DE2201585B2 - Process for the production of fluorescent screens - Google Patents

Description

1) When electrons penetrate or penetrate through or into a solid body is the depth of penetration of the electrons is a function of the acceleration voltage and changes non-linearly with the Tension;

2) When penetrating through or into a fluorescent material, the electrons cause a glow predominantly at a certain depth, where they give off the maximum of their energy. By Controlling the energy of the electron bundle can be the depth of penetration of the electrons into one Changing phosphor and, consequently, the depth of excitation of luminous centers.

In fluorescent colored screens, whose mode of operation is based on the penetration of electrons, a bundle of electrons is excited with low energy the phosphor with a luminescent color, and an energetic electron beam predominantly excites the phosphor with a different color.

According to the principle mentioned, such fluorescent screens are constructed so that between the Phosphor, which is excited by a higher energy electron beam, and the electron source a barrier layer for electrons is formed, in which the electrons with a predetermined smaller Energy to be absorbed. However, this layer leaves the electrons with a given higher energy by. The denser and thicker the barrier layer, the higher the energy the electron bundle must have, to penetrate this layer and to excite the luminescent material behind it.

From DE-OS 2t 26 889 a method of the type mentioned for the production of luminous screens is known with at least two phosphors of different luminescent color, according to which the Deposition of a zinc and / or cadmium sulfide layer on particles suspended in the aqueous salt solution of a luminescent chalcogenide after adding a Lye, especially concentrated sodium hydroxide solution, as well as thioacetamide at a pH value between 10 and 15 takes place. Investigations of such sedimentation products from zinc sulphide showed that apart from zinc sulphide they were considerable Contains proportions of zinc oxide and zinc hydroxide. The presence of zinc oxide in the barrier layer reduces the luminance when the fluorescent material shines, on whose surface the zinc sulfide is deposited. In addition, the phosphor ages due to alkali metal hydroxide absorption in the barrier

layer under the action of the electron oil bundle quite fast.

Furthermore, a method for producing a conductive, in particular photoconductive, layer is known (US-PS 31 48 084), according to the z. B. to generate a cadmium selenide photoconductive layer on a glass support this heated to 280 ° C, and with a solution of cadmium acetate and z. B. thioacetamide or Thiosemicarbazide being sprayed.

The invention is based on the object of improving the method mentioned at the outset in such a way that purer barrier layers and thus fluorescent screens with improved luminance and less susceptibility to aging be achieved.

According to the invention, this object is achieved by that

a) on blue luminescent cerium activated yttrium silicate of the composition

Y ₂ Si ₂ O, · Ce

the barrier layer from a solution of

4 vol% aqueous 5 m zinc sulfate solution,

4% by volume of aqueous 2 m gallium bromide solution, 0.2% by volume of aqueous 1 · 10- ⁴ m gold chloride solution

sung,
60% by volume aqueous 1-m-thioacetamide solution,

5% by volume of 2 m hydrochloric acid and the remainder water is formed;

or

b) on green luminescent zinc-cadmium sulfide of the composition

ZnSo.62 · CdS <u8 · Ag

the barrier layer from a solution of

2% by volume aqueous 0.5 m zinc chloride solution, 10% by volume of aqueous 1-m-thioacetamide solution, 10% by volume of 1-m-hydrochloric acid and as Remainder water is formed;

or

c) on green luminescent zinc-cadmium sulfide of the composition

ZnSoiCdSoi -Cu-Al

the barrier layer from a solution of

2% by volume aqueous 0.5 m indium nitrate solution, 20% by volume of aqueous 0.2 m-thioacetamide solution, 2% by volume of aqueous 0.5 m-thiosemicarbazide solution

sung,

20 vol .-% 2-m-acetic acid and the remainder water is formed.

55

Refinements of this method are characterized in the subclaims.

