DE1764940A1 - Energy responsive luminescent device - Google Patents

Description

The invention relates to an energy-responsive luminescent device in which an electroluminescent Element made to luminesce by an alternating electric field and controlled by a direct voltage at the same time is the amplitude of impedance fluctuations of an energy sensitive Element depends on an incident energy, whereby the electroluminescence output of the Element controllable depending on the incident energy is.

More particularly, the invention relates to an image plate for visualizing and amplifying one of light, x-rays or gamma rays or for storing and reproducing such an image with use

-2-

209808/0640

ORIGINAL INSPECTED

of the principle described above.

In conventional, energy-responsive luminescent devices the control of the luminescence is basically done by controlling the electroluminescent Element supplied alternating current, which in turn corresponds to the alternating current component of the fluctuation in the impedance of a photoconductive element is controlled. In such a device, however, there is sensitivity of the photoconductive element under AC excitation too low to be practically evaluable. According to the invention Therefore, a DC voltage is superimposed on the AC voltage for the control, whereby a DC voltage control becomes possible. You get a considerably improved, energy responsive luminescent device satisfactory for image conversion and enhancement Has characteristic curves and also enables the storage of an image.

Further details, advantages and features of the invention emerge from the following description. In the Drawing illustrates the invention by way of example, namely show

-3-209808 / 0540

Fig. 1 shows schematically and partially in section an embodiment of the invention with the associated electrical circuit, and

FIG. 2 shows a simplified electrical circuit which is equivalent to the circuit of the embodiment according to FIG. 1 Circuit.

Fig. 1 shows a layered AC-DG EL element 100 (this term is explained in the next paragraph are), which is arranged on the surface of a first, light-permeable electrode 110. On the of this one The side of the AC-DG EL element 100 facing away from the first electrode 110 is also an energy-sensitive one in the form of a layer Element arranged, which is, for example, a photoconductive element 200. The specific resistance this photoconductive element 200 changes depending on the excitation by an incident energy. The photoconductive element 200 is in contact with a second electrode 210 which is responsible for the incident energy is permeable. A subdivided or perforated composite electrode 310 consists of electrically conductive

209803/0540

capable parts 301 made with dielectric material 302 high resistivity are coated. The pierced electrode 310 is between the first and second Electrode arranged.

The term "AC-DC EL element" denotes an electroluminescent one Element consisting of electroluminescent material dispersed in a dielectric medium is. This is of the resistance type or of the heap polarizability type. When applying an external polarizing field in a fixed direction it carries the internal electric field and holds the residual component of this field upright when the external tension no longer acts on it. Next is the waveform of the luminescence output of the element due to an alternating electric field excitation by a constant electric field applied to it controllable.

The features of the construction and the manufacturing process of this device will be described in more detail below To be received. A support plate 120 is made of a transparent and heat-resistant material such as glass. On the Support plate 120 is stacked on the first electrode 110,

- b- 209808/0540

1764Ι4Θ

which consists of a heat-resistant and translucent metal oxide, for example tin oxide. Applied to this first electrode 110 and fused to it is a layer of AG-DC EL material with a thickness of the order of 20 to 50 microns. The AG-DG EL material consists of a powder of a dielectric material that has an electrical resistance or is frequently polarizable, for example, of a glass enamel that has an electrical resistance, i.e. a slightly conductive metal oxide, such as SnO ₉ and also Li and / or contains Ti. The dielectric material is mixed with a powder of a fluorescent electroluminescent material such as ZnS. An intermediate layer 600, which is also an electrical resistance layer, that is to say has a low conductivity, is applied to the AC-DC EL layer. The intermediate layer 600 consists, for example, of a mixture of an epoxy resin with a powder of an electrically resistive material, such as carbon or Sn0r>. It can also consist of a mixture of a powder of a frit with an inorganic black pigment and a powder of an electrically resistive material, such as SnO _? exist. The mixture is made to set by heating

-6-209808 / 0540

brought about, whereby it becomes an electrically resistive and impermeable layer. If the alternating current impedance of the layer produced is to be reduced, a ferroelectric material, such as BaTiO, can expediently be added to the mixture. The intermediate layer 600 prevents the luminescence output of the electroluminescent element 100 from being fed back to the photoconductive element. If a certain feedback is desired, then the intermediate layer 600 is made correspondingly semi-permeable. The intermediate layer 600 can also be designed as a composite layer, additional elements being inserted between the non-permeable layer and the AC-DC EL element 100. The additional layer can consist, for example, of a mixture of a frit powder or epoxy resin with a powder of a ferroelectric and light-reflecting material (preferably BaTiO) or an electrically resistive metal oxide such as SnO ^ ₄ . The mixture is then fused and set by heating to form an electrically resistive reflective layer. The thickness of the single or composite intermediate layer 600 is intended to be non-permeable

