Turn-off of fluorescence of styryl phenanthrimidazole on doping ZnO nanoparticles with Ce(3+)

ZnO nanoparticles were doped with Ce(3+) by sol-gel synthesis and characterized by high-resolution scanning electron microscopy (HR-SEM), powder X-ray diffraction (XRD) and UV-visible diffuse reflectance (DRS) and photoluminescence (PL) spectroscopies. The dynamics of photoinduced electron injection from styryl phenanthrimidazole to Ce(3+)-doped ZnO nanoparticles has been studied by absorption, fluorescence and lifetime spectroscopic methods. Both the absorption and fluorescence quenching results suggest association between Ce(3+)-doped ZnO and the phenanthrimidazole. The free energy change (ΔGet) for electron injection has been calculated. The critical energy transfer distance between the phenanthrimidazole and Ce(3+)-doped ZnO nanoparticles has been deduced. In contrast to our earlier observation of enhancement of fluorescence of the phenanthrimidazole by ZnO nanoparticles, doping ZnO with Ce(3+) turns off its fluorescence. These findings provide a method to test the presence of Ce(3+) in ZnO nanocrystals.