Thin-film electroluminescent device of emitting-light-color changeable type

• US 4,666,793 A
• Filed: 02/08/1985
• Issued: 05/19/1987
• Est. Priority Date: 04/10/1984
• Status: Expired due to Term

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Littelfuse Incorporated
• Inventors: Hirate, Takashi
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US06/700,014
• Time in Patent Office: 830 Days
• Field of Search: 313/503, 313/509, 428/690, 428/691, 428/917, 428/209, 428/210, 428/901
• US Class Current: 428/690
• CPC Class Codes: H05B 33/12 Light sources with substantially two-dimensional radiating surfaces
• CPC Class Codes: Y10S 428/917 Electroluminescent

Abstract

A thin-film light emitting element in which the light color emitted from the light emitting element can be voluntary changed in accordance with an electric power source applied to the light emitting element by utilizing scattering, accumulation, and discharge of an electric charge in a gate layer disposed between active layers of the light emitting element.

Claims

1. In a thin film electroluminescent device of the emitting-light color-changeable type, wherein the color of the light emitted from the device is changeable in accordance with an electrical condition applied to the device, said device comprising a substrate, at least one transparent electrode layer, and an insulation layer mounted on the electrode layer, and a second insulation electrode layer and a second electrode, said electrodes being arranged to cooperate electrically with a source of electrical power, the improvement comprising the combination of:

a first active layer to emit red light, said first active layer being composed of a mixture of zinc sulfide and samarium trifluoride;

a second active layer to emit green light, said second active layer being composed of a mixture of zinc sulfide and erbium trifluoride; and

a gate layer responsive to current from said source and being composed of a thin film of samarium fluoride, said gate layer being interposed between said first active layer and said second active layer and acting as a charge accumulating and scattering layer which transmits current from said source to effect activation of said pair of active layers by scattering the electric charge passing said gate layer, for accumulating and discharging the electric charge at the gate layer and at the interface between said at least one of the gate layer and either said first active layer or said second active layer, and interacting said charge with an accumulated charge at said gate layer and said interface

whereupon the intensity of the light emitted from said first and second active layers is changed in accordance with the voltage, frequency, polarity and waveform of the source of electric power so that the color of light seen from the side of the transparent electrode is controlled by the external electrical power source.

2. In a thin film electroluminescent device of the emitting-light color-changeable type, wherein the color of the light emitted from the device is changeable in accordance with an electrical condition applied to the device, said device comprising a substrate, at least one transparent electrode layer, and an insulation layer mounted on the electrode layer, and a second insulation electrode layer and a second electrode, said electrodes being arranged to cooperate electrically with a source of electrical power, the improvement comprising the combination of:

a first active layer to emit blue light, said first active layer being composed of a mixture of zinc sulfide and thulium trifluoride to emit blue light;

a second active layer to emit red light, said second active layer being composed of a mixture of zinc sulfide and samarium trifluoride to emit red light;

a third active layer to emit green light, said third active layer being composed of a mixture of zinc sulfide and erbium trifluoride to emit green light; and

a first gate layer interposed between said first active layer and said second active layer; and

a second gate layer interposed between said second active layer and said third active layer, each of said first and second gate layers being composed of a thin film of samarium fluoride and metal to act as a charge accumulating and scattering layer which transmits current from said source to effect activation of said pair of active layers by scattering the electric charge passing a gate layer, for accumulating and discharging the electric charge at each respective gate layer and at the interface between a gate layer and an adjacent active layer, and interacting said charge with an accumulated charge at said gate layer and said interface so that the intensity of the light emitted from the active layers can be changed in accordance with the voltage, frequency, polarity and waveform of the electric power source, whereupon the color of light seen from the side of the transparent electrode is controlled by the external electric power source.

3. A thin film electroluminescent device of an emitting-light, color-changeable type comprising a pair of electrodes, at least one of which is composed of transparent material;

an external electric power source for applying a voltage across said pair of electrodes;

at least one pair of active electrodes disposed between said electrodes, one of said pair of active electrodes comprising a first active layer composed of a material for emitting a light of a first color, the other of said pair of active electrodes composed of a material for emitting light of a second color;

the improvement comprising at least one gate layer responsive to current from said source disposed between said first and said second active layers, said gate layer being selected from a material and positioned relative to said first and second active layers to act as a charge accumulating and scattering layer which transmits current from said source to effect activation of said pair of active layers by scattering the electric charge passing said gate layer, for accumulating and discharging the electric charge at the gate layer and at the interface between the gate layer and either of said first active layer or said second active layer, and interacting said charge with an accumulated charge at said gate layer and said interface so that the intensity of the light emitted from the first and second active layers is changed in accordance with the voltage, frequency, polarity, and waveform of the source of electric power, whereupon the color of the light seen from the side of the transparent electrode is controlled by the external power source.

4. A device as set forth in claim 3, wherein one of said pair of active layers comprises a first active layer composed of a mixture of zinc sulfide and samarium trifluoride, the other of said pair of active layers comprises a second active layer composed of zinc sulfide and erbium trifluoride and said gate layer is composed of samarium trifluoride.

5. A thin film electroluminescent device of an emitting-light, color-changeable type comprising a pair of electrodes, at least one of which is composed of transparent material;

an external electric power source for applying the voltage across said pair of terminals;

a plurality of active layers disposed between said electrodes, said plurality of active layers comprising a first active layer for emitting a light of a first color, a second active layer for emitting light of a second color, and a third active layer for emitting light of a third color, the improvement comprising a first gate layer disposed between said first and second active layers, and a second gate layer disposed between said second active layer and said third active layer, each of said first and second gate layers selected from a material for acting as a charge accumulating and scattering layer which transmits current from said source to effect activation of said pair of active layers by scattering the electric charge passing said gate layer, for accumulating and discharging the electric charge at the gate layer and at the interface between either of said gate layers and its adjacent active layers, and interacting said charge with an accumulated charge at said gate layer and said interface so that the intensity of the light emitted from the active layers is changed in accordance with the voltage, frequency, polarity and waveform of the source of electric power, whereupon the color of light seen from the side of the transparent electrode is controlled by the external electric power source.

6. A device as set forth in claim 5 wherein said first active layer is composed of a mixture of zinc sulfide and thulium trifluoride, said second active layer is composed of a mixture of zinc sulfide and samarium trifluoride, said third active layer is composed of a mixture of zinc sulfide and erbium trifluoride, said first gate layer is composed of samarium fluoride, and said second gate layer is composed of metal.