Anomalous optical and magnetic behavior of multi-phase Mn doped Zn2SiO4 nanowires: a new class of dilute magnetic semiconductors

Abstract

We present the synthesis of Mn doped Zn₂SiO₄ dense nanowire bundles using the VLS mode of growth with unusual optical and magnetic properties. The synthesized Zn₂SiO₄ nanowires were identified with two phases, α-Zn₂SiO₄ as the major phase and β-Zn₂SiO₄ as the minor phase. XPS studies confirmed that Zn₂SiO₄ nanowires were Zn rich and Mn doped. Temperature dependent photoluminescence (PL) measurements showed three distinct emission bands: green, yellow and red due to Mn doping in the α-phase, β-phase and the substitution of Si with Mn in the α-phase, respectively. The PL analysis showed that these emission bands followed anomalous Berthelot-type behavior. The carrier escape energies were 70 ± 3 meV, 49 ± 2 meV and 65 ± 4 meV for the 530, 570 and 660 nm bands, respectively, while the radiation rates (E_r =) were 1.0 ± 0.4 meV, 3.10 ± 1.10 meV and 1.4 ± 0.4 meV corresponding to the three respective bands. Mn doping of Zn₂SiO₄ nanowires induced ferromagnetism, which was observed above room temperature, with a Curie temperature well above 380 K. The observation of magnetic behavior in this class of semiconductors has potential applications in high temperature spintronics and magneto-optical devices.