Photoluminescence and electroluminescence studies of polyvinyl carbazole films

Polyvinyl carbazole (PVK) film has been prepared by solution method. Its absorption, photoluminescence (PL) and electroluminescence (EL) have been studied. For PL and absorption studies, film of PVK was prepared by spreading PVK solution on clean glass plate. The dried film was taken out of the glass plate and used for absorption, thickness measurement and PL studies. The film is transparent in the visible region and absorption starts at 340 nm wavelength. The absorption peaks are obtained at 280, 250 and 220 nm, indicating that optical gap of film is 3.65 eV and molecular orbitals exist at 4.43, 4.96 and 5.64 eV. PL studies reveal that excitation by violet light gives luminescence at 430, 480 and 690 nm. For EL studies, cell is prepared by depositing PVK film on a portion of conducting glass plate and taking aluminum foil as second electrode. It is observed from the characteristics that the current varies linearly, where as EL intensity varies non-linearly with increasing voltage. Higher brightness has been observed at higher frequencies. EL spectrum shows a sharp peak at 400 nm and a broad and less intense peak at 700 nm, which are attributed to radiative decay of singlet exciton and defect centers, respectively.