Effect of Thickness in Electroluminescence Spectra on 2-5 Dialoxy-PPV (ROPPV) Films

Abstract

The optical properties and electroluminescence (EL) of ROPPV (2-5-dialoxy-PPV) films of various thicknesses have been studied. The thickness of ROPPV layer on glass slide was measured by Fizeau fringes interferometric technique which varied from 200 to 400 nm. The absorption spectra show that the absorption occurred only in ultraviolet region. Thick films show only one peak at 310 nm, whereas by decreasing the thickness, the peaks are obtained at lower wavelength also. Photoluminescence excited by violet light shows three peaks at 380, 450 and 510 nm and intensity is found to increase with thickness. EL from ROPPV films was studied by applying different AC voltage at various frequencies. The light emission starts at certain threshold voltage and then increases with voltage. It is observed that higher threshold voltage is required for thicker films but at higher voltages these give brighter EL. The threshold voltage is found to increase with frequency. The EL spectrum shows two main peaks, one at 510 and the other at 450 nm.