DE2126889A1 - Process for making a luminescent ornamental barrier-coated chalcogenide - Google Patents

Description

g, Hans-Dietrich cell *

Applicant: U.V. Philips'Gloftilampenfabneken Va / RV.

Files Na YBB-. 4907

Registration dated May 28, 1971

Method of making a luraineezator with a barrier layer provided chalcogenide.

The invention relates to a method for producing a luminescent one provided with a barrier layer Chalcogenide of zinc and / or cadmium. Furthermore, the invention relates to a luminescent zinc and / or cadmium chalcogenide produced by such a method and to such a method cathode ray tube containing luminescent chalcogenide.

They chalcogenides (i.e. sulfides, selenides, tellurides and Mixed crystals of the mentioned salts) of zinc and / or cadmium, which are inactivated or contain as an activator e.g. silver, gold or copper and optionally as a coactivator e.g. chlorine or aluminum known as phosphors. They can be excited by ultraviolet radiation and with electrons and then expand to a different emission color depending on the zinc / cadmium ratio and the type and concentration of the activator. The chalcogenides mentioned are mainly used in

109861/1830

-2- PHN. 4907 *

Screening of cathode ray tubes, e.g. oscilloscope tubes or television display tubes, used. The luminescent sulfides in particular have found a very wide range of applications.

As is known, two phosphors can be used to reproduce differently colored images with the aid of a cathode ray tube are «which each have their own emission color» where the color of the image to be reproduced is determined by the energy of the exciting electrons will. The two phosphors can e.g. in two discrete layers

_k th are mounted on the screen, these layers being separated by an intermediate layer of a non-luminescent material. If the screen is scanned by an electron beam with relatively low energy, the image to be reproduced will appear in the color that belongs to the first luminous layer lying closest to the electron gun. However, if the energy of the exciting electrons is increased in such a way that the electrons can also penetrate into the second luminous layer, an image is reproduced, the color of which is determined by the radiation emitted by the two luminous layers. By changing the electron energy

W gie various mixed colors can be reproduced. In practice, it turns out that the production of the double-layer screens described above is particularly difficult and expensive. The reproducibility of the thickness of the layers must be subject to high requirements, that is to say that the thickness of the layers must be constant over the entire screen.

It is also known to produce phosphors which have a threshold value for the excitation energy. For this purpose, the individual phosphor particles provided with a barrier layer in which only

1GS8S1 / 183Q

-3- PHN. 4907.

Electrons can penetrate with a certain minimum energy. The one with A phosphor provided with such a barrier layer may be coated with a different phosphor having an emission color different from that of the first phosphor has to be mixed · This mixture can be mixed in the usual way without Difficulty being attached to the screen of a cathode ray tube. Depending on the energy of the exciting electrons, the »central radiation consists of light coming from one phosphor or from the two phosphors.

From the USA patent 3,408,223 is a method for Manufacture of such a phosphor provided with a barrier layer is known, in which the phosphor particles with a heated gas stream in That contain oxygen and silane vapors. the thereby formed barrier layer consists of SiO- · Another method for Formation of a barrier layer is known from the US patent specification 3.449.148.- Here, the phosphor particles, especially luminescent Sulphide particles, superficially oxidized at an elevated temperature in an oxygen-containing atmosphere, after which the phosphor particles, again be exposed to an elevated temperature, a sulphurous atmosphere and the oxidized surface is re-sulphurised.

The mentioned known method for increasing the threshold value for the excitation energy of phosphors by attaching a Barrier layers have the disadvantage that they have to be carried out at a high temperature and that they require expensive equipment, such as ovens, require. Treatment at a high temperature affects the luminescent properties of the phosphors. Especially if Having to deal with large amounts of a phosphor is a special one intricate equipment required. When applying a SIO ^ layer

109851/1830 ^; "ύ

-4- PHN. 4907.

the known method gives a less precisely defined layer, the thickness of which is difficult to reproduce and the composition of which deviates considerably from the phosphorus composition. The risk of impurities being introduced is great. The known method, in which the sulphide grains are superficially oxidized and then re-sulphurized, still has the disadvantage that part of the phosphorus is lost ₉ because this part is converted into the barrier layer. Furthermore, thick barriers are difficult to apply in this way.

The invention aims to provide a method for producing a with a barrier layer provided phosphor, in which the disadvantages of the known methods mentioned are avoided.

Sin method according to the invention for producing a

luminescent barrier-coated chalcogenides of zinc and / or cadmium is characterized in that a suspension of a luminescent chalcogenides of zinc and / or cadmium in an aqueous Zinc and / or cadmium ions and a sulfur compound Solution is made in which suspension a layer of sulfide of Zinc and / or cadmium is deposited on the luminescent chalcogenide by homogeneous precipitation.

In the method according to the invention, a layer is made a niohtlurainescent sulfide of zinc and / or cadmium is deposited evenly on the luminescent chalcogenide crystals by homogeneous precipitation. The barrier layer grows on top of the existing ones Chalcogenide crystals uniformly * The grown layer shows the same or an analogous crystal structure as the lurainescent Chalcogenide on.

