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Composites of zinc oxide (ZnO) nanoparticles in silica matrix can be produced by initially synthesizing a ZnO colloid (containing ZnO nanoparticles in ethanol solution), mixed with tetraethoxysilane (TEOS), followed by spray drying, to produce powder comprised of submicrometer sized particles. The initial size of ZnO nanoparticles in the colloid is about 3 nm when the precursors are first mixed, but the size increases with aging, following an approximate equation D∝t^α, α=constant [J. Phys. Chem. B 102 (1998) 2854]. By using ZnO colloids that have been aged for different times, composites containing a specific size of ZnO can be produced. Since the excitation and emission luminescence spectral positions of ZnO are dependent on particle size (shift to blue region with reducing particle size), composites that emit a specific color can be produced using this method. We have been able to produce composites that emit …