-7-209808 / 0540

Layers b are up to 10 microns and, in the case of reflective layers, 10 to 20 microns, so that a sufficiently small electrical resistance compared to the resistance of the electroluminescent element 100 is obtained via the thickness of the intermediate layer 600. For practical use, the intermediate layer 600 can also be given a particularly non-linear specific resistance so that increases in direct current can be avoided. This can be achieved by using a non-linear resistor material such as CdS: Gl or SiQ in place of the resistor metal oxide for the composition described above. In this case, at least one of the two reflective or non-permeable resistive layers can be omitted.

On the intermediate layer 600 or, if it is omitted, on the AG-DC EL element 100, there is a split or openwork composite electrode 310 arranged, which consists of electrical conductors 301, for example made of tungsten or copper wire a 10 to 30 microns in diameter coated with a high dielectric constant dielectric material 302 is, for example, made of polyester resin or glass

-b-

209808/0540

exist and can have a thickness γόη 2 to 10 microns. In the embodiment described herein, the composite electrode 310 is in the form of a grid with adjacent grid lines. The composite electrode can also be produced, for example, by crosslinking the coated conductors described above or by coating a metallic mesh with the dielectric material mentioned above. The space factor of the conductor 301 of the composite electrode 310 is to be chosen so that the electrode 310, despite its open structure, achieves approximately the same effect in terms of an alternating electrical field as a fixed plate electrode when an operating alternating voltage V. composite electrode 310 is applied. The composite electrode 310 should therefore be constructed in such a way that the alternating current power exciting the AC-DC EL element 100 is not greatly influenced by fluctuations in the specific resistance of the photoconductive element 200. The distance between two adjacent lines of the composite electrode 310 shown in FIG. 1 should preferably be less than 100 microns. The network is said to be in a mesh grid electrode

209 8 0 8/0540

be finer than 50 mesh. Such spacing of the conductors in the composite electrode 310 allows the passage of Direct current between the AG-DG EL element 100 and the photoconductive element 200.

As to the similarity of the composite electrode 310 with a solid plate electrode in terms of the effect To ensure an alternating electric field, an auxiliary resistance layer is provided in the plane of the composite electrode 310 700 is provided which fills at least a portion of the free spaces in the composite electrode 310. The specific resistance of the auxiliary resistance layer 700 is selected to have a value that has a greater spread of the Direct current prevented. It is experimentally demonstrable that a resistance auxiliary layer 700 with a specific

6 9 Surface resistance of 10 to 10 ohm-cm-gives satisfactory results. So meets the specific surface resistance of the AC-DC EL element 100 together with the intermediate layer 600 this condition, an auxiliary resistance layer 700 is not required. The composite electrode 310 can then be on the intermediate layer 600 or the electroluminescent Element 100 can be arranged without the auxiliary resistance layer. The composite electrode 310 can

209808/0540 " ¹ °"

then partially or completely sunk into the intermediate layer 600 or the electroluminescent layer 100. In In the latter case, it can be assumed that the auxiliary resistance layer 700 is at least in the non-permeable layer or the reflective layer of the intermediate layer 6OC or in the AC-DC EL element.

If the intermediate layer 600 and the dielectric material 302 for the coating consist of a vitreous material, thus, the auxiliary resistance layer 700 is made of powder of an epoxy resin or a frit having a resistor containing metal oxide, such as SnOp, is mixed. The mixture is then fused by heating and allowing it to set brought. The intermediate layer 600 and the dielectric material 302 of the coating consist of a binding material with a low melting point, for example from an epoxy resin, so a similar binder in mixture with a a metal oxide exhibiting resistance is used. In this case, powder of a dielectric material with a high dielectric constant, In particular, a ferroelectric material such as BaTiO ^ can be added to the mixture to reduce the alternating current impedance of the resulting layer. The fat

-11-209808 / 0540

the auxiliary resistance layer 700 is, for example, 10 up to 50 microns in order to keep the resistance resulting from their strength small. The auxiliary resistance layer 700 can also be given highly non-linear resistance properties in order to avoid DC voltage losses reduce their thickness and direct current scatter in the direction of the plane. This property of the auxiliary resistance layer 700 can be achieved by using a nonlinear resistivity material such as GdS: Gl or SiC in place of the resistive metal oxide for those described above Composition can be achieved. The auxiliary resistance layer 700 may further have properties of a non-permeable layer or a light-reflecting layer by choosing the materials listed above for these purposes. When using such Resistance auxiliary layer can simplify the structure of the device according to the invention.

