ZnS and ZnO Semiconductor Nanoparticles Doped with Mn2+ Ions. Size Effects Investigated by EPR Spectroscopy

Aggregates of Mn2+ Ions in Mesoporous Self-Assembled Cubic ZnS:Mn Quantum Dots: Composition, Localization, Structure, and Magnetic Properties

“…Using the typical χ para = C/T Curie-type dependence of the paramagnetic susceptibility, with C a Curie−type constant (C = NP 2 /3k B , where N is the number of paramagnetic centers, P the effective magnetic moment per paramagnetic center, and k B the Boltzmann constant), one can estimate the number N of paramagnetic centers per gram of sample (noted by n), assuming a magnetic moment of 5 μ B per Mn 2+ center, where μ B is the Bohr magneton. According to the relationship n = 3k B Tχ para /P 2 there are (2.6 ± 0.2) × 10 18 Considering the experimental errors involved (±25%) one finds a reasonable agreement between the spin concentration of the paramagnetic centers from magnetic measurements C(χ para ) = 440 ppm and the total spin concentration C is + C aggr = 370 ppm provided by EPR in the case of the sample with 2000 ppm nominal concentration. These values are also in good agreement with the concentration of incorporated manganese C AA = 455 ppm determined by elemental atomic absorption (AA) analysis using a PerkinElmer atomic absorption spectrophotometer model PINAACLE 900T and standard quantitative analysis procedures.…”

“…The analysis of the electron paramagnetic resonance (EPR) spectra from Mn 2+ ions incorporated in cubic ZnS QDs has revealed the presence of isolated Mn 2+ ions localized at substitutional Zn 2+ sites in the core and on the surface of the NCs, as well as of an aggregated phase resulting in a broad, featureless Lorentzian component line, associated with exchange coupled Mn 2+ ions. − In recent quantitative EPR investigations of 2.9 nm diameter cZnS:Mn QDs prepared by coprecipitation we have shown that, up to the highest nominal concentration of 50 000 ppm, the Mn 2+ ions incorporated at isolated sites in the core and on the surface in a diluted paramagnetic state characterized by magnetic dipole–dipole interactions cannot be responsible for the collective magnetism properties. , Although one would expect that the aggregated Mn 2+ ions could determine the observed collective magnetism at least below a certain temperature, to our knowledge this possibility has not been investigated so-far. In fact, practically nothing is known about the composition, structure, and physical properties of the phase responsible for the Lorentzian line, also seen in other II–VI semiconductor NCs at higher doping levels. , It is therefore essential to determine in what manner the Mn 2+ aggregated phase contributes to the reported collective magnetism properties.…”

Doping Ultrasmall Cubic ZnS Nanocrystals with Mn2+ Ions over a Broad Nominal Concentration Range

“…Electron paramagnetic resonance (EPR) can detect with high sensitivity the presence and amount of paramagnetic centers, including TMIs at different lattice sites in semiconductor NCs. ,− Mn 2+ is the best suited TMI for such studies and has been extensively investigated in NCs of ZnS, ZnSe, ZnO, CdS, and CdSe. ,,− Studies of nanocrystalline samples exhibiting well resolved EPR spectra resulted in the identification of isolated Mn 2+ ions localized in the core and in the surface layer of the host NCs, as well as of agglomerates/separate phases of Mn 2+ ions observed at higher nominal concentrations. ,,, …”

Luminescent manganese-doped CsPbCl3 perovskite quantum dots

“…Emission and quantum confinement of CsPbX 3 QDs that form in Pb‒doped CsX scintillator crystals was reported in the late 1990’s 16 . For the II‒VI QDs such as ZnO, ZnS, ZnSe, CdS, CdSe there has been a strong effort to dope the QDs with transition metal (TM) ions such as Mn 2+ or Co 2+ aimed at introducing new optical and/or magnetic functionalities 17 18 19 20 21 . A large number of publications have reported different categories of doped QDs 22 23 24 .…”