We study the formation dynamics of a spontaneous ferromagnetic order in single self-assembled Cd1−xMnxTe quantum dots. By measuring time-resolved photoluminescence, we determine the formation times for QDs with Mn ion contents x varying from 0.01 to 0.2. At low x these times are orders of magnitude longer than exciton spin relaxation times evaluated from the decay of photoluminescence circular polarization. This allows us to conclude that the direction of the spontaneous magnetization is determined by a momentary Mn spin fluctuation rather than resulting from an optical orientation. At higher x, the formation times are of the same order of magnitude as found in previous studies on higher dimensional systems. We also find that the exciton spin relaxation accelerates with increasing Mn concentration. Doping semiconductor quantum dots (QDs) with magnetic ions offers a possibility of controlling magnetic properties of matter at nanoscale. Notably, several theoretical reports have proposed tailoring of QD magnetization by tuning the number of carriers in a dot.1-3 However, in order to achieve the control over magnetization a detailed knowledge of its dynamics is required. In compound II -VI QDs the Mn doping is performed routinely enabling studies of very dilute systems including QDs with single Mn ions 4 and of highly doped ones with molar contents up to 7%.5 Magnetic properties are comfortably monitored through optical experiments, since exchange interaction between the localized magnetic ions and the band carriers leads to pronounced magnetooptical effects.6 In particular, energy minimization of a complex consisting of a photocreated electron-hole pair (an exciton) interacting with Mn ions, results in a spontaneous formation of a local ferromagnetic order -a magnetic polaron (MP).Static and dynamic properties of MPs have been subject to intensive experimental and theoretical studies 5,[7][8][9][10][11][12][13][14][15][16][17][18][19] Experimental fingerprint of the MP formation is a redshift of the exciton photoluminescence (PL) by polaron energy E P -the energy gained by formation of the ferromagnetic order. The development of the magnetization can therefore be monitored in a time-resolved (TR) PL experiment, in which a transient shift of the exciton energy is observed allowing to evaluate the MP formation time, τ f .10,11 However, in bulk and 2D systems a prerequisite for the MP formation is an initial localization of the exciton.12 A precise experimental identification of E P and τ f is then hindered by processes related to trapping of the exciton. On the other hand, excitons in QDs are inherently localized by the QD potential, and thus the studies of MP formation dynamics in these nanostructures are free of the obscuring localization effects.14,18 The studies reported so far were performed on QD ensembles, in which the obtained τ f may be inaccurate due to inhomogeneities in dot morphology leading to variations in exciton lifetimes, 20 τ X , affecting in turn the TRPL transients. Previous reports have also lef...

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An effective, simple and practically useful method to incorporate fluorescent nanoparticles inside live biological cells was developed. The internalization time and concentration dependence of a frequently used liposomal transfection factor (Lipofectamine 2000) was studied. A user friendly, one-step technique to obtain water and organic solvent soluble Er(3+) and Yb(3+) doped NaYF4 nanoparticles coated with polyvinylpyrrolidone was obtained. Structural analysis of the nanoparticles confirmed the formation of nanocrystals of the desired sizes and spectral properties. The internalization of NaYF4 nanoparticles in HeLa cervical cancer cells was determined at different nanoparticle concentrations and for incubation periods from 3 to 24 h. The images revealed a redistribution of nanoparticles inside the cell, which increases with incubation time and concentration levels, and depends on the presence of the transfection factor. The study identifies, for the first time, factors responsible for an effective endocytosis of the up-converting nanoparticles to HeLa cells. Thus, the method could be applied to investigate a wide range of future 'smart' theranostic agents. Nanoparticles incorporated into the liposomes appear to be very promising fluorescent probes for imaging real-time cellular dynamics.

Magnetic nanoparticles of Fe 3 O 4 doped by different amounts of Y 3+ (0, 0.1, 1, and 10%) ions were designed to obtain maximum heating efficiency in magnetic hyperthermia for cancer treatment. Single-phase formation was evident by X-ray diffraction measurements. An improved magnetization value was obtained for the Fe 3 O 4 sample with 1% Y 3+ doping. The specific absorption rate (SAR) and intrinsic loss of power (ILP) values for prepared colloids were obtained in water. The best results were estimated for Fe 3 O 4 with 0.1% Y 3+ ions (SAR = 194 W/g and ILP = 1.85 nHm 2 /kg for a magnetic field of 16 kA/m with the frequency of 413 kHz). The excellent biocompatibility with low cell cytotoxicity of Fe 3 O 4 :Y nanoparticles was observed. Immediately after magnetic hyperthermia treatment with Fe 3 O 4 :0.1%Y, a decrease in 4T1 cells’ viability was observed (77% for 35 μg/mL and 68% for 100 μg/mL). These results suggest that nanoparticles of Fe 3 O 4 doped by Y 3+ ions are suitable for biomedical applications, especially for hyperthermia treatment.

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Inorganic nanomaterials able to generate reactive oxygen species (ROS) are promising components for modern medical applications. Activated by near-infrared light, up-converting b-NaYF 4 doped with Er 3+ -Yb 3+ and Tm 3+ -Yb 3+ pair ions nanoparticles (UCNPs), have a wide range of applications in biological imaging as compared to traditional reagents excited by ultra-violet or visible light. We analysed the green-red and the blue-red luminescence to explain the mechanism of the upconversion depended on the surface condition. The influence of SiO 2 coating on the cytotoxicity of the as-produced UCNPs towards HeLa cancer cells was reported. We demonstrated a possibility of a direct UCNPs application to photodynamic therapy, without need to attach additional molecules to their surface. The presence of Tm 3+ -Yb 3+ pair ions, thus ROS generation capability, renders the SiO 2 shell coated nanoparticles to become potentially useful theranostic agent.

Cathodoluminescence (CL) was studied in hybrid structures consisting of a diluted magnetic semiconductor (DMS) Cd1−xMnxTe (x=0.06 and 0.09) quantum well buried 300 Å below the surface on which Fe islands with micrometric dimensions were deposited. The CL at T=10 K collected from areas far away from the Fe island was consistent with the photoluminescence spectra obtained prior to Fe deposition as were the raster scans and spot excited CL spectra taken in nonmagnetized structures close to the Fe islands. After a magnetization at a magnetic field of 3 T, the CL peak related to DMS quantum well (QW) shifts by up to 4 meV to lower energy only when the exciting beam is focused close to edges of an island. The observed shifts are interpreted as due to a fringe field, affecting the DMS QW, of magnetic domains formed in the Fe islands. The experiments prove a feasibility of the concept of usage of the fringe fields to achieve further confinement of excitons in submicron DMS/ferromagnet hybrid structures.

Using resonantly excited photoluminescence (PL)