Investigation on colloidal Te doped CdSe (CdSe:Te) quantum dots suspension in a liquid-core fiber

Here, we demonstrate the use of a colloidal CdSe:Te quantum dots suspension as active liquid-core in a specially designed optical element, based on a double-clad optical fiber structure. The liquid-core fiber was realized by filling the hollow core of a capillary and waveguiding of the core was ensured by using a liquid host that exhibits a larger refractive index than the cladding material of the capillary. Since the used capillary possessed a cladding waveguide structure, we obtained a liquid-core double-clad structure. To seal the liquid-core fiber and e.g. prevent the formation of bubbles, we developed a technique based on SMA connectors. The colloidal CdSe:Te quantum dots were excited by cladding-pumping using a pump laser at 532nm operating in the continuous-wave regime. We investigated the photoluminescence emitted from the colloidal CdSe:Te quantum dots suspension liquid-core and guided by the double-clad fiber structure. We observed a red shift of the (core) emission, that depends on the liquid-core fiber length and the pump power. This shift is due to the absorption of unexcited colloidal quantum dots and due to the waveguiding properties of the core. Here we report a core photoluminescence output power of 79.2μW (with an integrated brightness of ≈ 215.5 W/cm2sr ). Finally, we give an explanation, why lasing could not be observed in our experiments when setup as a liquid-core fiber cavity.

Mode-locked diode-pumped vanadate lasers operated with PbS quantum dots

The use of glasses doped with PbS nanocrystals as intracavity saturable absorbers for passive Q-switching and mode locking of c-cut Nd:Gd0.7Y0.3VO4, Nd:YVO4, and Nd:GdVO4 lasers is investigated. Q-switching yields pulses as short as 35 ns with an average output power of 435 mW at a repetition rate of 6–12 kHz at a pump power of 5–6 W. Mode locking through a combination of PbS nanocrystals and a Kerr lens results in 1.4 ps long pulses with an average output power of 255 mW at a repetition rate of 100 MHz.

Efficient luminescent solar concentrators based on self-absorption free, Tm2+ doped halides

The optical and luminescence properties of CaI2 and NaCl doped with divalent thulium are reported for solar energy applications. These halides strongly absorb solar light from the UV up to 900 nm due to the intense Tm2+ 4f13→4f125d1 electronic transitions. Absorption is followed by emission of 1140 nm light due to the 2F5/2→2F7/2 transition of the 4f13 configuration that can be efficiently converted to electric power by thin film CuInSe2 (CIS) solar cells. Because of a negligible spectral overlap between absorption and emission spectra, a luminescent solar concentrator (LSC) based on these black luminescent materials would not suffer from self-absorption losses. The Tm2+ doped halides may therefore lead to efficient semi-transparent power generating windows that absorb solar light over the whole visible spectrum. It will be shown that the power efficiency of the Tm2+ based LSCs can be up to four times higher compared to LSCs based on organic dyes or quantum dots.

Quantum dot cytotoxicity in vitro: An investigation into the cytotoxic effects of a series of different surface chemistries and their core/shell materials

Abstract The aim of this study was to assess the effects of a series of different surface coated quantum dots (QDs) (organic, carboxylated [COOH] and amino [NH(2)] polytethylene glycol [PEG]) on J774.A1 macrophage cell viability and to further determine which part of the QDs cause such toxicity. Cytotoxic examination (MTT assay and LDH release) showed organic QDs to induce significant cytotoxicity up to 48 h, even at a low particle concentration (20 nM), whilst both COOH and NH(2) (PEG) QDs caused reduced cell viability and cell membrane permeability after 24 and 48 h exposure at 80 nM. Subsequent analysis of the elements that constitute the QD core, core/shell and (organic QD) surface coating showed that the surface coating drives QD toxicity. Elemental analysis (ICP-AES) after 48 h, however, also observed a release of Cd from organic QDs. In conclusion, both the specific surface coating and core material can have a significant impact on QD toxicity.

Nitrogen-Doping in ZnO via Combustion Synthesis?

We report the synthesis and characterization of colored ZnO-based powders via solution combustion reaction of urea and zinc nitrate hexahydrate in varying molar ratios between 1:1 and 10:1. Among other techniques, we employ X-ray diffraction, nuclear magnetic resonance, and Raman spectroscopy to characterize the products. Within a narrow range of reactant ratios, we reproducibly find an unidentified, crystalline precursor phase related to isocyanuric acid next to ZnO. Finally, we complement our investigations by performing Prompt Gamma Activation Analysis (PGAA) on selected products in order to directly determine elemental bulk compositions and compare these with X-ray photoelectron spectroscopy (XPS) measurements. Our data show traces of nitrogen mainly on the surface of the particles, and thus we question the solution combustion method as a reliable synthesis toward N-doped ZnO. Furthermore, we exclude nitrogen as being responsible for the appearance of the four controversially discussed Raman bands superimposed onto the spectrum of pure ZnO (at 275, 510, 582, and 643 cm–1) and show that the combination of PGAA and XPS is an excellent and complementary method to obtain information about the distribution of the elements in question.