US3564260A - Solid-state energy-responsive luminescent device - Google Patents

Solid-state energy-responsive luminescent device Download PDF

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US3564260A
US3564260A US707713A US3564260DA US3564260A US 3564260 A US3564260 A US 3564260A US 707713 A US707713 A US 707713A US 3564260D A US3564260D A US 3564260DA US 3564260 A US3564260 A US 3564260A
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layer
voltage
photoconductive
solid
resistive
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US707713A
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Kazunobu Tanaka
Tadao Kohashi
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00—Electroluminescent light sources
    • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
    • H05B33/22—Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of auxiliary dielectric or reflective layers
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00—Electroluminescent light sources
    • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
    • H05B33/20—Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of the material in which the electroluminescent material is embedded

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  • This invention relates to a solid-state energy-responsive luminescent device in which input energy signal is converted or amplified and displayed through a solid-state image plate which consists of a combination of photoconductive element and electroluminescent element and is connected to a power source.
  • This invention is intended to provide a wide range of controllability of the contrast, that is, gamma value, an improved characteristics in the low input energy range, and an extended input energy latitude (that is, an effective operating range of the input energy signal), by giving appropriate resistive impedances to respective appropriate elements out of constituents of said solid-state image plate, supplying an AC voltage superimposed with a DC voltage as the operating voltage and controlling the magnitude of this DC voltage.
  • the AC impedance of the photoconductive element depends on capacitive impedance of the photoconductive element determined by its geometrical structure in low input energy range. From this reason and because the photoconductivity is essentially less sensitive when an AC voltage is being imposed on it, the rate of variation in the AC impedance is extremely low in the conventional image plates.
  • the conventional image plates partly because of the photoelectrical nonlinearity of the electroluminescent element, has a low sensitivity and a high gamma value, and accordingly, a very limited input energy latitude.
  • the electrolumine element of the solid-state image plate and appropriate intermediate elements interposed between said electroluminescent element and the photoconductive element are endowed with resistive impedances, and the photoconductive element is of such property that its photoconductive sensitivity under an AC operating voltage is controllably increased by superimposing a DC voltage onto the AC voltage.
  • the DC voltage is superimposed on the AC voltage applied across the electroluminescent element and the photoconductive element, and by controlling the value of said DC voltage are attained an improved characteristics in low input energy range, a wide controllable range of gamma value and an extended input energy latitude.
  • FIG. 1 shows an equivalent circuit for explaining the principle of this invention
  • FIG. 2 is a schematic diagram showing a portion of the solid-state image plate embodying this invention.
  • FIG. 3 shows characteristic. curves concerning an embodiment of this invention.
  • marking Cp indicates the capacitive component of the photoconductive layer (hereafter, referred to as a PC layer), Rp the resistive component of the PC layer, Ce the capacitive component of the electroluminescent layer (hereafter, referred to as an EL layer), and Re the resistive component of the EL layer. Value of Re is selected to be appropriately lower than the dark resistance of Rp.
  • Mark Va indicates the operating AC voltage, Vb the variable DC voltage, L the incident energy signal and L: the output light.
  • Vb is zero volt
  • the circuit is equivalent to a conventional image plate of positive image type. Since the AC impedance due to the capacitance Cp determined by the geometrical structure is more dominant in the low input energy range than the AC photoconductive sensitivity of the PC layer, the characteristics of the output light intensity vs the input energy signal is not satisfactory, and
  • the input energy latitude is not sufficiently broad and further, the gamma value is considerably high.
  • a DC voltage Vb is applied; in a closed DC circuit composed by the resistive component Rp of the PC layer and the component Re of the EL layer, DC voltage Vbp determined by said resistive components Rp and Re is applied to the PC layer, being superimposed on AC voltage Vap.
  • the resistive component Rp of the PC layer is very high in comparison with the component Re, rendering the DC voltage Vbp nearly equal to the voltage Vb, thus a very high DC voltage being superimposed on the AC voltage Vap.
  • a satisfactory PC layer of which the photoconductive sensitivity under AC voltage can be controllably increased by the superimposition of a DC voltage is the one containing powder of photoconductive material.
  • AC photoconductive sensitivity of photoconductive powder increases nonlinearly with the increase of the superimposed DC voltage. Therefore, the characteristics is remarkably improved in the low input energy range where the proportion of the superimposed DC voltage is high. While, with the increase of the input energy signal intensity, the resistive component Rp of the PC layer decreases, accompanied by the decrease of the component DC voltage Vbp, thus diminishing the improving effect of the DC voltage to the AC photoconductive sensitivity of the PC layer. Upon the intent energy reaching a high intensity range, the resistive component Rp of the PC layer decreases to a value negligible in comparison with the resistive component Re of the EL layer and the component DC voltage Vbp of the PC layer becomes nearly zero.
  • the intensity of the output light L in this input range becomes equivalent in the value to that of the conventional solid-state image plate in which the voltage Vb is zero. That is, whereas the characteristics representing the intensity of output light vs the intensity of input energy signal in a high input range is almost equivalent to that of the conventional solid-state image plate of positive image type when the DC voltage is zero, the similar characteristics in a low input range is remarkably improved by the effect of the component DC voltage Vbp imposed upon the PC layer by applying the DC voltage Vb to the device, the effective range being extended greatly to the low input energy range depending on the value of the DC voltage Vb, thereby enabling a wide range control of gamma value and providing an extended input energy latitude. Moreover, the contrast in the obtained output image is almost as excellent as that in Vb 0, as the luminescence of the EL layer is little effected by DC voltage.
  • control of the resistive element Re of the EL layer concurrently varies the impedance of the EL layer.
  • the contrast hitherto limited by the ratio of capacitances of the EL layer and PC layer thus becomes freely controllable by adjusting the resistive component Re, without depending on the geometrical structure of the PC layer and EL layer.
