WO2007093928A1

WO2007093928A1 - Color filter for display application

Info

Publication number: WO2007093928A1
Application number: PCT/IB2007/050348
Authority: WO
Inventors: Thomas JÜSTEL; Jörg Meyer; Walter Mayr
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N.V.
Priority date: 2006-02-13
Filing date: 2007-02-02
Publication date: 2007-08-23
Also published as: TW200736670A

Abstract

The present application relates to a colour filter for display applications. Furthermore, the application relates to a colour display as well as to a method to produce a colour filter for a display. The object to provide an improved colour filter for display applications, which allows an improvement of the colour gamut is solved by a colour filter comprising at least NdPO4 particles, Nd3+ doped ortho-phosphates, preferably Nd3+ doped (Lu1-x-y-zGdxYyScz)PO4 (x, y, z = 0.0 - 1.0) particles and/or Nd3+ doped glass.

Description

Colour filter for display application

The present application relates in general to colour filters for display applications. Further, the application relates to a colour display as well as to a method to produce a colour filter for a colour display.

Emissive displays, such as Cathode Ray Tubes (CRT), Liquid Crystal Displays (LCD) and Plasma Display Panels (PDP) use luminescent materials, called phosphors, which emit at least the primary colours to be displayed. The colour gamut is defined, in the absence of colour filters, solely by the colour points of the different phosphors. From CRTs the use of colour filters is known, already. But for LCDs and PDPs colour filters are not usual and as a consequence the colour gamut is improvable. A PDP consists of a about a million of gas discharge cells, which are arranged in rows and columns. Usually in the gas discharge cells a Ne/Xe -plasma emits light in the vacuum-ultraviolet range (VUV) from 140 to 190 nm. To convert the invisible VUV-light of the plasma different phosphors are used. For instance in a PDP the phosphor for the emission of blue light is usually BaMgAlioOπiEu (BAM). The colour point of this phosphor is similar to the phosphor ZnS:Ag used for CRTs and therefore does not need an improvement regarding colour point. However, stability of the phosphor BAM could be improved. To emit green light the phosphor (Y₅Gd)BO₃ITb is discussed as a very efficient and stable VUV-light absorbing phosphor emitting green light. However, the application of the aforementioned green phosphor is impeded by its colour point which is less greenish than that of the less stable phosphors Zn₂SiO₄IMn (ZSM) or BaAli₂Oi₉:Mn (BAL). The phosphor applied in the red pixels of PDPs is usually (Y,Gd)BO₃:Eu, which colour point is much less saturated than that of the red-emitting CRT phosphor Y₂O₂SiEu. Alternative phosphors with a better colour point are known, but these materials have a much lower VUV- efficiency and stability, which prevents their application in PDPs. An overview on Europium activated red-emitting phosphors, their main emission peak, and their respective colour point is given in table 1.

Table 1

As can be derived from the colour point x- value the phosphor Y₂O₂SiEu, which is used for CRTs, this phosphor has the highest x-value of 0.660 combined with the lowest y-value of 0.332 which allows a high colour saturation. As a result, the other phosphors, which are used in PDPs, do not allow colour saturation as high as known from CRTs.

The same applies to LCDs, which comprise an array of fluorescent lamps as primary light source. Most often Hg discharge lamps are used, which uses the following phosphors to emit the primary colours blue, green and red: BaMgAlioOπiEu or (Sr,Ca,Ba)₅(PO₄)₃Cl:Eu as blue emitter, (Ce₅Tb)MgAIi ^₁₉ or LaPO₄:Ce,Tb as green emitter, and Y₂O₃ :Eu as red emitter. Furthermore, LCD units usually contain colour filters to optimise the emission spectrum of the backlight lamps in terms of the enlargement of the colour gamut. However, the colour filters as applied in LCDs are improvable on the one hand with respect to undesired absorption of radiation, on the other hand, however, with respect to desired absorption of undesired radiation. An enlargement of the colour gamut is further achievable by Xe excimer discharge lamps, since the Xe medium-pressure discharge does not emit visible radiation, which has a negative impact on the colour saturation of the green and red primary. However, the colour gamut of an LCD using a Xe excimer discharge lamp as a backlight will also strongly depend on the combination of the set of phosphors and the set of colour filters.

