metals, M.sup.2 represents one or more metals other than M.sup.1, in particular Pb, X represents one or more anions selected from the group consisting of halides, pseudohalides and sulfides, in particular Br, a represents 1-4, b represents 1-2, c represents 3-9, and wherein either M.sup.1, or A.sup.1, or M.sup.1 and A.sup.1 being present.

19. The self-supporting film according to claim 18, wherein M.sup.2 represents Pb, and wherein the concentration of Pb is 5-200 mg/m.sup.2, in particular 10-100 mg/m.sup.2, very particular 20-80 mg/m.sup.2.

20. The self-supporting film according to claim 16, wherein the solid polymer comprises an acrylate, in particular comprises or consists of repeating units selected from the group of cyclic aliphatic acrylates, in particular, and/or wherein the acrylate comprises repeating units selected from monofunctional acrylate monomers and multifunctional acrylate monomers.

21. The self-supporting film according to claim 16, wherein 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.

22. The self-supporting film according to claim 16, wherein the solid polymer has a glass transition temperature T.sub.g of T.sub.g≤120° C., in particular of T.sub.g≤100° C., in particular of T.sub.g≤80° C., in particular of T.sub.g≤70° C.

23. The self-supporting film according to claim 16, wherein the solid polymer is configured as a sheet-like polymer and/or wherein the solid polymer is sandwiched between two barrier layers.

24. A light emitting device, in particular a liquid crystal display (LCD), comprising the self-supporting film according to claim 15.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0130] The invention will be better understood and objects other than those set forth above will become apparent from the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:

[0131] FIG. 1a shows a schematic figure of a light source for emitting blue light with a first layer comprising red phosphor;

[0132] FIG. 1b shows a schematic figure of a light emitting component according to an advantageous embodiment of the invention;

[0133] FIG. 1c shows a schematic figure of a self-supporting film according to an embodiment of the invention;

[0134] FIG. 2 shows a schematic figure of a light emitting component according to a further advantageous embodiment of the invention;

[0135] FIG. 3 shows a schematic of a light emitting component according to a further advantageous embodiment of the invention;

[0136] FIG. 4 shows a schematic of a light emitting component according to a further advantageous embodiment of the invention;

[0137] FIG. 5 shows a light emitting device according to an advantageous embodiment of the invention;

[0138] FIG. 6a shows an emission spectrum of the device schematically shown in FIG. 6b; and

[0139] FIG. 7a shows an emission spectrum of the device schematically shown in FIG. 7b.

MODES FOR CARRYING OUT THE INVENTION

[0140] Embodiments, examples, experiments representing or leading to embodiments, aspects and advantages of the invention will be better understood from the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:

[0141] FIG. 1a shows a schematic of a component comprising 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 (K.sub.2SiF.sub.6:Mn.sup.4+). Upon absorption of the blue light aa, the red phosphor emits light in the red light spectrum bb.

[0142] In particular, the component shown in FIG. 1b 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 particles that are distributed adjacent to the light source 10.

[0143] FIG. 1b 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 comprising red phosphor and a second layer 2 comprising luminescent 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 h.sub.2 of 10%≤h.sub.2≤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.

[0144] In a further advantageous embodiment, the light emitting component in FIG. 1b might have a haze h.sub.2 of 20≤h.sub.2≤70%, preferably h.sub.2≤80%, preferably h.sub.2≤70%, very preferably h.sub.2≤60%.

[0145] 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.

[0146] 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 experimental section (experiment 1).

[0147] 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 (experiment 2).

[0148] In a further advantageous embodiment, the luminescent crystals 20 are selected from the compounds of formula (II), wherein M.sup.2 is Pb and wherein the concentration of Pb is 5-200 mg/m.sup.2, in particular 10-100 mg/m.sup.2, very particular 20-80 mg/m.sup.2.

[0149] 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 (monofunctional acrylates).

[0150] In another advantageous embodiment, the solid polymer is cross-linked and comprises a multi-functional acrylate. In addition to the monofunctional acrylates.

[0151] Such a polymer might further be configured as a sheet-like polymer.

[0152] In a further advantageous embodiment, the polymer can be sandwiched between barrier layers 21. An example of such barrier layers 21 are shown in FIG. 1c.

[0153] In a further advantageous embodiment the solid polymer has a glass transition temperature T.sub.g of T.sub.g≤120° C. (preferably T.sub.g≤100° C., very preferably T.sub.g≤80° C., very preferably T.sub.g≤70° C.)

[0154] In a further advantageous embodiment, the second layer might scattering particles embedded in the solid polymer, in particular for generating said haze (scattering particles are not shown in the figures).

[0155] FIG. 1c shows a schematic of an embodiment of the self-supporting film 200. The self-supporting film comprises 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 h.sub.2 of 20≤h.sub.2≤70%, preferably h.sub.2<80%, in particular of h.sub.2<70%, very particular of h.sub.2<60%.

[0156] Advantageously, the self-supporting film 200 comprises scattering particles embedded in the polymer (scattering particles are not shown in the figure).

[0157] In a further embodiment, the luminescent crystals 20 of the self-supporting film 200 are embedded in a cross-linked solid polymer.

[0158] In a further advantageous embodiment, the luminescent crystals 20 are selected from the compounds of formula (II).

[0159] In a further advantageous embodiment, the luminescent crystals 20 are selected from the compounds of formula (II), wherein M.sup.2 is Pb and wherein the concentration of Pb is 5-200 mg/m.sup.2, in particular 10-100 mg/m.sup.2, very particular 20-80 mg/m.sup.2.

[0160] In a further advantageous embodiment, the solid polymer comprises an acrylate, in particular comprises or consists of repeating units selected from the group of cyclic aliphatic acrylates, in particular, and/or wherein the acrylate comprises repeating units selected from monofunctional acrylate monomers and multifunctional acrylate monomers.

[0161] In a further advantageous embodiment of the self-supporting film 200, 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.

[0162] In a further advantageous embodiment, the solid polymer has a glass transition temperature T.sub.g of T.sub.g≤120° C., in particular of T.sub.g≤100° C., in particular of T.sub.g≤80° C., in particular of T.sub.g≤70°.

[0163] 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.

[0164] FIG. 2 shows a schematic of a further embodiment 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 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 h.sub.2 of 40%≤h.sub.2≤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.

[0165] 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.

[0166] All advantageous features as disclosed in FIG. 1b can also be combined with the embodiment in FIG. 1c.

[0167] FIG. 3 shows a schematic of a light emitting component for a specific backlight architecture, in particular 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.

[0168] FIG. 4 shows a further schematic of a further light emitting device for a specific backlight architecture, in particular for LCD displays. The device comprises a light emitting component with a light source 10 for emitting blue light aa, a first layer 1 comprising red phosphor, 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°.

[0169] 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 component, e.g. as shown in one of the embodiments in FIGS. 1 to 4.

[0170] An advantageous light emitting device comprises 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 addition, such an embodiment comprises one second layer 2 arranged remotely to the array. In particular, the array covers essentially the full liquid crystal display area 5.

[0171] 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≥150 Hz, in particular of f≥300 Hz, very particular of f≥600 Hz.

[0172] FIG. 6a shows an emission spectrum of an embodiment 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 respective 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.

[0173] As shown in FIG. 7b, a second layer 2 comprising 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%.

[0174] 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

[0175] 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 (K.sub.2SiF.sub.6:Mn.sup.4+). Upon absorption of the blue light aa, the red phosphor emits light in the red light spectrum bb.

[0176] The emission spectrum of the component shows peaks in the visible blue and red range of the spectrum.

[0177] In particular, the component shown in FIG. 1b 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 particles that are distributed adjacent to the light source 10.

[0178] To measure the data, a 2D-array of 200 individual 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

[0179] 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.

[0180] 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 backlight structure is measured with a spectrometer (Konica Minolta CS-2000) showing blue, red and green emission peaks, as shown in FIG. 7a.

EXAMPLE 3

[0181] Preparation of a green remote perovskite QD film as a self-supporting film, in accordance with the 3.sup.rd aspect of the invention, with low haze h.sub.2 and low T.sub.g:

[0182] Green perovskite QDs with composition formamidinium lead tribromide (FAPbBr.sub.3) are synthesized in toluene as follows: Formamidinium lead tribromide (FAPbBr.sub.3) was synthesized by milling PbBr.sub.2 and FABr. Namely, 16 mmol PbBr.sub.2 (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 diameter) for 6 h to obtain pure cubic FAPbBr.sub.3, confirmed by XRD. The orange FAPbBr.sub.3 powder was added to Oleylamine (80-90, Acros Organics, Geel (BE)) (weight ratio FAPbBr.sub.3:Oleylamine=100:15) and toluene (>99.5%, puriss, Sigma Aldrich). The final concentration of FAPbBr.sub.3 was 1 wt %. The mixture was then dispersed by ball milling using yttrium stabilized zirconia beads with a diameter size of 200 μm 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.

