DE1051401B - Voltage electroluminescent lamp - Google Patents

Description

GERMAN

INTERNAT. KL.

kl H 05 b

PATENT OFFICE

C 09k 11/56 G18791VIIIc / 21f

REPORTING DAY: JANUARY 16, 1 956

NOTICE "THE REGISTRATION 'AND ISSUE OF THE EDITORIAL: FEBRUARY 2, 1959

The invention relates to under the action of an alternating electric field directly Visible light emitting phosphors, hereinafter referred to as phosphors or electroluminescent substances for short and electroluminescent lamps made therewith.

Known electroluminescent substances emitting blue light were made from activated with copper Zinc oxide or mixtures of zinc oxide and zinc sulfide activated with copper.

Electroluminescent substances mixed with other activators such as silver or manganese or copper and lead are known. Such phosphors are used with and without flux and / or in special annealing atmospheres, such as hydrogen sulfide, manufactured. The brightness of the known phosphors is relatively low, and the luminous efficacy, the amount of light emitted per unit of energy consumed generally falls over time if the lamp or light cell is used for a long time. Usually a considerable loss occurs shortly after it has been used, and the lower the light output, the more slowly the end of the service life the lamp is reached. This loss of luminous efficiency during the life of the lamp are called instability. Electroluminescent cells with the known phosphors therefore have an undesirably great instability.

The object of the invention is to improve double-activated zinc sulfide-zinc oxide phosphors. It consists in the fact that the zinc sulfide-zinc oxide phosphor is next to the electroluminescent lamp Copper contains silver as a second activator and, by annealing, a common basic mixture of 95 bis 50 weight percent zinc sulfide and 5 to 50 weight percent zinc oxide together with 0.005 to 0.5 weight percent Copper and 0.002 to 0.1 percent by weight silver in the usual way in a closed The vessel is made at 800 to 1200 ° C. These phosphors that are either green or dark blue When excited, light emitting in an alternating electric field has a greater, approximately doubled Brightness compared to the known phosphors and better stability.

In addition, the temperature used to glow the phosphor can be adjusted regulate its luminous color. If, for example, a phosphor activated with silver and copper is used in accordance with the invention annealed at 1020 to 1200 ° C, it glows deep dark blue, when using annealing temperatures below 1020 to 800 ° C it lights up green. The fluorescent substance that glows blue is because the green one The copper band appears, the spectral light band is weakly broadened, or its tip is slightly behind Voltage electroluminescent lamp

General Electric Company, Schenectady, N.Y. (V. St. A.)

Representative:
Dr.-Ing. A. v. Kreisler, Dr.-Ing. K. Schönwald, Dipl.-Chem. Dr. phil. H. Siebeneicher

and Dr.-Ing. Th. Meyer, patent attorneys,

Cologne 1, Deichmannhaus

Claimed priority: '. St. v. America January 17, 1955

Herman Christian Froelich, Cleveland Heights, Ohio

(V. St. Α.),
has been named as the inventor ~

Shifted longer wavelengths compared to the emission of a phosphor activated only with copper. This spectral shift occurs with excitation with alternating voltage of low frequency (60 Hz), at higher frequencies, e.g. B. from 5000 Hz, the colors are closer together. Both the blue one than the green light emitting phosphor activated with silver and copper have compared to only one with copper activated phosphor greater stability and work satisfactorily when excited with high, medium and low frequencies.

Fig. 1 shows an example made using a phosphor according to the invention Embodiment of an electroluminescent cell, shown in perspective;

Fig. 2 and 3 show cross-sections, the other possible arrangements for the various Illustrate layers in electroluminescent cells.

Electroluminescent cells or lamps generally contain a layer of in a dielectric Means dispersed phosphor that is sandwiched between two conductive layers. The two leading ones Layers are energized to excite the phosphor. So that the device is practically usable Can emit light, at least one of the two conductive layers is transparent or translucent. For this purpose it is preferable to

809 767) 232

called conductive glass is used. The other conductive plate preferably reflects the light, though it can also be translucent if the lamp is to emit light on both sides.