The layered, energy-sensitive element, that is the photoconductive element 200 is in this embodiment from a mixture of a binder such as epoxy resin and a photoconductive material such as GdS, CdSe

-1? - 209808/0540

or CdS «Se. This mixture is applied in layers and set by heating. Consists of the dielectric material 302 for the coating, the auxiliary resistance layer 700 and the intermediate layer 600 made of heat-resistant material, for example of that described above glass-like material, the mixture applied to the layer structure carried by the support plate 120 can be used for five Minutes are heated to 600 C, which is done, for example, in a vacuum or an inert nitrogen atmosphere. Man thus receives a layer of sintered material as the photoconductive element 200, the CdS, CdSe or CdS »Se. contains.

The sintered photoconductive element has approximately linear voltage-photocurrent characteristics, which in comparison make operation with very high sensitivity possible with unsintered elements.

Is the auxiliary resistance layer in a layer structure 700 left, the photoconductive element 200 is formed as a layer containing the empty spaces of the composite electrode 310 fills. Is this compound Electrode 310 completely embedded in electroluminescent element 100 or intermediate layer b00,

-13-209808 / 0540

so the resistive auxiliary layer 700 becomes over the electroluminescent Element 100 or the intermediate layer 600 formed. However, is the composite electrode 310 not completely sunk into the electroluminescent element 100 or the intermediate layer 600, then the auxiliary resistance layer becomes 700 designed so that it fills the spaces 310.

The resistivity of the photoconductive element 200 increases depending on an incident energy, like light or X-rays. The specific dark resistance of the photoconductive element 200 is intended for example

be larger than 10 ohm-cm. The thickness of the photoconductive element 200 is chosen to be 50 to 500 microns, hence the dark resistance in the direction of the thickness of the photoconductive Element 200 is equal to or better than the specific resistance of the AC-DG EL element 100 in the direction its thickness.

The second electrode 210 is then applied to the photoconductive element 200. The second electrode 210 is designed in such a way that it is transparent to the incident energy, that is to say to light, X-rays or other radiation

-14-209808 / 0540

and is also electrically conductive. The second electrode 210 is, for example, as a thin foil made of gold or aluminum, as a thin metal layer or made with silver paint. The second electrode 210 can furthermore be designed in a grid-like manner and consist of metal wires, 10 to 50 microns in diameter and spaced 100 to 500 microns apart. If the composite electrode 310 is in the form of a similar grid, the grid of the second electrode should be be arranged so that the parts of its grid cross those of the grid of electrode 310 or in horizontal projection come to rest between these. The second electrode 210 can also be in the form of a metallic network be trained. If the second electrode 210 is designed to be perforated in this way, it can be partially or entirely in the photoconductive member 200 can be buried. A second electrode of this type also has the advantage that Fluctuations in the specific resistance in the direction of the plane can be exploited.

The first electrode 110 is connected to one terminal 401 of an alternating voltage source 400, to the other one Terminal 402 of composite electrode conductor 301

209808/05 ^ 0

is connected via a connecting rod 303. The AC operating voltage V. is applied in this way between the electrode 110 and the electrode 310. The second electrode 210 is connected to a connection 501 of a direct voltage source 500 which supplies a bias voltage, the other connection of which is connected to the terminal 402 of the alternating voltage source 400, whereby the second electrode 210 is supplied with a bias voltage Vn. The DC voltage source 500 is arranged so that the bias voltage V _Q , which is a DC voltage, is variable and its polarity is reversible. This makes it possible to give the AC-DC EL Element 100 different operating characteristics. Depending on whether the switch s is in contact with the contact ρ or the contact q (see FIG. 1), the electrode on the luminescence output side of the AC-DC EL element 100, i.e. the first electrode 1i0 _{t, is} negative or positively biased. In the first case, the device is mainly suitable for the reversal and amplification of an energy image and the deletion of the stored image mentioned above. In the second case, the device Lum is suitable for writing an image and for luminescence display of a stored image.

