Study Of Synthesis And Photoluminescence Properties Of ZnO Nanocrystals

Zinc oxide is a II-VI wide band-gap (3.3eV) compound semiconductor with wurtzitecrystal structure. Due to the large exciton binding energy of 60meV, which ensures the highefficient excitonic emission at room temperature, it is regarded as one of the most promisingmaterials for fabricating efficient ultraviolet (UV) and blue light emitting devices.Sol-gel method is employed to synthesize ZnO quantum dots and the molar ratio ofZnAc/LiOH has great influence on the photoluminescence (PL) properties of the ZnOnanocrystals. Acetate groups charge ZnO nanocrystals negatively and passivate the surfaces,reducing the surface defects and visible emission centers. Resultantly, the increase of acetategroups lead to the quench of visible emission and improvement of photoluminescenceproperties. At appropriate concentrations, the hydroxide groups mainly passivate the surfaceand improve the photoluminescence properties. However, further increase of hydroxidegroups resulted in converse results. The unreacted reagents absorbed on the surface of nucleiprevent their further aggregation and rendered small particles.One-dimensional materials like nanorods have better properties and wider uses thanquantum dots. By changing the concentration of zinc acetate in ZnO solutions, nanorods wereobtained. UV absorbance, infrared absorbance, photoluminescence, transmittance-electronicmicro-spectroscope (TEM) and X-ray diffraction (XRD) were employed to characterize thegrowth and properties of the ZnO nanostructures. The results show that the amount of zincacetate in the solution has decisive effects on the growth of ZnO nanocrystals. At low zincacetate concentration, the growth of ZnO based on Ostwald ripening process and the formedZnO particles are quais-spherical. At intermediate concentration, oriented growth occurredamong ZnO particles due to the dipole-dipole interaction and the particles wereoriented-aggregated. Furthermore, at high concentration of new formed ZnO cluster, theoriented aggregation of ZnO particles was fused to form ZnO nanorod.