BLUE FILTER FOR DISPLAY

Abstract

A display that includes an image producing system and a light filtering layer in the blue range, the light filtering layer having a limited impact on the gamut of the display. The image producing system has a gamut G.sub.0 defined in a color space The light filtering layer includes semi-conductive nanoparticles, and the absorbance through the light filtering layer is greater than 0.25 for each light wavelength ranging from 350 nm to λ.sub.cut, λ.sub.cut being in the range from 420 nm to 450 nm. The gamut G.sub.1 of the image producing system with the filtering layer has an area greater than 90% of the area of gamut G.sub.0 in the color space.

Claims

1.-13. (canceled)

14. A display comprising: a) an image producing system having a gamut G.sub.0 defined in a color space; b) a light filtering layer comprising semi-conductive nanoparticles; wherein the absorbance through said light filtering layer is greater than 0.25 for each light wavelength ranging from 350 nm to λ.sub.cut, λ.sub.cut being in the range from 420 nm to 450 nm; and wherein the gamut G.sub.1 of said image producing system with said filtering layer has an area greater than 90% of the area of gamut G.sub.0 in said color space.

15. The display according to claim 14, wherein the image producing system comprises a backlight unit, at least one polarizer, an active matrix, at least one layer of liquid crystals and a protective layer.

16. The display according to claim 15, wherein the light filtering layer is a coating applied on the internal side of the protective layer.

17. The display according to claim 14, wherein the image producing system comprises three light sources having different colours and a protective layer.

18. The display according to claim 17, wherein the light filtering layer is a coating applied on the internal side of the protective layer.

19. The display according to claim 14, wherein gamut G.sub.0 and gamut G.sub.1 are evaluated in the CIE Luv color space and the gamut G.sub.1 of said image producing system with said filtering layer has an area greater than 95% of the area of gamut G.sub.0 in said color space.

20. The display according to claim 14, wherein gamut G.sub.0 and gamut G.sub.1 are evaluated in the CIE xyY color space and the gamut G.sub.1 of said image producing system with said filtering layer has an area greater than 95% of the area of gamut G.sub.0 in said color space

21. The display according to claim 20, wherein gamut G.sub.0 and gamut G.sub.1 are evaluated in the CIE xyY color space and the gamut G.sub.1 of said image producing system with said filtering layer has an area greater than 98% of the area of gamut G.sub.0 in said color space

22. The display according to claim 14, wherein the semi-conductive nanoparticles comprise a material of formula
M.sub.xQ.sub.yE.sub.zA.sub.w   (I), wherein: M is selected from the group consisting of Zn, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd, Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Cs or a mixture thereof; Q is selected from the group consisting of Zn, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd, Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Cs or a mixture thereof; E is selected from the group consisting of O, S, Se, Te, C, N, P, As, Sb, F, Cl, Br, I, or a mixture thereof; A is selected from the group consisting of O, S, Se, Te, C, N, P, As, Sb, F, Cl, Br, I, or a mixture thereof; and x, y, z and w are independently a decimal number from 0 to 5; x, y, z and w are not simultaneously equal to 0; x and y are not simultaneously equal to 0; z and w may not be simultaneously equal to 0.

23. The display according to claim 14, wherein the light filtering layer is composed of a matrix in which semi-conductive nanoparticles are dispersed.

24. The display according to claim 22, wherein the matrix is a polymerizable composition comprising (meth)acrylics monomers or oligomers, epoxy monomers or oligomers, or mixture thereof.

25. The display according to claim 22, wherein the matrix is a polymerizable composition comprising monomers or oligomers selected from metal alkoxides, alkoxysilanes, alkylalkoxysilanes, epoxysilanes, epoxyalkoxysilanes, and mixtures thereof.

26. The display according to claim 22, wherein the matrix is a polymerizable composition and the amount of semi-conductive nanoparticles in the polymerizable composition is from 10 ppm to 10 wt %, based on the weight of the polymerizable composition.

27. The display according to claim 14, wherein the semi-conductive nanoparticles are capped with an organic layer or encapsulated in an inorganic matrix.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0139] FIG. 1 is a graph showing a chromaticity space CIE xy, with the gamut defined from three light sources: red (R), green (G) and blue (B).

