The asymmetry introduced by a complex or nonspherical basis promotes photonic band gap formation in three-dimensional photonic crystals. However, relatively few techniques have been demonstrated to produce uniform nonspherical colloids for use as photonic crystal bases. Here we expand the menu of basis types with high refractive index by preparing nonspherical zinc sulfide colloids of uniform size and shape. Dimers, trimers, and planar tetramers were precipitated from aqueous solution by the thermal decomposition of thioacetamide in the presence of zinc nitrate, manganese nitrate, and nitric acid. The well-defined morphological types were obtained from suspensions aged for 4-6 It at 26-32 degreesC and then for 20-35 min at 85 degreesC. Stereological techniques were used to analyze SEM images and determine the percentage of each particle class. For example, the quantitative characterization of a particle population prepared at 29 degreesC for 6 It and 85 degreesC for 22 min had the composition 59 +/- 3% spheres, 31 +/- 2% dimers, 7 +/- 1% trimers, 0.4 +/- 0.2% tetramers, and 2.5 +/- 0.8% complex clusters (encompasses all other varieties of shape). X-ray diffraction and X-ray photoelectron spectroscopy confirmed the zinc blend crystal structure and the stoichiometric composition of the particles. The refractive index was estimated as 2.25 (413 nin)-2.09 (709 nm) by fitting experimental absorption spectra to curves derived from Mie scattering calculations. This indicated an average porosity similar to24%. Such colloids offer the potential to form diamond-like lattices with large, stable photonic band gaps. (C) 2003 Elsevier Inc. All rights reserved.