Colour filters to enhance colour saturation consisting of a layer containing at least neodymium on a transparent substrate are known from the Japanese patent application JP 2000347024 A. In the former Japanese patent application it is proposed to select the source material to introduce neodymium into a neodymium layer from neodymium, neodymium oxide, neodymium chloride, neodymium fluoride, neodymium carbonate, neodymium nitrate, neodymium salts of saturated or unsaturated carboxylic acids and neodymium salts of aromatic acids. However, the transmission spectra of the so far used neodymium oxide containing colour filters is in particular with respect to the emission spectra of the above mentioned phosphors not optimal.

Therefore, it is one object of the invention to provide an improved colour filter for display applications, which results in an improvement of the colour gamut. Yet, it is another object of the invention to provide an accordant colour display, and a method to produce the inventive colour filter. Furthermore, it is an object to provide an advantageous use of the inventive colour filter. In order to solve the above-mentioned objects a colour filter for display applications is provided comprising at least NdPO₄ particles, preferably NdPO₄ nano- particles in a matrix and/or Nd³⁺ doped ortho-phosphate particles, preferably Nd³⁺ doped(Lui__x_y__zGd_xYySc_z)PO₄ (x, y, z = 0.0 - 1.0) particles. The NdPO₄ containing colour filters are able to improve the colour saturation of Eu or Tb doped phosphors. Compared to colour filters comprising neodymium oxides (Nd₂O₃)Ae set of emission lines of these Eu or Tb doped phosphors, which are responsible for a reduction of the colour saturation, are absorbed more effectively by absorption bands of the inventive NdPO₄ particles or Nd³⁺ doped ortho-phosphate particles. For example the interfering emission line of a typical phosphor of a Hg discharge lamp at a wavelength of 570 nm is suppressed very well by a deep absorption band. On the other hand, high transmission values are provided for the green light emission line at 550 nm. Furthermore, at a wavelength of about 430 nm less absorption is provided with the inventive particles. Additionally, NdPO₄ and Nd³⁺ doped ortho-phosphates combine the deep absorption bands with high band gaps of the ortho-phosphates, so that undesired absorption of radiation does not occur. As a result the inventive colour filter permits a higher colour saturation with respect to the primary colours, such as blue, green and red at the same time providing a higher transmission as known from standard colour filters. Due to a higher lattice energy it is expected that the proposed NdPO₄ and Nd³⁺ doped ortho-phosphate particles have a higher stability like for instance neodymium oxide particles. This applies particularly to the NdPO₄ nano-particles in a matrix, too, whereby as matrix a binder, for instance nitrocellulose, can be utilised. However, even other binders can be used to provide a binder for NdPO₄ nano-particles. To provide a good compromise between filtering and absorption with the inventive colour the Nd³⁺ doped ortho-phosphate particles preferably contain 10 to 20 mol-% Nd³⁺. Furthermore, with such a concentration the thickness of a colour filter layers comprising the above mentioned particles can be held at an applicable level. The inventive colour filter can preferably be integrated in an emissive colour display, preferably in a Plasma Display Panel (PDP) or in a Liquid Crystal Display (LCD). As outlined above, the inventive colour filter enhances the colour saturation of the primary colours and thereby leads to an enlargement of the colour gamut of emissive displays. Furthermore, the colour filter may be integrated in a PDP or in a discharge lamp of a LCD by a blend consisting of NdPO₄ particles, preferably NdPO₄ nano-particles in a matrix and/or Nd³⁺ doped ortho-phosphate particles, preferably Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ particles and phosphors as used in a PDP or in discharge lamps to emit visible light. Due to the distribution of the particles of the inventive colour filter in the phosphor blend of the discharge lamp of the LCD or in a PDP the light emitted from these phosphors is directly filtered, whereby a sufficiently high filter efficiency is achieved.

