Magnetic polaron-related optical properties in Ni(II)-doped CdS nanobelts: Implication for spin nanophotonic devices

Abstract

Emissions by magnetic polarons and spin-coupled d–d transitions in diluted magnetic semiconductors (DMSs) have become a popular research field due to their unusual optical behaviors. In this work, high-quality NiI2(II)-doped CdS nanobelts are synthesized via chemical vapor deposition (CVD), and then characterized by scanning electron microscopy (SEM), x-ray diffraction, x-ray photoelectron spectroscopy (XPS), and Raman scattering. At low temperatures, the photoluminescence (PL) spectra of the Ni-doped nanobelts demonstrate three peaks near the band edge: the free exciton (FX) peak, the exciton magnetic polaron (EMP) peak out of ferromagnetically coupled spins coupled with FXs, and a small higher-energy peak from the interaction of antiferromagnetic coupled Ni pairs and FXs, called antiferromagnetic magnetic polarons (AMPs). With a higher Ni doping concentration, in addition to the d–d transitions of single Ni ions at 620 nm and 760 nm, two other PL peaks appear at 530 nm and 685 nm, attributed to another EMP emission and the d–d transitions of the antiferromagnetic coupled Ni2+–Ni2+ pair, respectively. Furthermore, single-mode lasing at the first EMP is excited by a femtosecond laser pulse, proving a coherent bosonic lasing of the EMP condensate out of complicated states. These results show that the coupled spins play an important role in forming magnetic polaron and implementing related optical responses.