Light emission enhancing dielectric layer for EL panel

• US 4,613,793 A
• Filed: 08/06/1984
• Issued: 09/23/1986
• Est. Priority Date: 08/06/1984
• Status: Expired due to Fees

• Current Assignee: Sigmatron Nova Incorporated
• Original Assignee: Sigmatron Nova Incorporated
• Inventors: Panicker, Ramachandra M. P., Essinger, Walter F.
• Primary Examiner(s): Chatmon, Saxfield
• Application Number:
  US06/638,297
• Time in Patent Office: 778 Days
• Field of Search: 313/506, 313/507, 313/508, 313/509, 313/483, 313/494, 315/169.3, 340/781
• US Class Current: 315/169.3
• CPC Class Codes: G09F 13/22 electroluminescent electroluminescent light sources per se H05B33/00
• CPC Class Codes: G09G 3/30 using electroluminescent panels
• CPC Class Codes: H05B 33/22 characterised by the chemical or physical composition or the arrangement of auxiliary dielectric or reflective layers

Abstract

A thin-film electroluminescent panel which has a light sink layer deposited immediately behind the phosphor layer thereof is modified to have a light emission enhancing dielectric layer deposited between the phosphor layer and the light sink layer. The light emission enhancing dielectricphosphor interface provides for injecting hot electrons for impact-exciting the luminescent centers in the phosphor to enable the panel to generate light when the front electrode of the panel is positive in potential. Moreover, the light emission enhancing dielectric layer is formed of a material having the same index of refraction as the phosphor layer so that it will pass the incident ambient light and the rearwardly directed light generated in the phosphor layer without reflection into the light sink layer wherein it is trapped by internal reflection and absorbed.

Claims

1. An improved structure for a thin-film electroluminescent device comprising:

a substrate;

a plurality of transparent front electrodes deposited on said substrate and extending in one direction;

a front dielectric layer deposited over said transparent front electrodes;

a phosphor layer having luminescent centers deposited over said front dielectric layer, said phosphor layer having a given refractive index;

a light emission enhancing dielectric layer having a refractive index substantially equal to that of the phosphor layer deposited over said phosphor layer;

a light sink layer deposited over said light emission enhancing dielectric layer;

a back dielectric layer deposited over said light sink layer; and

a plurality of back electrodes deposited over said back dielectric layer and extending orthogonally to the direction of said transparent front electrodes;

said front and back electrodes adapted to having a driving potential applied first in one polarity and then the opposite polarity across intersecting portions thereof during a refresh cycle;

whereby during a refresh cycle when the back electrode at an intersecting portion is positive in potential the front dielectric layer coacts with the phosphor layer to generate light and when the front electrode at the intersecting portion is positive in potential the light emission enhancing dielectric layer coacts with the phosphor layer to generate light.

2. An improved structure for a thin-film electroluminescent device as defined in claim 1 wherein said light emission enhancing dielectric layer is just sufficiently thick enough to make it continuous.

3. An improved structure for a thin-film electroluminescent device as defined in claim 1 wherein said light sink layer is a high specific resistivity semiconductor material which includes CdTe doped with indium.

4. An improved structure for a thin-film electroluminescent device as defined in claim 1 wherein said light emission enhancing dielectric layer is comprised of material from the group consisting of Ta₂ O₅, BaTiO₃, CeO₂, Cr₂ O₃, As₂ S₃, PbCl₂, TiO₂, Ti₂ O₃ and TiO.

5. An improved structure for a thin-film electroluminescent device as defined in claim 1 wherein said light emission enhancing dielectric layer is at least 200 Angstrom units thick.

