GB2174536A - Colour display tubes - Google Patents

Abstract

A colour display tube has means for producing an electron beam directed at a penetron-type cathodoluminescent screen comprising a patterned array of at least first and second phosphor materials (25, 26) emitting differently coloured light and disposed beside one another for example in the form of repetitive groups of stripes or as a matrix of discrete elements of one material surrounded by the other. The beam facing surface of the first phosphor material (25) is covered by a barrier layer (28) penetrable by high energy electrons such that emission from the two phosphor materials respectively occurs at different electron energy levels. The barrier layer (28) may be co-extensive with the first phosphor material or extend continuously over that material and beneath the second phosphor material. A continuous electrode layer (29) may extend over the second phosphor material (26) and either also the barrier layer regions on the first phosphor material (25) or intermediate that layer and the first phosphor material. Three colour screens are also described. An electron multiplier may be disposed between the beam producing means and the screen. <IMAGE>

Description

SPECIFICATION Colour display tubes This invention relates to a colour display tube comprising means for producing an electron beam, and a cathodoluminescent screen for excitation by the electron beam for producing a colour display, the cathodoluminescent screen being a penetron type comprising first and second phosphor materials for producing respectively different colours in response to different electron beam energies.

The term penetron type screen is used herein to denote a screen which emits light of different colours depending on the energy of incident elec trons.

Penetron type colour display tubes employing penetron phosphors which change the colour of their emission in dependence upon the input elec tron energy have been used for datagraphic applications such as air traffic control displays and compu ter graphic displays. Such display tubes allow con siderably more information to be displayed at any one time than a monochrome display and have advantages over conventional shadow-mask colour display tubes in that they avoid the use of a shadow-mask and require only a single electron gun.

Shadow-mask displays can be sensitive to mic rophonics, have poor resolution and require that dynamic convergence of the plurality of electron beams needed is maintained.

Heretofore, two kinds of penetron-type screens in particular have commonly been used.

In the first kind, a multi-layer screen is prepared having two or more layers of phosphor extending continuously over a supporting transparent subs trate. Each layer comprises a different phosphor material capable of emitting different colour light.

The two or more layers may be separated by an inert, optically transparent, barrier layer(s). Low energy electrons cause the innermost phosphor layer, that is the layer remote from the substrate, to luminesce giving off light which passes through the other phosphor layer(s) and the substrate to a viewer. As electron energy is increased, by increas ing the accelerating potential, the electron penetrate deeper into the multi-layer structure progressively exciting the one or more successive phosphor layers to produce different colours, the dielectric barrier layer(s) serving to define distinct energy levels for luminescence of each phosphor layer.

The multi-layer structure of thins kind of screen requires thin layers of phosphor material, or at least the innermost layer, typically around 1/2 to lWm, and thus very fine phosphor particles to be used. The efficiency of such a screen is relatively low because of the small phosphor particle size and also because light emitted by the innermost phosphor layer must travel through the one or more successive, unex cited, phosphor layers and dielectric barrier layers, before reaching the transparent substrate, and the light observed by a viewer is therefore dependent on the transmissive properties of those other layers.In a two phosphor-layer screen for example, the inner most layer is typically of red-emitting green-emitting phosphor so that red light from the innermost layer must pass at least through the green-emitting phosphor layer before it can be observed.

The second kind of penetron-type screen is the so-called "onion skin" penetron screen. In one form of this kind of screen, the screen comprises grains with each grain being composed of an inner core of one colour emitting phosphor material, say greenemitting phosphor material, which is coated with a thin layer of a second, different colour emitting phophor material, say red-emitting phosphor material. A thin, inert, barrier layer may be used to separate the two phosphor materials. Low energy electrons excite the red-emitting coating of the grains but do not penetrate into the green-emitting core with sufficient energy to cause emission from the core. By switching the electron accelerating potential to a higher level, the high energy electrons produced penetrate into the core of the grains to cause emission of green light.