[0140] FIG. 2 illustrates a structure of a display apparatus as disclosed herein.

[0141] FIG. 3 shows the generic absorbance of a polymerizable composition or material comprising semi conductive nanoparticles (logarithm scale) as a function of wavelength of light from 350 nm to 780 nm (linear scale): A(λ) and the principle of determination of λ.sub.cut.

[0142] FIG. 4 is a graph showing a chromaticity space CIE xy, with the gamut defined from three light sources: red (R), green (G) and blue (B) without light filtering layer and with light filtering layer (blue source is shifted from B to B′).

[0143] FIG. 5 is a schematic representation of various shapes (spheres and plates) and structure (homostructure, core/shell, core/crown, dot in plate) of semi-conductive nanoparticles.

[0144] FIG. 6 shows Absorbance A of dispersion of nanoparticles NP1, NP2 and NP3 in heptane as a function of light wavelength (λ—in nm).

[0145] FIG. 7 shows Absorbance A of light filtering layers L1, L2 and L3 as a function of light wavelength (λ—in nm).

[0146] FIG. 8 shows intensity of light (I—in arbitrary unit) emitted by a blue LED as a function of light wavelength (λ—in nm) without light filtering layer (L0) and with light filtering layers L1, L2 and L3.

[0147] FIG. 9 shows intensity of white light (I—in arbitrary unit) emitted by a display as a function of light wavelength (λ—in nm) without light filtering layer (L0) and with light filtering layer L2.

EXAMPLES

[0148] The present invention is further illustrated by the following examples.

[0149] Light Filters

[0150] Light filtering layers have been prepared with ZnSe nanoparticles dispersed in a Sol-Gel coating. [0151] ZnSe semi-conductive nanoparticles

[0152] Semi-conductive nanoparticles of formula ZnSe (hereafter NP1) and having a shape of sphere with diameter of 7.1±0.2 nm were prepared according to procedure known by the man of the art and reported in New J. Chem., 2007, 31, 1843-1852. Specific purification steps included selective precipitation and redispersion in presence of organic ligands as alkylamines A monodisperse population of ZnSe nanospheres was obtained with a coefficient of variation less than 20%.

[0153] Similar experiments were conducted to synthesize ZnSe nanosphere, respectively with a diameter of 7.4±0.2 nm (NP2) and 7.7±0.2 nm (NP3). The same purification steps were used to obtain monodisperse populations of ZnSe nanospheres with a coefficient of variation less than 20%.

[0154] Absorbance curves of nanoparticles NP1, NP2 and NP3 in heptane were measured as a function of light wavelength in the UV-visible and are shown on FIG. 6 (logarithmic scale).

[0155] Characteristics of these nanoparticles are listed in Table 2 below:

TABLE-US-00002 TABLE 2 ZnSe NP 1 ZnSe NP 2 ZnSe NP 3 diameter (nm) 7.1 ± 0.2 7.4 ± 0.2 7.7 ± 0.2 λ.sub.max 425 nm 430 nm 435 nm λ.sub.0.9 (at 0.9*A.sub.max) 429 nm 434 nm 440 nm λ.sub.0.5 (0.5*A.sub.max) 434 nm 438 nm 445 nm λ.sub.0.1 (0.1*A.sub.max) 441 nm 447 nm 453 nm |λ.sub.0.5 − λ.sub.0.9| 4 nm 4 nm 5 nm |λ.sub.0.1 − λ.sub.0.9| 12 nm 13 nm 13 nm [0156] Layer with ZnSe semi-conductive nanoparticles

[0157] 5 mL of a dispersion comprising ZnSe nanospheres NP1 were mixed with 5 mL of 3-mercaptoproprionic acid (MPA). This mixture was heated at 60° C. for 2 hours and then washed three times with absolute ethanol and toluene. ZnSe nanoparticles capped with MPA were redispersed in water at pH=10. These nanospheres were encapsulated according to the procedure disclosed in EP3630683 within a silica shell and redispersed in 0.5 mL of methanol. This dispersion D1 had a weight content of 2.5% of nanospheres. Same experiments were reproduced with semi-conductive nanoparticles NP2 and NP3 to prepare respectfully dispersion D2 and D3.