6. An electroluminescent device which is energizable to a high luminance upon each reversal of the potential applied thereacross said device comprising:

a substrate means;

a front electrode carried on said substrate means;

a front dielectric layer disposed over said front electrode;

a phosphor layer having luminescent centers disposed over said front dielectric layer;

a light emission enhancing dielectric disposed over said phosphor layer, said enhancing layer having a refractive index substantially equal to that of said phosphor layer;

a light sink layer formed of a semiconductor compound disposed over said light emission enhancing dielectric layer;

said light emission enhancing dielectric layer receiving ambient incident light and rearwardly directed internally generated light from said phosphor layer without reflection and passing said light through to the light sink layer wherein it is trapped by internal reflection and absorbed;

an insulation layer disposed over said light sink layer; and

a back electrode disposed over said insulation layer;

said front and back electrodes adapted to have a potential applied first in one polarity and then the reverse polarity thereacross for energizing said device;

whereby when the potential across said front and back electrodes is such that said front electrode is positive in potential high energy electrons are injected from the light emission enhancing dielectric-phosphor interface to impact-excite the luminescent centers in said phosphor layer to generate light; and

whereby when the potential across said front and back electrodes is such that said back electrode is positive in potential high energy electrons are injected from the front dielectric-phosphor interface to impact-excite the luminescent centers in said phosphor layer to generate light.

7. An electroluminescent panel comprising:

a front electrode;

a back electrode; and

a multi-layer sandwiched between said electrodes;

said front and back electrodes being adapted to receive a voltage therebetween to provide an electric field across said multilayer;

said multilayer comprising;

a front dielectric layer disposed over said front electrode;

a phosphor layer formed of ZnS doped with Mn disposed over said front dielectric layer;

a light emission enhancing dielectric layer disposed over said phosphor layer and having substantially the same index of refraction as said phosphor layer;

a light sink layer disposed over said light emission enhancing dielectric layer; and

a back dielectric layer disposed between said light sink layer and said back electrode;

said light sink layer having a high absorption coefficient and a substantially higher index of refraction than the light emission enhancing dielectric layer on the front side thereof and the back dielectric layer on the back side thereof;

said light emission enhancing dielectric layer receiving ambient incident light and rearwardly directed internally generated light from said phosphor layer without reflection and passing said light through to the light sink layer wherein it is trapped by internal reflection and absorbed; and

whereby when said panel is provided with a voltage across said front and back electrodes such that said front electrode is positive in potential with respect to said back electrode high energy electrons are injected from the light emission enhancing dielectric-phosphor interface to impact-excite the Mn atoms in the phosphor layer to generate light; and

whereby when said panel is provided with a voltage between said front and back electrodes such that said back electrode is positive in potential with respect to said front electrode high energy electrons are injected from the front dielectric-phosphor interface to impact-excite the Mn atoms in the phosphor layer to generate light.

8. A thin-film electroluminescent device comprising:

a phosphor layer having luminescent centers, said phosphor layer having a given refractive index;

a front transparent dielectric layer deposited on the front of said phosphor layer;

a plurality of transparent electrodes in front of said first dielectric layer;

a light emission enhancing dielectric layer having the same refractive index as said phosphor layer deposited on the back of said phosphor layer;

a light sink layer of a semiconductor compound deposited on the back of said light emission enhancing dielectric layer; and

a back dielectric layer deposited on the back of said light sink layer;

said light sink layer having a high absorption coefficient and a substantially higher index of refraction than the light emission enhancing dielectric layer on the front side thereof and the back dielectric layer on the back side thereof; and

a plurality of counter electrodes on the back of said back dielectric layer;

said transparent and counter electrodes adapted to have a driving potential in one polarity and then the opposite polarity applied across intersecting pairs thereof;

whereby when said driving potential is applied such that said transparent electrode is positive in potential high energy electrons are injected from the light emission enhancing dielectric-phosphor interface into said phosphor layer to cause said phosphor layer to emit light, and when said driving potential is applied such that said counter electrode is positive in potential high energy electrons are injected from the front dielectric-phosphor interface into said phosphor layer to cause said phosphor layer to emit light; and

whereby ambient light and rearwardly directed internally generated light incident on the interface of the phosphor layer and the light emission enhancing dielectric layer is not reflected but passed through the light emission enhancing dielectric layer into the light sink layer wherein it is trapped by internal reflection and absorbed.