Through the choice of the components of the solution and, in particular, the pH values in the acidic range sulfide barrier layers are obtained for the deposition without any hydroxide or oxide admixtures, so that Luminous screens of improved luminance at low and high voltages are available and the The fluorescent substance has a long lifespan.

In the case of abutment of the barrier layer on a A fluorescent layer previously applied to a base is applied to a screen base after a any known method a phosphor layer

20th

25th

30th

35

40

45

50 is applied, then the surface of the produced layer is treated with the mentioned solution until a barrier layer with a predetermined thickness is deposited, whereupon the surface of this barrier layer is coated with another phosphor. Similarly, a multilayer screen can be made which consists of a predetermined number of different layers of phosphor separated by barrier layers

If barrier layers are to be formed on individual particles, a phosphor is dispersed in the mentioned solution during a certain period of time whereby on the surface of each particle a Barrier layer with the desired thickness settles The particles obtained in this way with a higher Excitation thresholds are mixed with particles of another phosphor that do not have a barrier layer, and the mixture obtained is applied to an umbrella pad.

Thanks to the advantages of the method according to the invention, the barrier layers produced with it result in better brightness and color purity characteristics of luminous screens compared with the known screens of a similar type.The barrier layers produced with this process are characterized by their closeness and uniform and uniform thickness and have no through holes or other Defects, as the barrier layers are deposited from a solution that evenly wets the surface to be coated. The aforementioned properties of the barrier layers enable the production of fluorescent screens with good color separation. The electrical conductivity of the barrier layers produced lies in the limits of 10 ~ ¹² to 10 ^{-6 ohm-1} · cm- ', and this favors a rapid bleed the charge that occurs when electron bombardment, wherein the color purity of the luminescent screens according to the invention is improved compared to the screens, in which the barrier layer material has dielectric properties. Good transparency of the barrier layers for the light in the visible range of the electromagnetic spectrum also contributes to increasing the luminance of screens.

The possibility of making luminescent Barrier layers make it possible to manufacture multicolored fluorescent screens with high energy yield. At the The method according to the invention can determine the thickness of the precipitated barrier layers and consequently the height of the The excitation threshold for the phosphor used can be easily controlled. By changing the concentration of starting components of the solution as well as by varying the precipitation temperature and -duration can e.g. B. obtained barrier layers with a thickness of 10 to 4000 nm and the height accordingly change the excitation threshold of phosphors from 50 V to 20 kV. The simple and in one stage ongoing process of barrier layer formation in the method according to the invention results in an essential one Shortening and making the technological process of manufacturing multicolored luminescent screens cheaper and the possibility of easily realizing this technological cycle under industrial conditions.

In the following, the invention is described in greater detail on the basis of the drawing and exemplary embodiments explained. It shows

F i g. 1 is a schematic sectional view of a screen with two superimposed and through one inert barrier layer with separate phosphor layers

different luminescent colors;

F i g. 2 shows a schematic sectional illustration of the phosphor particles with different excitation thresholds;

Fig. 3 is a schematic sectional view of a screen comprising a mixture of phosphor particles with different arousal thresholds contains;

F i g. 4 is a schematic representation of a phosphor particle coated with a luminescent barrier layer on average;

F i g. 5 shows a schematic sectional illustration of a screen with a phosphor layer formed from powder; which is covered with a luminescent barrier layer on the side of the electron source;

F i g. 6 shows the dependence of the luminance B, expressed in relative units, of the fluorescent screens produced using the method according to the invention with different excitation thresholds on the excitation voltage fyin kV.