[0158] In addition, a Sol-Gel solution SG was also prepared in a separated vial with 100 μL of (3-Glycidyloxypropyl)trimethoxysilane, 65 μL of diethoxydimethylsilane and 35 μL of 0.1 M HCl. Solution SG was stirred for 24 hours at room temperature.

[0159] 50 μL of dispersion D1 were added to 200 μL of solution SG to obtain a polymerizable composition then deposited by spin coating on a glass protective layer of a standard LCD display at 400 rpm during 30 s (dispensing step) then 2000 rpm during 2 min (spreading step). The resulting layer Ll was then heated at 150° C. for 6 h in order to obtain a condensed 5 μm thick Sol-Gel coating having a weight content in

[0160] ZnSe nanospheres of 1% after curing. Same experiments were reproduced with dispersion D1 and D3 to prepare respectfully layer L2 and layer L3.

[0161] Absorbance curves of layers L 1 , L2 and L3 were measured as a function of light wavelength in the UV-visible and are shown on FIG. 7 (logarithmic scale). Thickness of layers L1, L2 and L3 were adjusted to have an absorbance equal to 1 at λ.sub.cut. [0162] Display with light filtering layer

[0163] Layers L 1 , L2 and L3 (6) coated on the inner side of glass protective layer (55) were disposed in a display with a configuration shown on FIG. 2.

[0164] In this display, light sources of image producing system comprises blue LED. FIG. 8 shows intensity of light emitted by blue LED (I—in arbitrary unit) as a function of light wavelength (λ—in nm) without light filtering layer (L0) and with light filtering layers L1, L2 and L3.

[0165] High energy blue light emitted by blue LED is very efficiently filtered out with layers L1, L2 and L3. Indeed, light emitted corresponds to the area below intensity curve, and amount of light having a wavelength below 440 nm is dramatically decreased.

[0166] Table 3 below shows the amount of light filtered out for range of wavelength 400-440 nm (light to be filtered out) and range 440-500 nm (light to be maintained). Table 3 also shows the wavelength of maximum emission (nm). The characteristics of layers L1 , L2 and L3 for λ.sub.max, λ.sub.0.9, λ.sub.0.5 and λ.sub.0.1 are the same as the characteristics of dispersion of nanoparticles listed in table 2: incorporation of nanoparticles in Sol-Gel coating didn't change absorbance features.

TABLE-US-00003 TABLE 3 400-440 nm (%) 440-500 nm (%) Peak (nm) Layer L1 51 4.3 446 Layer L2 87 13.6 447 Layer L3 96 32 448

[0167] One can observe that layer L2 is a good compromise to filter out high energy blue light without changing too much the emission peak of blue light, in particular the wavelength of maximum emission is not shifted and remains at 454 nm.

[0168] In this display, fluorescent materials are used to produce green and red light, from blue light emitted by blue LED. FIG. 9 shows intensity of white light emitted by display (I—in arbitrary unit) as a function of light wavelength (λ—in nm) without light filtering layer (L0) and with light filtering layer L2.

[0169] Table 4 below shows coordinates of red, green, blue and white light emitted by this display, without light filtering layer (L0) and with light filtering layer L2, in the CIE Luv colour space. Taking for display without filter gamut G.sub.0 equal to 100, the gamut G.sub.1 of display with filter is 95.1.

TABLE-US-00004 TABLE 4 No filter Filter L2 Blue (0.15-0.05) (0.15-0.06) Green (0.31-0.63) (0.31-0.63) Red (0.65-0.35) (0.65-0.35) White point (0.33-0.33) (0.35-0.41)

[0170] In the CIE xyY color space, taking for display without filter gamut G.sub.0 equal to 100, the gamut G.sub.1 of display with filter is 97.4.

[0171] With filter L2, colour of white light has been slightly changed. However, colour of white light in such displays is defined by intensity of the three sources (red, green and blue). It is thus straightforward to increase intensity of blue source to restore a white light with coordinates of (0.33, 0.33) in CIE Luv. This adjustment has no effect on gamut.

[0172] Finally, filtering layer L2 demonstrates a very efficient compromise: emission of high energy blue light by display is strongly limited and ability to produce colours over a wide range is maintained.