US3165667A

US3165667A - Electroluminescent device

Info

Publication number: US3165667A
Application number: US35339A
Authority: US
Inventors: Claus H Haake
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1960-06-10
Filing date: 1960-06-10
Publication date: 1965-01-12
Anticipated expiration: 1982-01-12

Description

Jan. 12, 1965 c. H. HAAKE 3,

EILECTROLUMINE$CENT DEVICE Filed June 10, 1960 FIG. I.

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CONTINUOUS WAVE PULSE 615235? FlG.2.

CONTINUOUS WAVE HIGH FREQUENCY GENERATOR PULSE GENERATO R INVENTOR. C0405 H. f/fl/IKE United States Patent 3,165,667 ELEQTRQLUMINEdQENT DEVl'JE Claus H. Haake, Livingston, N..l., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa.,' a corporation of Pennsylvania Filed June 10, 1966, Ser. No. 35,339 5 Claims. (Cl. 315-169) This invention relates to electroluminescent devices and, more particularly, to a device comprising an elec troluminescent element and the associated element energization means.

The phenomenon of electroluminescence was first disclosed by G. Destriau, one of his earlier publications appearing in London, Edinburgh and Dublin Philosophical Magazine, Series 7, Volume 38, No. 285, pages 700-737 (October 1947). Since this early publication, electroluminescent lamps have been commercially marketed as light sources. The electric-field-responsive characteristics of electroluminescence has made possible many various types of image-presentation and image-intensification devices. An early type of electroluminescent device which operates as an image intensifier is disclosed in U.S. Patent No. 2,650,310, dated August 35, 1954. A cross-grid or so-called X-Y plotter electroluminescent image presentation apparatus is disclosed in U.S. Patent No. 2,698,915, dated I anuary 4, 1955. Many different constructions for signal presentation devices are known. In the operation of an X-Y plotter, for example, individual signals are placed across preselected cross grids and the electroluminescent phosphor which is positioned thereoetween emits light in response to the generated electric field. In order to present a moving image, it is necessary to apply pulses of energization potential in a predetermined and rapid fashion to the individual lead conductors which comprise the cross grids. For some applications of such devices, it is desirable to be able to minimize as much as possible the magnitude of the potential pulses which are required for energization. In addition, it is desirable in some X-Y plotter applications to minimize the light emission decay characteristics of the electroluminescent phosphor material, so that a fast moving image can be presented with greater clarity.

It is the general object of this invention to provide an electroluminescent device Which'is adapted to be operated with a pulsed energization and wherein a smaller potential magnitude can be used for the exciting pulses, while still achieving a high level of light output.

It is another object to provide an electroluminescent device adapted to be energized with a pulsed excitation, wherein the phosphor light output will decay in a rapid fashion after the energizing potential is removed.

The aforesaid objects of the invention, and other objects which will become apparent as the description proceeds, are achieved by providing a combination of electroluminescent element or elements and the associated energization means. The electroluminescent element is adapted to be excited to light emission by a first potential generator which delivers a continuous, high-frequency potential across the device electrodes and a second potential generator which simultaneously delivers potential pulses across the spaced electrodes. The continuous excitation and the pulsed excitation potentials are controlled relative to one another with respect to their frequencies, repetition rates and relative magnitudes, in order that the 3,165,567 Patented Jan. 12, 1965 ice resulting light output will be enhanced and the light output decay characteristics for the phosphor will be more rapid.

For a better understanding of the invention, reference should be had to the accompanying drawing wherein:

FIG. 1 is a sectional elevational view of an electroluminescent element with the associated energization means therefor shown in block diagram;

FIG. 2 -is a perspective view of a'por-tion of an XY plotter adapted to be energized with both a continuous high frequency potential and a pulsed potential, in accordance with the present invention.

