Since the first report of organic light emitting devices(OLEDs)in 1987 by C.W.Tang

much interest has been focused on the development of OLEDs for its potential application in full color flat panel display and optical communication.The balance of charge injection is of critical importance if highly efficient and low-voltage operating EL devices are to be realized.But in most OELDs

the injection of hole is much higher than the injection of electron.It was reported that the presence of a thin alkaline metal compound such as Li

2

O or LiF layer at an organic/Al interface significantly enhances electron injection.Among all these alkaline metal compounds

LiF gets the best effect.But the reason of this phenomenon is still unclear.In this paper

we studied the interaction between Alq

3

and the alkaline metal compound

LiF.Alq

3

samples with different LiF-doped concentrations on quartz substrate were made by means of co-evaporation.The ratios of LiF to Alq

3

is 1:1

1:5

1:7 and 1:20.We also made the Alq

3

sample without LiF.In all the samples

the thickness of Alq

3

is the same but the concentration of LiF varies.The absorption spectra and photoluminescence spectra were measured.And we found that with the increase of the LiF concentration

the absorption edge

absorption peak and photoluminescence peak of the samples had shifted to the direction of shorter wavelength.It is believed that there are some electron traps in Alq

3

and the LiF had filled some of the straps.So the absorption edge shifted to shorter wavelength with the increase of the LiF concentration.The shift of absorption peak and photoluminescence peak is believed to the due to the interaction between Alq

3

and LiF.The use of LiF introduced ionic bond into the Alq

3

film

so the distribution of the electronic clound of the quinoline group is changed

which caused the shift of the absorption peak and photoluminescence peak.