In another form of the penetron screen using so-called "onion skin" principles and more commonly referred to as a "mixture" screen, particles of a first colour emitting phosphor material, for example, green-emitting, are coated with an inert barrier layer coating to create a phosphor with a large dead voltage, that is, one requiring an impinging electron beam to have at least a certain energy level before luminescence and light production is achieved. The coated particles are mixed mechanically with standard, second colour-emitting, phosphor particles, for example red-emitting.With this form of screen, a changing phosphor emission with increasing voltage is given with initially only the red-emitting phosphor particles emitting light in respone to excitation by low-voltage, low-energy electrons which is gradually swamped by green light emitted by the green-emitting phosphor particles as the electron energy is increased to penetrate through the inert barrier layer coating on the green-coating phosphor particles.

Problems have been encountered with both these forms of "onion skin" penetron displays. In order to coat a phosphor particle with a further phosphor material and/or inert barrier layer, complicated preparation processes are required. The different phosphor and barrier layer materials employed must be chemically compatible. Moreover, the phosphor grains to be coated should ideally be of such a configuration, for example spherical, to ensure that the barrier layer coating thickness is uniform over the surfaces of the grains. Usually however, the grains are of irregular shape. In any case, since the electron beam travels along a certain direction with respect to the phosphor grains, the effective depth of the barrier layer presented to the beam varies across the area of each grain.Optimum conditions can not therefore be attained simultaneously for all electrons and hence this kind of penetron-type screen also tends to be of low efficiency.

It is an object of the present invention to provide a penetron-type screen for a colour display tube which overcomes to some extent the aforementioned disadvantages of the known kinds of screen.

According to the present invention, there is pro vided a colour display tube comprising means for producing an electron beam, and a cathodoluminescent screen for excitation by the electron beam for producing a colour display, the cathodoluminescent screen being a penetron type comprising first and second phosphor materials for producing respectively different colours in response to different electron beam energies, which is characterised in that the first and second phosphor materials for emitting first and second colours respectively in response to electron excitation are disposed beside one another in a patterned array with an inert barrier layer penetrable by higher-energy electrons covering the electron beam facing surface ofthe regions ofthe patterned array comprising the first phosphor material.

With such an arrangement, the second phosphor material is therefore exposed to incoming electrons and responds to relatively low energy electrons to emit light of one colour which is transmitted directly through a supporting substrate (rather than also through the first phosphor material) whilst the first phosphor material is effectively shielded from those electrons by the barrier layer. If the incoming electrons are switched to a relatively high energy level, penetration by electrons through the barrier layer into the first phosphor material takes place whereupon the first phosphor material emits light of a different colour, again directly through the substrate.By choosing the first and second phosphor materials to be green and red emitting respectively, and because green-emitting phosphors are generally more efficient, green light emitted from the first phosphor material in response to a high energy electron input will, by suitably defining the relative areas of the two phosphor materials, swamp the red light emitted by the second phosphor material so that to an observer, green light emission is predominant.

The display tube according to the invention enables standard phosphor materials to be used without any modification to their grains and therefore avoids cqmplicated particle coating processes: Moreover, since superposed phosphor layers are not involved and the phosphor materials receive electrons independently, the thickness of the two phosphors is not critical and so the phosphor particle size can be optimised for maximum efficiency.

The patterned array of first and second phosphor materials is preferably regular so that colour response at any particular point of the screen across the entire area is wholly predictable.

The phosphor materials may be disposed on a substrate using a photolithographic process, that is, in the manner whereby phosphor materials are conventionally applied in a shadow-mask type tube.

The barrier layer can be deposited over the regions of the patterned array comprising the first phosphor material simply and precisely for example vacuum deposition or sputtering sothata substantially constant, uniform, absorbtion thickness is offered to all electrons (i.e. substantially constant in the direction of the incoming electron beam).

In one embodiment of the invention, the barrier layer extends substantially only over the electron beam facing surface of the first phosphor material. In this case the barrier layer may comprise a material selected from the group consisting of aluminium, zinc sulphide, tin oxide, indium oxide and silicon dioxide.

A thin continuous aluminium layer serving as a screen electrode may be applied overthe electron beam facing surfaces of the barrier layer and second phosphor material. Alternatively the thin continuous aluminium layer may be disposed over the surfaces of the first and second phosphor materials and extend intermediate the first phosphor material and the barrier layer covering the first phosphor material.

