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The effect of DCJTB concentration on the photoluminescent and electroluminescent properties of PVK-PBD-perylene-DCJTB thin films

Cyap C. C., Yahaya M., Salleh M. M.

Materials Science Poland

2009

Vol. 27, No. 1

209--218

The paper reports a study of photoluminescent (PL) and electroluminescent (EL) properties of PVK- PBD-perylene-DCJTB thin film with variation of DCJTB doping concentrations. Poly(9-vinylcarbazole) (PVK) functioned as polymeric hole-transporting host, 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) as electron-transporting molecule, perylene as blue dopant, and 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7- tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as a red dopant. The relative intensity of the blue emission from perylene decreased and that of the red emission from DCJTB increased with the increase of DCJTB concentration in both PL and EL spectra. However, the EL spectrum showed stronger DCJTB emission compared to the PL spectrum at the same DCJTB doping concentration, due to the carrier trapping effect. Interestingly, white light emission with C.I.E. coordinates of (0.31, 0.36) was observed in the EL spectrum when 0.05 wt. % of DCJTB was doped into PVK-PBD-perylene blend film. As a result, PVK-PBD-perylene-DCJTB thin film has potential application in white organic light emitting diodes.

Size-dependent Fluorescence Spectra of Individual Perylene Nanocrystals Studied by Far-Field Fluorescence Microspectroscopy Coupled with Atomic Force Microscope Observation

Asahi T., Matsune H., Yamashita K., Masuhara H., Kasai H., Nakanishi H.

Polish Journal of Chemistry

2008

Vol. 82, nr 4

687-699

Single particle fluorescence spectroscopy coupled with AFM observation is reported for perylene nanocrystals. Fluorescence spectral measurement for individual nanocrystals with the size from 100 nm to 500 nm and fluorescence anisotropy analysis demonstrate that the size dependence in fluorescence is in the intrinsic nature of nanometer-sized crystal of perylene. Single nanoparticle fluorescence shows the enhanced monomer (M-) emission compared to the bulk crystal and a blue-shift of excimer (E-) emission peak wave length by decreasing the nanoparticle size. It is found for the first time that the size dependence is correlated well to the surface-to-volume ratio of nanocrystal. The size-dependent fluorescence is not attributed to a quantum confinement effect of exciton, but to a change in the elastic properties of nanocrystal with size, which in turn affects excimer formation. We discuss the decrease in elastic constant of crystal-line lattice due to large surface-to-volume ratio, and propose an empirical formula on the size-dependence of E-emission peak in the framework of the strong coupling model of exciton-phonon interaction.