NZ204031A - Colour crt,traid phosphor dots with colour notch filters - Google Patents

Description

2 0403 1 ORIGINAL Priority Date(s): \3Q.v4-.

Complete Specification Filed: Class: HQM3.1 ,}&Q Publication Date: .. [1 1. APR .1986 ! P.O. Journal, *!c: . . ;NEW ZEALAND ;THE PATENTS ACT, 1953 ;COMPLETE SPECIFICATION ;"AN IMPROVED DISPLAY SCREEN' ;?MS/y^ ;< ;- * & $ u I I & m WE, INTERNATIONAL STANDARD ELECTRIC CORPORATION , a Corporation of the State of Delaware, United States of America, of 320 Park Avenue, New York 22, New York, United States of America, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement $ JX' ( 2 040 3 1 The invention relates to a colour picture tube such as those comprising a fluorescent screen on the inside of the faceplate panel, consisting of a pattern of phosphor dots arranged in groups of three backed by a layer of aluminium, in which each dot trio comprises phosphor dots which, when excited by electron beams, produce red, green or blue light respectively.

Brightness and contrast determine the picture clarity. If, by using effective phosphors and a suitable technology for the screen assembly, the requirements for a sufficient brightness are met, then also all conditions for a good contrast are fulfilled. During operation of the colour picture tube, however, the contrast may be affected by extraneous light. Any kind of room lighting or work station lighting brightens the screen on its entire surface. As the intensity of this extraneous light increases, first of all the dark picture contents are lightened up, thus causing the colours of the picture to be weakened and, consequently, the colour range to be narrowed. Finally, the picture as written by the electron beams, is subjected to a glare or a light spillage, that is, the extraneous light chiefly brings out the body colour of the screen. The useful light of the phosphors contained in the fluorescent screen becomes subject to the superimposition effect.

There are several ways of avoiding this: The glass of 2 040 3 1 the faceplate panel of the colour picture tube is dyed or pigmented. In that case, a so-called neutral density grey glas filter is positioned in front of the screen. This almost uniformly absorbs the visible light throughout the wavelength range thereof. Useful light and extraneous light are equally weakened, but the extraneous light is weakened to double the extent or even to several times the extent at a suitable angle of incidence, because it passes twice through the glass of the faceplate panel or, in the case of a lateral incidence, even several times owing to reflections within the faceplate panel. Accordingly, when employing the faceplate panel as a neutral density grey glass filter there is obtained a more favourable ratio of the extraneous light blocking to the useful light blocking.

Moreover, the phosphors may be embedded in a layer which, by way of pigmenting, has been given the colour of the respective phosphor. The body colour, for example, of the red phosphor dots will then be red. The extraneous light and a stray or scattered radiation existing upon agitation of phosphors in the layer, will then illuminate the red pigmented layer. The other colour components of the extraneous light are extensively absorbed.

By coating the areas between the phosphor dots with a so-called black matrix it is still possible to make a more extensive use of the possibility of absorption. The black 2 040 3 1 matrix layer almost completely absorbs the entire visible spectrum, so that the areas between the phosphor dots do not contribute towards lightening up the fluorescent screen in the event of an extraneous light incidence.

Moreover, it is possible to deposit coatings on both sides of the faceplate panel blocking the extraneous light as reflected by the screen, just like the neutral density grey glass filter, at least twice, while blocking the useful light only onece. Such layers can also be designed to have a selective absorption.

This specification describes the use of an improvement over the comb filter which has an attenuation minimum at the wavelengths of all three phosphors. By doping the glass of the faceplate panel, however, this is not yet possible to the desired extent. Coatings of the faceplate panel acting as an interference filter, having the desired property, are very expensive and, therefore, likewise cannot be considered for practical use.

It is desirable to provide a simple comtrast-improving arrangement which is capable of being realized with the aid of conventional light filters.

There is described a colour method of providing extraneous light filtering on a fluorescent screen which serene comprises a plurality of phosphorescent areas excitable by an electron beam or other suitable e.m. radiation 2 0403 wherein the phosphorescent areas are coated with or have entrained therein one or more light filtering materials which act as a notch filter allowing only light of the wavelengths of the associated phosphorescent areas to pass 5 substantially unattenuated.

An embodiment of the invention will now be explained with reference to Figs. 1 to 3 of the accompanying drawings in which: Fig. 1 in a topview, shows part of the fluorescent 10 screen on a greatly enlarged scale, Fig. 2 shows a section taken on line A-B of Fig. 1 through the fluorescent screen, and enlargements of partial areas of this section relating to different types of embodiment of the invention, and 15 Fig. 3 shows a diagram in which, over the wavelength there are plotted the curves of the emission E of a phosphor and of the absorption A of light-filtering materials.

On the inside of the faceplate panel 1 (Fig. 1) there are provided in circular recesses 2 of the black matrix 3, 20 the respective phosphor dots 4 for the colours red (rt) green (gn) or blue (bl), and between these phosphor dots (Fig. 2) and the faceplate panel 1 there is arranged the layer 5 containing the light-filtering material. Such a structure is shown in the left-hand portion of the sectional 25 view in Fig. 2 taken on line A-B of Fig. 1. Next to this on 2 040 3 1 the right, likewise in a section taken on line A-B, there is shown a further embodiment in which the light-filtering material is already contained in the layer 6 forming the phosphor dot.

