Diamine

a derivative of triphenyldiamine

was synthesized.The absorption and photoluminescent properties of the diamine thin film were investigated.Its charge conductivity was measured also.A type of organic thin film electroluminescent device with two layer structure

using diamine as hole transporting material

Alq3 as emitting material

was fabricated.It was found that when diamine was used the EL brightness of device is increased by a order of magnitude

though the electrical current passing through the device is less than half at the same applied voltage

By analysing the change of the EL spectra of the device with the laser dye DCM doped thinner layer at different possition in the emitting film

the mechanism of electroluminescence of two type devices has been studied.It is showed that the molecular excitons are generated at the interface of diamine and Alq3 layer

diffused toward the Al cathode and formed a exponential distribution in two-layer device

while in single layer device

the excitons are generated at a narrow zone in Alq3 layer

30nm apart of ITO layer

diffused in both directions and formed a peak.A luminescent model is built up and the experimental results are well explained.The diffusion length is evaluated as 21nm according to an equation derived from diffusion law.