  • FIG. 2 which is showing schematically structure of a solid-state image plate embodying this invention and the manner in which the electric power is supplied to the device
  • numerals 101 to 107 indicate the constituting elements of the solid-state image plate, 101 being light-pervious support plate made of glass or the like, and 102 being light-pervious electrode, for example, made of metal oxide such as tin oxide.
  • Numeral 103 indicates semiconductive electroluminescent layer of approximately 30 to 60 micron in thickness which comprises powder of electroluminescent material such as ZnSzCuAl and powder of semiconductive metal oxide such as Sn0 or Ti0 which has good reflexibility against the luminescent spectrum of said EL material, said powders being binded by a vitreous material and formed in a layer.
  • the luminescent output is effectively taken out from the EL layer without being absorbed by resistive powder.
  • the resistivity of the EL layer can be easily controlled over a wide range by varying the amount of the resistive powder to be mixed. Accordingly, the matching of the PC layer to the load circuit including the EL layer can be easily attained in the series connected resistive circuit, and a very effective control of the AC photoconductive sensitivity of the PC layer is achieved by the control of DC voltage, with the aid of usage of a PC layer containing powdered photoconductive material.
  • gamma value becomes widely controllable and the effective operating range of the intensity of the input energy is extended.
  • the former is semiconductive reflecting layer of about 10 micron in thickness which comprises powder of a light-reflective and ferroelectric material such as BaTiO and powder of semiconductive metal oxide such as Snt) or Ti said powders being bonded with a vitreous material or a plastic material.
  • a vitreous bonding material is preferable for making ohmic layer, while a plastic material is advantageous for nonohmic layer.
  • Numeral 105 indicates impervious semiconductive layer of about micron in thickness which comprises, for example, black paint mixed with powder of nonlinear resistivity such as CdSzCl or powder of linear resistivity such as carbon black and which is formed in a layer.
  • resistivity of the series connected resistive load circuit including the EL layer can be adjusted by varying the resistivity of the intermediate layers, so that the resistivity of said load circuit is set at an appropriate value of the same order as the dark resistivity of the PC layer or lower than that. Therefore, limitation for the resistivity of the EL layer is much relieved. For example, if the EL layer has been produced with extremely low resistivity, the intermediate layer 104 is made so as to have an ohmic resistance asdescribed above, the resistivity being set at an appropriate value higher than that of the EL layer, thereby to attain the matching of the load to the PC layer in the resistances.
  • the intermediate layers allow easy fabrication of the resistive EL layer and eliminate the effect of limitation of the resistivity to luminescent characteristics, and further facilitate easy matching of the DC resistances between the series connected load circuit including the EL layer and the PC layer, thereby permitting very effective control of the AC photoconductive sensitivity of the PC layer by the DC voltage.
  • the DC voltage across the PC layer is made high when the intensity of input energy signal is zero or very low.
  • gamma value and input-to-output characteristics in low input energy range are improved, and the effective operating range of intensity of input energy signal is remarkably extended.
  • the resistivity can be freely controlled by varying the amount of the powder over a wide range. This makes very easy the adjustment of the resistance of the series-connected load circuit including the EL layer or the matching of resistances between said load circuit and the PC layer, and accordingly facilitates fabrication of the complete device, and further makes easy improvement of gamma value and the effective operating range of the intensity of input energy.
  • resistive intermediate layers contain powder of ferroelectric material such as BaTi0 the overall dielectric constant of the layers is raised. This raised dielectric constant lowers AC voltage loss in the intermediate layers. This fact is another advantage of the resistive intermediate layers, beside the above-mentioned advantages.
  • the ferroelectric material such as BaTill has a high specific resistivity. Therefore, when resistive binder material is used for the intermediate layer, the use of the ferroelectric material also makes possible controlling of resistivity of the intermediate layer by varying the amount of the material to be mixed, beside it serves to raise the overall dielectric constant of the layer.
  • the intermediate layer the resistivity of which is presented by adding of resistive powder, particles of highly resistive ferroelectric material are intermixed with particles of resistive material, as the ferroelectric material is also used. As the result, two dimensional uniformity in the resistivity of the intermediate layer is improved, as the condensation and maldistribution of the resistive powder are thus prevented.
  • numeral 106 indicates the photoconductive layer or PC layer of about 200 to 500 micron in thickness, which is formed of photoconductive powder bound by plastics or a similar binding material, said photoconductive powder being a material which is sensitive not only to the visible light but to a radiation such as X-ray, infrared ray and ultra-violet ray, such as, for example, cadmium sulfide activated with an element of IB group such as Cu or Ag and an element of VII B group such as C1, the latter element of Vll B group being able to be substituted by an element of III B group such as All or Ga.
  • Numeral 107 indicates electrode of vapourdeposited metal, for example, aluminum.
  • This electrode is pervious not only to a radiation such as X-ray, but to the visible light, and can be formed in a gappy pattern such as equispaced parallel lines, lattice or mesh.
  • Numeral 108 represents input energy signal, which is not limited to the visible light, but can be other radiation such as ultra-violet ray, infrared ray or X-ray.
  • Numeral 109 indicates output visible image.
  • Numerals 110 and 111 indicate voltage sources for the solid-state image plate applied across the electrodes 102 and 107, 110 being the AC operating voltage source and 111 being variable DC voltage source.
  • the semiconductive EL layer 103 the most important one for realizing the above-mentioned control by DC voltage is the semiconductive EL layer 103.
  • the resistivity of the EL layer is theoretically required to be appropriately lower than the dark value of resistive component of the PC layer; that is, to be in the semiconductive range of the order of 10 to 10 ohm-cm, where the characteristics is fairly linear.
  • This requirement for the resistivity presents several technical problems including difficulties relating to construction and manufacturing method.
  • the conventional techniques for imparting electroconductivity to a solid layer made of a highly resistive material such as plastic or glass include a process of dispersing resistive material into the plastic or glass body.
  • the resistivity obtained by such process is limited to one very near to that of a conductor or to one having directivity, and a solid layer which has a resistivity of 10 to 10 ohm-cm.
  • the semiconductive EL layer 103 as shown in FIG. 2 has been introduced by this invention.
