Large tunable luminescence by Mn(II) aggregates in Mn-doped ZnS nanobelts

Tunable emission from the visible to infrared region in II-VI semiconductor nanostructures makes them ideal candidates for the development of optoelectronic devices. In this study, Zn1-xMnxS (x = 0.01-0.15%) nanobelts (NBs) were prepared via the chemical vapor deposition (CVD) method. The as-grown NBs were investigated by XRD and electron paramagnetic resonance (EPR). A significant lower angle shift was observed in the XRD spectra, which indicated the incorporation of Mn ions. A hyperfine interaction constant A of 68.6 G obtained from the EPR spectra confirmed that Mn2+ ions were successfully incorporated into the ZnS matrix. For higher Mn concentrations, the broadening of the EPR profile was attributed to the aggregation of Mn2+ ions. Moreover, successful Mn-ion doping in individual ZnS NBs was itentified by SEM-EDS and Raman scattering analysis. Raman spectroscopy studies revealed a red-shift at the LO phonons, confirming the presence of Mn ions in ZnS NBs. Room-temperature photoluminescence (PL) showed that the Mn concentration plays an important role in tuning the emission from 452 nm to 877.6 nm (blue to near-infrared: NIR); whereby, up to 15% Mn, PL showed emissions are centered at 447, 535, 580.7, 651.1, and 877.6 nm. Herein, the first two peaks were assigned to anti-ferromagnetic coupling of 4 Mn ions, and the interaction of 2 Mn ions with stack faults in ZnS NBs. The next peak was from the typical d-d transition (T-4(1)((4)G) -> (6)A(1)(S-6)) of Mn2+, and the last two peaks were assigned to the aggregate made up of 2 Mn ions and (MnS)(5) cluster-related emission with ferromagnetic coupling. NIR emission was also detected from the 10% Mn-doped CdS NBs. To the best of our knowledge, herein, NIR emission was observed for the first time in ZnS nanostructures. These kinds of nanomaterials may have potential applications in photovoltaics, telecommunications, and remote sensing.