A process for the production of luminescent screens whose luminescent color depends on the energy of the electron beam is carried out by applying at least two phosphors to a substrate that when excited emit radiation in different areas of the electromagnetic spectrum emit, wherein a barrier layer is formed on at least one phosphor, which the electron energy partially absorbed This barrier layer is created by chemical deposition from a solution. For example, if the barrier layers are sufficiently thick, they absorb part of the electron energy and remain predominantly transparent to the light in the visible range. The discontinuation of the The barrier layer takes place at a given hydrogen ion concentration in the solution. To regulate the Deposition rate and creation of barrier layers with sufficient thickness is the hydrogen The ion concentration in the solution during the settling process is constant using one of the three buffer mixtures held, the buffer mixture being selected depending on the composition of the starting components. at Using the mentioned solutions one can get barriers both on the basis of the simple connections of the type ZnS, InS as well as on the basis of complex compounds (ZnGa2S4). At the Deposition of barriers from mixed chalcogenide compounds can be used to increase the index of refraction of the barrier layer can change within wide limits, with an increase in the screen brightness in the end becomes possible. Barriers are deposited at room temperature of the solution to speed up the process However, the formation of precipitates can be heated to a temperature below its boiling point.

In Fig. 1 shows a fluorescent screen. The screen contains two phosphor layers of different luminescent colors, which are separated by a non-luminescent barrier layer. In the production of such a screen is on a base 1, which can be the front glass plate of a tube bulb, a phosphor layer 2 with any, z. B. applied green, luminescent paint. A barrier layer 3 is formed directly on the surface of the phosphor layer produced. For this purpose, the above-mentioned solution is poured into the tubular flask, and the deposition of the barrier layer takes place for a time which is necessary for the formation of the top layer with a predetermined thickness. To accelerate the settling process, the temperature of the solution can be increased above room temperature (but not above the boiling point limit). After the formation of the barrier layer is complete, the solution is poured out and, using any known method, a phosphor layer 4 with a second, e.g. B. red luminescent paint applied. To increase the light output of the screen upon incidence of an electron beam Έ , the surface of the second phosphor layer can be coated with an aluminum layer 5 using conventional technology. Similarly, a three-color luminescent screen is also produced, the second barrier layer being applied to the second luminescent layer by the method described, and a luminescent layer with a third luminescent color being placed thereon. The composition of the barrier layers is chosen depending on the luminescent color and the mutual arrangement of the phosphor layers.

In the manufacture of a fluorescent screen, which is a mixture of phosphors with different excitation thresholds contains, the barrier layer is formed on phosphor particles. To this end, a Fluorescent powder with a z. B. green luminescent color in the solution with the composition mentioned dispersed and thereby deposited a barrier layer with a predetermined thickness on the particle surface. As in the example described above, the barrier layer thickness is determined by appropriate selection of the ^ precipitation time and the solution temperature are controlled. In Figure 2, fluorescent particles 6 are with different, e.g. B. red and green luminescent color, of which fluorescent particles with z. B. green luminescent paint are coated with a barrier layer 7 and compared with the red luminous particles have a higher excitation threshold. For the production of the luminescent screen the treated and barrier coated particles as well as the untreated particles become mixed, the weight ratio of the two phosphors in the solution of the desired Color characteristics of the luminescent screen is determined. The mixture obtained is applied to the screen pad by any known method, e.g. B.

by precipitation from potassium silicate solution, applied. The finished screen is shown schematically in Fig. 3 shown. The screen contains a base 1 made of glass with a phosphor layer lying thereon, which consists of a mixture of the phosphor particles 6 with different luminescent colors, the particles of a fluorescent material carry the barrier layer 7.

According to the method described, a barrier layer with a second predetermined thickness can be applied Fluorescent particles with a third, e.g. blue Making luminescent paint and mixing fluorescent particles with blue, green and red Luminescent color and with different excitation thresholds using any known one Apply procedure to the shield pad. On the screen formed in this way, a three-color display. When using phosphors with different excitation thresholds you can make a multi-layer fluorescent screen, each layer of fluorescent particles with a luminescent color and with the same excitation threshold, as well as a three-colored screen, in which a layer of a particle mixture of two phosphors with different luminescence

colored and with different increased excitation thresholds and the other layer of monochrome ordinary phosphor particles is formed.