Another way to integrate the inventive colour filter in a discharge lamp of a LCD is achieved by coating NdPO₄ particles, preferably NdPO₄ nano-particles and/or Nd³⁺ doped ortho -phosphate particles, preferably Nd³⁺ doped

(Lui__x_y__zGd_xYySc_z)PO₄ (x, y, z = 0.0 - 1.0) particles on the discharge lamp or on the phosphors of the discharge lamp. Due to the simple integration of the inventive colour filter in a discharge lamp of a LCD the costs to integrate the colour filer can be reduced. Furthermore, since the filtering level depends on the optical path, contrary to the use of a colour filters in a front glass of a display there is no viewing angle dependency of the colour filtering level. Hence, an improved colour gamut for a viewer of the display is provided independent from the viewing angle. At least, due to the small area of a discharge lamp to be coated less colour filtering material is necessary to achieve a sufficient filtering effect. The colour filter can be integrated in the light guide by a light guide coated or doped with NdPO₄ particles, preferably NdPO₄ nano-particles in a matrix and/or Nd³⁺ doped ortho-phosphates particles, preferably Nd³⁺ doped (Lui__x__y_ _zGd_x YySCz)PO₄ (x, y, z = 0.0 - 1.0) particles or a layer of such particles. The light guide is used in LCD displays to distribute the light emitted by the discharge lamp uniformly to the display surface. Since the light guide does not contain electrical components as for example a discharge lamp, the costs to produce the inventive colour filter can be further reduced.

At least, preferably the colour filter is integrated in the dielectric layer and/or MgO-layer of a PDP to provide a colour filter without changing the interior of the discharge cells.

According to another aspect of the invention the above-mentioned object is solved by a colour display, preferably a PDP or a LCD, comprising at least one inventive colour filter. As already described, such displays allow higher colour saturation due to the inventive colour filter.

Preferably the displays comprises at least one Hg low-pressure discharge lamp with a phosphor blend with at least one phosphor selected from BaMgAlioOπiEu or (Sr,Ca,Ba)₅(PO₄)₃Cl:Eu for the emission of blue light, Zn₂Si0₄:Mn or LaPO₄:Ce,Tb for the emission of green light, and (Y,Gd)₂O₃:Eu, (Y,Gd)NbO₄:Eu, YVO₄:Eu and/or Y(V,P)O₄:Eu or (Ce₅Gd)MgBsOi_OiMn for the emission of red light. On the one hand, these phosphors are already in commercial use and their use has been already intensively examined and understood. On the other hand, those emission lines of said phosphors responsible for reduction of the colour saturation of the display are absorbed with the inventive colour filter effectively. Hence, for instance, standard LCD displays comprising such Hg low-pressure discharge lamps can be improved in their colour reproduction.

The same applies to displays preferably comprising at least one Xe medium-pressure discharge lamp with a phosphor blend with at least one phosphor selected from BaMgAlioOπiEu for the emission of blue light, Zn₂Si0₄:Mn and/or (Y,Gd)BO₃:Tb for the emission of green light, and (Y,Gd)₂O₃:Eu, (Y,Gd)NbO₄:Eu and/or (Y,Gd)(V,P)O₄:Eu for the emission of red light.

