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Combining fluorescence and magnetic features in a non-iron based, select type of quantum dots (QDs) can have immense value in cellular imaging, tagging and other nano-bio interface applications, including targeted drug delivery. Herein, we report on the colloidal synthesis and physical and biophysical assessment of wurtzite-type manganese selenide (MnSe) QDs in cell culture media. Aiming to provide a suitable colloidal system of biological relevance, different concentrations of reactants and ligands (e.g., thioglycolic acid, TGA) have been considered. The average size of the QDs is ∼7 nm, which exhibited a quantum yield of ∼75% as compared to rhodamine 6 G dye(®). As revealed from time-resolved photoluminescence (TR-PL) response, the near band edge emission followed a bi-exponential decay feature with characteristic times of ∼0.64 ns and 3.04 ns. At room temperature, the QDs were found to exhibit paramagnetic features with coercivity and remanence impelled by TGA concentrations. With BSA as a dispersing agent, the QDs showed an improved optical stability in Dulbecco's Modified Eagle Media(®) (DMEM) and Minimum Essential Media(®) (MEM), as compared to the Roswell Park Memorial Institute(®) (RPMI-1640) media. Finally, the cell viability of lymphocytes was found to be strongly influenced by the concentration of MnSe QDs, and had a safe limit upto 0.5 μM. With BSA inclusion in cell media, the cellular uptake of MnSe QDs was observed to be more prominent, as revealed from fluorescence imaging. The fabrication of water soluble, nontoxic MnSe QDs would open up an alternative strategy in nanobiotechnology, while preserving their luminescent and magnetic properties intact.

We report here synthesis and optical absorption study of energetic ion-irradiated hydroxyl-free ZnO semiconductor quantum dots. Quantum dot samples were synthesized by a quenching technique and 100-MeV chlorine ion was selected for the irradiation experiment with doses 1 × 10[sup 11], 5 × 10[sup 11], 5 × 10[sup 12], and 10[sup 13] ions/cm². With an increase in fluence, the optical absorption spectra of irradiated quantum dots reveal redshift of the energy-gap parameter with respect to unirradiated (virgin) quantum dots. The narrowing of the energy gap of nanoparticles indicate particle growth under ion irradiation which is confirmed from transmission electron microscope images. The possible reason for such variations was encountered using an effective-mass approximation model which fits well for small effective mass and high-dielectric constant (∈[sub 0]). [ABSTRACT FROM AUTHOR]

We report processing and luminescence decay characteristics of Cd1-xZnxS composite nanocrystals (NCs) conjugated with bovine serum albumin (BSA) proteins. Time-resolved study on unconjugate NCs (with dimensions less than the bulk exciton Bohr radius) suggests that in the radiative emission, the fast (τ1) and the slow (τ2) carrier components are equally competitive for a given stoichiometry. Conversely, bioconjugate NCs advocate that the decay component due to the free exciton recombination is ∼9 times faster than the component due to the surface recombination emission. The observation of two distinct decay parameters is due to the fact that the NCs have experienced photostability by way of binding and protecting NC surface with biomolecules (BSA) as binding agents. The occurrence of two decay constants would help in extracting information with regard to the nature of surface recombination, free-exciton relaxation along with the strength of emission. Furthermore, with the increase in % Zn, slow carrier component gets slower owing to the incorporation of extra surface traps due to Zn/Cd incompatibility while making perfect lattice sites in the NCs. As a result, surface emission intensity gets improved compared to the radiative intensity due to core-state direct transitions. Understanding photoluminescence decay of bioconjugated NCs, on a comparative basis, would find scope for biomolecular labelling, sensing and electrophysiology applications. [ABSTRACT FROM AUTHOR]

Abstract: We report clear evidence of third order nonlinearity χ (3) in polymer embedded cadmium sulfide quantum dot system as a result of nonresonant nondegenerate four frequency mixing. We notice thickness dependent enhancement of nonlinear absorption with increase in incident intensity of light. Two pump beams (λ =1064nm) were oppositely directed into the sample and to receive phase conjugated signal, a probe beam was focused at the point of intersection on the sample. In the conditions satisfying self diffraction phenomena, we have measured change in refractive index as a function of incident power. We have observed very high value of third order susceptibility (χ (3) ∼10−7 e.s.u.) and predict figure of merit as high as ∼1.9 for the thinnest quantum dot sample (0.54μm). Nonlinear susceptibility drops by nearly 10 times for the thickest sample (1.211μm) due to considerable suppression in nonlinear absorption. [Copyright &y& Elsevier]

PbS quantum dots of the average size 10 nm are synthesized in the polymer matrix (PVA) following chemical route. Optical absorption spectra reveal a large blue shift from the bulk absorption cutoff wavelength. Instead of using a high power laser, we have measured for the first time the third order nonlinear susceptibility (χ³) of PbS quantum dots using a low power continuous wave laser with the Degenerate Four Wave Mixing (DFWM) technique. The result is encouraging in nonlinear optical application at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: PbS quantum dots of average size 10nm are encapsulated in a matrix (polyvinyl alcohol (PVA)) following chemical route. They are irradiated with 160MeV Ni12+ ion beam with fluences 1012–1013 ions/cm2. Red shift in the absorption response in the optical absorption spectra reveal size enhancement of the quantum dots after irradiation and was confirmed by transmission electron microscopy (TEM). Photoluminescence (PL) study was carried out with excitation wavelength 325nm on both unirradiated and irradiated samples at different fluences and fluence-dependent surface states and excitonic emission is observed in the PL study. The Huang–Rhys coupling constant decreases significantly after swift heavy ion (SHI) irradiation and shows a decreasing trend with increase in ion fluence. [Copyright &y& Elsevier]

