Synthesis of hafnium germanate (HfGeO₄) particles: Impact of crystallization route on X/UV conversion properties

The crystallization route - calcination or hydrothermal ripening - of an amorphous hafnium and germanium oxide coprecipitate determines the X/UV conversion properties of the resulting hafnium germanate (HfGeO₄). The calcination of the amorphous precipitate leads to micrometric aggregated particles exhibiting strong X/UV conversion whereas its hydrothermal crystallization resulted in well individualized nanoparticles with no X/UV conversion property. To explain these phenomena, the crystalline structure and chemical composition of the final products were investigated with X-ray diffraction (XRD) and inductively coupled plasma-mass spectrometry (ICP-MS). The key result is that germanium is partially solubilized from the amorphous precursor in hydrothermal conditions, resulting in the crystallization of a Ge deficient hafnium germanate possessing no X/UV conversion properties.