With specific reference to the form of the invent-ion illustrated in the drawing, the electroluminescent element ill as shown in FIG. 1 generally comprises a glass foundation 12 having coated thereover a first electrode 14 which can be formed of tin oxide. Coated over the electrode-l4 is a layer 16 comprising electroluminescent phosphor and coated over the layer 16 is a second electrode 18 which can be formed of vacuum-metallized aluminum or copper iodide for example. Connected to the element electrodes 14 and 18 are a continuous-wave, high-frequency potential generator 20 and a pulsed potential generator 22, both potential generators being shown in block diagram. The

potential sources

20 and 22 desirably are selected to have a high impedance and are conventional in design. The respective performance characteristics of these sources will be considered in detail hereinafter. The manner in which the sources 2% and 22 are connected to the electrodes 14 and 18 is immaterial.

Any electroluminescent phosphor can be used in forming the layer 16 and, as an example, a green-emitting zinc sulfide phosphor activated by copper and coactivated by chlorine has been found to be very suitable. The phosphor is desirably mixed with a dielectric such as equal parts by weight of phosphor and polyvinyl-chloride acetate dielectric material. Alternatively, the phosphor can be included between the spaced electrodes without any admixed dielectric or a separate layer of dielectric material can be included between the electrodes 14 and 18. The thickness of the layer 16 is not critical and can be varied considerably and a thickness of two mils has been found to be very satisfactory. Either or both of the electrodes 14 and 18 can be replaced by a mesh of wires, such as can be used in a conventional X-Y plotter. Alternatively, the electrodes can be replaced by an interlacing mesh of wires with phosphor therebetween, as disclosed in U.S. Patent No. 2,684,450, dated July 20, 1954. For some special applications, it is desirable to include other material layers between the electrodes 14 and 1-8, such as a layer of photoconductive material if the device is to be used as a light amplifier. Alternatively, an additional layer of non-linear resistive material can be included between the electrodes 14 and 18 in order to increase the sensitivity of the element 10 to respond with greatly in creased brightness when excited by relatively intense electric fields. The element lit, as shown in FIG. 1 thus comprises spaced electrodes having electroluminescent phosphor included therebetween. The element Ill can be of various size or configuration depending upon its intended application.

In FIG. 2 is shown a portion of an X-Y plotter 24 which comprises a first set or grid of parallel conductive strips 25 and a closely spaced second set or grid of parallel conductive strips 23. In the embodiment as amass? shown, at least one set of the conducting

strips

26 or 28 is light transmitting. The conductors 26 and 2S comprising the individual grids are disposed at an angle with respect to one another, and preferably at approximately right angles. Material comprising electroluminescent phosphor Si) is included between contiguous portions of the conductive strips 26 and 23 comprising the individual grids. As a matter of manufacturing convenience, the phosphor 3%) will normally be formed as a continuous layer. In the device 24, each of the contiguous crossing points of each of the

conductors

26 and 28 and the phosphor thcrebetwecn essentially comprise an electroluminescent element, such as disclosed in FIG. 1. The cross grids are adapted to be energized through suitable synchronized commutating means 32, which distribute a part of the energizing potential to predetermined conducting strips comprising the grids, in order to present a predetermined composite image. Such a device and the commutation therefor is generally disclosed in heretoforenlentioned US. Patent No. 2,698,915.

In the modification of the XY plotter 24 in accordance with the present invention, the continuous output of the potential generator 29 is applied at all times across each of the

conductive strips

26 and 28. The pulsed output of the potential generator 22 is commutated and distributed across the conductor 26 and 23 in predetermined fashion so that the enhanced light output obtained through the application of the continuous potential and the pulsed potential produces the desired, predetermined visible signal. A conventional video input 34 controls the voltage of the pulses in accordance with the predetermined signal desired to be displayed.

