The structure of opal-ZnO composites is studied by transmission electron microscopy and X-ray phase analysis. It is shown that, under thermal treatment of infiltrated samples, a solid-phase reaction proceeds at the opal-ZnO interface. As a result, zinc silicate beta-Zn2SiO4 and its high-temperature phase, willemite Zn2SiO4, are formed. The structure and emission properties of the nanocomposite are studied in relation to the degree of filling. For a sample subjected to 25 cycles of filling, luminescence controlled by the beta-Zn2SiO4 phase is detected in the blue spectral region (at 430 nm). The angular dependences of the luminescence and reflection spectra of an opal-ZnO composite sample subjected to four cycles of filling show the effect of suppression of a spontaneous emission of zinc oxide in the photonic band gap. (c) 2005 Pleiades Publishing, Inc.