  • the resistive material is selected from the semiconductive metal oxides including Sn0,, W0 Sb O and Tit! which are stable at a considerably high temperature in the atmospheric environment and readily available in the form of pulverized product, and which have high reflexibility to the light in the visible spectrum emitted from the EL powder.
  • the binder of the EL layer is used a vitreous material which is thermally stable up to a considerably high temperature and into which metal oxide such as Sn0 is preferably fusible in some extent, the ohmic characteristics of the resistivity and thermal stability of the electrical properties being taken into consideration.
  • vitreous binder the softening point of which is lower than that of the support plate 101 and the heat expansion coefficient of which is substantially the same as that of the support plate, so as to ensure satisfactory application of the EL layer to the support plate.
  • the binder must be light-pervious, as it is used in the EL layer.
  • the control of the resistivity of the semiconductive EL layer according to the above-mentioned construction is made by varying the volumetric ratio of the metal oxide powder in relation to the total volume. In this process, it is important to properly select the relative gradings of the resistive powder, EL powder and binding vitreous powder, in order to ensure sufficient adhesion among the resistive powder, EL powder and support plate 101 and to obtain smooth layer.
  • the following table 1 shows the gradings and volumic percentages of the ingredients of the above-described mixture: that is, Sn0 powder used as the resistive material, ZnS:CuAl powder as the electroluminescent material and the vitreous material as the binder.
  • Table 2 shows an example of the composition of the vitreous binder.
  • Table 3 shows volume expansion coefficients and softening points of the vitreous binder and the light-pervious support plate (a glass plate).
  • Vitreous binder X- Support plate glass
  • the percentage of Sn0 powder can be varied in a range of 10 to percent, causing corresponding variation in the resistivity.
  • the heating temperature was set at 640 C. in this embodiment.
  • the resistivity of thus obtained EL layer showed a fairly good linearity in the semiconductor range of 10 to 10 ohm-cm. Moreover, thus obtained EL layer is highly resistive against heat and environmental conditions.
  • the resistivity of the intermediate layers is selected so that the total of the resistances of the two intermediate layers and the EL layer is at most not higher than the dark resistance (that is, resistance under no light input) of the PC layer 106.
  • the resistance of the intermediate layers may be approximately the same or lower in comparison with that of said EL layer, and may have a nonlinear current-voltage characteristics.
  • AC voltage loss in the intermediate layers is decreased by the above-mentioned nonlinearity of resistance, thereby the AC voltage being effectively impressed on the EL layer.
  • drop of the distinction in the output image due to dispersion of AC current in the intermediate layers is prevented. Therefore, the nonlinearity of the characteristics is rather preferable, when satisfactory matching between the resistance of the EL layer and the dark resistance of the PC layer is obtainable without adjustment of the resistance of the intermediate layers.
  • the EL layer 103 can be made in the form of a compound layer consisting of a layer for displaying output image and a layer for feedback of the light, with a semiconductive nonpervious layer therebetween.
  • FIG. 3 shows input versus output characteristics of the embodiment shown in FIG. 2, as plotted on a logarithmic chart, where the AC operating voltage is fixed at 450v., its frequency being 1 kc. and the DC voltage is varied, as the parameter, from zero to 400v.
  • the intensity of input energy signal is represented by dose rate of continuous X-ray from a 113 kVP X-ray tube.
  • gamma value is variable widely and continuously in a range of l to 3, and input energy latitude is extended by nearly one hundred times of the conventional value.
  • the AC photoconductive sensitivity of the PC layer in relation to the intensity of input energy can be controlled, and characteristics in low input energy range, gamma value and effective operating range for the input energy intensity can be adjusted widely and continuously.
  • the operating characteristics can be varied only by changing the polarity of the DC voltage without varying magnitude of the voltage. Therefore, a wide variability of the operating characteristics is obtained by providing means for controlling at least either one of magnitude or polarity of the DC voltage to be superimposed on the AC voltage.
  • the photoconductive material CdSzCuCl is essentially less sensitive to the radiations such as X-ray than to the visible light.
  • an appropriate amount of radiation luminescent fluorescent powder for example, orange luminescent ZnCdSzAg
  • the sensitivity is increased by more than ten tifies of the original value. This is because the radiation luminescent fluorescent material is excited by the incident radiation (for example, X-ray) at the same time when the PC material is excited, and the PC material is further excited by the visible light converted by the radiation luminescent material.
  • operating characteristics of the energy-responsive luminescent device is improved particularly in low input range, and gamma value of the solid-state image plate becomes widely variable, and further the input energy latitude is remarkably extended, by imparting resistive impedances to the EL layer and the required intermediate layers interposed between the EL layer and the PC layer with unique constitution and manufacturing method and by controlling the DC voltage superimposed on the AC operating voltage.
  • the EL layer of this invention is formed from a mixture which contains powder of vitreous material, powder of BL fluorescent material and powder of at least one lightreflective and semiconductive metal oxide selected from group containing Sn Ti0 W0 and Sb 0 the mixture being heated to fuse the vitreous material.
  • the EL layer of this invention presents an ohmic resistivity which is well stable even in high voltage range and a highly efficient EL luminescence, without possible decrease of the luminescent efficiency.
  • a solid-state energy-responsive luminescent device comprising an electroluminescent layer which is excited to luminescence by an AC voltage applied thereto, a photoconductive layer provided on said electroluminescent layer, the AC impedance of said photoconductive layer being variable depending on the intensity of an incident energy and said AC impedance in a dark state being higher than the AC impedance of said electroluminescent layer, a pair of electrodes sandwiching the combination of said two layers therebetween, at least that one of said electrodes which is disposed on the electroluminescent layer being light-pervious, and means for applying an AC voltage and a DC voltage superimposed on said AC voltage across said layers by means of said electrodes, whereby the AC voltage across said electroluminescent layer, and therefore the luminescent output, is controlled substantially according to the variation of the AC impedance of said photoconductive layer due to the variation in the intensity of the incident energy thereto, wherein said photoconductive layer comprises a powder of photoconductive material bound with a binding material so that the photoconductive sensitivity of said photoconductive layer under an AC voltage
  • said two powders being mixed with a vitreous medium.