Polymer embedded cadmium sulfide nanoparticles/quantum dots were synthesized by a chemical route using polyvinyl alcohol (lmw) as the desired matrix. In an attempt to measure the electrical properties of nano-CdS/Ag samples, we propose that contribution from surface traps are mainly responsible in determining the I∼ V and C∼ V characteristics in high frequency ranges. To be specific, beyond 1.2 MHz, the carrier injection from the trap centers of the embedded quantum dots is ensured by large current establishment even at negative biasing condition of the junction. The unexpected nonlinear signature of C∼ V response is believed to be due to the fact that while trying to follow very high signal frequency (at least 10-3 of recombination frequency), there is complete abruptness in carrier trapping (charging) or/and detrapping (decay) in a given CdS nanoparticle assembly. The frequency dependent unique role of the trap carriers certainly find application in nanoelectronic devices at a desirable frequency of operation. [ABSTRACT FROM AUTHOR]

Abstract: Quantum dots were fabricated in two varieties of polymer matrices, namely, polyvinyl alcohol (PVOH) and carboxylated styrene butadiene rubber (SBR). They were irradiated with a 100-MeV chlorine beam at fluences 1011, 5×1011, 5×1012 and 1013 ions/cm2. The melting of grains and coalesce of quantum dots have been observed in case of powder CdS and PVOH-embedded CdS quantum dot samples, respectively, while grain bursting predominates in quantum dots embedded in SBR hosts, as revealed from high-resolution electron microscopy. The splitting or melting of nanometric grains (quantum dots) was found to be dependent on irradiation fluence and the physical properties of host matrices for the same energy value of the projectile ion. [Copyright &y& Elsevier]

The pH of the dispersing media has an influential role on the optical and radiative features of quantum particles/dots (QDs). Herein, we report size dispersity and luminescence response of sodium dodecyl sulphate (SDS)-coated MnSe QDs dispersed in extreme natural extracts. The hydrothermally processed QDs exhibited wutzite phase and numerous Raman active modes as revealed through the X-ray diffraction and Raman spectroscopy studies; respectively. Of varied pH (typically, from 2.5 to 9), distinctly different extracts were derived from starfruit, sugarcane, chilli, and neem leaves available locally. The hydrodynamic size of the QDs experiences a declining trend with increasing pH, with dispersing media being a buffer solution or a natural extract. Zeta potential makes a clear transition from the positive to the negative values, as one moves from a low (acidic) to high (basic) pH of the natural extracts, and subsequently, the isoelectric point (IEP) of the QDs in a medium has been predicted at pH 6.3. Whereas a more acidic medium offered a relatively lowered luminescence profile, the extracts of high pH ensured an intense blue–violet emission of the QDs located at ~ 428 nm along with defect-mediated peaks, expected at relatively higher wavelengths. Furthermore, the acidic environment tends to suppress both near band edge and defect-mediated emissions substantially. The optical stability of surfactant-coated QDs would find immense value in the areas of nano-bio interface applications, such as nano-bioconjugation, bio-imaging, and drug formulation in nano-medicine. [ABSTRACT FROM AUTHOR]

In this work, we discuss Raman active vibrational and photoluminescence (PL) features of hydrothermally derived cubic phase, manganese selenide (MnSe) quantum dots (QDs) coated with markedly different coating agents, such as, cetyl trimethyl ammonium bromide (CTAB), thioglycolic acid (TGA) and dextran molecules. The homogeneously grown QDs, upon adequate coating, offered a size variation between 5 and 11 nm as evident from imaging through transmission electron microscopy (TEM). The Raman spectra of the QDs have revealed the most prominent peak positioned at ∼680 nm and is ascribed to the third overtone of the longitudinal optical (LO(Γ)) mode. Moreover, the numerous, mixed modes which existed for the uncoated QDs, were found to be suppressed after adequate surface passivation due to surfactant coating. The prominent blue-violet emission response of the MnSe QDs, was seen to be highly symmetric and positioned at ∼428 nm. Furthermore, time resolved PL studies have predicted bi-exponential decay characteristics with a fast component (τ 1 ∼ 0.10 ns) that remains nearly unaffected, but the slow component (τ 2) has varied with the nature of coating agent. In particular, the dextran coated MnSe QDs exhibited a maximal τ 2 value (∼5.5 ns) due to complete surface passivation of the QDs. The influence of surfactants on the vibrational and PL emission parameters of a magneto-fluorescent candidate, like MnSe, would bring new insights for their relevance in nano-photonics and nano-biotechnology to act as active probes for imaging, sensing and targeted therapeutics. • Surface anchored MnSe quantum dots (QDs) have been derived through a rapid hydrothermal route. • Raman active, mixed vibrational modes are found to be suppressed after coating with surfactants. • Highly symmetric, blue-violet emission and positioned at ∼428–430 nm, has been witnessed for all the QD-types. • While fast decay parameter is approximately 0.10 ns, the slow decay component is altered with the nature of coating agent. [ABSTRACT FROM AUTHOR]

Abstract: Bare and silica coated CdS quantum dots are prepared following chemical route. Swift heavy ion (SHI) irradiation of the samples was carried out with 160MeV Ni12+ ion beam with fluences 1012–1013 ions/cm2. Photoluminescence (PL) studies of all the samples were carried out with excitation wavelength 325nm. The surface state emission is dominant in case of bare samples while e–h recombination is observed in case of coated samples. Red shift in the absorption response in the optical absorption spectra of bare samples reveal size enhancement of the quantum dots after irradiation. No such shift is observed for coated samples. The coated samples also exhibit enhanced photo stability. [Copyright &y& Elsevier]