Zinc Oxide (ZnO) colloidal spheres comprising numerous nanocrystallites are synthesized by hydrolysis of zinc acetate dihydrate, Zn(OOCCH3) 2 · 2H2O, in diethylene glycol, HOCH2CH 2OCH2CH2OH. By varying the reaction parameters, it is possible to alter the diameter and crystallite size of the spheres. In addition to in situ control of the crystallite size, it is also possible to grow the crystallites through post-synthetic thermal annealing. Monodisperse spheres can be produced using seeded growth techniques in which solutions containing ZnO nucleation sites are added to the reaction.; The random lasing properties of these spheres is discussed. It is found that laser-like emission can arise in layers of ZnO spheres as a consequence of photon localization. The lasing threshold, a measure of lasing efficiency, is found to depend directly on the scattering length within the layer, with shorter scattering lengths corresponding to more efficient lasing. In addition to bulk layers of spheres, the emission properties of single ZnO spheres are studied, and it is found that single spheres can act as random microlasers.; The production of monodisperse ZnO spheres makes it possible to generate self-assembled colloidal crystals. These crystals can be formed simply by drying a drop of reaction solution on a substrate at temperatures near 200°C, but more sophisticated techniques can yield higher quality crystals if the spheres are resuspended in a Mg(NO3)2/isopropanol solution.; It is found that the self-assembled periodic structures formed from monodisperse ZnO colloidal spheres act as photonic crystals. They exhibit a photonic band gap in the (111) direction of the FCC lattice at approximately 2.2 times the sphere diameter with a width of approximately 4–5%. These experimental results are compared with theoretical calculations. Finally, the lasing properties of periodic structures are explored, and these structures are found to exhibit significantly lower lasing thresholds than comparable, random structures.
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