Annealing effects on the structure, photoluminescence, and magnetic properties of GaN/Mn3O4 core–shell nanowires

Nanowires consisting of GaN/Mn3O4 were prepared using a two-step approach that involved dipping the as-synthesized GaN nanowires into an aqueous manganese acetate solution. To examine the effects of annealing, GaN/Mn3O4 core–shell nanowires were heated thermally to 700 °C in N2 ambient. Transmission electron microscopy showed that the continuous Mn3O4 shell layer had agglomerated to expose a bare GaN core surface after thermal annealing. The magnetic measurements showed that the ferromagnetic behavior of the GaN nanowires had been suppressed by coating with the Mn3O4 shell, without significant change by the subsequent thermal annealing. The GaN/Mn3O4 core–shell nanowires exhibited blue, green, and red photoluminescence (PL) emission. The red emission was enhanced by thermal annealing. This paper discusses the associated mechanism for the variations in PL and magnetic properties of GaN/Mn3O4 core–shell nanowires.