According to another aspect of the present invention a method to produce a colour filter according to the invention for a display, preferably for a LCD, is provided, comprising the following steps: a) preparing a first suspension by suspending NdPO₄ and/or Nd³⁺ doped ortho-phosphate, preferably Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)Pθ₄ (x, y, z = 0.0 - 1.0)in water in which polyethylenoxide and polyacrylic acid are dissolved, b) coating of the inner side of a glass tube with the first suspension, c) removing organic contaminants by annealing, d) preparing a second suspension by suspending a phosphor blend of BaMgAIi₀Oi₇, LaPO₄:Ce,Tb and Y₂O₃:Eu in butylacetate, e) coating of the coated inner side of the glass tube with the second suspension, f) removing organic contaminants by annealing, g) fusing electrodes at both ends of the glass tubes, h) exhausting the tube, i) filling the tube with Ar and 0,1 to 20 mg Hg and j) sealing the tube to obtain a discharge lamp. With the inventive method a colour filter can easily be integrated in a discharge lamp. The discharge lamp than emits light allowing higher colour saturation of a LCD. With the inventive method the colour filter can be easily provided as an integrated part of the discharge lamp. No additional measures have to be taken to integrate the colour filter to a LCD display. Preferably the second suspension contains a phosphor blend consisting of approximately 24 weight-% BaMgAIi₀Oi₇, 50 weight-% LaPO₄:Ce,Tb and 26 weight-% Y₂O₃:Eu so that the discharge lamp emits white light allowing a high colour saturation.

If the second suspension is prepared by suspending a phosphor blend of BaMgAIi₀Oi₇, (Y,Gd)BO₃:Tb, and (Y,Gd)VO₄:Eu in butylacetate and the tube is filled with 200 - 300 mbar Xe after exhausting, a Xe discharge lamp with an approved colour saturation can be provided.

A Xe discharge lamp emitting white light permitting an optimised colour saturation can be provided by using a second suspension which contains a phosphor blend consisting of approximately 20 weight-% BaMgAIi₀Oi₇, 50 weight-% (Y,Gd)BO₃:Tb, and 30 weight-% (Y,Gd)VO₄:Eu.

Finally, according to another aspect of the invention the above- mentioned object is solved by the use of a colour filter comprising at least NdPO₄ and/or Nd³⁺ doped ortho-phosphates, preferably Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ (x, y, z = 0.0 - 1.0)and/or Nd³⁺ doped glass for display applications. As outlined above the use of the inventive colour filter allows the production of a higher colour saturation even if standard phosphors and Hg low-pressure discharge lamps are used.

These and other aspects of the application will be described in more detail exemplarily within the following figures.

The figures depict

Fig. 1 the emission spectrum of a low-pressure discharge lamp and the corresponding transmission spectra of standard LCD colour filters known from the prior art, Fig. 2 the emission spectrum of a Xe excimer discharge lamp and the corresponding transmission spectra of standard LCD colour filters known from the prior art, Fig. 3 the reflection spectrum of NdPO₄,

Fig. 4 the emission spectrum of a Hg low-pressure discharge lamp and the transmission spectrum of the NdPO₄ particle layer, Fig. 5 the emission spectrum of a Xe medium-pressure discharge lamp and the transmission spectrum of a NdPO₄ particle layer, Fig. 6 a schematic sectional view of a tube of a discharge lamp with a colour filter according to an embodiment of the present invention and Fig. 7 a schematic perspective expansion view of a PDP with a colour filter according of one embodiment of the invention.

In Fig. 1 and 2 the emission spectra of a tubular Hg low-pressure discharge lamp and of a Xe excimer discharge lamp are shown. The emission spectrum El of the Hg low-pressure discharge lamp from Fig. 1 shows, due to the use of standard phosphors, three distinct maxima at approximately 440 nm, 544 nm and 620 nm according to the use of different phosphors for each colour. The according colour filters and their transmission spectra b, g, r matches nearly with their maximum transmission values to the emission maxima of the respective phosphor. However, as can be derived from the transmission spectra of the different LCD colour filters b, g, r the emission peak el of the emission spectrum of the Hg low-pressure discharge lamp is not suppressed effectively, since the absorption of the colour filters in this spectral range is not high enough. The peak lead to a reduction of the colour saturation of the LCD, since it contributes to higher y- value of the colour point value of the emitted red light and to higher x- value for the colour point value of the emitted green light. This applies to the spectrum of the Xe excimer discharge lamp, too. The peak e2 is not effectively suppressed by the standard, for example Nd₂O₃ containing, LCD colour filters. As a result the colour saturation is improvable.