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US707713A 1967-02-24 1968-02-23 Solid-state energy-responsive luminescent device Expired - Lifetime US3564260A (en)

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DE (1) DE1639329C3 (fr)
FR (1) FR1557227A (fr)
GB (1) GB1223153A (fr)
NL (1) NL6802600A (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3790867A (en) * 1972-02-22 1974-02-05 Matsushita Electric Ind Co Ltd Light-intensifying device
US3849707A (en) * 1973-03-07 1974-11-19 Ibm PLANAR GaN ELECTROLUMINESCENT DEVICE
US4634934A (en) * 1982-05-19 1987-01-06 Matsushita Electric Industrial Co. Ltd. Electroluminescent display device
US5164582A (en) * 1988-07-01 1992-11-17 B.V. Optische Industrie "De Oude Delft" Method for operating an image intensifier tube by generating high frequency alternating electric field between cathode and channel plate thereof
EP0781076A3 (fr) * 1995-12-20 1997-10-15 Mitsui Toatsu Chemicals Laminé transparent conducteur et élément électroluminescent
US20030090797A1 (en) * 2000-09-12 2003-05-15 Michael Mueller License plate
US20060261722A1 (en) * 2005-05-23 2006-11-23 General Electric Company Phosphor admixture, phosphor screen and imaging assembly

