WO2012042415A1

WO2012042415A1 - Light conversion layer comprising an organic phosphor combination

Info

Publication number: WO2012042415A1
Application number: PCT/IB2011/053968
Authority: WO
Inventors: Martinus Petrus Joseph Peeters; Rifat Ata Mustafa Hikmet; René Theodorus WEGH; Ties Van Bommel
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-09-28
Filing date: 2011-09-12
Publication date: 2012-04-05
Also published as: TW201224112A

Abstract

A light conversion layer comprising at least one sub-layer, for obtaining light having a color rendering index (CRI) of at least 80, comprising an organic phosphor combination comprising at least one yellow-green emitting dye showing an intrinsic emission below 510 nm, and/or an emission below 530 nm after self-absorption is disclosed. Also disclosed is a light emitting device comprising such a light conversion layer, as well as a method for manufacturing such a device.

Description

Light conversion layer comprising an organic phosphor combination

FIELD OF THE INVENTION

The present invention relates to a light conversion layer comprising an organic phosphor combination for use in a light emitting device. BACKGROUND OF THE INVENTION

Blue light from LEDs may be converted to other colors using organic luminescent molecules, i.e. phosphors. The phosphors are generally chosen in order to obtain a light source with a desired correlated color temperature (CCT) and color rendering index (CRI).

One problem with such a system is the pronounced self-absorption of the phosphors. As a result of self-absorption, and also phosphor-phosphor interaction, the emission peak position may red-shift up to 50 nm. The effect of this red shift on CRI is most important for the phosphors with the emission spectrally nearest to the blue LED emission, in other words the green-yellow emitting phosphors. As a result of the pronounced red shifting of the yellow green phosphor (due to self-absorption), there will be a gap in the spectrum between blue and the green-yellow emission from the phosphor which reduces the CRI considerably.

US 6,903,626 B2 describes that a wide range of CCTs from about 3000 K to about 6000 K and CRI from about 60 to 95 can be obtained depending on combinations of organic light emitting material and photoluminescent materials.

There is however a need in the art for a specific phosphor combination avoiding a CRI reduction due to self-absorption of the phosphors.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome this problem, and to provide a light conversion layer comprising a phosphor combination leading to a desired CCT and CRI at high efficiency.

According to a first aspect of the invention, this and other objects are achieved by a light conversion layer for obtaining light having a color rendering index (CRI) of at least 80, comprising at least one sub-layer, and an organic phosphor combination comprising at least one yellow-green emitting dye showing an intrinsic emission below 510 nm and/or an emission below 530 nm after self-absorption.

Suitably, the yellow-green emitting dye shows an intrinsic emission within the range of 450 nm to 510 nm, or 470 to 510 nm. Furthermore, the yellow-green emitting dye suitably has an intrinsic absorption peak within the range of 430 nm to 480 nm.

The light emitting layer further comprises at least one red emitting dye and/or at least one orange emitting dye, in order to provide white light. The red emitting dye may e.g. have an intrinsic emission within the range of 550 nm to 700 nm, and the orange emitting dye may e.g. have an intrinsic emission within the range of 510 nm to 650 nm.

Suitable examples of yellow-green emitting dyes are phosphor Lumogen^® F Yellow 083 (BASF), BASF Thermoplast F 084 Green Gold (CAS Registry Number: 2744- 50-5), and Solvent yellow 98 (CAS Registry Number: 12671-74-8);

Suitable examples of red emitting dyes are phosphor Lumogen^® F Red 305 (BASF), Lumogen^® F Pink 285 (BASF), and Lumogen^® F Red 300 (BASF).

Suitable examples of orange emitting dyes are phosphor Lumogen^® F Orange 240 (BASF), Lumogen^® F Yellow 170 (BASF), and compounds of the following formula (F2DPI):

The yellow-green, red and orange emitting dyes are incorporated in a single sub-layer, or alternatively, the yellow-green, red and orange emitting dyes are incorporated in separate sub-layers.