-16-209808 / 0540 bad OB1G1NAL

FIG. 2 shows, in simplified form, an equivalent circuit of the arrangement described above with reference to FIG. 1. In order to simplify the explanation, the functions of the auxiliary resistance layer 700 and the intermediate layer 600 are not taken into account in FIG. 2. The photoconductive element 200 has a variable resistance Hp over its thickness. Due to the dielectric material 302 of the coating on the composite electrode 310, a capacitance C ₁₃ is obtained via this coating. The conductor 301 is an electrode. The AG-DC EL element 100 has a capacitance C ″ and a resistance R ″ across its thickness. Fig. 2 shows

χι Üj

that the resistance E _p falls as a function of the intensity of an incident energy L *, which can occur, for example, as light rays or X-rays. As a result, the DC bias voltage V ^ distributed across the AG-DC EL element increases. The result of this decrease in bias is that the waveform of the AC luminescent output L _? , which arises through the AC power supplied via the capacitance C ^, is controlled in such a way that the amplitude of the wave is significantly reduced in a certain half-period of each period of the AC voltage.

-17-209808 / 0540

In this way, in the embodiment described, an energy image L 1, which is present as a light or X-ray image falling on the photoconductive element, is converted and amplified with high sensitivity and high gain in image, the luminescence output of which is negative polarity Has. It should be noted that in the device according to the invention, the DC bias voltage V _{D is applied} between the energy-sensitive element represented by the variable resistor EL and the capacitive element represented by the capacitance C ^. Correspondingly, the dielectric _{strength of the capacitance C 13} , at which a relatively low DC bias voltage Y Jd i)

corresponding preload should not be very high. Adjustment of the source voltage Vg also affects the AC power supplied to the AC-DG EL Element 100.

The above-described luminescent device in the form of a solid image plate can be used as a preamplifier for television cameras that are equipped with a vidicon or other image pickup tube. The high sensitivity and the high energy amplification factor of the luminescent device according to the invention allows implementation and intensify even very weak images and that too

-1b-209808/0540

Taking pictures for sorting, i.e. for selecting and separating luminescent pulses with the help of a light chopper 1000 driven by a synchronous motor 110. The opening time of the light chopper 1000 should at least be shorter than a period of the AC operating voltage V.

Jn.

and preferably even shorter than half a period. The opening hours should be adjustable. The frequency of the sorting operation is based on the frequency of the operating AC voltage V. discontinued. Fig. 1 below shows how the luminescent controlled waveform output image generated by the electroluminescent Element 100 is emitted as a function of the incident image L., with regard to special ones stored in it Luminescence pulses is sorted. According to the invention, the Polarity of the video signal obtained is reversed in order to reproduce a visible image of positive polarity with respect to to obtain the incident energy image on the screen of a television system 300. Such a device using a closed-loop television system is particularly useful for x-ray television systems in industrial or medical applications Use.

Are there devices in the television system for setting or controlling the image reproduction characteristics, for example the

209808/0540

trastes, provided, the device described below for sorting the luminescence pulses is not absolutely necessary.

To improve the image reproduction, the light chopper 1000 can be incorporated into the optical system of a television camera 2000. The photoelectric screen of a picture tube in the television camera 2000 is represented by the output image of the luminescence pulse L _? excited.

In a system employing a television camera, the ratio is the sub-frame rate of the picture tube the sorting frequency of the Luminesenζimpulse or the Frequency of the alternating operating voltage V. to be selected as an integer,

Jn.

so that beats or flickering of the television picture can be avoided. The latter frequency is usually chosen to be higher than the former. To maintain a synchronized relationship between the two frequencies, the Kippoder Synchronization signal for horizontal or vertical scanning of the television system as input signal E «of the alternating voltage source 400 used and the time or synchronization signal as the drive signal E ^ of the synchronous motor 1010. The signals Eg and Ejj become from the time signal in electrical circuits

-20-209808 / 0540

and 1020 is generated so that the ratio of the frequency of the signals "E ₀ and E _n" to that of the timing signal becomes an integer and further the phase relationship between the former and the latter can be adjusted. With this arrangement, adjustability of the operational characteristics is achieved In the embodiment of the invention described here, the composite electrode 310 lies between the AC-DC EL element 100 and the energy-sensitive element, i.e. the photoconductive element 200. In this construction, the total thickness of the layers including the intermediate layer 600, the auxiliary resistance layer 700 or other additional elements can be made equal to or smaller than the thickness of the composite electrode, so that the elements can be incorporated as a whole in the free space of the composite electrode 310. Such a structure is advantageous in that the leakage of the direct current is avoided.

The composite electrode 310 can be partially incorporated into the DC-AC EL element 100 or the energy sensitive element 200 can be embedded.

