GB973340A - Electroluminescent device - Google Patents

Abstract

An electroluminescent display device, for example for displaying numbers or letters, comprises an electroluminescent layer 22 having on one side thereof an opaque area electrode 121 and an opaque strip electrode 16 and on the other side thereof a transparent electrode group 241 in registration with the area electrode 121 and M separate transparent conductive rectangular members 28 in registration with the strip electrode 16, the electrode group 241 containing M spaced electrode elements each connected to one of the conductive members 28, a photo-conductive strip 40 arranged over the conductive members 28, a further transparent electrode 44 over the photo-conductive strip 40, and means for selectively energizing the electrode elements of the group 241 through the members 28. The device can include N area electrodes 121, 12 electrically connected together by an opaque electrode 141, N electrode groups 241, 24 and MN conductive members 28. N staircase conductors 211, 21 each containing <PICT:0973340/C4-C5/1> <PICT:0973340/C4-C5/2> M electrically connected opaque square segments 18 are arranged on one side of the electroluminescent layer 22 and a conductive film 30 is secured to the other side of the electroluminescent layer, the film being provided with a plurality of spaced holes 32 each in registration with a corresponding connection 20, between adjacent segments 18 of the staircase conductors 211, 21. The electrodes 14 and 16 are connected directly to a terminal 100 and each staircase conductor 211, 21 can be connected to terminal 100 through a corresponding one of N group selector switches 104, 106, 108. The energizing means for selectively energizing the electrode elements of each electrode group 241, 24 includes M light transparent conductive strips 36 on a transparent non-conductive enamel layer 34, the strips 36 being connected to M switches 112, 124 and the conductive film 30 being connected to one terminal of a supply source. A photo-conductive layer 38 is applied over the strips 36 and N conductor arrays 43, 431 are applied over the layer 38, each array containing M transparent conductive members 42, 43, 431, and being in registration with a corresponding staircase conductor 21, 211. Each of the members 42 of each array is connected through a conductive line 26 and a conductive rectangle 28 to a corresponding element of the electrode group 241, 24 associated with the array, and each of the members 42 extends over the photo-conductive layer 38 in registration with the corresponding segment 18 of the corresponding staircase conductor 211, 21. As shown, each member 42 terminates in a position in registration with the corresponding segment 18 but can extend across the entire width of the layer 38. In a modification the transparent enamel layer 34 and the conductive film 30 can be eliminated, the conductive strips being applied directly over the electroluminescent layer 22 in registration with the segments 18. In other modifications the photo-conductor circuit connections, instead of being of the layer type with electrodes placed on opposite sides of a photo-conductive layer, can be of the gap type with spaced electrodes on one surface of a photo-conductive layer. The device can be constructed so that any group of electrode elements will display for as long as desired so that each group can display simultaneously. Alternatively the information displayed by any group can be erased before the next group is energized. Transparent conductive materials used can be stannic oxide and opaque conductive materials can be gold or aluminium. The transparent conductive materials can be substituted for the opaque materials and vice versa in some instances, for example the electrode elements 24, 241 can be transparent or narrow and opaque because of the light produced by fringe electric fields around the edges of the elements. The electroluminescent layer can comprise phosphor grains embedded in a ceramic material and the photo-conductive layer can comprise photo-conductor grains embedded in a glass enamel.