DE2201585C3 - 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;

- 25 2) When penetrating or 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 Can control the energy of the electron beam So you get the depth of penetration of the electrons into you 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, an electron beam with low energy also excites the phosphor a luminescent color, and an energetic electron beam predominantly excites the phosphor 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 2126 889 a method is the The type mentioned at the beginning for the production of luminescent screens with at least two phosphors of different luminescent color is known, 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 the addition of an alkali, in particular concentrated sodium hydroxide solution, as well as of thioacetamide at a pH between! 0 and 15 takes place. Investigations of such sedimentation products Zinc sulfide showed that, in addition to zinc sulfide, they contain considerable amounts of zinc oxide and zinc hydroxide. That The presence of zinc oxide in the barrier layer reduces the luminance when the Phosphor, on the surface of which the zinc sulfide is deposited. In addition, the phosphor ages due to alkali metal hydroxide absorption in the barrier

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layer relatively quickly under the action of the electron beam.

Furthermore, a method for producing a conductive, in particular photoconductive, layer is known (US-PS 3t 48 084), according to the z. B. to generate a photoconductive cadmium selenium layer on a glass base this heated to 280 "C, and with a solution of cadmium acetate and e.g. thioacetamide or Thiosemikarba? Id is 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.

This object is achieved according to the invention by is 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,

0.2% by volume of aqueous 1 · 10- ⁴ -m gold chloride solution

sung,
60% by volume aqueous lm-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 ■ CdSojg · 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

ZnS ₀ JiCdSa ₂ · 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 aqueous 0.5 m thiosemicarbazide solution

sung,

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

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Refinements of this method are characterized in the claims.

Through the choice of the components of the solution and, in particular, the pH values in the acidic range sulfide barrier layers without hydroxide * and oxide admixtures are obtained for the deposition, 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 the deposition of the barrier layer on a A fluorescent layer previously applied to a base is applied to a ί / screen base after a any known method a phosphor layer

30th

35

40

• "5

50 is applied, then the surface of the layer produced is treated with the solution mentioned 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 produced which consists of a predetermined number of different phosphor layers 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 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 heüigkeits- and color purity characteristics of luminous screens in comparison with the known screens of similar ArL do not have any through-holes or other defects, as the barrier layers are deposited from a solution by which the surface to be coated is evenly wetted. 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 is within the limits of 10- ^l2 to 10 ^-6 ohm '· cm-', and this favors a rapid bleed the charge that occurs when electron bombardment, wherein the color purity of the Leixhtschirme according to the invention is improved compared to the screens in which the barrier layer 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 producing luminescent barrier layers makes it possible to produce multicolored luminescent screens with a high energy yield. In the method according to the invention, the thickness of the precipitated barrier layers and consequently the level of the excitation threshold in the phosphor used can be easily controlled. By changing the concentration of starting components of the solution and by varying the precipitation temperature and duration, one can e.g. B. get barrier layers with a thickness of 10 to 4000 nm and change the height of the excitation threshold of phosphors from 50 V to 20 kV accordingly. The simple and in a stage running process of the barrier layer formation in the method according to the invention results in a substantial shortening and cheaper the technological process of producing multicolored luminescent screens and the possibility of easily realizing this technological cycle under industrial conditions.

In the following, the invention is explained in more detail with reference to the drawing and exemplary embodiments explained. It shows

Fig. 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;

2 shows a schematic sectional illustration of the phosphor particles with different excitation thresholds;

3 shows a schematic sectional illustration of a screen which contains a mixture of phosphor particles with different arousal thresholds contains;

4 shows a schematic representation of a with a h / minescent barrier layer coated phosphor particles on average;

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;

6 shows the dependence of the in relative units expressed luminance flder with the invention Process produced luminescent screens with different excitation thresholds from the excitation voltage i7in kV.

A method for producing luminescent screens, the luminescent color of which depends on the energy of the electron beam, is carried out by applying at least two luminescent substances to a base which, when excited, emit radiation in different areas of the electromagnetic spectrum, with at least one luminescent substance having a barrier layer which partially absorbs the electron energy. This barrier layer is created by chemically depositing it 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 deposition of the barrier layer takes place at a given hydrogen ion concentration in the solution. To regulate the rate of precipitation and to create barrier layers of sufficient thickness, the hydrogen ion concentration in the solution is kept constant during the settling process by means of one of the three buffer mixtures, the buffer mixture being selected depending on its composition. Using the solutions mentioned above, one can create barrier layers on the basis of simple compounds of the ZnS type. InS as well as on the basis of the complex compounds (ZnGaJS ₄ ). When depositing barrier layers made of mixed chalcogenide compounds, the refractive index of the barrier layer can be changed within wide limits, which ultimately makes it possible to increase the brightness of the screen. Barriers are deposited at the solution's room temperature, but to accelerate the formation of precipitates, the solution 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 replaced by a non-luminescent Barrier layer are separated. In the production of such a screen is on a base 1. the Can be front glass plate of a tube bulb, a phosphor layer 2 with any, z. B. green. Luminescent paint applied. A barrier layer 3 is produced directly on the surface of the Phosphor layer formed - for this purpose, the erA'ährite solution is poured into the flask. and the Deposition of the barrier layer takes place during a time that is predetermined for the formation of the top layer Thickness is required To accelerate the settling process, the temperature of the solution can be about the room temperature (but not above the boiling point limit) can be increased. After the barrier formation is complete the solution is poured out, and on the surface of the created layer is using any known method a phosphor layer 4 with a second, z. B. red luminescent color applied. To increase the light output of the screen when an electron beam is incident e can be the surface of the second phosphor layer

