Optical characterisation of SrS : Cu and SrS : Cu,Ag EL devices

The electroluminescent behaviour of SrS : Cu and SrS : Cu,Ag electron beam evaporated EL devices was investigated. Using time-resolved optical measurements at 15 K and RT, a study of the emission processes was performed. Upon square wave excitation, trailing peaks are only present in Ag codoped SrS : Cu EL devices. If codoping with Ag is performed, the decay time of Cu centres increases at low temperature. The decay time of Ag is strongly temperature-dependent and increases with increasing temperature. A study of the EL intensity as a function of temperature allowed to evaluate the thermal quenching behaviour and an unexpected intensity peak at about 54 K. Using XPS depth profile measurements, activator diffusion into the insulators and precipitation at the insulator/phosphor interface were observed.