The method according to the invention enables in variant a) the division of luminescent s Barrier layers, with additional possibilities for the formation of colored fluorescent screens. Included gold is introduced as an activation metal by adding a small amount of a soluble gold salt to the The starting solution is added, from which the deposition of the barrier layer takes place, whereupon the finished layer is a Is subjected to heat treatment at a temperature above 250 ° C. A barrier layer can also be activated by treating the inert barrier layer formed on a phosphor with an aqueous solution of a r> Gold salt treated and the structure created afterwards treated at a temperature above 250 ° C. In this case one can change the time and the Temperature of heat treatment control the depth of activator diffusion into the barrier layer thereby forming a barrier layer in which part of the layer is luminescent and the other part the function the inert barrier layer met.

In Fig. 4, a phosphor particle 6 is shown, the one luminescent barrier layer 8 carries. Such particles are obtained by dispersing a phosphor powder in the starting solution from which the barrier layer is deposited and which also contains gold chloride as Contains activation metal salt. One chooses such an activation metal that the luminescent color of the barrier layer to be applied differs from the luminous color of the particles to be coated. Then the treated phosphor powder is filtered and annealed at a temperature of over 250 ° C, wherein the barrier layer becomes a luminescent layer which, when excited, emits light in the desired region of the electromagnetic spectrum emitted. Those made in this way "Multicolored" fluorescent particles are used to produce various types of screens, e.g. B. one Screen made of a mixture of particles of two phosphors with different luminescent colors in which the particles are coated with a barrier layer which glows in a third color; of an umbrella which the fluorescent particles of a luminescent color «5 are covered with a barrier layer that shines in a different color; an umbrella made of mixed Particles of two phosphors with different luminescent colors, of which the particles are one Phosphor are coated with an inert barrier layer of a certain thickness and the particles of the other phosphor carry a luminescent barrier layer of a second predetermined thickness, which emit radiation with a third color. Such screens are described by applying the Particles onto a screen pad by any known method, e.g. B. by means of sedimentation, manufactured.

In Fig. 5 shows a sectional view of a further luminescent screen which carries a base 1 made of glass a phosphor layer 2 which is covered with a luminescent barrier layer 9 This screen becomes is created as follows: The inner surface of an umbrella pad that forms the front glass plate of the bulb Can be cathode ray tube is b5 any known method with the phosphor layer 2 covered that glows in one color. The finished layer is then used to form the starting solution treated with an inert barrier layer. The precipitation takes place over a period of time, which leads to the generation of the Barrier layer 9 with the desired thickness is necessary. After the settling process has ended, the The solution is poured off, and the finished inert barrier layer is at least one with an aqueous solution of a salt metal selected from the range of silver, gold, copper, manganese. The chosen metal determines the Luminescent color of the barrier layer. The barrier layer is activated by heat treatment of the Shield cover at a temperature of over 250 ° C, the depth of the activation metal diffusion into the Barrier layer is controlled by the choice of temperature and the duration of the heat treatment.

In the following, exemplary embodiments for different variants of the method according to the Invention for the manufacture of fluorescent colored screens, whose mode of operation is based on the principle of Electron penetration is based:

Embodiment 1

A two-color fluorescent screen can be produced using two-color fluorescent particles, in which the luminescent color changes depending on the depth to which the electron beam is in a Particle penetrates.

To produce such particles, 5 g of cerium-activated fluorescent powder (Y2S12O7 · Ce) made on the basis of yttrium silicate is treated with a solution composed of the following components: 20 ml of aqueous 5 M zinc sulfate solution, 20 ml of aqueous gallium bromide solution , 1 ml of an aqueous l, 10- ⁴ -m-gold chloride solution, 300 ml of aqueous 1 -m-Thioazetamidlösung, 25 ml of 2 m hydrochloric acid solution to adjust the pH of 1. the remaining part of the total volume of the solution of 500 ml of water is . The treatment takes place at a temperature of 95 ° C. for 1.5 hours and leads to the formation of a _{barrier layer consisting of the compound ZnGa 2} S ₄ · Au on the surface of the phosphor particles. The finished barrier layer luminesces when excited in the red spectrum. To increase the radiation intensity, the manufactured phosphor is annealed in an inactive medium at 350 ° C. for 1 hour. To produce a luminescent screen, the particles produced in the manner described are placed on a screen pad. When excited with electrons, which have an energy of 4 to 6 kV, the screen glows red; when the voltage increases, the glow changes into the area of violet-red hues.