ίο Use common technology with a Aluminum layer 5 are coated. Similarly, a three-color luminescent screen is also produced, with on the second luminescent layer is applied according to the method described, the second barrier layer,

Ii and on top of it you put a layer of fluorescent material with a third luminescent color. 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

jo precipitation time and the solution temperature controlled. In Fig. 2 phosphor particles 6 with different, z. B. red and green luminescent paint, of which fluorescent particles with? .. B. green luminescent paint are coated with a barrier layer 7 and have a higher excitation threshold compared with the red-luminescent particles. The treated and coated with a barrier layer as well as the untreated particles Tcilchen are mixed for the production of the fluorescent screen, wherein the weight ratio of the beiiien Leui.iHMuiie is determined in ütri LuMiiig yum licit gcwüiiM-iiicii color characteristics of the fluorescent screen. The resulting mixture 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 umbrella contains a pad! the end Glass with a luminescent layer lying on it, which consists of a mixture of the luminescent particles 6 with different?

dener luminescent color is where the particles of a luminescent material carry the barrier layer 7.

According to the method described, a barrier layer with a second predetermined thickness can be applied Phosphor particles with a third, e.g. B. 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 the procedure to the umbrella underlay. 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 and a three-colored screen, in which a layer of a particle mixture of two phosphors with different luminescence

colors and nil different increased excitation thresholds and the other layer is made up of single-color ordinary phosphor particles.

The method according to the invention enables the production of luminescent in the first half of a) 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 The starting solution is added, from which the deposition of the barrier layer takes place, whereupon the finished layer is a Heat treatment is subjected to 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 Gold salt treated and the structure produced afterwards treated at a temperature of over 250 "C. In In this case, by changing the cell and the temperature of the heat treatment, the depth of the Control activator diffusion into the barrier layer, thereby forming a barrier layer in which part of the Layer luminesces and the other part fulfills the function of the inert barrier layer.

In Fig. 4 shows a phosphor particle 6 which carries a luminescent barrier layer 8. Such particles are obtained by dispersing a phosphor powder in the starting solution from which the barrier layer is set and which additionally contains gold chloride as an activating metal salt. An activation metal is chosen so that the luminescent color of the barrier layer to be applied differs from the luminescent color of the particles to be coated. The treated phosphor powder is then filtered and ^{annealed at a temperature of over 250 °} C., the barrier layer becoming a luminescent layer which, when excited, emits light in the desired range of the electromagnetic spectrum. The "multicolored" fluorescent particles produced in this way are used to produce veibuiiicdcncn Siiimnai icn. / - "· lm'ics 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: a screen in which the phosphor particles of one luminescent color with one in another A screen of mixed particles of two phosphors with different luminescent colors, of which the particles of one phosphor are coated with an inert barrier layer of a certain thickness and the particles of the other phosphor have a luminescent barrier layer of a second predetermined thickness, which emitting radiation with a third color Such screens are produced by applying the described particles to a screen substrate by any known method, for example by means of sedimentation.

In Figure 5 is a sectional view of another Luminescent screen shown. The base 1 made of glass carries a phosphor layer 2 with a luminescent Barrier layer 9 is covered.This screen is created as follows: The inner surface of an underlay, which can be the front glass plate of the bulb of a cathode ray tube, is after a any known method with the phosphor layer 2 covers the luminous in one color The finished The layer is then treated with the starting solution to form an inert barrier layer. The knockdown takes place over a period of time which is necessary to produce the barrier layer 9 with the desired thickness. After the settling process has ended, the solution is poured off and the finished inert barrier layer at least one of the series silver, gold, copper, manganese is chosen with an aqueous solution of a salt Metal treated. The chosen metal determines the Lumincs / cn / farbc of the barrier layer. The activation The barrier layer is made by heat treatment of the screen cover at a temperature of over 250 "C. the running of the activation metal · diffusion into the barrier layer by the choice of temperature and the The duration of the heat treatment is controlled.

The following are general examples 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 I.

