SOLID POLYMER COMPOSITION, A SELF-SUPPORTING FILM AND A LIGHT EMITTING DEVICE

Abstract

The invention refers in a first aspect to a solid polymer composition (100) comprising green luminescent crystals (1), non-perovskite red phosphor particles, and a polymer (3). The polymer (3) 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. A second aspect of the invention refers to a self-supporting film comprising the solid polymer composition (100) of the first aspect. A third aspect of the invention refers to a light emitting device comprising either the solid polymer composition (100) according to the first aspect of the invention or the self-supporting film according to the second aspect of the invention.

Claims

1. A solid polymer composition comprising green luminescent perovskite crystals, non-perovskite red phosphor particles, and a polymer, wherein the green luminescent perovskite crystals are selected from compounds of formula (I):
[M.sup.1A.sup.1].sub.aM.sup.2.sub.bX.sub.c  (I), wherein: A.sup.1 represents one or more organic cations, M.sup.1 represents one or more alkaline metals, M.sup.2 represents one or more metals other than M1, X represents one or more anions selected from the group consisting of halides, pseudohalides and sulfides, 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; wherein the non-perovskite red phosphor particles are Mn+4 doped phosphor particles of formula (II):
[A].sub.x[MF.sub.y]:Mn.sup.4+  (II), 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 the absolute value of the charge of the [MFy] ion; and Y represents 5, 6 or 7; wherein the polymer has a molar ratio of the sum of (oxygen+nitrogen) to carbon z, wherein z≤0.4, and wherein the non-perovskite red phosphor particles have a volume-weighted average particle size s.sub.p of s.sub.p≤10 μm.

2. The solid polymer composition according to claim 1, wherein the green luminescent perovskite crystals and the non-perovksite red phosphor particles are embedded in the polymer without an encapsulation.

3. The solid polymer composition according to claim 1, wherein the green luminescent perovskite crystals are of formula (I′):
FAPbBr.sub.3  (I′).

4. The solid polymer composition according to claim 1, wherein the non-perovskite red phosophor particles are Mn+4 doped phosphor particles of formula (II′):
K.sub.2SiF.sub.6:Mn.sup.4+  (II′).

5. The solid polymer composition according to claim 1, wherein a difference in concentration Δc.sub.Mn of Mn between the center of each non-perovskite red phosphor particle and an area 100 nm below the respective red phosphor particle surface is Δc.sub.Mn≤50%.

6. The solid polymer composition according to claim 1, wherein the concentration c.sub.Mn of Mn in each non-perovskite red phosphor particle is essentially homogenously over the volume of the respective non-perovskite red phosphor particle.

7. The solid polymer composition according to claim 1 wherein the non-perovskite red phosphor particles are free of an inorganic surface coating.

8. The solid polymer composition according to claim 1 wherein the non-perovskite red phosphor particles have a Mn-concentration c.sub.Mn of c.sub.Mn≥6 mol %.

9. The solid polymer composition according to claim 1, wherein the polymer comprises an acrylate.

10. The solid polymer composition according to claim 1, wherein the solid polymer composition has a glass transition temperature T.sub.g of T.sub.g≤120° C.

11. The solid polymer composition according to claim 1, wherein the solid polymer composition comprises scattering particles selected from the group consisting of metal oxide particles and polymer particles.

12. A self-supporting film comprising a solid polymer composition according to claim 1.

13. The self-supporting film according to claim 12, wherein the solid polymer composition is sandwiched between two barrier layers.

14. A light emitting device, in particular a liquid crystal display (LCD), comprising a solid polymer composition according to claim 1.

15. The light emitting device according to claim 14 comprising an array of more than one blue LED, wherein the array of LEDs covers essentially the full liquid crystal display area, and wherein a diffusor plate is arranged between the array of more than one blue LED and the self-supporting film.

16. The solid polymer composition according to claim 1 wherein: A.sup.1 is formamidinium, M.sup.1 is Cs, M.sup.2 is Pb, X is Br, A is K, M is Si, x is 2; and Y is 6.

17. The solid polymer composition according to claim 1 wherein the non-perovskite red phosphor particles have a Mn-concentration c.sub.Mn of c.sub.Mn≥9 mol %.

18. The solid polymer composition according to claim 1, wherein the polymer comprises a cyclic aliphatic acrylate.

19. The solid polymer composition according to claim 1, wherein the solid polymer composition has a glass transition temperature T.sub.g of T.sub.g≤100° C.

20. The solid polymer composition according to claim 1, wherein the solid polymer composition comprises scattering particles selected from the group consisting of TiO2, ZrO2, Al2O3 and organopolysiloxanes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0084] 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:

[0085] FIG. 1 shows a schematic of a solid polymer composition according to an embodiment of the invention;

[0086] FIG. 2 shows a schematic of a sheet-like material according to an embodiment of the invention; and

[0087] FIG. 3 shows a light emitting device according to an embodiment of the invention.

MODES FOR CARRYING OUT THE INVENTION

[0088] 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:

[0089] FIG. 1 shows a schematic of a solid polymer composition 100 according to an embodiment of the first aspect, wherein the solid polymer composition comprises 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.

[0090] Further embodiments of the solid polymer composition in FIG. 1 might comprise further features according to the first aspect of the invention.

[0091] 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 demonstrated in the figure, the self-supporting film might comprise barrier layers 4 that sandwich the solid polymer composition 100.

[0092] 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 invention. 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 liquid 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

[0093] Green perovskite QDs (FAPbBr.sub.3): 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.

[0094] 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) and 10 wt % non-perovskite red phosphor particles (“KSF”, K.sub.2SiF.sub.6:Mn.sup.4+), commercially available in solid form, in a speed mixer and the toluene was evaporated by vacuum (<0.01 mbar) at room temperature.

[0095] The non-perovksite red phosphor particles K.sub.2SiF.sub.6:Mn.sup.4+ were manufactured by state of the art methods. Such particles are known to have sizes with a diameter of typically 2-50 μm.

[0096] 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 homogeneously 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.

[0097] The volume-weighted average KSF particle size was 3 μm as determined by SEM.

[0098] The resulting mixture 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) to thereby obtain a self-supporting film wherein the inventive solid polymer composition is sandwiched between two barrier layers. The resulting KSF quantity per film area was around 6 g/m2.

[0099] 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.sub.2SiF.sub.6:Mn.sub.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 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).

[0100] The glass transition temperature Tg of the UV-cured solid polymer 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 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.

[0101] 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.sup.2 at a film temperature of 50° C. Furthermore 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 optical parameters were as following:

TABLE-US-00001 x-value y-value Luminanance test condition (—) (—) (%) initial 0.23 0.20 100%  150 h high flux 0.23 0.19 95% (410 mW/cm.sup.2) 150 h 60° C./90% r.H. 0.23 0.19 93%

Example 2: Preparation of a Self-Supporting Film Comprising a Solid Polymer Composition with a Large KSF Particle Size

[0102] KSF particles with a volume-weighted average particle size of 20 μm (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 homogeneously 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 coordinates 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 15 g/m.sup.2. This shows that a KSF particle size of 3 μm is preferred compared to 20 μm because 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.

[0103] Conclusion: These results show that a self-supporting luminescent film could be obtained whereby the green provskite crystals and non-perovskite red phosphor particles (K.sub.2SiF.sub.6:Mn.sub.4+) both show a good chemical compatibility 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.