Synthesis and photoluminescence of amorphous Ca5Ge2O9 nanowires

A new method to prepare amorphous Ca5Ge2O9 nanowires is demonstrated in the present study. Germanium nanoparticles with the size ranging from 10 to 50 nm were first prepared by a vapor condensation technique. Upon immersing the nanoparticles in Ca(OH)2 aqueous solution, hydrated Ca5Ge2O9 nanowires were formed rapidly. The phase was determined by X-ray diffraction, and the stoichiometry of Ca:Ge was further confirmed by energy-dispersive X-ray spectroscopic and inductively coupled plasma-mass spectrometric analyses. The diameter of nanowires varied from several tens to more than 100 nm, and the length increased with aging time up to the completion of reaction. After dehydrating at 400 degrees C, the nanowires became amorphous, and the stoichiometry of Ca:Ge remained unchanged. A blue-violet luminescence was detected from these amorphous nanowires. The emission band distributed from 300 to 550 nm, with the main peak locating at 380 nm. Ge-associated luminescence centers are proposed to be responsible for this emission. The formation of amorphous Ca5Ge2O9 nanowires may provide a new thinking to prepare other kinds of amorphous one-dimensional nanomaterials.