LOW TEMPERATURE ELECTROLUMINESCENCE

Electroluminescent phosphors are used as the display portion of infrared image converters, operated at liquid-nitrogen temperature. These phosphors lose considerable brightness upon cooling, giving a dim display. This report demonstrates the sources of this brightness loss during cooling as (1) due to spectral shift to wavelengths less visible to the eye and (2) changes in dielectric constant of the binder during cooling, causing a decrease in effective electric field applied to the phosphor particles. Some improvement in brightness can be demonstrated by using very thin phosphor layers, thereby increasing the effective applied field.