In Fig. 3 the reflection of NdPO₄ particles versus the wavelength is shown. The reflection spectrum of NdPO₄ is characterised by a quite high reflection in the area of blue coloured light from 400 nm to 500 nm with a precipitous lowering to a minimum around 520 nm, followed by a strong increase of the reflectivity around 550 nm in the regime of green light. The regime of the green light which has high values of the reflection from 530 nm to 560 nm is followed by a steep reduction of the reflection around 580 nm. The steep rise of the reflection from 580 nm to 610 nm provides high reflection values in the regime of red light. The steep reduction between the wavelength regime of the blue light and green light respectively between the green light wavelength range to the red colour light wavelength range are caused by Nd³⁺ absorption bands. Obviously, these absorption bands determine the transmission spectrum, too.

Fig. 4 shows the transmission spectrum of a NdPO₄ particle layer together with the emission spectrum of a Hg low-pressure discharge lamp comprising the following phosphors: BaMgAlioOπiEu for the emission of blue light, LaPO₄:Ce,Tb for the emission of green light, and Y₂O₃IEu for the emission of red light. The respective emission peaks bl, gl, rl are clearly given in the emission spectrum El of Fig. 4. The transmission spectrum of the NdPO₄ particle layer Tl shows maxima in transmission, which correspond to the position of the peaks of the emission spectrum El. Furthermore, due to the steep lowering of the transmission at 530 nm and 580 nm, the colour saturation of the emission spectra is improved, since in particular the emission peak around 595 nm pi is suppressed effectively, which otherwise would lead to a reduction of the colour saturation. This transmission spectra can be achieved even when NdPO₄ nano-particles in a matrix and/or Nd³⁺ doped ortho-phosphate particles, preferably Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ (x, y, z = 0.0 - 1.0) particles are utilised for the colour filter.

The emission spectrum of a Xe discharge lamp comprising as luminescent material a blend of the phosphors BaMgAlioOπiEu for the emission of blue light, (Y,Gd)BO₃:Tb for the emission of green light, and (Y,Gd)VO₄:Eu for the emission of red light is plotted in Fig. 5. Like in Fig. 4, in Fig. 5 the peaks would provide the primary colour to achieve white light, b2, g2, r2 are distinctively shown in the emission spectrum E2 of the different phosphors of the Xe discharge lamps. The inventive colour filter provides a transmission spectrum Tl, which has low transmission values in the range of the emission peak p2, which is responsible for the colour saturation reduction of the red and green colour, when using a standard colour filter. As a consequence using the inventive filter together with a Hg or Xe discharge lamp with suitable luminescent materials leads to an improved saturation of primary colours. Further phosphors, with their peak emission position, quantum efficiency and their colour point values are shown in table 2 and table 3. Table 2 shows different phosphors for Hg low-pressure discharge lamps, which can be used advantageously together with the inventive colour filter. To the contrary table 3 shows phosphors, which are preferably used together with Xe discharge lamps.

Table 2

Table 3 Since the colour point values x and y relate to the primary colours red and green, it is possible to define said values for all primary colours by the equation x + y + z = 1.

Hence, phosphors with a lowest sum of the x and y colour values are most suitable for emitting blue colour light with a high colour saturation. For high colour saturation the y- value of the green-emitting and the x- value of the red-emitting primary have to be maximised.

A schematic sectional view of a discharge lamp 1 of a LCD display is given in Fig. 6. The inventive colour filter is integrated by a coating 3, which is applied to the tube 2 of the discharge lamp. However, to generate white light from the gas discharge in the tube volume 4 a second coating 5 is applied to the inner walls of the tube 2. This inner coating comprises a layer of phosphors, which emit all three primary colours if excited, for instance by the 254 nm line of a Hg gas discharge. Alternatively, the luminescent material is chosen to be optimally adapted to the application of a Xe gas discharge, which emits in the VUV-range from 140 nm to 190 nm having the peak intensity at 172 nm. The coating 3 of the tube 2 with NdPO₄ particles, preferably NdPO₄ nano-particles in a matrix and/or Nd³⁺ doped ortho-phosphate particles, preferably Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ (x, y, z = 0.0 - 1.0) particles can be achieved by suspending the particles into water in which polyethylenoxide and polyacrylic acid is dissolved as matrix. As shown in Fig. 6 the inner side of the tube 2, which can have a diameter between 3 mm to 5 mm, is coated with this suspension.

