GB965084A - Improvements in or relating to an electroluminescent device - Google Patents

Abstract

In order to obtain optimum transmission of the radiated light and to reduce internal reflections, the thicknesses of the various layers of an electroluminescent light source are based on formulae derived from Maxwell's wave equations. In a lamp comprising the following layers on a metallic or metallized plastics foundation:-a first dielectric or semi-conductive, a phosphor, a noble metal or alloy and a second dielectric or semi-conductive layer, the foundation layer has a thickness of 2.9.10-2 m1., <FORM:0965084/C4-C5/1> cms., the electroluminescent layer, which can be of ZnS in a dielectric, a thickness of <FORM:0965084/C4-C5/2> units, the first dielectric layer a thickness of lambda.K.5.101/n <\>rA units and the noble metal layer, which may be of gold, a thickness of 2.9.10-2 <FORM:0965084/C4-C5/3> cms. The second dielectric layer, which can be applied both to the metal layer and to the foundation layer, preferably has a thickness equal to the difference between that of the first dielectric layer and the noble metal layer. In the above formulae, lambda is the wavelength of the emitted radiation, m1 and m3 are even integers, r the resistivity, e r the dielectric constant, m 1 the permeability, n the refractive index, and K = e - n2, in each case for the material of the relevant layer. A layer of dielectric of thickness not greater than one-sixteenth of the thickness of the phosphor layer can be located between the phosphor layer and the metal layer. An example is described in which the foundation layer is a plastic plate metallized with aluminium, the first dielectric layer is an epoxy or urea resin, the phosphor layer is ZnS in an epoxy resin, and the metal layer is gold. Contacts are made to the gold layer by silver or graphite and leads attached thereto and to the metallic foundation layer.