We studied the possible correlations between defects and photoluminescence spectra in ZnO nanoparticles of sizes ranging from 43 nm to 73 nm in diameter. The defects and impurity contents were characterized by Fourier-transform infrared (FTIR) spectroscopy. The results show fewer carboxylate and hydroxyl impurities for particles of larger sizes. No significant variation in oxygen vacancy content was found among samples. Annealing in vacuum at 300 °C significantly reduces the carboxylate and hydroxyl impurities in the samples. The total luminescence intensity (UV + visible) increases as the particle size grows for both the unannealed and annealed samples. This suggests that both types of luminescence are subject to nonradiative quenching by near surface defect centers, possibly carboxylate and hydroxyl impurities. There may be quenching due to intrinsic lattice defects too. It is found that annealing in vacuum enhances the visible luminescence both absolutely and relative to the UV exciton luminescence. In addition to the 2.5 eV green luminescence peak, a peak centered at 2.8 eV can also be resolved, espeically for the 43 nm sample. . Understanding the roles of defects and especially surface defects are important for these applications utilizing nano-structured ZnO. During or after nanostructure synthesis, the surfaces can often be easily contaminated by impurities and other defects. These surface defects usually reduce the performance for such applications. For example, surface defects such as hydroxyl are known to quench the exciton luminescence in ZnO [4]. It can also prevent efficient charge transfer between ZnO and adsorbed molecules at the interfaces. The most obvious trend versus particle size is that the surface-to-volume ratio increases for smaller particles, and the transport distance from any interior point to surface traps and recombination sites decreases in the same trend. Examining nanoparticle ZnO photoluminescence (PL) spectra provides us a way to understand the roles of defects in the above photon-excited processes. In this paper, we report our study of ZnO nanoparticles ranging from 43 to 73 nm. The defect and impurity content in these materials were characterized by Fourier transfer infrared spectroscopy (FTIR). We correlate the particle size and defects/impurities to the measured PL spectra. It is found that annealing treatment significantly reduces the surface impurities.

Obtaining spherical-shaped semiconductor nanoparticles of uniform size is essential for the fabrication of photonic crystals. We report the synthesis of nanometer-size spherical titania particles with narrow size distribution from glycolated precursors. Through controlled hydrolysis of glycolated precursors, particles of 683 to 50 nm average diameters, with narrow size distribution, could be produced for the first time. Effects of air annealing on the morphology, size shrinkage, and phase transition of the nanoparticles are studied by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and high-resolution electron microscopy techniques. Probable mechanisms for formation of titania nanoparticles and their size control are discussed.

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