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US2905830A (en) * 1955-12-07 1959-09-22 Rca Corp Light amplifying device
US2972692A (en) * 1958-05-02 1961-02-21 Westinghouse Electric Corp Method for operating electroluminescent cell and electroluminescent apparatus
US2988646A (en) * 1958-03-25 1961-06-13 Westinghouse Electric Corp Solid state image-producing screens
US3217168A (en) * 1960-12-29 1965-11-09 Philips Corp Photosensitive solid-state image intensifier
US3300645A (en) * 1963-09-16 1967-01-24 Electro Optical Systems Inc Ferroelectric image intensifier including inverse feedback means
US3358185A (en) * 1965-08-20 1967-12-12 Hartman Huyck Systems Co Inc Gated electroluminescent display device having a plurality of electroluminescent cells with one cell includng a photoconductor element

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2905830A (en) * 1955-12-07 1959-09-22 Rca Corp Light amplifying device
US2988646A (en) * 1958-03-25 1961-06-13 Westinghouse Electric Corp Solid state image-producing screens
US2972692A (en) * 1958-05-02 1961-02-21 Westinghouse Electric Corp Method for operating electroluminescent cell and electroluminescent apparatus
US3217168A (en) * 1960-12-29 1965-11-09 Philips Corp Photosensitive solid-state image intensifier
US3300645A (en) * 1963-09-16 1967-01-24 Electro Optical Systems Inc Ferroelectric image intensifier including inverse feedback means
US3358185A (en) * 1965-08-20 1967-12-12 Hartman Huyck Systems Co Inc Gated electroluminescent display device having a plurality of electroluminescent cells with one cell includng a photoconductor element

Non-Patent Citations (1)

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Title
Thornton, ac-dc Electroluminesce , Physical Review, Vol 113, Number 5, March 1, l959, pp. 1187 90 250/213 *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3790867A (en) * 1972-02-22 1974-02-05 Matsushita Electric Ind Co Ltd Light-intensifying device
US3849707A (en) * 1973-03-07 1974-11-19 Ibm PLANAR GaN ELECTROLUMINESCENT DEVICE
US4634934A (en) * 1982-05-19 1987-01-06 Matsushita Electric Industrial Co. Ltd. Electroluminescent display device
US5164582A (en) * 1988-07-01 1992-11-17 B.V. Optische Industrie "De Oude Delft" Method for operating an image intensifier tube by generating high frequency alternating electric field between cathode and channel plate thereof
EP0781076A3 (fr) * 1995-12-20 1997-10-15 Mitsui Toatsu Chemicals Laminé transparent conducteur et élément électroluminescent
US6351068B2 (en) 1995-12-20 2002-02-26 Mitsui Chemicals, Inc. Transparent conductive laminate and electroluminescence light-emitting element using same
US20030090797A1 (en) * 2000-09-12 2003-05-15 Michael Mueller License plate
US20060261722A1 (en) * 2005-05-23 2006-11-23 General Electric Company Phosphor admixture, phosphor screen and imaging assembly
EP1727159A1 (fr) * 2005-05-23 2006-11-29 General Electric Company Melange de phosphore, dispositif et ensemble d'imagerie
US7586252B2 (en) 2005-05-23 2009-09-08 General Electric Company Phosphor screen and imaging assembly

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DE1639329C3 (de) 1975-01-16
DE1639329B2 (de) 1974-06-12
FR1557227A (fr) 1969-02-14
DE1639329A1 (de) 1972-03-09
NL6802600A (fr) 1968-08-26
GB1223153A (en) 1971-02-24

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