Fluorescence Spectrum Of Quantum Dots Research Articles

Microwave-Prepared Quantum Dots and Their Potential Applications as Adsorbents and Chemosensors.

A combination of different eco-friendly materials prepared promising fluorescent quantum dots (QDs) through the one-step process using the microwave heating of urea with cellulose, chitosan, and biochar. Characterizations of the prepared QDs, including the investigation of their structure by infrared spectroscopy, Raman analysis, X-ray diffraction, thermal gravimetric analysis, morphology, and optical properties, were performed. The results showed that QDs possess a small size, high UV absorption, and excitation wavelength-dependent fluorescence. The prepared QDs were also tested for metal ions removal from aqueous solutions. The adsorption at different contact times was investigated to optimize the adsorption efficiency of the prepared QDs. All QDs were found to be an ideal sorbent for Cr(II), Cu(II), Mn(II), and Pb(II). From the data, Cr(II) was more highly adsorbed than other metal ions. The results of the kinetic investigation showed that the pseudo-second-order kinetic model fit the adsorption process effectively. In addition, the fluorescence spectra of QDs were changed after the adsorption of metal ions; hence, the prepared QDs could be utilized in environmental sectors such as wastewater pollution detection, adsorption, and chemical sensing applications.

A global method for handling fluorescence spectra at high concentration derived from the competition between emission and absorption of colloidal CdTe quantum dots.

We investigate the effects of the concentration of CdTe quantum dots (QDs) on their fluorescence in water. The emission spectra, acquired in right angle geometry, exhibit highly variable shapes. The measurements evidence a critical value of the concentration beyond which the intensity and the spectral bandwidth decrease and the fluorescence maximum is redshifted. To account for these observations, we develop a model based on the primary and secondary inner filter effects. The accuracy of the model ensures that the concentration dependent behaviour of QD fluorescence is completely due to inner filter effects. This result is all the more interesting because it precludes the assumption of dynamic quenching. As a matter of fact, the decrease of the emission intensity is not a consequence of collisional quenching but an effect of competition between fluorescence and absorption. We even show that this phenomenon is linked not only to the QD concentration but also to the geometric configuration of the setup. Hence, our analytical model can be easily adapted to every fluorescence spectroscopy configuration to quantitatively predict or correct inner filter effects in the case of QDs or any fluorophore, and thus improve the handling of fluorescence spectroscopy for highly concentrated solutions.

Optical Properties of Planar Nanostructures Based on Semiconductor Quantum Dots and Plasmonic Metal Nanoparticles

The optical properties of a composite material consisting of a thin polymer film, which is activated by semiconductor CdSe/ZnS quantum dots (QDs) and silver nanoparticles, on a transparent dielectric substrate have been investigated. It is revealed that the presence of silver nanoparticles leads to an increase in the QD absorption (by a factor of 4) and in the fluorescence intensity (by a factor of 10), whereas the fluorescence time drops by a factor of about 10. Excitation of the composite medium by a pulsed laser is found to result in narrowing of the fluorescence band and a sublinear dependence of its intensity on the pulse energy. In the absence of silver nanoparticles, the fluorescence spectrum of QDs is independent of the excitation-pulse energy density, and the fluorescence intensity depends linearly on the pulse energy in the entire range of energy densities, up to 75 mJ/cm2.

Complexes of functionalized quantum dots and chlorin e<sub>6</sub> in photodynamic therapy

Recently, it has been suggested that quantum dots (QDs) could be used in the photodynamic therapy of cancer as resonance energy donors for conventional porphyrin type photosensitizers. Here we present the results of the spectroscopic studies on the formation of a non-covalent complex between QDs and photosensitizer chlorin Ce6 in an aqueous medium and in the presence of bovine serum albumin (BSA). Changes in the absorption and fluorescence spectra of QDs and Ce6 revealed the formation of a QD-Ce6 complex which occurs due to hydrophobic interaction between the nonpolar moiety of an amphiphilic photosensitizer and the hydrophobic part of the lipid-based coating of the QD. The photosensitizer conjugated with the QD could be indirectly excited by the Forster resonance energy transfer (FRET) from the QD to Ce6. The investigation on the capacity of such complex to generate 1O2 showed that the QD-Ce6 complex irradiated by visible light is able to produce 1O2 more efficiently than QDs or Ce6 taken separately. The photoinactivation of cells incubated with the QD-Ce6 complex and irradiated in the spectral region where the photosensitizer does not absorb provided evidence that such complex could induce FRET-mediated cell destruction.