Investigation of undoped ZnO@SiO₂ core–shell phosphors with green luminescence

Abstract

In this study, ZnO nanoparticles (NPs) with the structure of hexagonal prisms and different diameters (20–45 nm) and lengths (80–320 nm) were used as a precursor with tetraethyl orthosilicate to fabricate ZnO@SiO₂ core–shell NPs. After SiO₂ was coated on the surfaces of the ZnO NPs as the shell, the ZnO@SiO₂ core–shell NPs were heated at temperatures of 900–1300 °C. The zinc orthosilicate (α-Zn₂SiO₄) phase was observed as the ZnO@SiO₂ core–shell NPs were heated at temperatures of 800–1300 °C. Analysis of the X-ray diffraction patterns showed that at 900 °C, unknown or secondary phases were observed in the ZnO@SiO₂ core–shell NPs. When the temperature exceeded 900 °C, no secondary or unknown phases were observed. The effect of calcining temperature on the luminescence properties of the ZnO@SiO₂ core–shell phosphors was readily observable. We found two important novelties in the synthesized ZnO@SiO₂ (or undoped α-Zn₂SiO₄) powders. First, the fabricated ZnO@SiO₂ phosphors could emit green light with no activators. Second, measurement of the decay time of the ZnO@SiO₂ phosphors revealed a long decay time.