In another embodiment of the invention,the barrier layer may be optically transparent and extend as a continuous layer over the regions of the patterned array comprising the first phosphor material and areas intermediate those regions with the second phosphor material being disposed over the continuous barrier layer in those intermediate areas.

The patterned array may further include a third phosphor material for emitting light of a different colour to the first and second phosphor materials in response to electron excitation, which third phosphor material is disposed beside the first and second phosphor materials in the patterned array, the electron beam facing surface of the regions of the patterned array comprising the third phosphor material being covered by a further inert barrier layer whereby electrons of different energy to those required for penetrating the first mentioned barrier layer associated with the first phosphor material are required to cause excitation of the third phosphor material.

The phosphor materials of the patterned array may be in the form of stripes of phosphor materials arranged parallel to one another in repetitive groups, for example with stripes of one phosphor material alternating with stripes of the other phosphor material or in the case of three phosphor materials being used, in repetitive groups of three stripes each stripe comprising a respective phosphor material. In this case, adjacent stripes may abut one another.

Alternatively, the patterned array may comprise a matrix of discrete elements, for example dots, of one of the first and second phosphor materials with the other phosphor material occupying an area between those discrete elements. Where three phosphor materials are used, the third phosphor material may also comprise a matrix of discrete elements, e.g.

dots. In both cases, the aforementioned other phosphor material may completely cover the area between the matrix, or matrixes as the case may be, of discrete elements.

The colour display tube mayfurther comprise an electron multiplier situated between the means for producing an electron beam and the cathodoluminescent screen. The inclusion of such an electron multiplier is advantageous in that the change in electron energy necessary for switching colours is controlled in this case by varying the accelerating potential applied between the multiplier and the screen following deflection of the electron beam for scanning purposes. This avoids the need to adjust the supply to the tube's beam deflecting means, be it magnetic or electrostatic, to compensate for changes in accelerating potentials in the deflection region and maintain deflection amplitude constant.

Embodiments of colour display tubes in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic cross-sectional view of a display tube; and Figure 23 and 4 are schematic, cross-sectional views respectively through portions of alternative cathodoluminescent screens of the display tube of Figure 1.

Referring to Figure 1,the display tube is intended for data graphic display purposes and comprises an evacuated envelope 12 having an opticallytransparent faceplate 10 (here shown substantially flat but which may be curved) having a penetron-type cathodoluminescent phosphor screen 14. Means such as an electron gun 16 with a cathode for generating a continuous electron beam 18 is disposed in a neck portion of the envelope. An electromagnetic beam deflector 17 is provided at the neck-cone transition of the envelope in order to deflect the electron beam 18 in raster fashion across the screen 14. The cathodoluminescent screen 14 may alternatively be provided separate from the faceplate 10 on an optically transparent support mounted generally parallel to the faceplate.

The electron beam 18 produced by the electron gun 16 is accelerated by an electrical potential applied between the gun and the screen in conventional manner. Electrons impinging on the screen cause phosphor material thereof to luminesce, the light emitted thereby being transmitted through the faceplate 10 to an observer. The accelerating potential is switchable, or alternatively continuously variable, between high and low levels by means of a acceleration voltage control unit referenced 20.

The penetron type screen 14, intended to produce multi-colour colour images, comprises a regular (at least on a macroscopic scale) patterned array of at least first and second phosphor materials for emitting different coloured light, in this case the primary colours green and red respectively, in response to excitation by the electron beam. A portion of one form of the screen 14, illustrating its construction, is shown highly magnified to Figure 2.Referring to Figure 2, the first and second phosphor materials, comprising for example, green-emitting P31 (Zn,Cd)S : Cu, Ag, Al) phosphor and red-emitting P22 (Y2O2S: Eu) phosphor, respectively are deposited in the form of alternate, parallel stripes 25 and 26 respectively beside one another repetitively on the inner surface of the faceplate 10 extending continuously along the height of the screen and at right angles to the line scan direction of the electron beam. As shown in Figure 2, the sets of stripes are of generally rectangular cross-section with adjacent stripes abutting one another and of substantially equal depth so that the combined inner surface defined by the stripes, that is their surface remote from the faceplate 10 and closest to the electron gun, is generally smooth, continuous and extends parallel to the faceplate 10.Adjacent stripes may, a shown, abut one another or may be spaced apart, this space being filled with an inert, black-coloured material.

