Effect of ZnO nanoparticle on morphology and optical properties of yellow emissive bulk Alq₃ for OLED application

We observe a distinct blue shift of the electronic absorption band in a composite nanoparticle system consisting of wide band gap semiconductor ZnO grains embedded into tris(8-hydroxyquinolinato)aluminium (Alq₃) matrix and calcined at 50 °C. This is followed by successive red shifts of absorbance intensity when weight percentage of ZnO NPs in ZnO/Alq₃ nano-composite is varied from 0.1 to 0.4 wt %. To investigate the morphology and optical properties, we prepared coordination complex Alq₃ by using wet synthesis method, with the absorption peak found to be at 358 nm in room temperature. For 0.1 wt% ZnO:Alq₃ composite, it exhibits lower energy band gap of 2.85 eV as compared to wide band gap ZnO nanoparticle (3.37 eV) and as-prepared bulk Alq₃ (2.89 eV). On illuminating with excitation wavelength of 385 nm, as-prepared Alq₃ shows a fluorescence band peak at around 520 nm but with the increasing concentration of ZnO nanoparticles, it exhibits broad peaks which are found to be shifted to higher wavelengths. The composites show yellow colored emission at 548.7 nm wavelength which is an essential requisite condition for white colored OLEDs. Further, XRD, FESEM confirm the rod shaped ZnO nanoparticle get embedded and agglomerated onto Alq₃ surface resulting in the increase in structural volume (662.8 c. c.) compared to that of individual constituents 47.6 c. c. For ZnO and 386.72 c. c. For Alq₃ powder. Experimental analysis suggests that incorporation of ZnO filler into Alq₃ matrix offers a significant improvement in the optical & structural properties as compared to pristine Alq₃ thus opening a room for futuristic OLED applications.