Magneto-optical properties of Cd1−xMnxS nanoparticles: influences of magnetic doping, Mn2+ ions localization, and quantum confinement

Abstract

Cd(1-x)Mn(x)S nanoparticles (NPs) were successfully grown in a glass matrix and investigated by optical absorption (OA), magnetic circularly polarized photoluminescence (MCPL) measurements, and magnetic force microscopy (MFM). The room temperature OA spectra have revealed the formation of two groups of Cd(1-x)Mn(x)S NPs with different sizes: bulk-like nanocrystals (NCs) and quantum dots (QDs). The MCPL spectra were recorded at 2.0 K with several magnetic fields up to 15 T, allowing a detailed comparison between the degrees of circular polarization of the two groups of NPs. The different behaviours of magneto-optical properties of bulk-like NCs and QDs were explained by taking into account a considerable alteration of exchange interaction between the carrier spins and the substitutional doping magnetic ions incorporated into the NPs. As a main result, we have demonstrated that self-purification is the dominant mechanism that controls the doping in semiconductor QDs grown by the melting-nucleation synthesis approach due to the relatively high temperature that was used in thermal annealing of samples.

Raman spectroscopy of very small Cd1−xCoxS quantum dots grown by a novel protocol: direct observation of acoustic‐optical phonon coupling

“…It was recently demonstrated that the magnetization of Cd 1−x Mn x S QDs cannot be probed by MFM measurements when the magnetic ions (Mn 2+ ) are located near to the dot surface . Therefore, it is concluded that the sp‐d exchange interaction is larger for Cd 1−x Co x S QDs than for Cd 1−x Mn x S QDs, in agreement with the behavior of the corresponding bulk materials .…”

“…Therefore, it is concluded that the sp‐d exchange interaction is larger for Cd 1−x Co x S QDs than for Cd 1−x Mn x S QDs, in agreement with the behavior of the corresponding bulk materials . This accumulation of Co 2+ ions at sites near the Cd 1−x Co x S QD surface can be understood as a direct result of the self‐purification effect, which is the dominant mechanism controlling the doping in semiconductor QDs grown by the melting‐nucleation synthesis route because of the relatively high temperature used while thermally annealing the samples …”

“…This finding is quite reasonable as the ionic radius of Co 2+ is smaller than that of Cd 2+ . Certainly, the presence of Cd 2+ vacancies in the QD CdS wurtzite structure grown by the melting‐nucleation approach promotes a strong contribution to the incorporation of Co 2+ ions into the Cd 1−x Co x S QDs. Possibly, part of Co 2+ ions can also be incorporated into octahedral interstitial sites contributing with the relaxation of the d‐spacing value .…”

“…Thus, different synthesis routes for II–VI‐based DMS nanostructures, as for instance colloidal chemistry, hot wall epitaxy, and chemical bath deposition among others, have been developed in an attempt to provide full control of their optical properties. However, stable and transparent materials should be used as host templates for the growth of doped nanostructures to target several technological applications, which may require them to work on a wide range of temperatures. Therefore, selection of thermally stable host templates that allow controllable and reproducible in situ growth of II–VI‐based DMS QDs is as important as to assess and understand their very basic properties.…”

Cd1−xMnxTe ultrasmall quantum dots growth in a silicate glass matrix by the fusion method

“…This SNAB glass matrix, developed by NO Dantas, proved to be an excellent host for the growth of various types of quantum dots synthesized in the group, which presents glass transition temperature around at 798.15 K. 24 The optical properties of the quantum dots are modified with the incorporation of magnetic ions due to the sp-d hybridization that occur between the electronic subsystems. [25][26][27] This exchange interaction causes a blueshift in the peak energy with increasing x of Cd 1Àx Mn x Te compared to CdTe QDs. 28 QDs.…”