In the centre right-hand portion of the sectional view of Fig. 2 taken on line A-B of Fig. 1, a further embodiment is shown in which the layer 5 containing the light-filtering material, is arranged between the phosphor dot 4 and the aluminium layer 7.

Next to this, in the right-hand portion of the section A-B of Fig. 2, there is shown another advantageous embodiment. The light filtering-material is contained in the coverings 8 of the phosphor particles 9. Accordingly, the layer 10, just like the layer 6, likewise contains the phosphor as well as the light-filter material and is arranged between the faceplate panel and the layer of aluminium.

Further (not shown) examples of embodiment consisting of combinations of the examples explained hereinbefore, can be used for solving the problem underlying the invention. It is of advantage for the phosphor dot to contain a light-filtering material of a first kind (corresponding to layer 6), with a second kind of light-filtering material being contained in the coverings 8 of the phosphor particles 9, as is the case with layer 10. Both kinds of light-filtering 2 0403 material do not block the light of the colour of the respective phosphor dot, but absorb the remaining light spectrum in a way supplementing each other.

Relative thereto, it is shown in Fig. 3 how an optical bandpass filter is obtained by the cooperation between a first kind of light-filtering material with a high-pass filter behaviour, and a second kind of light-filtering material having a low-pass filter behaviour. Over the wavelength of the light there is plotted the characteristic of the emission E of the respective phosphor. Light having a wavelength lying below the emission wavelength is absorbed by a first light-filtering material according to the absorption characteristic Al, and above it, a second light-filtering material absorbs the light in accordance with the absorption characteristic A2.

Thus, the colour gamut is extended by the introduction of filters strongly attenuating the entire light spectrum of the ambient lighting, except the light spectrum of the emission range of the respective phosphor. A filter with an appropriate absorption characteristic is assigned to each of the three phosphors, because filters with pass ranges for all three phosphor emission ranges (multipass, comb filter) which would be capable of covering the entire screen, are extremely expensive.

The filters arranged or designed in accordance with the 2 0403 1 invention are manufactured either by adding the light-filtering material to the film-forming slurry during the screening processes or else by adding the light-filtering material to the coverings of the phosphor particles prior 5 to the preparation of the slurry. In the course of this, also several light-filtering materials with a spectrally supplementing absorption may be added to the film-forming slurry as well as to the coverings of the phosphor particles. For the colour red it is suitable to use compounds contain-10 ing either neodymium or erbium, while for the colour green it is advisable to use praseodymium or compounds containing chromium, and for the colour blue it would be suitable to use the metallic element cobalt. It is favourable to use these in connection with a silicate, borate or phosphate 15 basis, because such a basis at the same time improves the processibility (workability; "'of the phosphor particles.

As phosphors (fluorescent materials) there are preferably used substances possibly having a linear emission spectrum, for which light-filtering materials with well-20 matched absorption spectra are available.

The advantages of the invention have favourable effects especially upon fluorescent screens without a black matrix, because with respect to the extraneous light, the then comparatively larger phosphor layer itself will act as a 25 black matrix. If red, green or blue portions are contained 2 0403 1 in the extraneous light, lying within the red, green or blue pass range of the light-filtering materials, only these portions of the extraneous light are not absorbed. Accordingly, any unwanted brightness on the screen is only still produced in so far as the portions of the extraneous light spectrum coinciding with the colour spectrum of the phosphors are reflected by the body colours of the respective phosphor dots.

The employment of different filters for each of the colours is advisable also with a view to the colour or white purity. The white purity is usually adjusted chiefly by adapting the electron beam intensity to the luminosity of the phosphors (luminous materials). The intensity and spectral balance of the three phosphors can be taken into consideration when selecting suitable light-filtering materials to help achieve the white parity.

Claims (6)

201031 What we claim is:-

1. A colour picture tube including a fluorescent screen on the Inside of the faceplate panel, consisting of a pattern of phosphor dots arranged in groups of three backed by a layer of aluminium, in which in each group of three dots the respective dots, when excited by electron beams, produces red, green or blue light respectively wherein each phosphor dot is associated with several light-filtering materials supplementing each other in their absorption spectrum which only permit the passage of the light, or the colour of the associated phosphor dot and absorbs the light of other colours,and wherein the light-filtering materials arc contained in the layers forming the phosphor dots.

2. A colour picture tube as claimed in claim 1, wherein the light-filtering materials envelop the phosphor particles.

3. A method of providing extraneous light filtering on a fluorescent screen which screen comprises a plurality of phosphorescent areas excitable by an electron beam or other suitable e.m. radiation wherein the phosphorescent areas have entrained therein several light filtering materials which act as a notch filter allowing only light of the wavelengths of the associated phosphorescent areas to pass substantially unattenuated.

A colour picture tube comprising a fluorescent screen which screen comprises a plurality of phosphorescent areas excitable by an electron beam or other suitable e.m. radiation wherein the phosphorescent areas have entrained therein several light filtering materials which act as a notch filter allowing 201031 only light of the wavelengths of the associated phosphorescent areas to pass substantially unattenuated.

5. A colour picture tube as claimed in claim 1 or 2 or claim , wherein the phosphor dots are red, blue and green and wherein the red dots are doped with compounds containing neodymium or erbium, the blue with cobalt and the green with praseodymium or chromium compounds.

6. A colour picture tube as claimed in claim 4, wherein silicates., borates or phosphates of the doping filter elements are used. INTERNATIONAL STANDARD ELECTRIC CORPORATION P.M. Conrick Authorized Agent P'J/l/l^B