Hafnium germanate (HfGeO4) presents under X-ray excitation a high UV fluorescence at around 365 mit that may be used for X-ray imaging. Its synthesis by different co-precipitation routes with sodium hydroxide, ammonia, potassium hydroxide, dimethylamin and tetramethylammonium hydroxide was studied. Precipitated amorphous hydroxides were then washed, dried and calcined at 1100 degrees C for 6 h to make HfGeO4 crystallize. Hydroxides and oxides were characterized by Fourier transformed infrared spectroscopy, X-ray diffraction and X-ray fluorescence. Hence we could emphasize importance and role of ammonium ions on the structure and optical properties of the synthesized products. More particularly, it has been demonstrated that only amorphous products precipitated in the presence of ammonium ions lead to single-phase HfGeO4. (C) 2006 Elsevier B.V. All rights reserved.