Both of the electroluminescent combinations as shown in FIGS. 1 and 2 generally comprise an electroluminescent element or plurality of electroluminescent elements and the associated energization means therefor. The element or elements each comprise spaced electrodes with electrolurninescent phosphor included between the spaced electrodes and the energization means comprises a continuous-wave, high-frequency potential generator and a pulsed potential generator. As will be described in greater detail hereinafter, when a predetermined continuous potential and pulsed potential are applied across the electrodes, the resulting electroluminescent light output is considerably enhanced. In addition, the decay in electroluminescent output is faster by a factor of about 30% than would be encountered if only the exciting pulses were to be applied across the electrodes. In order to realize the enhanced light output and more rapid decay, the continuous alternating potential should have a frequency of at least 10 kilocycles and desirably should be considerably higher. Also, in order to minimize the background lighting effects of the continuous potential, the magnitude of the potential of the pulses should be at least as great as the magnitude of the continuous alternating potential. Desirably the magnitude of the potential of the pulses should be at least ten times greater than the magnitude of the continuous alternating potential. In addition, the duration of each pulse and the quiescent period between successive pulses should both extend over a time period which is at least ten times as long as the time period required for one complete cycle of the continuous alternating potential. If either the pulse duration or the quiescent period between each individual pulse becomes sufiiciently short in time to approach the period required for one complete cycle of the continuous high-frequency potential, the increased light output over and above that light output to be expected is lost, as are the more rapid decay characteristics. The so-called phosphor emission decay characteristics represent the period of time required for the light emission to decrease to twenty percent of the value of the maximum light emission realized. Of course the summation of the potential magnitudes of the continuous wave and pulsed potentials used to excite the phosphor should be less than that potential required to cause an electrical breakdown between the electrodes. The summation of the applied potentials should be suflicient, however, to excite the phosphor to generate the desired radiations.

As a specific example for operating the electroluminescent device as shown in FIG. 1, the pulse generator 22 is designed to produce square wave potential pulses having a magnitude of volts, a pulse duration from 10* to 10* second and a pulse frequency variable from 10 to 10 cycles per second. The continuous-wave generator Ed is desi ned to produce a 200 kcs. output potential, variable between 2 and 12 volts (R.M.S.). The outputs of the pulse generator 22 and continuous-wave generator 23 are simultaneously applied across the electrodes 14 and 13 of the electroluminescent element 10, or any generally-similar element in'an imaging apparatus. In the following Table I, the left-hand indicates the repetition rate for the square wave pulses. The second column indicates the duration of each square wave pulse. The third column indicates the rms. voltage of the continuous high-frequency excitation. The fourth and fifth columns indicate the percent increase or enhancement of light output which is obtained when exciting the element 10 with both pulses and continuous wave potential, as compared to the light output obtained when exciting the electroluminescent element It? only with equivalent pulses. It should be noted that when an electroluminescent element is excited with a square wave potential, a light flash will be obtained when the potential is applied (rising side of the square wave) and when the square wave potential is removed (falling side of the square wave), as the phosphor responds to changes in the applied electric field. The percent enhancement of the light output obtained when the pulse is applied is shown in column four and the percent enhancement of the light output obtained when removing the pulse is shown in column five.

It should be understood that the foregoing example represents a preferred embodiment and is subject to considerable variation. In addition, there does not appear to be any upper limit to the frequency of the continuous potential, except that limit imposed by capacitive effects due to the construction of the electroluminescent element. As an example, if a light-transmitting, tin oxide electrode layer is used, frequencies appreciably greater than 400 kcs. may introduce excessive losses in such a layer. Also, the pulsed potential need not be in the form of square waves, but can be any form of voltage pulses. Square waves are preferred, however, because of the normally rapid response and decay of the phosphor light emission to such excitation.

The X-Y plotter as disclosed in FIG. 2 represents a conversion of electrical input to optical output. The

present electroluminescent device also has use in other.

optical signal by an apparatus such as described and the optical signal used to trigger a photo-transistor in order to generate a corresponding electrical signal. Such a system achieves complete decoupling between the components and can be rendered more sensitive by the use of an electroluminescent apparatus such as described hereinbefore.

It will be recognized that the objects of the invention have been achieved by providing an electroluminescent device which is adapted to be operated with a pulsed energization and wherein a smaller potential magnitude can be used for the exciting pulses, while still achieving a high level of light output. In addition, there has been provided an electroluminescent device wherein the phosphor light output will decay in a rapid fashion after the energizing potential is removed.