An inert barrier layer 28 consisting of nonluminescing material stable to electron bombardment such as Al, ZnS, SnO, InO or SiO2 is superposed directly over and co-extensive with the flat exposed innermost surfaces of the stripes 25 so as completely to cover the regions comprising those surfaces.

The repetitive patterned array of two phosphor materials is applied to the faceplate (or separate supporting substrate as the case may be) using photolithographic techniques similar to those usually employed in the manufacture of conventional shadow mask display tubes to deposit patterns or groups of phosphor elements. The stripes of a first phosphor material (25) are deposited on the faceplate in one step and thereafter the stripes of the second phosphor material (26) deposited in the spaces between the first-applied stripes. The depth of the stripes is dependent to some extent on the particular phosphor materials used and typically is around 151 mm (around 3 particles).Deposition of each of the phosphor materials is accomplished in a known manner by dispersing the material in a U-V sensitive laquer which is spun onto the faceplate, exposing the laquer to U-V light to define wanted phosphor regions using masking assemblies (stencils), hardening those regions and then washing away unwanted, unexposed, regions of laquer so as to leave phosphor materials restricted to the corresponding one of the stripe regions.

The inert barrier layer 28 is applied to each stripe 25 simultaneously using vacuum deposition or sputtering techniques through a suitable masking element aligned with the stripes 26 to shield the stripes 26. The material of the barrier layer 28 is deposited to a uniform thickness of around 0.8im.

Finally a thin continuous layer 29, around 1000at 2000Â, of aluminium substantially transparent to electrons is disposed by vacuum evaporation or sputtering completely over the exposed surfaces of the stripes 26 and barrier layers 28 (with, in accord ante with conventional practice in laying aluminium on phosphor material, an inorganic lacquer being applied prior to deposition of the aluminium which is subsequently baked away) to act as a screen anode and, in addition, for maximising optical efficiency of the screen.

In another form of the screen, as shown in Figure 3, the thin, continuous, aluminium layer 29 is deposited directly over the surfaces of both the second and the first phosphor materials and the barrier layer 28, for example also of aluminium, applied onto the layer 29 in registration with the stripes 25 of the first phosphor material, again by vacuum deposition or sputtering through a mask.

In an alternative arrangement, the patterned array of the two phosphor materials consists of a matrix of regularly-spaced, generally circular dots of the first, green-emitting, phosphor material disposed on rhe faceplate 10 with the second phosphor material disposed in the areas on the faceplate 10, between those dots. The uninterrupted area of the second phosphor material completely fills the space between the dots of first phosphor material such that, in section, the screen appears similar to that shown in Figure 2 with the inner surfaces of the materials combining to define a continuous, smooth surface.

However, if desired, the total area of the second phosphor material may be reduced by surrounding each dot of the first phosphor material with a contacting annulus of inert, non-luminescing material (again to the same depth of the dots) which may be coloured black and then filling the spaces between the annuli of inert material with the second phosphor material.

The inert barrier layer is applied solely over the generally flat inner surface of the dots of the first phosphor material so as to cover completely their inner surfaces. The patterned array of the two phosphor materials (and the inert annuli if used) and the barrier layer are applied using similar techniques to those described with reference to the firstmentioned arrangement and to around the same depth. As before, the aluminium layer 29 serving as screen anode may be disposed over the barrier layer or intermediate the barrier layer and first phosphor material.

