Organic light emitting diodes(OLEDs) have been attracting a lot of attention because of its potential application in flat panel displays(FPD).In the past two decades since efficient double-layer OLEDs was first reported by C W Tang et al.

tremendous progress has been made in device fabrication and performance optimization

highly efficient and colorful devices have already been fabricated for commercial use.Almost all giants in display around the world

e.g.

Samsung

Sony and Philips

were involved in developing OLEDs for the next generation of FPD.Some people even estimate that OLEDs will replace liquid crystal displays(LCDs) in the next decade.However

there still remain some fundamental mechanisms of devices for scientists to deal with

such as long-term stability of organic materials or device

transportation and recombination of carriers

energy transferring process.In addition

finding a simple fabricating way to realize full-color OLEDs is also an important and imperative approach to reduce manufacturing cost in industrial production.As a promising technology for flat panel display

OLEDs have attracted a great deal of attention since 1987.During the past few years

remarkable progress has been made in the development of multicolor and full-color OLED displays.The mechanism for electroluminescent(EL) phenomenon involves in the injection of holes from anode and electrons from cathode under forward bias voltage

then the hole-electron forming the exciton

and light emission through the radiative recombination of excitons.The influence of bias voltage on the charge carrier recombination zone of doping organic light-emitting diodes(OLEDs) with the ELspectra improvement of red dopant 4-(dicyanomethylene)-2-t-butyl-6-(1

1

7

7-tetramethyljulolidyl-9-enyl)-4H-pyran(DCJTB) doped into tris-(8-hydroxylquinoline)aluminum(Alq

3

) host material has been investigated

and different doping effect of host material Alq

3

and N

N'-diphenyl-N

N'-bis(1-naphthyl)(1

1'-biphenyl)-4

4'-diamine(NPB) through studying the electroluminescence(EL) spectra and photoluminescence(PL) spectra was discussed.The results showed that charge carrier recombination zone moved to hole transport layer with increasing bias voltage and optimum host material should have higher energy transfer efficiency and lower charge carrier quenching property.