Energy Transfer of PVK/ SiO2 Nanometer Composite Films

Poly (9-vinylcarbazole) (PVK) is a typical hole-transporting polymer and is often used as a host in electroluminescence devices. In this paper, Forster energy transfer from organic molecules (PVK) to inorganic nanoparticles (SiO2) was discussed. SiO2 nanoparticles, which are confirmed to be 60nm using transmission electron microscope (TEM), have been synthesized through the sol-gel method. The structure scheme of poly (9-vinylcarbazole) (PVK) molecule is shown firstly. The emission of luminescence is the result from π*-π transition of π electrons. Photoluminescence (PL) spectra of the PVK/ SiO2 composite film on Si substrates were employed to study the interface effect. In the PL spectra of PVK molecules, three obvious peaks (417, 458, 495nm) can be seen. The emission of 417nm comes from free exciton. The emission of 458nm comes from bound exciton. And the emission around 495nm is correlated to surface defect states. The intensity of short-wavelength emission (about 400nm) is higher than that of visible luminescence (about 495nm). Two luminescence peaks can be observed in the PL spectra of 60nm SiO2 nanoparticles. In contrast to the PL spectra of PVK molecules, the luminescence intensity about 495nm is higher than that about 400nm in SiO2 nanoparticles PL spectra. Furthermore, UV-Vis absorption spectroscopy of 60nm SiO2 nanoparticles was measured. The spectrum indicates that the scale of absorption is wide enough from 200nm to 500nm. The ratio of PVK to SiO2 in the composite was increased orderly in weight. In the PL spectra of different concentration composite films, we found that Forster energy transfer occurred between PVK and SiO2 nanoparticles. Overlap is observed between the UV-Vis absorption spectrum of the SiO2 nanoparticles and the emission spectrum of PVK molecules. This overlap is the necessary condition of Forster energy transfer. Further investigation indicates that 40 % ( the content of PVK in composite films) is regarded as an optimized content for Forster energy transfer from PVK molecules to SiO2 nanoparticles. The reason maybe is the surfaces of SiO2 nanoparticles are modified successfully and the disperse of SiO2 nanoparticles is unified in this concent ration.