The dielectric in which the phosphor is distributed preferably has a high dielectric constant. Optionally, between the phosphor layer and one or both conductive layers an insulating layer, for example a nitrocellulose layer of uniform thickness, is included will. If a nitrocellulose layer is arranged over the conductive layer on a glass plate, so the phosphor can be embedded in a methyl cellulose or polystyrene layer.

In the luminescent plate according to FIG. 1, a glass plate 1 is provided with a conductive coating 2 a layer 3 of the phosphor distributed in a dielectric is applied. The phosphor layer 3 is covered with a conductive layer 4, for example a metal plate or a translucent one Head, covered. The voltage is generated between the metal chip 5 and the conductive layer 4 applied, so that an electric field is created which excites the phosphor layer 3 to glow.

Another layer arrangement is shown in FIG. The glass plate 6 is in the usual way with a Conductive layer 7 is provided, on which an insulating layer 8, usually made of nitrocellulose, is applied is. The phosphor layer (phosphor dispersed in a dielectric) is located on the layer 8 9). Finally, another insulating layer 10 and a conductive layer 11 follow. «, *"%

In Fig. 3, a corresponding arrangement is shown in which only that in the arrangement
provided conductive layer 10 is omitted.

A typical approach for a phosphor consists, for example, of 600 g of the purest, precipitated zinc sulfide and 200 g of the purest zinc oxide, mixed with water to form a paste. A solution of 0.4 g of copper as copper nitrate and 0.08 g of silver as silver nitrate in 100 cm ^{3 of} water is added to this batch. The metal sulfides precipitate immediately. The mixture is stirred until it has taken on a uniform, slightly gray color. It is then dried at 150 ° C., sieved through a fine sieve and placed in the annealing vessel. The annealing vessel is preferably designed in such a way that the powder to be annealed can be annealed without too great an excess of air. A quartz tube closed at one end is expediently used for annealing and is pushed into a corresponding somewhat larger one in such a way that the open end of the quartz tube is at the bottom of the outer tube. The annular gap between the two pipes can be filled with zinc sulfide or zinc oxide to further suppress air circulation.

The tubes are placed in a cold oven, which is then heated to 1040 ° C. The load is held at this temperature for 15 to 20 hours, then removed from the oven while still hot and left to cool. The phosphor is then sieved and stirred into a cold solution of 500 cm ^{3 of} glacial acetic acid in 200 cm ^{3 of} water. After stirring the mixture for three hours, it is heated to the boil and shortly thereafter filtered while it is still hot. The residue is washed with cold, dilute acetic acid and then with water.

The filter cake is ^{slurried again in 1000 cm 3 of} lukewarm water and treated for 1/2 hour with a solution of 25 g of sodium cyanide in water with stirring. Then it is filtered, washed, dried and finally sieved through a sieve with sieve openings of about 75 μ.

A phosphor produced in this way gives, if annealed at temperatures above 1020 ° C, in an electroluminescent cell at 240VoIt, 60 Hz a brightness of 25 units on an arbitrary one Scale. A corresponding phosphor that was activated only with copper, i.e. without silver, only has a brightness of 11 of these units. Corresponding results are obtained with the green one, at 900 ° C obtained annealed phosphor.

In addition to doubling the brightness of both the blue and the green phosphor, both Cases get a significantly improved stability. For example, a shows double according to the above activated luminescent material after 1800 hours of operation in an electroluminescent lamp a loss of light yield from only half to a fifth of a phosphor activated only with copper. The stability of the In other words, phosphor activated with copper and silver is twice to five times as good as that of a phosphor activated only with copper.

Good results are achieved with activator concentrations of 0.005 to 0.5 percent by weight copper and Obtained 0.002 to 0.1 weight percent silver. Optimal brightness is achieved when using 0.05 percent by weight Copper and 0.01 weight percent silver based on the total weight of the applied Base material, achieved and if the base material consists of 75 percent by weight zinc sulfide and 25 percent by weight Zinc oxide. The composition of the base material can be within wide limits, for example between 95%> zinc sulphide and 5% zinc oxide and 50% zinc sulphide and 50% zinc oxide, vary.

