Enhanced photophysical properties of plasmonic magnetic metal-alloyed semiconductor heterostructure nanocrystals: a case study for the Ag@Ni/Zn1−xMgxO system

Abstract

Understanding the effect of homovalent cation alloying in wide band gap ZnO and the formation of metal–semiconductor heterostructures is very important for maximisation of the photophysical properties of ZnO. Nearly monodisperse ZnO nanopyramid and Mg alloyed ZnO nanostructures have been successfully synthesized by one pot decomposition of metal stearate by using oleylamine both as activating and capping agent. The solid solubility of Mg(II) ions in ZnO is limited to ∼30% without phase segregation. An interesting morphology change is found on increasing Mg alloying: from nanopyramids to self-assembled nanoflowers. The morphology change is explained by the oriented attachment process. The introduction of Mg into the ZnO matrix increases the band gap of the materials and also generates new zinc interstitial (Zn_i) and oxygen vacancy related defects. Plasmonic magnetic Ag@Ni core–shell (Ag as core and Ni as shell) nanocrystals are used as a seed material to synthesize Ag@Ni/Zn_1−xMg_xO complex heterostructures. Epitaxial growth is established between Ag(111) and ZnO(110) planes in the heterostructure. An epitaxial metal–semiconductor interface is very crucial for complete electron–hole (e–h) separation and enhancement of the exciton lifetime. The alloyed semiconductor–metal heterostructure is observed to be highly photocatalytically active for dye degradation as well as photodetection. Incorporation of magnetic Ni(0) makes the photocatalyst superparamagnetic at room temperature which is found to be helpful for catalyst regeneration.