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 yttrium silicate-based material are treated. Blue fluorescent powder activated with cerium (YjSijO; · Ce) with a solution which is composed of the following components: 20 ml aqueous 5 M zinc sulfate solution, 20 ml aqueous gallium bromide solution. 1 ml aqueous 1.10 ⁴ -m gold chloride solution. 300 ml aqueous 1m-thioacetamide solution. 25 ml of 2 m hydrochloric acid solution to adjust the pH value 1. The remaining part of the total volume of the solution of 500 ml is made up of water. The treatment takes place at a temperature of 95 ° C in the course of 1.5 hours and leads to the formation of a barrier consisting of the compound ZnGa; S ₄ ■ Au

i: i f j rk

k__fi £ "u" J ~ - ι ".." u

finished barrier layer luminesces when excited in the red spectrum range. To increase the radiation intensity of the phosphor manufactured in an inactive medium during I h is annealed at 350 C ^c. 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 lights up 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 sulphide activated with silver and glowing green (ZnSo £ 2 · CdSoj8 Ag), which is precipitated from a potassium silicate solution. The coating density is 23 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, which is made up 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 of water. The finished solution

22 Ol 585

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pours mar. into the tube bulb, which is placed in a thermostat with a constant temperature of 50 "C. A barrier layer consisting of zinc sulfide is deposited from the solution on the surface of the phosphor. At the concentration and temperature of the solution, the rate of precipitation is 6 -Γ nni per minute. The deposition takes 1.5 h, a barrier layer with a thickness of 400 to 450 nm forms Barrier layer, red fluorescent phosphor is precipitated on the base of yttrium oxysulfide activated with europium (Yi / iMKuniwiOjS). The density of the / wide l. Fluorescent layer is 1.5 to 2 mg / cm- '. The screen produced is aluminized in the usual way. When excited with an electron beam of b kV, a red glow is observed on the screen, which was produced in the manner described increase in electron beam energy up to <? kV shifts the luminescent color into the yellow-orange area.

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

When using different combinations of phosphors and when changing the thickness of the barrier layer You can use the procedure described to put umbrellas in place Manufacture 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 fluorescent screen is c.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 UB of the periodic table exhibits the indiumsuifiri 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 IHA have a larger atomic number. As a result, can a large value of the Leuchtsturf 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 with the following composition in a flask: 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 what scr. 10 g of green luminous phosphor powder ZnSnn · CdSd ₁ ) Cu · Al are dispersed in the solution mentioned. and the suspension obtained is kept at b0 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 oil particles. The oil particles treated in this way are separated from animal solution and dried at a temperature of 120 C. The straight line "e"

> n shows in FIG. 7 the luminance Ii of the phosphor produced as a function of the excitation voltage Ll. The excitation threshold of this phosphor is 8 kV. When changing the duration of the fluorescent powder treatment in the solution, phosphors can be used with

> -, the excitation threshold 2.5 kV (straight line »f«). 4 kV (straight line “g”), 6 kV (straight line “h”) and 10 kV (straight line “i”) . Carrying out the treatment in a liquid medium helps to form a uniform barrier layer on the surface of particles

to any in the range from 1 to 50 μΐη Diameters at. Subsequent fractionation of the polydisperse barrier phosphor gives Luminous material parts with different and for each part specific sizes of the mean particle

] · -, durchniessers. however, the excitation threshold remains the same for individual groups. Because the barrier formation occurs at low temperatures (below the boiling point the solution) takes place, the luminance of the phosphor becomes practical in the treatment described not diminished.

For the production of a fluorescent colored screen, the green one is used in the manner described 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 resulting mixture becomes from a 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 phosphors of different types Luminescent paint in which at least one of the phosphors has a barrier layer that partially absorbs the energy of the electrons is applied 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 in Layer or particle form present phosphor is deposited, the pH of the solution is set in a range favorable for slight precipitation, characterized in that 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 of aqueous 2 m gallium bromide solution sung, 0.2% by volume of aqueous 1 x 10 - <- m gold chloride solution, 60% by volume of aqueous 1-m-thioacetamide solution, 5% by volume of 2 m hydrochloric acid and as The rest of the water is formed; or b) on green luminescent zinc-cadmium sulfide of the composition ZnSo.62 ■ CdSoje · Ag the barrier layer from a solution of 2% by volume of 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 the remainder Water is formed; or c) on green luminescent zinc-cadmium sulfide of the composition Cu ■ Al the barrier layer from a solution of 2% by volume aqueous 0.5 m indium nitrate solution su ng, 20% by volume of aqueous 0.2 m-thioacetamide solution sung, 2% by volume 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 manner according to process a) is annealed coated phosphor in an inactive medium for 1 hour at 35O ⁰ C. 3. The method according to claim 1, characterized in that according to procedure c) coated phosphor is dried at a temperature of 120 ° C. The invention relates to a method for producing luminescent screens with at least two luminescent materials different luminescent color in which on 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 on that present in 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 for color display devices. £, en suitable where the illustration 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: