US2858363A - Electroluminescent image reproduction - Google Patents

Description

Oct. 28, 1958 B, KAZAN l ELECTROLUMINESCENT IMAGE REPRODUCTION Filed oct. 20, 1952 2 sheets-smet 1 TTORNEY' Oct. 28, 1958 B. KAZAN ELECTROLUMINESCENT IMAGE REPRODUCTION 2 Sheets-Shea?l 2 Filed Oct. 20, 1952 I NVENTOR.

n' TTORNE Y United States Patent Otice ELECTROLUMINESCENT llVIAGE REPRODUCTION Benjamin Kazan, Princeton, N. J., Yassignor to Radio Corporation of America, a corporation of Delaware Application October 20, 1952, Serial No. 315,695 6 Claims. (Cl. 178-5.4)

This invention relates to apparatus for reproducing light images and more particularly to improved appartus for converting electrical energy into light images by means of electroluminescent devices.

One means for converting electrical energy into light energy utilizes the principle of electroluminescence, wherein a phosphor is excited by the application of a voltage or an electric field to the phosphor. Particles of a suitable phosphor may be embedded in aplastic and an electric held applied to the phosphor by conducting sheets placed in close association with the plastic.

The principal object of this invention is to provide an improved means for reproducing light images which utilizes the principle of electroluminescence.

Y Another object of this inventiony is to provide a light image of relatively large area from a modulated electrical signal.

According to this invention, light images may be reproduced by elementally varying the electric field across a layer of. electroluminescent material in accordance with an electrical signal by means of a photoconductive layer placed in close association with an electroluminescent layer, and means for activating elemental vareas of the photoconductive layer.

Other and incidental objects of this invention will becorne apparent upon a reading of the following specitcation and an inspection of the drawings, in which:

v Figure 1 shows an embodiment of the present invention for reproducing light images wherein a dying spot scanner and a wave amplitude modulated with signal in'- formation energize an electroluminescent device;

Figure 2 shows another embodiment of the invention for reproducing light images wherein a ying spot scanner isV modulated with a wave, and an electroluminescent device is energized by a phase modulated wave thereby providing a light image; and

Figures 3 and 4 show in side elevation constructional details of electroluminescent devices adapted to provide color images.

Turning now in more detail to Figure l, there is shown an electroluminescent device 6. One form of the electroluminescent device suitable for use in the practice of this invention comprises a sandwich type of construction including a luminescent layer 7 and an adjacent photoconductive layer 9. More specically, the sandwich includes on one side a transparent base member which may be glass, having deposited thereon a transparent conductive coating 11. On the other side, there is employed a similar glass base member 17 also coated on its inside surface with a transparent conductive coating 13. The luminescent layer 7 and photoconductive layer 9 are sandwiched between the members 15 and 17 and are in contact with each other and the conductive layers 11 and 13.

As to the materials of which the electroluminescent device 6 is composed, the luminescent layer 7 may comprise any of the common phosphors such as copper activated zinc sulfide, zinc beryllium silicate, etc., the choice 2,858,363 Patented oct. 2s, 195s of which depends on the desired color output. In preparing the luminescent layer or sheet, the particles of phosphor material are mixed with or embedded in alight transmitting insulating material, i. e. a plastic lacquerl wax or the like.

According to one method of preparing the luminescent body, a unit quantity ofa plastic matrix material for the phosphor was prepared with the following ingredients in approximately the given quantities:

Grams Ethyl cellulose 1,2 lso-amyl alcohol 16.5 Amyl acetate 25.5 Acetone 14.5 Di-octyl phthalate 1.5 Octyl acetate 1.0

This mixture was blended with approximately two grams of linely divided phosphor particles, for example,cop per activated. Zinc sulfide particles having a diameter of the order of one to live microns. The mixture of plastic and phosphor was then ball milled for approximately one hour. Finally the milled preparation was sprayed onto a suitable base plate. In a device actually built, the thickness of this layer was of the order of 1 to 3 mils.

The photoconductive layer 9 may be made of any photoconductive material sensitive to the type of radiation to be employed in activating the layer, and may be made in a manner similar to that described above Vfor the luminescent layer. The radiation maybe visible light, ultra-violet, infrared, X-ray radiation, or particle radi-ation such as that produced by radioactive materials. The photoconductor may be antimony trisulde, selenium or the like. The photoconductive layer may have a thickness comparable to that of the luminescent layer. The relativey thicknesses of these layers is determined by the types of materials involved and the desired voltage drop across each layer when` the electroluminescent device is` in the unenergized condition.

The conductive layers 11, 13, may one or both, be constituted of metal plates or sheets lor iilms of material adapted to be transparent to the type of radiation to be employed in operation of the electroluminescent device. One method of forming these layers is to appl-y transparent conductive material to the base plates 15, 1'7 having the desired radiation transmitting qualities. The transparent conductive material may be of the type formed by deposition of the vapors of stannic chloride, water and methanol. Constructional details of the electroluminescent device or sandwich also are described in my concurrently lled copending application entitled Electroluminescent Device, Serial No. 315,694.

An additional opaque or semiopaque layer may be interposed between the photoconductive layer 9 and the electroluminescent layer 7 to limit the amount of light feedback to the photoconductive layer 9 from the electroluminescent layer 7. Such a layer may be of a density to allow enough light to pass to utilize regenerative action. However, where the device is tov be used for reproducing varying light images, this layer should' be sutliciently opaque to preclude any possibility of enough light being fed back to result in self energizati'on; In operation, the elemental areas of the photoconductive layer 9 become conductive in an amount more or less proportional tothe incident radiation on each of the elemental areas. As a result of this increased conductivity of the photoconductive layer, each elemental area of the electroluminescent layer has a larger voltage applied across it. With increased voltage across each-electroluminescent area, each such areaY emits light as a function of the voltage increase. Since the electroluminescent device is comparatively thin, light emitted from a given area of the electroluminescent layer represents radiation striking the corresponding varea of the photoconductive layer.

A liying spot scanner, which may be, for example, a

"cathode ray tube 35, is used to energize the photoconductive layer 9 of the electroluminescenty device 6. A suitable D. C. voltage source is connected between the cathode of the cathode ray tube 35 and ground reference potential, and a variable tap on the D. C. source is connected to the control electrode 36 of the cathode ray tube 35 to provide means for varying the intensity of the electron beam from the cathode, and hence the intensity of the flying spot appearing at the face of the cathode ray tube 35. Suitable positive operating potential may be applied to the cathode ray tube 35 by means of the terminal 37. A signal source 38, which may comprise a conventional television receiver or other signal generating means, supplies signals to the modulator 39 and suitable synchronizing pulses to the deflection wave generators 40, which in turn supply the yoke 41 with deection currents for purposes of deecting the electron beam in the cathode ray tube 35.

The ying spot produced by the cathode ray tube 35 may be optically focused on the photoconductive layer of the electroluminescent sandwich 6 by means of a lens system shown diagrammatically at 42. Varying voltage waves, from the varying voltage source 43, are applied to the modulator 39 where the signals from the signal source 38 function to amplitude modulate the varying voltage waves in accordance with the signal information. The modulated varying voltage waves are then applied across the electroluminescent device 6 by means of the conducting layers previously described. The source 43 must furnish signals to the modulator 39 which have changes in amplitude. The electroluminescent layer 7 is responsive principally to changes in an applied voltage whether the voltage wave be of an A.C. type, or whether it is pulsating D.C., or even square waves.

In operation, the embodiment of Figure l provides an image on the side of the electroluminescent device 6 opposite from the photoconductive layer 9 on which the Y ying spot was focused. The flying spot energizes elemental areas of the photoconductive layer 9 which reduces the impedance across elemental areas of the photoconductive layer 9 so that larger modulated varying voltage waves are applied across elemental areas of the electroluminescent layer 7. Since the varying voltage wave is modulated in accordance with signal information, the amount of light produced in each elemental area will depend upon the modulation of the varying voltage wave. In this manner an image may be elementally reproduced by the electroluminescent device 6.

In general, electroluminescent layers energized by an varying voltage such as an A.C. wave produce two maxima of light during each A.C. cycle rather than continuous light. As the flying spot from a cathode ray tube scans the device with an unmodulated A.C. voltage applied to the device, the electroluminescent light will vary periodically at twice the A.C. frequency. As a result, if signals are used for amplitude modulating the A.C energizing Voltage, the A.C. frequency must be at least half as high as the highest signal frequency employed. Also, the A.C. frequency must be sufficiently high relative to the speed of the iiying spot so that the electroluminescent light will not appear in the form of a sequence of dots or dashes.