While best embodiments of the invention have been illustrated and described hereinbefore, it is'to be particularly understood that the invention is not limited thereto or thereby.

I claim:

1. The combination which comprises an electroluminescent element and associated energization means: said element comprising, spaced electrodes, and electroluminescent phosphor included between said spaced electrodes; said energization means comprising, a first potential generating means and a second potential generating means; said first potential generating means adapted to deliver across said spaced electrodes a continuous alternating potential having a frequency of at least kcs.; said second potential generating means adapted to deliver across said spaced electrodes potential pulses having a magnitude at least greater than the magnitude of the continuous alternating potential adapted to be delivered across said spaced electrodes by said first potential generating means; the duration of each pulse and the quiescent period between successive pulses adapted to be delivered across said spaced electrodes by said second potential generating means both extending over a time period at least ten times as long as the time period required for one complete cycle of the continuous alternating potential adapted to be delivered across said spaced electrodes by said first potential generating means; the summation of potential magnitudes of the continuous and pulsed potentials adapted to be delivered by said first and second potential generating means being less than that potential required to cause breakdown across said electrodes, but sufficient to energize said phosphor to produce radiations; and said first and second potential generating means adapted to deliver their respective potentials simultaneously across said spaced electrodes.

2. The combination which comprises an electroluminescent element and associated energization means: said element comprising, spaced electrodes, and electroluminescent phosphor included between spaced electrodes; said energization means comprising, a first potential generating means and a second potential generating means; said first potential generating means adapted to deliver across said spaced electrodes a continuous alternating potential having a frequency of at least 10 kcs.; said second potential generating means adapted to deliver across said spaced electrodes potential pulses having a magnitude at least ten times greater than the magnitude of the continuous alternating potential adapted to be delivered across said spaced elecrodes by said first potential generating means; the duration of each pulse and the quiescent period between successive pulses adapted to be delivered across said spaced electrodes by said second potential generating means both extending over a time period at least ten times as long as the time period required for one complete cycle of the continuous alternating potential adapted to be delivered across said spaced electrodes by said first potential generating means; the summation of potential magnitudes of the continuous and pulsed potentials adapted to be delivered by said first and second potential generating means being less than that potential required to cause breakdown across said electrodes, but sufficient to energize said phosphor to produce visible radiations; and said first and second potential generating means adapted to deliver their respective potentials simultaneously across said spaced electrodes.

3. The combination which comprises an electroluminescent element and associated energization means: said element comprising, spaced electrodes, and electroluminescent phosphor included between said spaced electrodes; said energization means comprising, a first potential generating means and a second potential generating means; said first potential generating means adapted to deliver across said spaced electrodes a continuous alternating potential having a frequency of 200 kcs. and a magnitude of from 2 to 12 volts R.M.S.; said second potential generating means adapted to deliver across said spaced electrodes a series of potential pulses having a magnitude of about volts, a repetition rate of from 10 to 10 pulses per second, and an individual pulse duration of from 10- to l04 second; the summation of potential magnitudes of the continuous and pulsed potentials adapted to be delivered by said first and second potential generating means being less than that potential required to cause breakdown across said electrodes, but sufficient to energize said phosphor to produce visible radiations; and said first and second potential generating means adapted to deliver their respective potentials simultaneously across said spaced electrodes.

4. The combination which comprises an electrolumi: nescent element and associated energization means: said element comprising, spaced electrodes, and electroluminescent phosphor included between said spaced electrodes; said energization means comprising, a first potential generating means and a second potential generating means; said first potential generating means adapted to deliver across said spaced electrodes a continuous alternating potential having a frequency of 200 kcs. and a magnitude of about 5 volts R.M.S.; said second potential generating means adapted to deliver across said spaced electrodes a series of potential pulses having a magnitude of 150 volts, a repetition rate of 1000 pulses per second, and an individual pulse duration of 10- second; the summation of potential magnitudes of the continuous and pulsed potentials adapted to be delivered by said first and second potential generating means being less than that potential required to cause breakdown across said electrodes, but sufiicient to energize said phosphor to produce visible radiations; and said first and second potential generating means adapted to deliver their respective potentials simultaneously across said spaced electrodes.

