US2770749A

US2770749A - Cathode-ray tube comprising a luminescent screen

Info

Publication number: US2770749A
Application number: US317716A
Authority: US
Inventors: Bril Alfred; Hendrik A Klasens; Zalm Pieter
Original assignee: Hartford National Bank and Trust Co
Current assignee: Hartford National Bank and Trust Co
Priority date: 1952-08-21
Filing date: 1952-10-30
Publication date: 1956-11-13
Anticipated expiration: 1973-11-13

Description

Nov. 13, 1956 A. BRIL ET AL 2,770,749

CATHODE-RAY TUBE COMPRISING A LUMINESCEINT SCREEN Filed Oct. 50, 1952 2 Sheets-Sheet l INVENTORS ALF-RED BRILL HENDRIK ANNE KLASENS PIETER ZALM AGENT Nov. 13, 1956 A. BRIL ET AL 2,770,749

OATHODE-RAY TUBE COMPRISING A LUMINESCENT SCREEN Filed Oct. 30, 1952 2 Sheets-Sheet 2 m Fig. 2

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\ INVENTORS Alfred Bril Hendrik Anne Klosens BY Pieter Zulm AGENT United States Patent CATHODE-RAY TUBE COMPRISING A LUMINESCENT SCREEN Alfred Bril, Hendrik A. Klasens, and Pieter Zalm, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application October 30, 1952, Serial No. 317,716

Claims priority, application Netherlands August 21, 1952 1 Claim. (Cl. 313-92) This invention relates to a cathode-ray tube comprising a luminescent screen, of which the decay time is shorter than 10" sec. The invention furthermore relates to an apparatus for converting radiation pulses into electrical pulses, which comprises such a cathode-ray tube.

In cathode-ray tubes comprising a luminescent screen, it is in certain cases desirable that the luminescent material should exhibit a luminescence having a decay time shorter than sec. The term decay-time of the luminescence is to be understood here to mean the time in which the intensity of the emitted radiation, after the excitation has ceased, decreases to l/e of its maximum value. Such a case occurs, for example, when a cathoderay tube is used as a source of radiation in apparatus for converting radiation pulses into electrical pulses. One of the representatives of this kind of apparatus which is most known is the flying spot scanner which is used inter alia for the transmission of television images of films or lantern slides. In flying-spot scanners the cathode-ray describes on the screen of the cathode-ray tube a frame which serves as a source of rays for lighting the image of the film or the lantern slide. The radiation traversing the image is received by a photo-electric cell and converted thereby into electrical pulses.

The wavelength corresponding to the maximum of the spectral distribution of the emitted radiation is comprised between 3800 A. and 5500 A. for most cathode-ray tubes used for this purpose. A luminescent substance which is frequently used is, for example, green-luminescent zincoxide which has a decay-time of about 10- sec. The use of silicates of the alikaline-earth metals or alkaline metals, activated with trivalent cerium, is also known in this connection.

For uses other than for a flying-spot scanner, it may also be important to dispose of a cathode-ray tube having a luminescent screen with a decay time shorter than 10- sec. As examples thereof may be mentioned radar and fascimile transmission.

Our invention will be more apparent after referring to the following specification and attached drawing in which:

Figure 1 is a view partially in perspective and partially in section of a cathode-ray tube manufactured according to our invention; and

Figure 2 is a graph showing the relationship of the wavelength of the radiation emitted by the luminescent material of our invention to the intensity of the emitted radiation.

A cathode-ray tube according to the invention comprises a luminescent screen having a decay time shorter than 10- sec. and is characterized by the fact that the luminescent screen contains ultra-violet-luminescent zirconium pyrophosphate and that the window consists of material which allows the passage of radiation emitted by zirconium pyrophosphate.

The zirconium pyrophosphate, upon being excited by Patented Nov. 13, 1956 electrons, emits a radiation, of which the spectral distribution exhibits a maximum at about 2900 A.

Quartz, for example, may be used as a window for the passage of such short-wave ultraviolet radiation.

The energy output of zirconium pyrophosphate upon excitation by electrons of 20 kilovolts is comparatively high, viz. 4%.

Owing to the ultra-short radiation, a cathode-ray tube according to the invention may advantageously be utilised for some particular uses for which the conventional cathode-ray tubes comprising a luminescent screen having a decay time shorter than 10 sec. cannot be employed. Thus, a tube according to the invention may be used, for example, as a source of radiation for measuring the decay time of luminescent substances which are required to be excited by short-wave ultraviolet radiation, since it is extremely simple to obtain rapidly extinguishing radiation pulses from such a cathode-ray tube by supplying a suitable voltage, for example a so-called block voltage, to the electrode controlling the intensity of the cathode-ray. The use of a cathode-ray tube according to the invention is furthermore of particular importance in devices in which the radiation from the luminescent screen traverses a microscope in a direction which is inverse to the ordinary path of the light rays in a microscope, that is to say through the ocular, then through the objective and finally through the object. Such devices are already known for use with visible light. In such devices, a greatly reduced image of the raster appearing on the screen of the cathode-ray tube is reproduced on the object and the light transmitted by the object is received by a photoelectric cell and converted into electrical pulses, which may serve, if desired after being amplified, to produce an image identical with the object on the screen of a cathode-ray tube. It is evident, that, as an alternative, the electrical pulses may be transmitted via a transmitter and received at far distant places to be used in a cathode-ray tube for the composition of an image. Since, as is well-known, a greater resolving power is obtained if ultraviolet radiation and preferably shortwave ultraviolet radiation instead of light is used, it is evident that a cathode-ray tube according to the invention is very important for such a use, since it emits radiation with a maximum at about 2900 A. Furthermore, it is possible to make visible objects which absorb solely ultraviolet radiation. In such a device the microscope is naturally required to comprise lenses which allow the passage of ultraviolet rays and hence consist, for example, of quartz.

The zirconium pyrophosphate used in a cathode-ray tube according to the invention is self-activated, i. e., unactivated, and may be manufactured in the following manner.

Example One prepares a mixture of:

26.5 gs. of (NH4)2HPO4 32.2 gs. of ZrOClz-SHzO in 0.1 litre of water. This suspension is dried by vaporisation and the dry substance is heated in air at about 400 C. for 1% hours. The resultant product is ground and, if necessary, sieved, whereafter renewed heating in air follows at 1050 C. for about 4 hours. The substance obtained after this heating is ground, if desired sieved, and heated in air at about 1000 C. for about 2 hours. Finally, the substance is prepared for use by grinding and sieving.

Instead of utilising the above-mentioned zirconium oxychloride, use may be made of an equivalent amount of an other zirconium compound, for example zirconium oxide.

' example deposited on the inside of quartz Window 4.

Figure 2 in the drawing shows a curve in which the wavelength of the radiation emitted by zirconium pyrophosphate manufactured in accordance with the preceding example upon excitation by electrons of 20 kilovolts and the intensity of the emitted radiation in arbitrary units are plotted on the axis of abscissae and the axis of ordinates respectively.

What we claim is:

In a cathode-ray tube with a decay time shorter than 10- seconds and emitting ultra-violet radiation, the spectral distribution of which exhibits a maximum at about 2900 A., including an envelope having a quartz Window at one end and means for producing a beam of electrons 43. within said tube, a luminescent screen consisting of selfactivated zirconium pyrophosphate.

References Cited in the file of this patent UNITED STATES PATENTS 2,225,044 George Dec. 17, 1940 2,450,548 Gisolf et a1. Oct. 5, 1948 2,455,415 Froelich Dec. 7, 1948 2,488,733 McKeag et al Nov. 22, 1949 2,521,571 DuMont et a1. Sept. 5, 1950 2,596,509 Ranby May 13, 1952 FOREIGN PATENTS 311,282 Great Britain Aug. 7, 1930 OTHER REFERENCES Some Aspects of the Luminescence of Solids by F. A. Kroger 1948, pages 159-161.