One-step synthesis, growth mechanism and photoluminescence properties of hollow GeO2 walnuts

Abstract

Hollow GeO₂ walnuts were synthesized via a simple one-step process in an emulsion system. We investigated the growth mechanism and optical properties of the products and found that the reactive temperature and the addition of ethanol were crucial factors in controlling the morphology of GeO₂ crystals. Above the ethanol boiling temperature, hollow walnuts were formed, whereas well-dispersed solid GeO₂ polyhedrons and dimers were obtained below the critical point. A possible formation mechanism of the hollow interior of GeO₂ walnuts is proposed suggesting that it was formed from the gas bubble released by the boiling ethanol and followed by the Ostwald ripening process of the encapsulating crystals. Photoluminescence measurement shows an enhanced emission peak at 538 nm for hollow GeO₂ walnuts with blue shift compared with that of the solid structure. Our results indicate hollow GeO₂ walnuts may have potential applications in light-emitting nanodevices. This method also suggests a new approach for fabricating other particles with hollow structure.