In both the forms of screens shown in Figure 2 and 3 and with either stripe or dot matrix patterns a third phosphor material emitting in response to electron excitation a third colour different to the colours emitted by the first and second materials may be included in the patterned array to provide a three colour display. In one example, this third phosphor material, which may be blue emitting, is deposited in the form of stripes, using the same technique as described above, beside the stripes 25 and 26 so that the screen compries repetitive groups of three parallel stripes, each comprising a respective phosphor material. A further barrier layer similar to the barrier layer 28 is deposited in the manner described previously over the electron beam facing surface regions of this third phosphor material, either above or below the layer 29 as the case may be.The barrier layer associated with the third phosphor material may be the same materials as the barrier layer 28 but is thicker than, and therefore has different electronpenetration characteristics to, the barrier layer (28) associated with the first phosphor material so that an even higher electron energy level is required for luminescence of the third phosphor material. Alternatively, where a dot-matrix pattern is used, the third phosphor material may be deposited as a further, regular matrix of dots interspersed with the matrix of dots interspersed with the matrix the first phosphor material and surrounded by the second phosphor material, with the barrier layer for the third phosphor material being applied over the electron beam facing surface regions comprising that material.

In another screen arrangement, as shown in Figure 4 and comprising a two colour screen, the barrier layer 28 associated with the first phosphor material, deposited in either a stripe or dot matrix pattern, extends continuously over the surface of the regions of that material and the intermediate areas of the faceplate 10. The second phosphor material is deposited over the continuous barrier layer in the areas intermediate the stripes or dots of the first phosphor material and a thin continuous aluminium layer, serving as a screen anode, applied over the exposed surfaces of the second phosphor material and barrier layer 28. The barrier layer 28 is in this case necessarily optically transparent (e.g. of ZnS, SnO, InO or SiO2 as light emitted by the second phosphor material must travel through the layer to reach an observer.The phosphor materials, barrier layer and aluminium layer are applied using the same techniques as described previously, only in this case, the barrier layer 28 is, of course, applied without using a masking element.

This form of screen arrangement may be modified to provide a three colour display by including a third phosphor material, in the patterned array emitting a different colour, e.g. blue, light in response to excitation by electrons of higher energy than those required for exciting the first phosphor material. This modified form of screen may be fabricated by depositing the third phosphor material on the substrate in the desired pattern, i.e. stripes or dots, and disposing a barrier layer of optically transparent (e.g.

ZnS, SnO, InO or S:O2) material over the electron beam facing surface of the phosphor material. The first phosphor material (25) is then deposited, (in stripe or dot form) alongside the third phosphor material and the continuous barrier layer 28 applied over the surface of the first phosphor material (as previously), the surface of the barrier layer on the third phosphor material and the surface of the faceplate 10 not covered by the first and third phosphor material so that in effect two layers of barrier material are provided over the third phosphor material. Thereafter, the second phosphor material is applied over those areas of the barrier layer 28 alongside and intermediate the first and third phosphor materials so that only the barrier layer 28 separates the second phosphor material from the faceplate 10.A thin, continuous aluminium layer is then applied overthe inner exposed surfaces of the second phosphor material and the barrier layer 28. Thus, the second phosphor material is not covered by a barrier layer, the first phosphor material is covered by the barrier layer 28 and the third phosphor material is covered by both the barrier layer 28 and its own barrier layer whereby electrons having progressively higher energy levels are required to excite the second, first and third phosphor materials respectively.

In operation of all the described screen arrangements, a comparatively low energy, low velocity, electron beam, accelerated by an accelerating voltage of around 9 kV,from the electron gun directed onto the screen (along the direction indicated by arrow A in Figure 2) will excite the second phosphor material to luminescence so that a red light emitted by the material is transmitted directly through the faceplate 10 to a viewer. At this comparatively low electron energy, electrons are prevented from reaching the green-emitting second phosphor material by the inert barrier layer (and the third phosphor material if provided by its associated barrier layer).

Thus only red emission is visible.

Upon the electron beam energy being increased to a comparatively higher level by suitably increasing the acceleration voltage by around 9kV, through the voltage switching unit 20, the higher velocity electrons produced are able to penetrate through the inert barrier layer covering the first phosphor material and excite that material to luminescence whereupon emitted green light is transmitted directly through the faceplate 10 to a viewer. Although the second, red-emitting phosphor material is excited as well by higher energy electrons, green-emitting phosphor materials are in use more efficient than red-emitting phosphor materials so that the green emission effectively swamps the red emissions and the viewer sees a generally green display.The ratio of the green and red emissions can be adjusted as desired by appropriately altering the relative areas of the two phosphor materials such that a greater proportion of the overall screen area is devoted to one or other of the colour emissions. Thus, for example, in order to increase green light emissions, the width of the stripes 25 may be increased relative to the stripes 26 or the size of the dots of greenemitting phosphor material either enlarged or spaced more closely as the case may be.