Embodiment 2

A fluorescent screen, which consists of two fluorescent layers with different luminescent colors separated by a barrier layer, is produced directly on the inner surface of the front glass plate of a cathode ray tube. The fluorescent material used for the first luminescent layer is zinc cadmium sulfide activated with silver and glowing green (ZnSo, 62CdSo38 Ag), which is precipitated from a potassium silicate solution. The coating density is 2.5 to 3 mg / cm ² . A barrier layer is then formed on the surface of the phosphor layer produced. For this purpose, 500 ml of solution are prepared, consisting of 10 ml of aqueous 0.5 m zinc chloride solution, 50 ml of aqueous 1 m-thioacetamide solution, 50 ml of 1 m hydrochloric acid solution (to achieve pH 1) and the rest is composed of water. The finished solution

it is poured into the flask, which is placed in a thermostat with a constant temperature of 50 ° C. A barrier layer consisting of zinc sulfide is deposited on the surface of the luminescent material from the solution. At the concentration mentioned and the temperature of the solution, the rate of precipitation is 6-7 nm per minute. The deposition takes 1.5 hours, a barrier layer with a thickness of 400 to 450 nm is formed. After the process is complete, the solution is decanted, the inner surface to of the tube flask is rinsed with deionized water, and the surface of the barrier layer becomes more red-luminous Phosphor precipitated on the base of yttrium oxysulfide activated with europium (Yi, 934Euo.m> 602S). The density of the second layer of fluorescent substance is 1.5 to 2 mg / cm ² . The screen produced is aluminized in the usual way. When excited with an electron beam of 6 kV, a red glow is observed on the screen, which was produced in the manner described. The increase in the electron beam energy up to 9 kV shifts the luminescent color into the yellow-orange region.

When excited with a 12 kV electron beam the screen lights up green.

When using different combinations of phosphors and when changing the barrier layer thickness you can use the method described to produce screens that differ from each other by luminescent color and excitation energy of the phosphor layers differentiate.

Embodiment 3

To produce one from a mixture of two phosphors with different luminescent colors and different excitation thresholds existing luminescent screen becomes the barrier layer on particles of a of the two phosphors formed. Indium sulfide can be used as the material for this barrier layer. in the Comparison with the chalcogenide compounds of the elements from subgroup HB of the periodic table exhibits the indium sulfide as well as all other chalcogenide compounds of the elements from the Subgroup IHA of the periodic table has a higher absorption capacity with respect to the electron beam because the elements of the subgroup ΠΙΑ have a larger atomic number. As a result, can a high value of the fluorescent excitation threshold is obtained with a small barrier layer thickness and reduce the optical losses of the radiation in the barrier layer.

