Organic light-emitting diodes (OLEDs) based on conjugated polymers have been attracting much attention because of their cheap and easy fabrication with solution-based processing techniques. Full color displays based on organic materials have very attractive prospects and one of the most exciting ones is the use of ink-jet printing to allow direct patterning of conjugated polymer LED pixels. However

achieving "pure-red" emission has proved relatively challenging. In this work the optical properties of varying 5

10

15

20-tetra-p-tolyl-21H

23H-porphine (TTP) doped poly [2-methoxy-5-(2'-ethylhexyloxy)-1

4-phenylenevinylene] (MEH-PPV) were studied. The UV-Vis absorption of Q-band of TTP overlapped the photoluminescent spectra of MEH-PPV. This is a priority for occurrence of Förster-type energy transfer. The photoluminescent spectra of varying TTP doped MEH-PPV showed that the emission of TTP increased as the increasing of the doping level at the excitation wavelength of 500 nm

at which TTP didn't absorb energy

indicating the existence of Frster energy transfer from MEH-PPV to TTP. However

the continuous addition of TTP resulted in the enhanced emission of MEH-PPV at the doping level above 4 percent

due to the self-quenching caused by crystallization of TTP. The devices with varying TTP doped MEH-PPV as light-emitting layers were also fabricated and the structure of the devices was ITO/PEDOT:PSS/TTP doped MEH-PPV/Al[PEDOT:PSS=poly(2

3-dihydrothieno[3

4-b]

-1

4-dioxin)/poly(styrenesulfonate)]. The layers of PEDOT/PSS (20 nm) and TTP doped polymers (80 nm) were spun onto ITO substrates and aluminum cathode (100 nm) was deposited under vacuum pressure of about 1×10

-3

Pa. The electroluminescent properties of the devices were investigated and TTP dominated red emission was observed. The electroluminescent emission from TTP increased as the increasing of doping level in light-emitting layer. On the other hand

the emission of MEH-PPV reduced gra-dually until the doping level of 8 percent. Then it began to grow. The results of photoluminescence and electroluminescence expressed that the two emission processes followed different mechanisms. TTP could be a center for capturing exitons in electroluminescence and the emission of TTP involved the capture of electrons and holes by itself apart from Frster-type energy transfer from MEH-PPV. The researches on TTP doped conjugated polymers will be helpful to enlarge the application of dye

porphyrin

in OLEDs. Moreover

the researches on the mechanisms of photoluminescence and electroluminescence for the blended systems will provide scientific basis for color tuning of composite materials.