Figure 2 shows an embodiment of the invention wherein the electron beam intensity and therefore the intensity of the light of the ying spot produced by cathode ray tube 47 is modulated at a frequency corresponding to the frequency of the light variation at the electroluminescent device 6', which may be of the same construction as the electroluminescent device 6 of Figure l. By varying the phase between the ying spot modulation on the cathode ray tube 47 and the phase of the A.C. voltage applied across the electroluminescent device 6', the energization of the electroluminescent device by the light of the flying spot may be intensity modulated in accordance with the modulating signal. Thus, signals from a signal source 43 are applied to a phase modulator 44, suitable synchronizing signals are applied to the deflection wave generators 45, and an alternating current source 46 has its output phase modulated and then applied across the conductive layers associated with the electroluminescent device 6. Alternating current waves from the alternating current source 46 also are applied to the frequency doubler 50 which in turn supplies a wave having a frequency twice that of the wave from the alternating current source 46 to the iiying spot scanner. The flying spot scanner may comprise a cathode ray tube 47, which has its cathode connected to ground reference potential, and to which may be applied a suitable positive operating potential by means of a terminal 48. Deflection waves from the deliection wave generators 45 are applied to windings in the yoke 49 for purposes of deiiecting the electron beam originating at the cathode of cathode ray tube 47. The ying spot modulated by a wave of the frequency of the light variation will be focused on the electroluminescent device 30 by means of a lens Si).

The systems described above may also be employed for the reproduction of color pictures. Devices suitable for this purpose are shown in Figs. 3 and 4. The devices are divided, in one way or another, into elemental regions each of which is smaller than a picture element. The individual regions are arranged in a desired sequence and each region produces a particular color of electroluminescent light. The desired elemental regions may be obtained by dividing the electroluminescent phosphors into elemental regions having appropriate color response, or with phosphors having white response in combination with suitable filters.

For example, in Fig. 3, an electroluminescent device 56 comprises the same basic components as the device of Fig. 1 and includes glass plates 51 and 54, a photoconductive layer 57, an electroluminescent layer 59, conducting layers 52 and 53, and color filter 58 mounted on the free surface of the glass sheet 54. The lter comprises a repeating series of elemental units R, B, G adapted to produce dilerent colors of light, for example, red, blue and green. The conducting layers 52 and 53 are adapted to be connected to some suitable energizing means such as is shown in either Figure 1 or Figure 2.

In Fig. 4, an electroluminescent device 60 is provided with a photoconductive layer 61, glass plates 65 and 66, conducting layers 63 and 64, along with an electroluminescent layer 62 which is mounted adjacent to the photoconductive layer 57 and comprises a repeating series of elemental regions R', B', G', each of the said regions having a different color response. The phosphors may be silver activated zinc sulfide for blue, manganese activated alpha willemite for red, and chromium activated aluminum berylliate for green. The conducting layers 63 and 64 may be connected to a suitable energizing means as shown in either Figure l or Figure 2.

Each of the devices shown in Figures 3 and 4 may be used to advantage for the reproduction of color images in the systems shown in Figures l and 2. It will be noted that it is only necessary to provide elemental color means associated with the electroluminescent layer since the flying spot is of one color. However, it is necessary to accurately register the position of the flying spot with respect to the color image signal. In the case of the system shown in Figure 1, the signal source 38 may comprise a suitable color image source. In other respects, the system for reproducing color images can be identical to that shown in Figure l, except for the aforementioned `registering of the position of the flying spot from the cathode ray tube 35 with the appropriate elemental color ,filters 58 in the case of Figure 3v and the elemental color areas of the electroluminescent layer 62 in the case of Figure 4.

Thus, through the embodiment of the present invention shown in Figures l and 2, means are provided for reproducing either monochrome or color images from an electroluminescent device. Although the apparatus may be used to reproduce television images, it will be appreciated that the apparatus might well be employed to reproduce images in other fields of art such as, for example, radar, or the like.

While the forms of the present invention have been described above in terms of a lying spot generator such as a cathode ray tube it is understood, of course, that other types of flying spot generators may be employed.

Also, there are many types of mechanical ying spot generators which can be substituted for the cathode ray tube apparatus illustrated herein.

What is claimed is:

1. Apparatus for reproducing a light image in accordance with signal information including the combination of, an electroluminescent device comprising a layer of electroluminescent material and a layer of photoconductive material positioned in intimate Contact with said layer of electroluminescent material along one surface of said electroluminescent layer, means for applying a varying voltage wave modulated with signal information across said photoconductive layer and said electroluminescent layer, and means for successively illuminating elemental areas of said photoconductive layer.

