Magnetic Control of the Manganese Photoluminescence in Fe3O4/l-Cys ZnS:Mn Nanocomposites.

We investigated the magnetic control of the Mn photoluminescence (PL) in iron oxide/l-cysteine-capped zinc sulfide (Fe3O4/l-cys ZnS:Mn) nanocomposites via temperature- and field-dependent PL intensity studies. Fe3O4/l-cys ZnS:Mn was synthesized following a wet chemical deposition route and then its physicochemical, morphological, and magnetic properties were characterized. X-ray diffraction analysis indicates the formation of a semiconducting composite material with coexisting phases with high crystalline quality and purity. Electron microscopy reveals that the surfaces of the nanoparticles are clean and smooth, sized between 15 and 30 nm, without any sheathed amorphous phase. Vibrating sample magnetometry and UV light excitation show a clear superparamagnetic behavior and an optical response of Fe3O4/l-cys ZnS:Mn, which revealed its bifunctional nature. Magnetoluminescent coupling at 1.0 T is seen in the form of PL suppression in Fe3O4/l-cys ZnS:Mn from low temperature (10 K) to room temperature, with a PL intensity drop of ∼5% at 10 K and a maximum drop of 10% at room temperature. This observation can be explained by restriction of the energy transfer to Mn orbitals through magnetic ordering and Jahn-Teller distortions. Fe3O4/l-cys ZnS:Mn shows promise as a bifunctional biocompatible compound that can be applied as a theranostic agent and a quantum computational element. A deeper understanding behind the magnetic control of the optical response in bifunctional materials brings forth new arenas in diagnostics and drug delivery.

Novel magneto-luminescent effect in LSMO/ZnS:Mn nanocomposites at near-room temperature.

We report the tuning of the internal Mn photoluminescence (PL) transition of magnetically-ordered Sr-doped lanthanum manganite (LSMO)/Mn-doped zinc sulfide (ZnS:Mn) nanocomposites (NCs) by applying a static magnetic field in the range of 0-1 T below the critical temperature of ∼225 K. To do that, we have systematically fabricated LSMO/ZnS:Mn at different concentrations (1:1, 1:3, 1:5 and 1:10 wt%) via a straightforward solid-state reaction. X-ray diffraction and Raman analyses reveal that both phases coexist with a high degree of crystallinity and purity. Electron microscopy indicates that the NCs are almost spherical with an average crystal size of ∼6 nm, and that their surfaces are clean and smooth. The bifunctional character of LSMO/ZnS:Mn was evidenced by vibrating sample magnetometry and PL spectroscopy analyses, which show a marked ferromagnetic behavior and a broad, intense Mn orange emission band at room temperature. Moreover, the LSMO/ZnS:Mn at 1:3 wt% exhibits magneto-luminescent (ML) coupling below 225 K, and reaches the largest suppression of Mn-band PL intensity (up to ∼10%) at 150 K, when a magnetic field of 1.0 T is applied. The ML effect persists at magnetic fields as low as 0.2 T at 8 K, which can be explained by evoking a magnetic-ordering-induced spin-dependent restriction of the energy transfer to Mn states. No ML effect was observed in bare ZnS:Mn nanoparticles under the same experimental parameters. Our findings suggest that this NC can be considered as a new ML compound, similar to FeCo/InGaN-GaN and LSMO/ZnO NCs, useful as q-bits for quantum computation. The results presented here bring forth new avenues to better understand the interaction between semiconductors and perovskites, and exploit their synergistic effects in magneto-optics, spintronics and nanoelectronics.