To create a barrier layer on fluorescent particles, prepare 500 ml of solution in a flask with the following composition: 10 ml of aqueous 0.5 M indium nitrate solution, 100 ml of aqueous 0.2 M thioacetamide solution, 10 ml of aqueous 0.5 M -Thiosemicarbazide solution, 100 ml 2 m acetic acid solution to adjust the pH value 2 and the rest of the water. 10 g of fluorescent green phosphor powder ZnSo, 8 · CdSo.2 -Cu-Al are dispersed in the solution mentioned, and the suspension obtained is kept at 60 ° C. for 1 h with constant stirring. As a result of this treatment, a barrier layer of indium sulfide is deposited on the surface of the phosphor particles. The thus treated phosphor particles are separated from the solution and dried at a temperature of 12O ⁰ C. The straight line “e” in FIG. 7 shows the luminance B of the phosphor produced as a function of the excitation voltage U. The excitation threshold of this phosphor is 8 kV. If the duration of the fluorescent powder treatment in the solution is changed, phosphors with an excitation threshold of 2.5 kV (straight line “f”), 4 kV (straight line “g”), 6 kV (straight line “h”) \ md 10 kV ( Just received "i") . Carrying out the treatment in a liquid medium contributes to the formation of a uniform barrier layer on the surface of particles with any diameters in the range from 1 to 50 μm. The subsequent fractionation of the polydisperse barrier layer phosphor produces phosphor batches with different mean particle diameter sizes that are specific for each batch, but the excitation threshold size remains the same for individual fractions. Since the barrier layer is formed at low temperatures (below the boiling point of the solution), the luminance of the phosphor is practically not reduced in the treatment described.

For the production of a fluorescent colored screen, the green one treated in the manner described is used Phosphor with a produced on the basis of yttrium orthovanadate, activated with europium and red Luminous phosphor powder mixed in a weight ratio of 1: 1 The mixture formed is made of one Potassium silicate solution deposited on an umbrella pad using a known method.

1 sheet of drawings

Claims (3)

Patent claims: 1. A method for producing fluorescent screens with at least two different phosphors Luminescent color in which at least one of the phosphors has an energy-stimulating electron partially absorbent barrier layer is applied in that from an aqueous solution of metal salts, optionally zinc chloride or zinc sulfate, and with the addition of thioacetamide a layer of a metal sulfide compound on the phosphor present in sheet or particle form is deposited, the pH of the solution in a range favorable for easy precipitation is set, characterized in that a) on blue luminescent cerium activated yttrium silicate of the composition Y ₂ Si ₂ O ₇ · Ce the barrier layer from a solution of 4% by volume aqueous 5 m zinc sulfate solution, 4% by volume aqueous 2 m gallium bromide solution sung,
0.2% by volume of aqueous 1x10 tm gold chloride solution,
60% by volume of aqueous 1-m-thioacetamide solution, 5% by volume of 2 m hydrochloric acid and as
Remainder water is formed; or b) on green luminescent zinc-cadmium sulfide of the composition ZnSo.62 ■ CdS ₀₃ * Ag the barrier layer from a solution of 2% by volume aqueous 0.5 m zinc chloride solution, 10% by volume aqueous 1 m thioacetamide solution, 10% by volume 1 m hydrochloric acid and the remainder
Water is formed; or c) on green luminescent zinc-cadmium sulfide of the composition ZnSo.sCdSo. ₂ -Cu-Ai the barrier layer from a solution of 2% by volume aqueous 0.5 m indium nitrate solution sung, ^v > 20% by volume of aqueous 0.2 m-thioacetamide solution sung,
2% by volume of aqueous 0.5 m thiosemicarbazide solution, 20% by volume of 2-m-acetic acid and as
Remaining water is formed. 2. The method according to claim 1, characterized in that the phosphor coated according to procedure a) is annealed ^{in an inactive medium at 350 ° C. for 1 h.} 3. The method according to claim 1, characterized in that in accordance with procedure c) coated phosphor at a temperature of 120 ⁰ C dried. The invention relates to a method for producing luminescent screens with at least two luminescent materials different luminescent color, in which at least one of the phosphors has the energy Exciting electrons partially absorbing barrier layer is applied in that from a aqueous solution of metal salts, optionally zinc chloride or zinc sulfate, and with the addition of Thioacetamide a layer of a metal sulfide compound ίο on top of the layer or particle form Phosphor is deposited, the pH of the solution in a favorable for easy precipitation Range is set. These luminescent screens are suitable for color display devices in which the image color is through Control of electron energy is changed. The mode of action of the fluorescent screens of this type is based on two well-known phenomena: