In the present paper the formation mechanism of zinc aluminate (gahnite, ZnAl2O4) under hydrothermal and thermovaporous conditions has been investigated. The gahnite was obtained by treatment in water medium of a mixture of zinc oxide and oxide or hydroxide of aluminum at 180-400 degrees C and under pressure of water vapor 1-26 MPa. It was found that formation of gahnite goes in accordance with the solid-phase mechanism. The impurities added into the reaction medium have an influence upon the rate of transformation. In this case the rate of reaction is controlled by nucleation. The impurities incorporate into the structure of gahnite and change the structural characteristics of the microcrystals, defects concentration and the optical properties of gahnite. The luminescence of EU3+ ions is sensitive to the change of gahnite structure. Gahnite synthesized in ammonia medium has photoluminescence bands at 382 and 547 nm with the excitation band at 267 nm. These PL bands are attributed to oxygen vacancies. (c) 2006 Springer Science + Business Media, Inc.