Subsequently, the binder and any other organic contaminants are removed by annealing the tube at preferably 580 ⁰C for several minutes. However, different temperatures and different times can be used to achieve the removal of the contaminants depending on the different organic materials used. The phosphor layer 5 can be prepared by a phosphor blend of 24 weight-% BaMgAlioOπiEu for the emission of blue colour light, 50 weight-% LaPO₄:Ce,Tb for the emission of green light and 26 weight-% Y₂O₃IEu suspended in butylacetate to which nitrocellulose as a binder an adhesive, for example alon-c, to improve adhesion is added. The inner side of the tube 2, which has already been coated is coated again with the suspension described above. After removal of any other organic contaminants by a suitable annealing step the glass tube 2 the electrodes 6 can be fused to the tube. After fusing the tube is exhausted and filled with preferably Ar and 1 mg to 20 mg Hg. In the same way it is possible to integrate the inventive colour filter to a Xe medium-pressure discharge lamp. Fig. 7 shows a PDP in a schematic perspective expansion view as an embodiment of the invention with a first dielectric layer 8, a protective MgO-layer 9, webs 10 and a second dielectric layer 11. In the present embodiment of an inventive PDP the webs 10 separate different stripes comprising different phosphors for emitting the primary colours, excited by a local plasma, which is sparked by a local electrical field, constituting the single colour pixels of the PDP. The inventive colour filter is integrated in the MgO-layer and/or the first dielectric layer preferably by an inventive particles layer so that these layers have the additional function of a colour filter. Furthermore, the stripes separated by the webs 10 which contain the different phosphors may be coated with NdPO₄ particles, NdPO₄ nano-particles in a matrix, Nd³⁺ doped ortho-phosphates, preferably with Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ (x, y, z = 0.0 - 1.0) with an amount of doped Nd³⁺ of 10 to 20 mol-%. However, as phosphors 12 of the stripes a blend of NdPO₄ particles, preferably NdPO₄ nano-particles in a matrix and/or Nd³⁺ doped ortho-phosphate, preferably Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ (x, y, z = 0.0 - 1.0) particles with the phosphors emitting the primary colours can be applied to improve the colour saturation of such a PDP.

Why there have been shown and described and pointed out fundamental novel features of the invention as applied to several preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices and methods described may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps, which performs substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognised that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the invention, therefore, to be limited only as indicated by the scope of the claims appended hereto. It should also be recognised that any reference signs shall not be construed as limiting the scope of the claims.

Claims

CLAIMS:

1. Colour filter for display applications comprising at least NdPO₄ particles, preferably NdPO₄ nano-particles in a matrix, Nd³⁺ doped ortho-phosphate particles, preferably Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ (x, y, z = 0.0 - 1.0) particles.

2. Colour filter according to claim 1, characterised in that, the Nd³⁺ doped ortho-phosphate particles preferably contain 10 to 20 mol-% Nd³⁺.

3. Colour filter according to claim 1 or 2, characterised in that, the colour filter is integrated in a emissive colour display, preferably in a plasma display panel(PDP) or in a liquid crystal display (LCD).

4. Colour filter according to claims 1 to 3, characterised in that, the colour filter is integrated in a PDP or in a discharge lamp of a LCD by a blend consisting of NdPO₄ particles and/or Nd³⁺ doped ortho-phosphates particles, preferably Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ (x, y, z = 0.0 - 1.0) particles and phosphors used in a PDP or in discharge lamps to emit visible light.