[0183] 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 1 wt % photoinitiator Diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TCI Europe, Netherlands) and 2 wt % polymeric scattering particles (Organopolysiloxane, 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 spectroscopy (ICP-OES) and was then coated with 50 micron layer thickness on a 100 micron barrier film (supplier: I-components (Korea); Product: TBF-1007), then laminated with a second barrier film of the same type. Afterwards the laminate structure was UV-cured for 60 s (UVAcube100 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=emitted 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).

[0184] 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 F1 Phoenix (Netzsch) was used. The T.sub.g was determined on the second heating cycle (the first heating from −90° C. to 250° C. showed overlaying effects besides the glass transition). For the DSC measurement the UV-cured resin composition was removed from the QD film by delaminating the barrier films. The measured Tg of the UV-cured resin composition was 75° C.

[0185] The stability of the QD film was tested for 1′000 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 1′000 hours was measured with the same procedure as for measuring the initial performance (described above). The change of optical parameters were as following: [0186] Change of y-value: from 0.15 to 0.119 (−0.031) [0187] Change of LCF: from 50% to 40% (−10%) [0188] Change of green emission wavelength: from 526 nm to 525 nm (−1 nm) [0189] Change of green FWHM: 0 nm

[0190] Similar results are obtained when replacing FAPbBr.sub.3 by [CsFA]PbBr.sub.3. Such perovskites are described in Document WO2018/028869 A1, e.g. example 10.

COMPARATIVE EXAMPLE 1 FOR EXAMPLE 3

[0191] Preparation of a green remote perovskite QD film with high haze and low T.sub.g.

[0192] The procedure was the same as in the previous procedure for the QD film with low haze, except the following parameters were changed:

[0193] Pb amount of the whole UV curable acrylate mixture is 200 ppm

[0194] 12 wt % scattering particles KMP-590 were mixed into the UV curable acrylate mixture to increase the haze of the final QD film.

[0195] 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 coordinates).

[0196] The change of optical parameters of the QD film after flux testing for 1′000 hours were as following: [0197] Change of y-value: from 0.149 to 0.058 (−0.091) [0198] Change of LCF: from 43% to 14% (−29%) [0199] Change of green emission wavelength: from 525 nm to 521 nm (−4 nm) [0200] Change of green FWHM: 0 nm

[0201] 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

[0202] Preparation of a green remote perovskite QD film with low haze and high T.sub.g.

[0203] 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 monomer mixture:

[0204] 0.7 g FA-DCPA, Hitachi Chemical, Japan/0.3 g FA-320M, Hitachi Chemical, Japan.

[0205] 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.

[0206] The change of optical parameters of the QD film after flux testing for 1′000 hours were as following: [0207] Change of y-value: from 0.153 to 0.068 (−0.085) [0208] Change of LCF: from 49% to 21% (−28%) [0209] Change of green emission wavelength: from 526 nm to 525 nm (−1 nm) [0210] Change of green FWHM: 0 nm

[0211] These results show that a high T.sub.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.sub.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-US-00001 TABLE 1 Summary of the parameter changes after high-flux testing for experiment 3 and comparative examples 1 and 2: Ex. #: haze, test y-value PP FWHM LCF Tg condition (—) (nm) (nm) (%) Ex. 3, inventive initial 0.150 526 22 50 50% Haze, l000 h 0.119 525 22 40 75° C. Tg high flux Δ −0.031 −1 −0 −10 Comparative Ex. 1 initial 0.149 525 22 43 98% Haze, l000 h 0.058 521 22 14 77° C. Tg high flux Δ −0.091 −4 −0 −29 Comparative Ex. 2 initial 0.153 526 22 49 51% Haze, l000 h 0.068 525 22 21 144° C. Tg high flux Δ −0.085 −1 −0 −28