GB1330172A - Light-producing means - Google Patents

Abstract

1330172 Electroluminescence GENERAL ELECTRIC CO Ltd 24 May 1971 [25 June 1970] 30944/70 Heading C4S Light producing means comprises a D.C. EL device comprising a phosphor layer, capable of conducting D.C., sandwiched between two electrodes and means for applying between the electrodes an operating voltage in the form of a succession of unidirectional pulses such as to cause light pulses to be emitted from the device in phase with the voltage pulses, the pulse repetition frequency being such, in relation to the pulse duration, to produce a steady light. Reference is made to increased light emission in relation to power dissipation and the reduction of ageing in the form of a continual increase in electrical resistance. The frequency may be such that the time between pulses equals the decay time of the individual light pulses. The phosphor may be ZnS: Cu, Mn and Cl, and incorporated as a 10Á thin film deposited by evaporation. The phosphor may also be in the form of a 10Á layer of powder deposited as a dispersion in a binder. The device may be indicator lights such as in vehicle instrument panels or an alpha-numeric display. Rise times for powder and thin film layers of ZnS may be 250 and 20 Ásecs. respectively. In an embodiment, a powder phosphor layer (ZnS: Cu, Cl, Mn) is between a light transmissive electrode on a glass base, and a metal backing electrode. Operation may be by spiked or square wave forms e.g. 90 v. square pulses of 10Á width, light emission decay time being 5 ms. for a 35Á thick layer, and 250 Ásecs. rise time. A thin film of the same phosphor had a 500 Ásecs. decay time. Decay time increases with phosphor thickness.