2. Apparatus for reproducing a light image in accordance with signal information including the combination of, an electroluminescent device comprising an electroluminescent layer and a photoconductive layer placed in contact therewith, means for applying a varying voltage wave across said electroluminescent layer and said photoconductive layer, means for modulating said varying voltage wave in accordance with signal information, and means scanning said photoconductive layer with a ying spot of light.

3. Apparatus for reproducing a light image in accordance with signal information including the combination of, a ying spot scanner and an electroluminescent device, said electroluminescent device comprising an electroluminescent layer and a photoconductive layer placed in contact therewith, means for applying a phase modulated alternating voltage across said electroluminescent device thereby providing two light maxima from said electroluminescent layer for each cycle of alternating voltage applied, said modulated alternating voltage varying in accordance with said signal information means for modulating the light intensity of said ying spot scanner at twice the frequency of said alternating voltage, and focusing means positioned between said flying spot scanner and said electroluminescent device.

4. Apparatus for reproducing color light images in accordance with signal information including the combination of, an electroluminescent device comprising a layer of electroluminescent material, a layer of photoconductive material, an elemental color means associated with said electroluminescent layer, said photoconductive layer being positioned in intimate Contact with said layer of electroluminescent material along one surface of said electroluminescent layer, means for applying an alternating voltage across said photoconductive layer and said electroluminescent layer, means for amplitude modulating said alternating voltage with signal information, and means illuminating elemental areas of said photoconductive layer.

5. Apparatus for reproducing a light image in color from signal information including the combination of, an electroluminescent device comprising an electroluminescent layer, a photoconductive layer placed in contact therewith, elemental color reproducing means associated with said electroluminescent layer, means for applying an alternating voltage across said electroluminescent layer and said photoconductive layer, means for modulating said alternating voltage in accordance with signal information, and means scanning said photoconductive layer with a flying spot of light.

6. Apparatus for reproducing a light image in color from signal information including the combination of, a ying spot scanner and an electroluminescent device, said electroluminescent device comprising an electroluminescent layer, a photoconductive layer placed in contact therewith, elemental color reproducing means associated with said electroluminescent layer, means for applying a phase modulated alternating voltage across said electroluminescent device thereby providing two light maxima from said electroluminescent layer for each cycle of alternating voltage applied, said modulated alternating voltage varying an accordance with said signal information means for modulating the light intensity of said ying spot scanner at twice the frequency of said alternating voltage, and focusing means positioned between said ying spot scanner and said electroluminescent device.

References Cited in the le of this patent UNITED STATES PATENTS 2,072,455 Kannenberg Mar. 2, 1937 2,239,887 Ferrant Apr. 29, 1941 2,108,132 Lora Feb. l5, 1948 2,594,740 De Forest Apr. 29, 1952 2,605,335 Greenwood July 29, 1952 2,650,310 White Aug. 25, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. @858,363 Oetobeic 289 1958 Benjamin Kazan lt is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Lettere Patent should read as Corrected below.

Column 3y line 6, after device 6N and before AY inse'ft the following;

The photooonduotive layeT 9 is energized because tne light from the flying spot produeed at the end of Cathode Tay tube 35 is made to fall sequentially upon elements of the eleetrolumineseent devise o thus causing the resistance of layer 9 to deoTease as a function of the intensity of the light.

Signed and sealed this 7th day of Apfil M9590 (SEAL) Attest:

KARL H., AXLTNE RUBERT C. WATSN Attesting Ofcer Commissioner of Patents UNITED STATES PATENT oEEICE CERTIFICATE 0F CORRECTION Patent Noa 2,858,363 October 289 l958 Benjamin Kazan It is hereby certified that error appears in the printed Specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line o, after "device 6:," and before A11 insert the following-z;

--f The photooonduotive layer 9 ie energized becauee the light from the flying spot produced at the end of cathode ray tube 35 ia made to fall sequentially upon elemente of the electrolumineecent device o thus eaueing the resistance of layer 9 to decrease ae a funotion of the intensity of. the

Signed and sealed this Y7th day of April l959o (SEAL) Attest: n KARL Ii., AXLINE ROBERT C.. WATSGN Commissioner of Patents Atteating Oicer

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