109851/1830

-5- PHN. 4907.

Although it is known to have a luminescent chalcogenide in an aqueous medium with a non-luminescent precipitate To coat zinc sulphide in order to obtain a free-flowing powder or to increase the resistance of the phosphor to temperature treatments (see e.g. U.S. Patent 2,908,588). With these processes, however, free zinc sulfide is formed in the solution, which is considered to be a very fine-grained powder on and between the luminescent chalcogenide grains precipitates. The phosphor grains coated in this way cannot be used as a barrier phosphor.

It is useful in a method according to the invention to suspend such an amount of luminescent chalcogenide in the solution that the suspension can be stirred well · The suspension not diluted to such an extent that non-luminescent zinc and / or cadmium sulfide nuclei can be formed in the solution.

A method according to the invention has the advantage that no treatment at high temperature is required, so that the luminescent properties of the phosphor material as such are not impaired »A method according to the invention can be used in any amount with particularly simple Apparatus can be carried out while the starting materials to be used are cheap and easily available in its very form. «The course of the reaction when the barrier layer grows is simple and easy control so that very precisely defined barrier layers are formed can. The phosphor crystals themselves are not attacked.

ι- Preferably in a method according to the invention a aqueous solution of a soluble zinc and / or cadmium al ze 8, a lye, . a complexing agent for zinc and / or cadmium and an organic one thio compound which slowly splits off sulfide ions is used in the case of hydrolysis.

109851/1830

-6- PHN. 4907.

Organic thio compounds in association with an alkali and a This is because complexing agents form particularly suitable compounds for implementation homogeneous precipitation. By using a complexing agent for zinc and / or cadmium, a sufficient number of zinc and / or Cadmium ions are kept in solution · This complex-forming function but can be fulfilled by the alkali to be used when using zinc ions will. If the lye is strong enough, it becomes soluble Zincates formed. As complexing agents, e.g. ammonia or Ethylenediaminetetraacetic acid (EDTA) use.

According to a preferred embodiment of a method according to the invention, an aqueous solution of a soluble zinc and / or cadmium salt, an alkali and optionally a complexing agent is first prepared, in which the luminescent chalcogenide is then suspended. The suspension is then brought to a temperature between 50 and 100 ° C. and only then is a thio compound added to the suspension with stirring, after which the suspension is kept at the temperature between 50 and 100 ^° C. for at least 5 minutes with stirring. In this way, the speed and the duration of the homogeneous precipitation can be controlled with great accuracy, so that a barrier layer with a precisely defined threshold value for the excitation energy of the electrons can be formed.

Thioacetate and thioureum, for example, can be used as thio compounds be used. The latter connection is preferred because that Thioacetamide has a high toxicity. The Thioureum is in a Amount applied that is at least equal to that according to the stoehiometry Precipitation of the required amount of zinc and / or cadmium sulfide required Amount is

1 OiSSI / 1830-

-7- PHN. 4907.

In a method according to the invention, preferably an 18-liter zinc salt is used, because then colorless barrier layers are obtained and because then no complexing agent is used in addition to the lye needs to become.

The amount of caustic to be used is in accordance with a method of the invention preferably such) that the pH assumes a value between 15 and 15. The homogeneous precipitation works with this value very easily in front of you. The rate of deposition is greater »ever after the alkali concentration and the concentration of the sulfur compound used are greater. The thickness of the barrier layer - is through the amount of zinc and / or cadmium salt used, the amount of sulfur compound used as well as the total reaction time and the reaction temperature is determined. The amount of zinc and / or cadmium sulfide, which is deposited in a certain case depends on the required thickness of the barrier layer and on the grain size of the starting material used luminescent chalcogenides depending.

A method according to the invention is preferably used for Manufacture of a luminescent sulfide with a barrier layer is used because the luminescent sulfides in practice are the most important phosphors are.

The one provided with a barrier layer according to the invention

Chalcogenide can be filtered, washed, and dried from the suspension to be deposited.

The invention will now be explained using a few examples.
example 1

0.82 g of ZnCl ₂ is dissolved in 200 ml of a 4N NaOH solution. In

109851/1830

3 g of green luminescent (Zn, Cd) S-Ag, Cl are then suspended in this clear solution. After heating to 90 ° C., 0.45 S thioureum (CS (NHp) ₂ ) is added under tubes, after which the suspension is kept for three quarters of an hour is stirred at 90 ^{° C.} Then the luminescent sulfide is separated from the liquid by filtration and washed with water. After drying, the sulfide provided with a barrier layer is ready for use. When excited with electrons, the sulfide has a threshold value for the excitation energy of 3 kV.
Example 2

The process according to Example 1 is repeated, except that 1.80 g of thioureum are used under the same conditions. The threshold value for the excitation is now 6.9 kV. Example 3

_{0.82 g of ZnCl 2 is} dissolved in 200 ml of 4N NaOH solution. After heating this solution at 90 ⁰ C Jg green luminescent (Zn, Cd) S Ag ₉ are Cl and 0.91 g Thioureum added. The suspension is kept at a temperature of 90 ° C. for a quarter of an hour while stirring. Then the luminescent sulfide is filtered off, washed and dried. P The threshold value for excitation with electrons is now 2.5 kV, example 4

The process according to Example 3 is carried out under the same conditions, with the difference that the reaction is continued for half an hour. The threshold is now at 3 # 7 kV.
Example 5 .

