Thermal activated energy transfer between luminescent states of Mn2+-doped ZnTe nanoparticles embedded in a glass matrix.

Zn(1-x)Mn(x)Te nanocrystals (NCs), at various concentrations x, were successfully grown in a host glass matrix by the fusion method after appropriate annealing. Growth of these NCs was evidenced by optical absorption (OA), X-Ray Diffraction (XRD), magnetic force microscopy (MFM) and photoluminescence (PL) measurements. From the room temperature OA spectra, it was possible to observe the formation of two well defined, different sized groups of NCs, one attributed to quantum dots (QDs) and the other to bulk-like nanocrystals (NCs). XRD results have confirmed that the cubic zincblend structure of nanoparticles is not altered by the substitutional incorporation of Mn(2+) ions into the ZnTe NCs. MFM images supported the OA spectra results and thus provided additional confirmation of the formation of Zn(1-x)Mn(x)Te magnetic nanoparticles in the host glass matrix. The two groups of NCs were also observed in the PL spectra as well as deep defects attributed to the presence of oxygen centers in the electronic structure of the Zn(1-x)Mn(x)Te NCs. Strong agreement between the fitting model, based on rate equation, and experimental PL intensity data at different temperatures demonstrates that this model adequately describes the energy transfer processes between the NCs and the defects of the Zn(1-x)Mn(x)Te system at different temperatures.

Magneto-optical properties of Cd(1-x)Mn(x)S nanoparticles: influences of magnetic doping, Mn2+ ions localization, and quantum confinement.

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.

Carrier dynamics in the luminescent states of Cd(1-x)Mn(x)S nanoparticles: effects of temperature and x-concentration.

Optical absorption (OA), magnetic force microscopy (MFM), and photoluminescence (PL) measurements were employed to study Cd(1-x)Mn(x)S nanoparticles (NPs), grown in a glass matrix, at different x-concentrations. The formation of two well defined groups of NPs with different sizes was detected by OA spectra at room temperature and confirmed by MFM images, from which they were identified as quantum dots (QDs) and bulk-like nanocrystals (NCs). Emissions from luminescent states were observed in the temperature dependent PL spectra of both groups of NPs, including those from deep defects which were attributed to the presence of divacancies (V(Cd)-V(S)) in the hexagonal wurtzite structure. Furthermore, we have come up with a model based on rate equations that describes energy transfers involving the excitonic states of QDs, the conduction band of bulk-like NCs, and the shallow virtual levels of NPs. This model was used to fit the integrated PL intensity of the corresponding NP groups, and a good agreement between them confirms that the model suitably describes the temperature dependent carrier dynamics of Cd(1-x)Mn(x)S NPs.

Control of luminescence emitted by Cd 1-x Mn x S nanocrystals in a glass matrix: x concentration and thermal annealing.

Cd(1-x)Mn(x)S nanocrystals (NCs) were successfully grown in a glass matrix and investigated by photoluminescence (PL), electron paramagnetic resonance (EPR) and magnetic force microscopy (MFM). We verified that the luminescent properties of these NCs can be controlled both by changing the x concentration and by thermal annealing of the samples. The EPR and PL data showed that the characteristic emission of Mn(2+) ions ((4)T(1)-(6)A(1)) is only observed when this magnetic impurity is substitutionally incorporated in the Cd(1-x)Mn(x)S NC core (site S(I)). Besides, it was observed that the emission ((4)T(1)-(6)A(1)) suppression, caused by the Mn(2+) ion presence near the surface (site S(II)) of the Cd(1-x)Mn(x)S NCs, is independent of the host material. The MFM images also confirmed the high quality of the Cd(1 - x)Mn(x)S NC samples, showing a uniform distribution of total magnetic moments in the nanoparticles.