5. An electroluminescent X-Y plotter comprising: a first grid comprising substantially parallel and spaced conductors; a second grid comprising substantially parallel and spaced conductors separated from said first grid, with the axes of the conductors comprising said second grid axially aligned at an angle to the axes of the conductors comprising said first grid; material comprising electroluminescent phosphor between said grids; a first potential generating means adapted to deliver at all times across said first grid and said second grid a continuous alternating potential having a frequency of at least 10 kcs.; a second potential generating means adapted to deliver potential pulses having a magnitude at least greater than the magnitude of the continuous alternating potential adapted to be delivered across said grids by said first potential generating means; the duration of each pulse and the quiescent period between successive pulses adapted to be delivered by said second potential generating means both extending over a period of time at least ten times as long as the time period required for one complete cycle of the continuous alternating potential adapted to be delivered by said first potential generating means; the summation of potential magnitudes of References (Jited in the file of this patent UNITED STATES PATENTS Hanlet a- Apr. 21, 1959 Sack Dec. 15, 1959 Jay Apr. 12, 1960 FOREIGN PATENTS Great Britain Nov. 30, 1955

Claims

1. THE COMBINATION WHICH COMPRISES AN ELECTROLUMINESCENT ELEMENT AND ASSOCIATED ENERGIZATION MEANS: SAID ELEMENT COMPRISING, SPACED ELECTRODES, AND ELECTROLUMINESCENT PHOSPHOR INCLUDED BETWEEN SAID SPACED ELECTRODES; SAID ENERGIZATION MEANS COMPRISING, A FIRST POTENTIAL GENERATING MEANS AND A SECOND POTENTIAL GENERATING MEANS; SAID FIRST POTENTIAL GENERATING MEANS ADAPTED TO DELIVER ACROSS SAID SPACED ELECTRODES A CONTINUOUS ALTERNATING POTENTIAL HAVING A FREQUENCY OF AT LEAST 10 KCS.; SAID SECOND POTENTIAL GENERATING MEANS ADAPTED TO DELIVER ACROSS SAID SPACED ELECTRODES POTENTIAL PULSES HAVING A MAGNITUDE AT LEAST GREATER THAN THE MAGNITUDE OF THE CONTINUOUS ALTERNATING POTENTIAL ADAPTED TO BE DELIVERED ACROSS SAID SPACED ELECTRODES BY SAID FIRST POTENTIAL GENERATING MEANS; THE DURATION OF EACH PULSE AND THE QUIESCENT PERIOD BETWEEN SUCESSIVE PULSES ADAPTED TO BE DELIVERED ACROSS SAID SPACED ELECTRODES BY SAID SECOND POTENTIAL GENERATING MEANS BOTH EXTENDING OVER A TIME PERIOD AT LEAST TEN TIMES AS LONG AS THE TIME PERIOD REQUIRED FOR ONE COMPLETE CYCLE OF THE CONTINUOUS ALTERNATING POTENTIAL ADAPTED TO BE DELIVERED ACROSS SAID SPACED ELECTRODES BY SAID FIRST POTENTIAL GENERATING MEANS; THE SUMMATION OF POTENTIAL MAGNITUDES OF THE CONTINUOUS AND PULSED POTENTIALS ADAPTED TO BE DELIVERED BY SAID FIRST AND SECOND POTENTIAL GENERATING MEANS BEING LESS THAN THAT POTENTIAL REQUIRED TO CAUSE BREAKDOWN ACROSS SAID ELECTRODES, BUT SUFFICIENT TO ENERGIZE SAID PHOSPHOR TO PRODUCE RADIATIONS; AND SAID FIRST AND SECOND POTENTIAL GENERATING MEANS ADAPTED TO DELIVER THEIR RESPECTIVE POTENTIALS SIMULTANEOUSLY ACROSS SAID SPACED ELECTRODES.