Single-channel dual tunable emission in the visible and near-infrared region using aggregations of Mn(II) ions in an individual Mn-doped CdS nanosheet

In this study, high-quality single crystalline Mn-doped CdS nanosheets were synthesized by the chemical vapor deposition method and their photoluminescence (PL) properties were determined. Energy dispersive X-ray analysis, the non-uniform peak shifts in the Raman spectra, and micro-PL mapping demonstrated the presence of Mn ions in the nanosheets. The temperature-dependent (78–400 K) micro-PL spectra showed that the multi-peak emissions ranged from 455.302 to 749.901 nm. The band-edge emission exhibited a pronounced red shift (∼8 nm) as the temperature increased from 78 to 400 K due to the formation of exciton magnetic polarons (EMPs). The orange emission (597.621 nm) was due to the ⁴T₁(⁴G) → ⁶A₁(⁶S) d–d transition between the excited state and ground state of Mn²⁺. The shorter lifetimes compared with the forbidden d-d transition and deep traps due to structural relaxation confirmed that the red (670.832 nm) and near-infrared (749.901 nm) emissions were associated with localized EMPs. The PL emission centered at 471.780 nm appeared at 80 K due to free-exciton C (FXC). Emissions centered at 455.302 and 463.501 nm were detected for the first time in our samples. Interestingly, both of these emissions appeared on the higher energy side of FXC and unlike EMP, they did not follow the Varshni function. Therefore, we assigned these emissions to bound magnetic polarons. These novel emissions in dilute magnetic semiconductors could be beneficial for further applications in photovoltaics, full-color displays, and nanoscale devices.