Tunable emission properties by ferromagnetic coupling Mn(II) aggregates in Mn-doped CdS microbelts/nanowires.

Tunable optical emission properties from ferromagnetic semiconductors have not been well identified yet. In this work, high-quality Mn(II)-doped CdS nanowires and micrometer belts were prepared using a controlled chemical vapor deposition technique. The Mn doping could be controlled with time, precursor concentration and temperature. These wires or belts can produce both tunable redshifted emissions and ferromagnetic responses simultaneously upon doping. The strong emission bands at 572, 651, 693, 712, 745, 768, 787 and 803 nm, due to the Mn(II) (4)T1((4)G)  → (6)A1((6)s) d-d transition, can be detected and accounted for by the aggregation of Mn ions at Cd sites in the CdS lattice at high temperature. These aggregates with ferromagnetism and shifted luminescence are related to the excitonic magnetic polaron (EMP) and localized EMP formations; this is verified by ab initio calculations. The correlation between aggregation-dependent optical emissions and ferromagnetic responses not only presents a new size effect for diluted magnetic semiconductors (DMSs), but also supplies a possible way to study or modulate the ferromagnetic properties of a DMS and to fabricate spin-related photonic devices in the future.