CHAPTER 2
 LITERATURE REVIEW

 2.1 History of Electroluminescence

 Electroluminescence (EL), by definition, is a phenomenon that converts electrical

energy to luminous energy without thermal energy generation. Though the first report of

electroluminescence is often attributed to a famous paper by Destriau in 1936, the first

observations of the effect of electric fields on luminescence were reported by Gudden and

Pohl in 1920 [3]. They found that the luminescent intensity increases as an electric field

of several KV/cm is applied to a ZnS:Cu phosphor which is insulated from the electrodes.

George Destriau in 1936 observed light emission from a suspension consisting of ZnS:Cu

and oil [4].

 Afterwards, the development of EL experienced a relatively silent period until the

1950s when GTE Sylvania received a patent for an EL powder lamp. However, the

devices were limited to powder phosphors embedded in a dielectric matrix. In the 1950s

and 1960s more attention is drawn to how to improve EL efficiency reaching or even

exceeding the 15 Im/W of the existing incandescent lamp. However, problems in these

devices, such as low light output, short operating lifetime, and a rapid deterioration when

operated above room temperature led to the virtual abandonment of powder EL studies.

 Fortunately, great progress was made in thin film technology in the 1960s, which

helped Soxman and Ketchpel fabricate thin film devices. In 1961, Soxman et al. [5]

successfully discovered AC thin film electroluminescence using a device containing a

ZnS:Mn phosphor with a dielectric. These devices had acceptable lifetimes (several