Exciplex formation at the organic interface and its potential application for emission color tuning have been investigated.The bilayer electroluminescent devices using N

N ’-bis(3-methylphenyl)-N

N’-diphenyl-[1

1’-biphenyl]-4-4’diamine(TPD) as an hole-transport layer and 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1

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4-oxadiazole(PBD) as an electron-transport layer was prepared.The thickness of the TPD and PBD were both 60nm

and the cathode material is air stable aluminum.The EL spectra of this device were different from the PL spectra of TPD and PBD

showing a new band in the wavelength region of visible light together with weak emission in the wavelength of 400-430nm originating from the emission of TPD.The exciplex formation was evidenced by measurement and comparison of the photoluminescence spectra of the TPD

PBD and TPD:PBD equimolar vacuum evaporated thin films.The EL spectra were changed with different driving current densities.With an increase of the current density

the emission resulting from TPD became stronger relative to that from exciplex

when the current density was larger than 12mA/cm

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the strength of emission from TPD became smaller relative to that from exciplex.Meanwhile

the peak of the EL spectra shifted towards longer wavelength as the current density was increased.The change of EL spectra with the increase of the current density leads to change of emission color from white with the current density more than 2mA/cm

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to yellowish green at current density of 40mA/cm

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.Consideration of the energy levels of TPD(LUMO:2.4eV;HOMO:5.5eV) and PBD(LUMO:2.8eV

HOMO:6.2eV) suggests that the energy barrier for the electrons injection from the PBD layer into the TPD layer is much lower than that for the holes injection from the TPD layer to the PBD layer.Therefore

it is suggested that the exciplex is formed by the interaction between the electronically excited singlet-state generated by recombination of holes and electrons in the bulk of TPD layer and the ground-state of PBD.The maximum luminance of this bilayer device is 149cd/m

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at a bias voltage of 18.6V.