The annealing temperatures for the blue modification of the phosphor can be 1020 to 1200 ° C will. With the use of higher temperatures, however, the brightness generally falls and the grain becomes coarser and accordingly, the optimum annealing temperature for the blue modification became 1040 ° C found. The green fluorescent phosphor is annealed at 800 to 1020 ° C, preferably at 900 ° C.

So the main difference between making the blue and green modification is the annealing temperature. The blue modification is formed during annealing over 1020 ° C, the green during annealing at 1020 ⁰ C. Although 1020 ° C is just the transformation temperature from cubic to hexagonal zinc sulfide, can not be said with certainty that the crystal modification alone determines the luminous color.

Although there are certain proportions of activator and base material in the phosphor formulation, the proportions in the finished phosphor may be different because of the treatment With acetic acid and cyanide free metal sulfides and practically all of the zinc oxide can be removed.

Zinc oxide is readily soluble in zinc sulfide and it is therefore possible that a small amount of zinc oxide may be present in the solid solution in zinc sulfide is not attacked by treatment with acetic acid or cyanide.

From the examples it can be seen that the use of a special protective gas atmosphere or evacuated Incandescent chambers for the production of the improved phosphors are not required, it is sufficient rather, to restrict or to restrict the air admission, for example in the manner described above impede.

Of course, in the context of the invention, the amounts of activators, the calcination temperatures, the Basic components independent of one another and in their relationship to one another within wide limits vary.

Claims (6)

Patent claims: 1. Elektrolum ineszenzlampe consisting of a layer of a "by an electric field stimulable electroluminescent material from dop pelt_ ^a. Ktivjerten ZmksiilM-Zinkoxydleuchtstofiteilchen between conductive layers, of which at least one is transparent, characterized in that the zinc sulfide Zinkoxydleuchtstoff nehpn" K "" pfpr Si ' l h / y ^a ls contains a second activator and by annealing a conventional base mixture of 95 to 50 percent by weight of zinc sulfide and 5 to 50 percent by weight of zinc oxide together with 0.005 to 0.5 percent by weight of Kupier and 0.002 to 0.1 percent by weight of silver in is usually made in a closed vessel at 800 to 1200 ° C. 2. Electroluminescent lamp according to claim 1, characterized in that the phosphor is about 0.05 percent by weight copper and about 0.01 percent by weight silver, based on the total weight of the raw material mixture. 3. Electroluminescent lamp according to claim 1 or 2, characterized in that the basic current mixture in a known manner 75 percent by weight of zinc sulfide and 25 percent by weight of zinc oxide contains. 4. Dark blue light emitting electroluminescent lamp according to claim 1 to 3, characterized characterized in that the zinc sulfide-zinc oxide phosphor activated with copper and silver at 1020 to 1200 ° C, preferably at 1040 ° C, has been annealed. 5. Green light emitting electroluminescent lamp according to claim 1 to 3, characterized in that that the zinc sulfide-zinc oxide phosphor activated with copper and silver at 800 to 1000 ° C, preferably at 900 ° C, has been annealed. 6. Process for the production of an electroluminescent material which can be excited in an alternating electric field for use in electroluminescent lamps according to claim 1, characterized in that that a mixture of 95 to 50 percent by weight zinc sulfide and 5 to 50 percent by weight Zinc oxide with 0.005 to 0.5 percent by weight copper and 0.002 to 0.1 percent by weight silver on 800 is annealed to 1200 ° C, the annealing product is boiled in acetic acid in a known manner, filtered and the residue is washed with acetic acid and water and the filter residue after Slurry in water is treated with a cyanide solution. Considered publications:
Belgian Patent No. 497,702;
French Patent No. 1,075,643;
U.S. Patent No. 2,566,349. 1 sheet of drawings > 809 767/232 2.