Improvement of the triple colors

red

green and blue is the most basic and the most important technology for full color display.Green and blue emission from the organic light emitting diodes (OLED) have been employed successfully to organic display

but the red light performance still need to improved.So far

host-guest system and rare earth complexes were used for red emission.In these two kinds of OLEDs

the energy transfer efficiency were generally limited by the concentration quenching and the phase separation.Ones have paid great effort to explore some novel materials and devices structures for red emission with high perfor-mance.In this paper

an ionic organic pyridyl salt [ASPT (trans-4-[P-(N-ethyl-N-(hydroxylethyl)-amino) styryl]-N-methylpyridinium tetraphenyl-borate) ]

was employed as active layer for an organic light-emitting diode with stable red emission.The investigation on the electroluminescent properties demonstrated that ASPTis a good luminescent molecule for red emission.Astable red electroluminescence was obtained by using this material as emitting layer in a monolayer structure.The luminescence mechanism was discussed based on the influence of the external electrical field on the energy barrier in the interfaces between the active layer and the electrodes.In order to understand the charier charge transport and their recombination process

and to improve the ELperformance

double-layer TPD/ASPTor ASPT/Alq

3

and triple-layer TPD/ASPT/Alq

3

structures were designed and the ELproperties were further studied.Brighter red ELand red-blue variable emission depended on the applied voltage were observed in the double-layer and the triple-layer structures

respectively.Consi-dering the different function of each layer in the triple-layer structure

the color variation is assumed to the change of the recombination region.The mechanism was discussed by analyzing the spectra and the corresponding energy level structures.