Where a third phosphor material is provided, increasing the electron energy level to an even higher level will allow electrons to penetrate through the barrier layer associated with the third phosphor material whereby light is produced by this material.

Again, the relative areas of the three phosphor materials are chosen, bearing in mind their respective efficiencies, such that this light predominates at these higher electron energy levels.

Naturally, whilst some variation is possible in this respect, the width and pitch of the phosphor material stripes (25 and 26) or the dot spacing must be such as to match display resolution requirements. Typically, in a two colour display, the stripes 25 and 26 will have widths of around 150im and 75yam repectively, (the phosphor material particles being around 5 to 10ism diameter on average). In the alternative arrangement using dots of a first phosphor material on a background of a second phosphor material, the dots will be around 1501*m in diameter and spaced in a regular matrix of around 200m pitch.

As previously mentioned, the electron beam (A) is raster scanned across the screen. Colour information display can be achieved line sequentially or field sequentially rather than simultaneously or dot sequentially. In the simplest approach of the latter mode, sensitive fields are presented in only one colour and a straightforward red-green colour sequence for successive fields is adopted.

The display tube described has the advantage generally found in single-gun colour tubes, for example the absence of convergence problems.

Whilst a conventional form of cathode ray tube structure has been described, the cathodoluminescent screen 14 may be used in other kinds of cathode ray display tubes. For example, in another embodiment, the display tube comprises a so-called "flat display tube" in which the electron gun is arranged such that the electron beam generated thereby travels firstly in a direction generally parallel to the screen and is thereafter deflected by means of a folded electron optical system and electrostatic deflection electrodes onto the screen, the electrostatic deflection electrodes serving to effect frame scanning whilst line scanning is accomiplished by means of additional electrostatic deflection electrodes disposed adjacent the electron gun.

In further embodiments, the above-described kinds of display tubes are modified by the provision of an electron multiplier parallelly adjacent to, and spaced from, the cathodoluminescent screen. The electron multipler may be either a glass matrix microchannel plate electron multiplier (such as that described in Acta Electronica, Volume 14, No.2, April 1971, and having millions of channels of say 12.5im diameter and 15 > m pitch), which is particularly suitable for small, high resolution datagraphic displays, or a metal dynode channel plate electron multipler comprising a stack of apertured metal dynodes.In this way, the beam forming and raster scanning sections of the tube are operated at low voltages, the low voltage, low current scanning electron beam produced thereby being amplified by the electron multiplier. The low energy electron beam is scanned across the iniput face of the electron multiplier to produce at its output, through each channel successively, a current mulltiplied electron beam. The electron beam emanating from each channel of the electron multiplier is directed at the screen and line scanning effected by the electron beam being produced from successive channels in turn.The width and pitch of the phosphor stripes or size and pitch of the phosphor dots as the case may be is selected relative to the width of the emanating electron beam (which may be around 0.4mm diameter) so that the beam covers a plurality of stripes or dots and avoiding any need to deflect the beams for colour selection. The current multiplied electron beam produced by the electron multiplier is accelerated towards the screen by a voltage sufficient to cause phosphor excitation applied between the electron multiplier and the screen, this accelerating voltage being switchable between higher and lower levels so as to control colour emission in the aforementioned manner.Typical examples of display tubes employing electron multipliers are described in, for example, UK Patent Specifications 1 434053,2 101 396 and 1 208314 details of which are incorporated by way of reference. This kind of colour display tube has the additional advantage in that the beam deflection scanning function is completely divorced from the colour selection functions so that the need for deflection adjustment to compensate for the kinds of effects which would otherwise be caused as a result of switching the voltages between the electron gun and the screen, thus altering electron velocity whilst the beam is undergoing deflection, is avoided. Also, it is possible to employ scanning modes other than the normal TV raster mode, for example pseudo-random scans as required when the tube is to be used for alphanumeric data or graphics displays.