For example, the yellow-green emitting dye may be incorporated in a first sublayer and the red and orange emitting dyes may be incorporated in a second sub-layer; or the yellow-green emitting dye and the red emitting dye may be incorporated in a first sublayer and the orange emitting dye may be incorporated in a second sublayer; or the yellow-green emitting dye and the orange emitting dye may be incorporated in a first sublayer and the red emitting dye may incorporated in a second sublayer.

The relative amounts in weight of the dyes are suitably in the range of 1 for the yellow-green emitting dye, 0 to 0.4 for the orange emitting dye and 0 to 0.3 for the red emitting dye. Preferably, the relative amounts in weight of the dyes are 1 for the yellow- green emitting dye, 0.1 to 0.3 for the orange emitting dye and 0.05 to 0.2 for the red emitting dye.

The light conversion layer may further comprise scattering particles, i.e. a diffuser function, in at least one of said sub-layers or in a separate sub-layer.

The sub-layers suitably comprise poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET), copolymer of PET, polyethylene naphtalate (PEN), poly(methyl methacrylate) polystyrene, polycarbonate, silicone, polysiloxane, and/or acrylate polymers.

In one embodiment of the invention, the light conversion layer is arranged on a diffuser.

The present invention also relates to a light emitting device comprising a light conversion layer as described above. Such a light emitting device suitably comprises a light source emitting blue light in the wavelength range of 400 - 500 nm, preferably 420 - 480 nm, more preferably 440 - 460 nm.

Furthermore, the present invention relates to a method for manufacturing a light emitting device comprising:

providing a light source; and

arranging a light conversion layer as described above to receive at least a part of the light emitted from said light source.

It is noted that the invention relates to all possible combinations of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

the application, "Y" means Yellow-green phosphor, "O" means Orange phosphor, "R" means Red phosphor, and "D" means Diffusor.

The denotations (ROYD), (ROY)D, (RO)YD, and (Y)(0)(R)(D) describe different configurations of a light conversion layer in accordance with the invention, where capitals arranged within parantheses relate to the phosphors/diffusor being arranged in a common layer. In other words: (ROYD) = red, orange, yellow phosphor and diffusor particles mixed to form a single layer; (ROY)D = red, orange and yellow phosphor are mixed in a single layer placed on top of a layer with diffusor particles to form a double layer stack; (RO)YD = red and orange phosphor are mixed in a single layer placed on top of a yellow layer and a layer with diffusor particles to form a triple layer stack; (R)(0)(Y)(D) = four separate layers placed on top of each other.

Fig. 1 shows the emission spectra of the phosphor Lumogen^® F Yellow 083 (BASF), and the phosphor Lumogen^® F Yellow 170 (BASF) in absence of self-absorption.

Fig. 2 shows the effect of self- absorption on the emission spectrum of the phosphor Lumogen^® F Yellow 083 (BASF).

Fig. 3 shows the effect of self- absorption on the emission spectrum of the phosphor Lumogen^® F Yellow 170 (BASF).

Fig 4 shows the structure of the phosphor molecule F2DPI.

Fig 5 shows the luminescence from the phosphor molecule F2DPI at various thicknesses.

Fig. 6 shows different configurations of a light emitting device comprising a light conversion layer in accordance with the invention.

Fig. 7 shows the efficiency and CRI as a function of R/(R+0) for a device containing red and orange phosphors combined in a single layer ((RO)YD system).

Fig. 8 shows the interpolated white spectrum for combinations of lumogens as measured in a downlighter module (CCT=3000K).

Fig. 9 shows the relation between spectral fraction of the red phosphor and the weight fraction of red phosphor based on the spectrum of Fig. 8, for the (RO)YD system.

Fig. 10 shows a theoretical emission spectrum for a yellow-green emitting dye consisting of a broad emission band.

DETAILED DESCRIPTION

In the research work leading to the present invention, it was surprisingly found that the problem with self-absorption of the phosphors can be solved by a light conversion layer comprising an organic phosphor comprising at least one yellow-green emitting dye having at least some intrinsic emission below 510 nm, and/or emission below 530 nm after self-absorption in the matrix to be used (depending on the overlap between emission and absorption band of the dye). Such phosphors may also be combined with other colors for obtaining white light. By using the inventive combinations, it is possible to obtain light with an efficiency of >180 Lm/Wopt and a CRI of > 80 at 2700 and 3000 K. The phosphor combination has the ability to convert blue light within a wavelength range of 400-500 nm into light in the wavelength range of 530-700 nm.

As used herein, "self-absorption" relates to the process in which some of the radiation emitted by the phosphor is absorbed by the phosphor itself. In the context of the present invention, "intrinsic emission" relates to the emission of the phosphor without self- absorption effects.

Self absorption increases as the absorbance in a layer increases, for example by increasing the layer thickness, or by increasing the dye concentration within the layer. In a device this occurs when the emitted light from the LED is not at the position where the yellow/green band has its maximum. This means that the thickness of the layer or the dye concentration within the layer needs to be increased in order to get sufficient absorption of the LED light as compared with the situation where the luminescent molecule would be excited by light corresponding to its absorption maximum.

The basic idea underlying the invention is illustrated by two experiments showing the effect of using two different types of green-yellow emitting phosphors:

In the first experiment, the phosphor Lumogen^® F Yellow 083 (BASF) (in the following referred to as "F083") with an intrinsic emission characteristic as shown in Fig. 1 was used in combination with blue (450 nm) emitting light emitting diodes. The material has a low wavelength emission peak at around 485 nm and the emission starts at around 460 nm. This phosphor was combined with red and orange emitting phosphors in a PMMA matrix (red/orange weight ratio of 1 :1) and demonstrated a CRI of 90 at 3000K.

Figure 2 shows the effect of self absorption for increasing dye amount in a layer. It can be seen that the peak at 485 nm starts to disappear and the peak at 530 nm starts to increase in intensity. However, the remaining intensity below 520 nm is sufficient to obtain CRI>80. When deconvoluted the peak at 485 nm has a full width at half maximum (FWHM) of 20 nm.

When the phosphor Lumogen^® F Yellow 170 (BASF) (in the following referred to as "F170"), having an intrinsic emission spectrum as shown in Fig. 1, was used, white light with a CCT of 3000K could be made by combining with orange and red emitting phosphors. Based on the intrinsic emission spectrum, having a strong emission peak at 525 nm, CRI =80 would be expected. However for all combinations of this phosphor with orange and red emitting phosphors, it was not possible to reach a CRI higher than ~55. In Figure 3 the effect of self absorption for different amounts of F 170 in a PMMA layer is shown. Here it can be seen that the peak present at 525 nm starts disappearing.

Another yellow-green emitting compound called F2DPI, of which the structure is shown in Figure 4, was also tested. This molecule was also combined with orange and red emitting phosphors. Here again it was not possible to obtain white light with a CRI above 60. The luminescence from this molecule is shown at various thicknesses in Figure 5. (The emission spectrum of the molecule starts at 500 nm; the strong peak at 450 nm is the excitation light used for recording the emission spectra.)

These examples show that a light source with a desired correlated color temperature (CCT) and color rendering index (CRI) can be achieved by careful selection of the green-yellow emitting dye in a phosphor combination for conversion of blue light from a light source such as LEDs. In particular, the organic phosphor needs to comprise a yellow- green emitting dye which absorbs blue light at 450 nm and has at least some intrinsic emission intensity below 510 nm, and/or at least some emission intensity below 530 nm after self-absorption. Thereby, the gap in the spectrum between blue and green-yellow emission from the phosphor is small enough to obtain CRI values for white light higher than 80. In other words there will be enough green light in the spectrum for obtaining CRI values larger than 80.

The intrinsic emission spectrum of a yellow-green emitting dye often consists of several relatively narrow (overlapping) emission peaks, for example in the case of F083, F170 (Figure 1) and F2DPI (Figure 5). Relatively narrow refers in this respect to a deconvo luted full width at half the maximum intensity (generally denoted by FWHM) of 0 to 40 nm, for example 20 nm. In such a case, the condition of having at least some intrinsic emission below 510 nm is fulfilled by showing at least one intrinsic emission peak below 510 nm.

Alternatively, the intrinsic emission spectrum of a yellow-green emitting dye can consist of one or more broader emission bands, i.e. the FWHM is higher than 40 nm. An example of an emission spectrum consisting of one broad band is shown in Figure 10. The densely dashed trace is intrinsic emission, and the loosely dashed trace is emission after reabsorption.

In this case, the condition of having at least some intrinsic emission below 510 nm is fulfilled by having the spectral position of the short- wavelength edge of the intrinsic emission band at half the maximum intensity below 510 nm, even though the maximum of the intrinsic emission band lies above 510 nm. In the case of an emission spectrum consisting of more than one broad emission band, the spectral position of the short-wavelength edge at half the maximum intensity of at least one deconvoluted intrinsic emission band should be below 510 nm.

In the context of the present invention, the feature "showing at least an intrinsic emission below 510 nm" is considered fulfilled when the spectral position of the short wavelength edge at half the maximum intensity of at least one intrinsic emission peak is below 510 nm.

Similarly, in the context of the present invention, the feature "showing at least an emission below 530 nm after self- absorption" is considered fulfilled when the spectral position of the short wavelength edge at half the maximum intensity of at least one emission peak after self-absorption is below 530 nm.

It has surprisingly been found that a light emitting device comprising specific combinations of Lumogen F083 (green-yellow), Lumogen F240 (orange) and Lumogen F305 (red) leads to excellent properties in terms of efficiency and CRI.

Other suitable phosphors which may be used in accordance with the invention instead of F083, i.e. as yellow-green emitting dye with at least some intrinsic emission below 510 nm, are for example BASF Thermoplast F 084 Green Gold (CAS Registry Number: 2744-50-5), and Solvent yellow 98 (CAS Registry Number: 12671-74-8).

Other suitable phosphors which may be used in accordance with the invention instead of F240 and F305, i.e. as orange - red emitting dyes in order to reach CRI >80 in combination with the yellow-green emitting dye, are for example Lumogen^® F Pink 285 (BASF), Lumogen^® F Red 300 (BASF), Lumogen^® F Yellow 170 (BASF), and F2DPI (see Fig. 4). In addition, by routine experimentation, a man skilled in the art will be able to find other phosphors having the required properties as defined in the appended claims.

The number of red-orange emitting dyes to be used in combination with the at least one yellow-green emitting dye with at least some intrinsic emission below 510 nm can be any number, preferably from 1 to 5, more preferably 2.

The lumogens may be incorporated in common or separate layers. Different color points may be achieved by using different layer thicknesses and / or different luminescent dye concentrations in the layers. The dye concentration in the matrix material is preferentially below 5 wt%, more preferably below 0.1 wt%. Preferably, the total layer thickness is less than 3 mm, more preferably less than 500 micron. When a layered structure is used, the thickness of individual layers is preferably less than 1 mm, more preferably less than 100 micron.

Suitably, the red and orange emitting dyes are mixed in one layer, the green- yellow emitting dye in a separate layer and a third layer has diffuser function. The layers are stacked on top of each other, for example in a sequence (RO)YD (i.e. Red+Orange - Yellow- green - Diffuser), where the red-orange layer is closest to the blue light source (although the order of the layers may be varied).

Alternatively, all three lumogens are mixed in a single layer, with a diffuser layer on top. In another embodiment, all components (red, orange, green-yellow lumogens and light scattering particles for diffuser function) are incorporated in a single layer.

The relative amounts in weight of the lumogens in each of the suggested embodiments is in the range of 1 for yellow, 0 to 0.4 for orange and 0 to 0.3 for red

(depending on the target CCT). More preferably, relative to the yellow-green dye amount the orange dye amount is in the range of 0.1 to 0.3 and the red dye amount is in the range of 0.05 to 0.2.

The lumogens are suitably incorporated in layers of poly(methyl methacrylate) (PMMA). Other materials which may be used as matrix comprise polyethylene terephthalate (PET), copolymers of PET, polyethylene naphtalate (PEN), poly(methyl methacrylate) polystyrene, polycarbonate, silicone, polysiloxane, and acrylate polymers. When

incorporating several layers of phoshors/diffusers, the layers are to be arranged in optical contact with each other.

For the diffuser function inorganic particles such as aluminium oxide or titanium oxide particles or polymeric scattering particles can be brought into the layer.

As used herein, "dye", "phosphor" and "Lumogen" are used interchangeably to describe a luminescent material which converts light of a first wavelength to light of a second wavelength.

Suitable light sources to be used according to the present invention are e.g. a light emitting diode (LED), a lamp or a laser. Preferably, the light source to be used according to the present invention emits blue light, i.e. with the intensity maximum in the wavelength range 400 - 500 nm, preferably 420 - 480 nm, more preferably 440 - 460 nm.

A light emitting device comprising a phosphor combination according to the invention may be manufactured in the following way: The dye is mixed in the polymer and then a film is produced. This can be done by first producing a compound containing the dye and eventually the diffuser particles.

Subsequently it can be melt processed (extruded) to produce films of luminescent material in a polymer matrix. In an alternative method, the polymer and the dye can be dissolved in a suitable solvent and then applied on top of a substrate to produce luminescent coatings. Various configurations may be used to produce devices.

In figure 6 two schematic examples of a light emitting device comprising a light conversion layer in accordance with the invention are shown. Figure 6a shows the configuration where the LEDs are placed in a mixing chamber with highly reflecting surfaces, further called downlighter. The light converting unit is placed at the exit surface for producing white light. In figure 6b a configuration is shown where LEDs are placed at the bottom half of a cylinder covered with highly reflective diffusor. The other half of the cylinder is covered by the light converting layer from which light exits the device. Examples

Example 1: Layered system (Y)(0)(R)(D)

Three Lumogens were used:

F083,

Lumogen^® F Red 305 (BASF) (in the following referred to as F305), and

Lumogen F Orange 240 (BASF) (in the following referred to as

F240)

Four separate layers were used in a device schematically shown in figure 6a. The use of three different Lumogen emitters can lead to white light with a high efficiency and a high CRI. Using a red/orange ratio of 1 (weight) in PMMA, a CRI > 95 and an efficiency exceeding 190 Lm/Wopt for both 2700K and 3000K was obtained.

Example 2: Red and orange combined in a single layer [(RO)YD]

Lumogen F083 (yellow-green), Lumogen F240 (orange) and Lumogen F305 (Red) were used as phosphors in a configuration shown in Figure 6a. The red and orange Lumogen were mixed in a PMMA foil. This foil was used in combination with a foil containing the yellow-green lumogen and the stack was put on top of a diffuser film. Optical contact between the layers was assured. Different color points were made by using different thicknesses of the red/orange foil (RO) and the yellow foil (Y). In the foils the dye concentration was kept constant. These foils were applied on a standard diffuser (D). Figure 7 shows the efficiency and the CRI as a function of R/(R+0), i.e. the amount in weight of F305 relative to the sum of the amount in weight of F305 and F240 in the red/orange foil.

The performance of the downlighter (=6a) was measured in an integrating sphere. Conversion efficiency (CE) is defined as lumen out of the white downlighter (i.e. including light conversion layer) divided by the optical watts of blue light out of the same downlighter (fig 6a) (i.e. without light conversion layer and diffuser). For this system the efficiency at CCT =3000K at black body line (BBL) is estimated to be 187 Lm/Wopt, with a CRI of ~88 for R/(R+O)=0.6. Efficiency of the organic phosphor system is in that case comparable with an inorganic remote phosphor system.

Due to the use of three different Lumogens and one blue light source spectrum, there is more than one solution that can lead to the same white color point. More experiments were performed using different R/(R+0) ratios. Surprisingly, it was found that the same CRI can be obtained with different combinations of Lumogens, with significantly different efficiencies. For example, at 3000 K (Figure 7) a CRI of 85 is possible with an efficiency of only 180 Lm/W_opt for R/(R+O)=0.6 or 210 Lm/W„_pt for R/(R+O)=0.2. With increasing orange fraction (=decreasing red fraction) the CE increases. This is expected due to the increase in lumen equivalent of the spectrum, due to the replacement of red (low LE) with orange (high LE).

The spectra of different configurations (all interpolated to 3000 K at the BBL) are given in Fig. 8. Note that the spectral contribution of the three components is different from the weight ratio. The spectral ratio of red and orange from the different spectra as a function of the weight ratio is shown in Fig. 9. It can be seen that in the range for R/(R+0) 0.2 to 0.6 the spectral ratio changes only slightly. These spectral changes nevertheless have a significant influence on the efficiency and the CRI, as shown above.

Example 3: Red, orange and yellow combined in a single layer (ROY)D

In example 2, the orange and red lumogen were mixed in a single layer of PMMA and the yellow lumogen and diffuser were in separate layers (all in optical contact). In this embodiment we describe the experiments with the three lumogens in a single layer, with the diffuser on top using Lumogen F083 (yellow), Lumogen F240 (orange) and

Lumogen F305 (Red) as phosphors in the configuration shown in Figure 6b. Different color points were made by adjusting the concentration and thickness of the lumogen layer. The ratio R/(R+0) lumogen was at first instance fixed at 0.3 (derived from the (RO)YD system, example 2). The efficiency and CRI of the system was measured using a the configuration of Figure 6b in an integrating sphere.

The fact that the CRI decreased, red rendering decreased and the efficiency increased relative to the results in example 2 might indicate that the spectral contribution of yellow, orange and red changed. When studying the spectra for the different systems, it was found that due to the mixing of the different lumogens in one layer, the spectrum for the (ROY)D system with R/(O+R)=0.3 resembles more the spectrum with R/(O+R)=0.15 for the (RO)YD system, i.e. with a CRI below 80. In case of mixing the three lumogens into a single layer, the weight ratio of the red and orange lumogen needs to be adjusted in order to obtain the required CRI. It was found that for the (ROY)D system a weight ratio of R/(R+0) of 0.35 is close to optimal, i.e. leads to a CRI of 84 at CCT 3000K. Example 4: Red, orange, yellow and scattering particles combined in a single layer (ROYD)

Lumogen F083 (yellow), Lumogen F240 (orange) and Lumogen F305 (Red) were used as phosphors in configuration shown in Figure 6b. In this embodiment, all components (three lumogens and the scattering particles) were mixed into a single layer. The R/(0+R) by weight was fixed at 0.35 in order to obtain CRI=80 at 3000K with highest efficiency. At lower concentrations of R, CRI was below 80. The efficiency and CRI of the system was measured in an integrating sphere. Again the CRI was lower than for the (RO)YD system (at the same R/(0+R) weight ratio) and the CRI was lower. By adjustment of the R/(0+R) ratio the CRI and efficiency can be adjusted.

Example 5: Using (ROYD) , (R)(0)(Y)(D), (ROY)D, (RO)YD

Three Lumogens were used:

F170,

Lumogen^® F Red 305 (BASF) (in the following referred to as F305), and

Lumogen^® F Orange 240 (BASF) (in the following referred to as

F240)

It was possible to make a lamp using a blue LED light source with a

CCT=3000K. However, a CRI larger than 60 could not be obtained. The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Claims

CLAIMS:

1. Light conversion layer for obtaining light having a color rendering index (CRI) of at least 80, comprising:

at least one sub- layer, and

an organic phosphor combination comprising at least one yellow-green emitting dye showing an intrinsic emission below 510 nm and/or an emission below 530 nm after self-absorption.

2. Light conversion layer according to claim 1, wherein said yellow-green emitting dye shows an intrinsic emission within the range of 450 nm to 510 nm, or 470 to 510 nm.

3. Light conversion layer according to claim 1 or 2, wherein said yellow-green emitting dye has an intrinsic absorption peak within the range of 430 nm to 480 nm.

4. Light conversion layer according to any one of the claims 1-3, further comprising at least one red emitting dye and/or at least one orange emitting dye.

5. Light conversion layer according to claim 4, wherein said red emitting dye has an intrinsic emission within the range of 550 nm to 700 nm.

6. Light conversion layer according to claim 4 or 5, wherein said orange emitting dye has an intrinsic emission within the range of 510 nm to 650 nm.

7. Light conversion layer according to any one of the claims 4-6, wherein

the yellow-green emitting dye is phosphor Lumogen^® F Yellow 083 (BASF), BASF Thermoplast F 084 Green Gold (CAS Registry Number: 2744-50-5), or Solvent yellow 98 (CAS Registry Number: 12671-74-8);

the red emitting dye is phosphor Lumogen^® F Red 305 (BASF), Lumogen^® F Pink 285 (BASF), or Lumogen^® F Red 300 (BASF), and the orange emitting dye is phosphor Lumogen^® F Orange 240 (BASF), Lumogen^® F Yellow 170 (BASF), or a compound of the following formula (F2DPI):

8. Light conversion layer according to any one of the claims 4-7, wherein said yellow-green, red and orange emitting dyes are incorporated in a single sub-layer.

9. Light conversion layer according to any one of the claims 4-7, wherein said yellow-green, red and orange emitting dyes are incorporated in separate sub-layers.

10. Light conversion layer according to any one of the claims 4-7, wherein

said yellow-green emitting dye is incorporated in a first sub-layer and said red and orange emitting dyes are incorporated in a second sub- layer, or

said yellow-green emitting dye and said red emitting dye are incorporated in a first sublayer and said orange emitting dye is incorporated in a second sublayer, or

said yellow-green emitting dye and said orange emitting dye are incorporated in a first sublayer and said red emitting dye is incorporated in a second sublayer.

11. Light conversion layer according to any one of the claims 8-10, wherein the relative amounts in weight of the dyes are in the range of 1 for the yellow-green emitting dye, 0 to 0.4 for the orange emitting dye and 0 to 0.3 for the red emitting dye, preferably, 1 for the yellow-green emitting dye, 0.1 to 0.3 for the orange emitting dye and 0.05 to 0.2 for the red emitting dye.

12. Light conversion layer according to any one of the claims 8-11, further comprising scattering particles in at least one of said sub-layers or in a separate sub-layer.

13. Light conversion layer according to any one of the claims 8-12, wherein said sub-layers comprise poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET), copolymer of PET, polyethylene naphtalate (PEN), poly(methyl methacrylate) polystyrene, polycarbonate, silicone, polysiloxane, and/or acrylate polymers.

14. Light conversion layer according to any one of the claim 1-13, wherein said light conversion layer is arranged on a diffuser.

15. Light emitting device comprising a light conversion layer according to any one of the claims 1-14.

16. Light emitting device according to claim 15, comprising a light source emitting blue light in the wavelength range of 400 - 500 nm, preferably 420 - 480 nm, more preferably 440 - 460 nm.

17. Method for manufacturing a light emitting device according to claim 15 or 16, comprising:

providing a light source; and

arranging a light conversion layer according to any one of the claims 1-14 to receive at least a part of the light emitted from said light source.