The effect of ammonia contained in water fluid on the synthesis and properties of gahnite (ZnAl2O4) doped with (0.4-4 mol%) europium was investigated. Gahnite synthesized in water-ammoniac fluid has a smaller crystal size than does the one synthesized in water fluid, and bound nitrogen is detected in its structure. However, europium ions more effectively incorporate into the structure of nascent gahnite during synthesis in water fluid and generate formation there of complexes with oxygen vacancies. The excitation efficiency of luminescence of Eu3+ ions in the absorption band of oxygen vacancies in gahnite increases with the concentration of Eu3+. After annealing in air of gahnite samples synthesized in fluids of various compositions, the changes of Eu3+ ions luminescence differ. We conclude that ammonia not only participates in the processes of gahnite formation, causing an increased nucleation rate but it also remains in the gahnite structure. (c) 2007 Elsevier B.V. All rights reserved.