Synthesis, structure, and luminescence properties of In2Ge2O7/SnO2 core-shell nanowires

In2Ge2O7/SnO2 core-shell nanowires were synthesized by using a two-step process: thermal evaporation of a mixture of In and Ge powders and atomic layer deposition of SnO2. The core-shell nanowires were characterized using by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and photoluminescence spectroscopy. The In2Ge2O7 cores in these core-shell nanowires varied from 50 to100 nanometers in diameter and up to a few hundreds of micrometers in length, and the SnO2 shell layer thickness ranged from 5 to 15 nm. Photoluminescence measurements showed that the In2Ge2O7 nanowires had a weak broad violet emission band centered at approximately 405 nm. In contrast, the In2Ge2O7/SnO2 core-shell nanowires had a taller blue-violet emission peak at approximately 440 nm. The optimum shell layer thickness of the In2Ge2O7/SnO2 core-shell nanowires for the highest PL intensity was found to be 15 nm. Our results also showed that the intensity of the blue-violet emission was increased further by thermal annealing in an Ar atmosphere. The origins of the change on and the enhancement of the luminescence of the In2Ge2O7 nanowires by SnO2 coating and annealing are discussed.