Claims (22)

1. A colour display tube comprising means for producing an electron beam, and a cathodoluminescent screen for excitation by the electron beam for producing a colour display, the cathodoluminescent screen being a penetron type comprising first and second phosphor materials for producing respectively different colours in response to different electon beam energies, characterised in thatthefirst and second phosphor material for emitting first and second oclours respectively in response to electron excitation are disposed beside one another in a patterned array with an inert barrier layer penetrable by higher-energy electrons covering the electron beam facing surface of the regions of the patterned array comprising the first phosphor material.

2. A colour display tube according to Claim 1, wherein the patterned array is higher.

3. A colour display tube according to Claim 1 or Claim 2, wherein the barrier layer extends substantially only over the electron beam facing surface of the first phosphor material.

4. A colour display tube according to Claim 3, wherein the barrier layer comprises a material selected from the group consisting of Al, ZnS, SnO, InO and SiO2.

5. A colour display tube according to Claim 3 or Claim 4, wherein a thin continuous aluminium layer is disposed over the electron beam facing surface of the barrier layer and the second phosphor material.

6. A colour display tube according to Claim 3 or Claim 4, wherein a thin continuous aluminium layer is disposed over the surfaces of the first and second phosphor materials and extends intermediate the first phosphor material and the barrier layer covering the first phosphor material.

7. A colour display tube according to Claim 1 or 2, wherein the barrier layer is optically transparent and extends as a continuous layer over the regions of the patterned array comprising the first phosphor material and areas intermediate those regions, the second phosphor material being disposed over the continuous barrier layer in said intermediate areas.

8. A colour display tube according to Claim 7, wherein the barrier layer comprises a material selected from the group consisting of ZnS, SnO, InO and SlO2.

9. A colour display tube according to Claim 7 or Claim 8, wherein a thin continuous aluminium layer is disposed over the electron beam facing surface of the barrier layer and the second phosphor material.

10. A colour display tube according to any one of Claims 1 to 9, wherein the patterned array further includes a third phosphor material for emitting light of a different colour to the first and second phosphor materials in response to electron excitation, which third phosphor material is disposed beside the first and second phosphor materials in the patterned array, the electron beam facing surface of the regions of the patterned array comprising the third phosphor material being covered by a further inert barrier layer whereby electrons of different energy to those required for penetrating the first-mentioned barrier layer associated with the first phosphor material are required to cause excitation of the third phosphor material.

11. A colour display tube according to Claim 10, wherein said further barrier layer comprises a material selected from the group consisting of Al, ZnS, SnO, InO and SiO2.

12. A colour display tube according to any one of the preceding claims, wherein the patterned array is in the form of stripes of phosphor materials arranged parallel to one another in repetitive groups.

13. A colour display tube according to Claim 12, when dependent on any one of Claims 1 to 6, 10 to 11, wherein adjacent stripes abut one another.

14. A colour display tube according to any one of Claims 1 to 9, wherein the patterned array comprises a matrix of discrete elements of one of the first and second phosphor materials with the other phosphor material occupying an area between said discrete elements.

15. A colour display tube according to Claim 14, wherein said other phosphor material covers completely the areas between the matrix of discrete elements.

16. A colour display tube according to Claim 10, wherein the patterned array comprises respective matrices of discrete elements of two of said first, second and third phosphor materials. with the other phosphor material occupying an area betwen the discrete elements.

17. A colour displaytube according to Claim 16, wherein said other phosphor material covers completely the area between the discrete elements.

18. A colour display tube according to any one of the preceding claims, wherein the two or more phosphor materials are deposited on a supporting substrate by a photolithographic technique.

19. A colour display tube according to any one of the preceding claims, wherein the one or more barrier layers are deposited by vacuum deposition or sputtering.

20. A colour display tube according to any one of the preceding claims, wherein the barrier layer, or the portion thereof, covering the first phosphor material is of uniform thickness.

21. A colour display tube according to any one of the preceding claims, wherein the display tube further includes an electron multiplier situated between the means for producing an electron beam and the cathodoluminescent screen.

22. A colour display tube substantially as hereinbefore described with reference to, and as such in, any one of Figures 2 to 4 of the accompanying drawings.