If, in the method according to Example 3, the reaction time is extended to 1.5 hours, it turns out that the threshold value

10 9 8 B 1/1 8 3 0

-9- PHN. 4907.

voltage of the sulfide provided with a barrier layer is 6.5 kV. Example 6

The procedure is exactly the same as in Example 2, but now 3 g of blue-luminescent ZnS-Ag, Cl are provided with a barrier layer. * The sulfide obtained lights up when the incident electrons have passed through a voltage difference of at least 7.0 kV. Example 7

Using a method corresponding to that of Example 2, 3 g (Zn _n oCd _n .) S-Cu, Al are provided with a barrier layer. It turns out that the threshold voltage is 6.8 kV. Example 8

The procedure of Example 3 is repeated, but 1 _f 72 g ZnSO..7H ₂ O are used instead of ZnCl. It turns out that the threshold voltage is the same as that in Example 3. Example 9

25 mg of a red luminescent Y ₂ OpS-O.05Eu are deposited on a glass screen together with 100 mg of a green luminescent (Zn _ü gCcL As-Ag, Cl with a threshold voltage of 7 »2 kV provided with a barrier layer. This screen is in At an acceleration voltage of the electrons of 4 kV the color of the emission of the screen is red, at 7.5 kV red, at 8.5 kV orange, at 10.2 kV yellow, at 12.2 kV yellow-green, green at 14.2 kV and higher. Example 10

A screen is produced in the same way as in Example 9, but using a green luminescent sulfide with a threshold value

109851/1830

-10- PHN. 4907.

voltage of 5f2 kV is used. At an acceleration voltage of With exciting electrons of 5 »2 kV, the emission of the screen is red, at 5.8 kV orange, at 6.5 kV yellow, at 7.5 kV yellow grlin, green at 9.5 kV.

10 9 8 51/18 3

Claims (10)

-11- PLIN. 4907. PATENTA U PROVISION Egg 1. Method of making a luminescent with a Barrier-coated chalcogenides of zinc and / or cadmium, thereby characterized in that a suspension of a luminescent chalcogenide of zinc and / or cadmium in an aqueous zinc and / or cadmium ions and a solution containing sulfur compound is prepared, in which suspension a layer of sulfide of zinc and / or cadmium is deposited by homogeneous precipitation on the luminescent chalcogenide. 2. The method according to claim 1, characterized in that the aqueous solution a soluble salt of zinc and / or cadmium, a lye, a complexing agent for zinc and / or cadmium and an organic one Hydrolysis contains thio compounds which slowly release sulfide ions 3. The method according to claim 2, characterized in that an aqueous solution is prepared which contains a soluble salt of zinc and / or cadmium and a lye. that the luminescent chalcogenide is suspended in the solution; that the suspension formed in this way is brought to a temperature between 50 and 100 ° C., and that the thio compound is then added while stirring the suspension, after which the suspension is kept at a temperature between 50 and 100 ^° C. for at least 5 minutes with stirring will. 4. The method according to claim 2 or 3ι characterized in that that thioureum is used as the thio compound, in an amount the amount required to be at least equal to the stoichiometric amount Precipitation of the required amount of zinc and / or cadmium sulfide is. 5. The method according to claim 1, 2, 3 or 4 * characterized in that the aqueous solution contains a soluble zinc salt 109851/1830 P 21 2β 389.3 JA Hamburg, July 20, 1971 / A / Tö N.V. Philips' Gloeilarnpenfabrieken ^ t.Akt.Z. PHN 4 ^ - New page 12 - 6. The method according to claim 2, 3 * ^ or 5 *, characterized in that that the aqueous solution contains such an amount of alkali that the pH has a value between 10 and 15. 7 «Method according to one or more of the preceding claims, in which the luminescent chalcogenide is a luminescent sulfide. ™ 8. Method according to one or more of the preceding Claims, characterized in that the luminescent chalcogenide provided with a barrier layer from the suspension • sion is deposited by filtering, washing and drying. 9, By a method according to one or more of the preceding Claims made luminescent chalcogenide of Zinc and / or cadmium, which is provided with a barrier layer is that of uniformly deposited non-luminescent Sulphide consists of sink and / or cadmium. 10. Use of an iuminescent chalcogenide according to claim 9 in the fluorescent screen of a color image reproduction electron beam tube. ■■■■ ".- · ORIGINAL 10 9 8 5 1/18 3 0