5. Colour filter according to claims 1 to 4, characterised in that, the colour filter is integrated in a discharge lamp of a LCD by coating NdPO₄ particles, preferably NdPO₄ nano-particles in a matrix and/or Nd³⁺ doped ortho-phosphate particles, preferably Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ (x, y, z = 0.0 - 1.0) particles on the discharge lamp or on the phosphors of the discharge lamp.

6. Colour filter according to claims 1 to 5, characterised in that, the colour filter is integrated in the light guide by a light guide coated or doped with NdPO₄ particles, preferably NdPO₄ nano-particles in a matrix and/or Nd³⁺ doped ortho- phosphate particles, preferably Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ (x, y, z = 0.0 - 1.0) particles or a layer of such particles.

7. Colour filter according to claims 1 to 3, characterised in that, the colour filter is integrated in the dielectric layer and/or MgO-layer of a PDP.

8. Colour display, preferably a PDP or LCD, comprising at least one colour filter according to claim 1 to 7.

9. Colour display according to claim 8, characterised in that, the display comprises at least one Hg low-pressure discharge lamp with a phosphor blend with at least one phosphor selected from BaMgAlioOπiEu and/or

(Sr,Ca,Ba)₅(PO₄)₃Cl:Eu for emission of blue light, Zn₂Si0₄:Mn and/or LaPO₄:Ce,Tb for emission of green light and (Y,Gd)₂O₃:Eu, (Y,Gd)NbO₄:Eu, YVO₄:Eu, Y(V,P)O₄:Eu and/or (Ce,Gd)MgBsOio:Mn for emission of red light.

10. Colour display according to claim 8, characterised in that, the display comprises at least one Xe medium-pressure discharge lamp with a phosphor blend with at least one phosphor selected from BaMgAlioOπiEu for emission of blue light, Zn₂Si0₄:Mn and/or (Y,Gd)BO₃:Tb for emission of green light and (Y,Gd)₂O₃:Eu, (Y,Gd)NbO₄:Eu and/or (Y,Gd)(V,P)O₄:Eu for emission of red light.

11. Method to produce a colour filter according to claim 1 to 7 for a display, preferably for a LCD, comprising the following steps:

a) preparing a first suspension by suspending NdPO₄ and/or Nd³⁺ doped ortho-phosphates, preferably Nd³⁺ doped Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ (x, y, z = 0.0 - 1.0) in water in which polyethylenoxide and polyacrylic acid are dissolved,

b) coating of the inner side of a glass tube with the first suspension,

c) removing organic contaminants by annealing,

d) preparing a second suspension by suspending a phosphor blend of BaMgAIi₀Oi₇, LaPO₄:Ce,Tb and Y₂O₃:Eu in butylacetate,

e) coating of the coated inner side of the glass tube with the second suspension,

f) removing organic contaminants by annealing,

g) fusing electrodes at both ends of the glass tubes,

h) exhausting the tube,

i) filling the tube with Ar and 0,1 to 20 mg Hg and

j) sealing the tube to obtain a discharge lamp

12. Method according to claim 10, whereby the second suspension contains a phosphor blend consisting of approximately 24 weight-% BaMgAIi₀Oi₇, 50 weight-% LaPO₄:Ce,Tb and 26 weight-% Y₂O₃:Eu.

13. Method according to claim 10, whereby the second suspension is prepared by suspending a phosphor blend of BaMgAIi₀Oi₇, (Y,Gd)BO₃:Tb and (Y,Gd)VO₄:Eu in butylacetate and the tube is filled with 200 - 300 mbar Xe after exhausting.

14. Method according to claim 11, whereby the second suspension contains a phosphor blend consisting of approximately 20 weight-% BaMgAIi₀Oi₇, 50 weight-% (Y,Gd)BO₃:Tb and 30 weight-% (Y,Gd)VO₄:Eu.

15. Use of a colour filter comprising at least NdPO₄, Nd³⁺ doped ortho-phosphates, preferably Nd³⁺ doped (Lui__x__y__zGd_xY_ySc_z)PO₄ (x, y, z = 0.0 - 1.0) and/or Nd³⁺ doped glass for display applications.