Further, the relative thickness of the composite electrode 310 is determined by the thickness of the electroluminescent egg

-21-209808 / 0540

176A94Q

mentes 100 and the photoconductive member 200 are not limited. It only has to be less than the distance between the first electrode 110 and the second electrode 210. As far as the position of the composite electrode 310 is concerned, it only has to be between the first electrode 110 and the second electrode 210. Other conditions do not have to be met. Therefore, at least corresponds w neither the electroluminescent element 100, or the photoconductive element 200 in the free spaces of the composite electrode are introduced 310th

In the above description, the photoconductive element is used as an energy sensitive element. In a device constructed according to the principle of the invention, however, the energy-sensitive element is only required to essentially change its resistance as a function of excitation by any incident energy. It is therefore also possible, instead of the photoconductive element, to use other energy-sensitive elements, for example a Piezoelectric element or a magneto-resistance element, to be used, their specific resistance by elastic Energy or magnetic energy is controllable.

-22-209808 / 0540

Claims (8)

Patent claims: 1. Energy-responsive luminescent device, characterized in that on one side a first Electroluminescent electrode (110) which is transparent to light Layer (100) is arranged, whose -when excited Luminescence output resulting from an alternating electric field in terms of its waveform due to an electric field can be controlled in a fixed direction and on the side thereof remote from the first electrode (110) a second electrode (210) is provided, between the and the electroluminescent layer (100) at least its specific resistance energy-sensitive layer (200) which changes as a function of an incident energy lies that between the first (110) and the second (210) electrode has a perforated composite electrode (310) arranged thereon consisting of at least one Conductor (301), which is coated with a dielectric material (302) and that the waveform of the at AC excitation obtained luminescence output by the electric field of a fixed direction according to the fluctuations the resistance of the energy-sensitive layer (200) is controllable. -23- 209808/0540 2. Luminescence device according to claim 1, characterized in that the composite electrode (310) has the shape of a grid with adjacent grid lines. 3. Luminescence device according to claim 1, characterized in that the composite electrode (310) Is formed like a network. 4. Luminescence device according to one of claims to 3, characterized in that the composite electrode (310) consists of metallic conductors (301) which are electrically insulated from one another and which are coated with a dielectric material (302) are coated. 5. Luminescent device according to claim 1, characterized in that between the electroluminescent Layer (100) and the energy-sensitive layer (200) an intermediate layer (600) is arranged, which has an electrical Has resistance. 6. Luminescence device according to claim 5, characterized in that the intermediate layer (600) has a non-linear specific resistance. 7. luminescent device according to claim 5 or 6, characterized in that the intermediate layer (600) is a ferro- 20 9 8 08/0540 contains electrical material. " 8. Luminescent device according to one of the claims 5 to 7, characterized in that the specific resistance of the intermediate layer (600) is lower than that of the electroluminescent layer (100). 9 · Luminescence device according to one of Claims 5 to 8, characterized in that the composite Electrode (310) is arranged on the surface of the intermediate layer (600). 10. Luminescent device according to one of claims 5 to 8, characterized in that the composite Electrode (310) is extended into the energy-sensitive layer (200) and the intermediate layer (600). 11. Luminescence device according to one of claims 5 to 8, characterized in that the composite electrode (310) is embedded in the intermediate layer (600), 12. luminescent device according to claim 1, characterized in that the resistance of a to the ener giesensitive layer (200) adjoining the electroluminescent layer (100) containing layer in Rich- -25-209808 / 0540 176A940 direction of the electric field fixed direction is lower than the resistance of the energy-sensitive layer (200) over its thickness when the specific resistance of the energy-sensitive layer (200) assumes its highest value. 13 · Luminescent device according to claim 1, characterized in that between the first (110) and the second (210) Electrode an electrical equalization voltage is applied, whose Value and polarity are adjustable, and that between the first Electrode (110) and the composite electrode (510) AC voltage is applied, 14 · Luminescence device according to claim 1, characterized in that a device for determining the alternating current excited luminescence output of the electroluminescent ^ Layer (100) as a video signal and to reproduce this signal in a closed television system (300) is provided, the consists of a receiver device, an image playback and display device and a device for changing the contrast, polarity, etc. of the video signal. 15 · Luminescent device according to claim 14, characterized in that, by sorting the change stroeer 209808/0540 BAD stimulated luminescence output a light chopper (1000) is provided that works synchronously with the AC voltage and has an opening time that is at least shorter than one Period of the alternating voltage. 16. Luminescent device according to claim 15, characterized in that a device for controlling the opening time of the light chopper (1000) and / or the phase position of the Opening time is provided in each period of the AC voltage. 17. Luminescent device according to claim 14, characterized in that a device for synchronizing the Frequency of the AC voltage is provided with the field frequency of the closed television system (300), and that the both frequencies have an integer ratio to each other after synchronization. 209808/0540 Blank page