Multi-photon excitation properties of CdSe quantum dots solutions and optical limiting behavior in infrared range.
ABSTRACT Multi-photon absorption and excitation properties of CdSe quantum dots in hexane with different dot-sizes have been investigated. The two- and three-photon absorption (2PA and 3PA) coefficients were measured by using ~160-fs laser pulses at wavelengths of ~775-nm and ~1300-nm, respectively. The dependence of one-, two- and three-photon induced fluorescence spectra as well as their double-exponential decay on the dot-sizes was studied. Based on the fluorescence emission spectra and temporal decay constants for a given sample solution excited by one-, two-and three-photon absorption, it can be concluded that the transition pathways for fluorescence emission and decay under one-, two- and three-photon excitation are nearly identical. The optical power limiting capabilities based on 2PA and 3PA mechanisms are demonstrated separately. In addition, a saturation behavior of 3PA at ~1300 nm was observed.
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ABSTRACT: Single crystal of 1-(2-Methyl-6-nitro-4-phenyl-3-quinolyl) ethanone was grown using slow evaporation solution growth technique. Single crystal X-ray diffraction study reveals the lattice parameters of the grown crystal. The modes of vibration of different molecular groups present in 2M6NQE were identified by FTIR spectral analysis. Its optical behavior was examined through UV-vis-NIR absorption and PL emission spectrum. They signify that the crystal has transparency in the region between 383 and 1100nm. The PL spectrum of the title compound shows green emission in the crystal. From the thermal analysis, 2M6NQE has found to be thermally stable up to 263°C, and the melting point of the material is 170°C. The estimations of third order non-linear optical properties like non-linear absorption coefficient (β), non-linear refractive index (n2) and susceptibility [χ((3))] were calculated using Z-scan technique. It has observed that, crystal exhibits reverse saturation absorption and self-defocusing performance. Etching study was carried out for the grown crystal using different solvents.Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 01/2014; 123. · 2.13 Impact Factor
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ABSTRACT: CdSe/CdS-Quantum-dots-quantum-rods (QDQRs) with an aspect ratio of ∼6 are prepared via the seeded growth method, encapsulated within a shell of crosslinked poly(isoprene)-block-poly(ethylene glycol) (PI-b-PEG) diblock copolymer, and transferred from the organic phase into aqueous media. Their photoluminescence quantum yield (PLQY) of 78% is not compromised by the phase transfer. Within a period of two months the PLQY of QDQRs in aqueous solution at neutral pH decreases only slightly (to ∼65%). The two-photon (TP) action cross sections of QDQRs (∼10(5) GM) are two orders of magnitude higher than those of CdSe/CdS/ZnS-core/shell/shell quantum dots (QDs, ∼10(3) GM) with comparable diameter (∼5 nm). After applying PI-b-PEG encapsulated QDQRs onto the small intestinal mucosa of mice in vivo, their strong red fluorescence can easily be observed by two-photon laser scanning microscopy (TPLSM) and clearly distinguished from autofluorescent background. Our results demonstrate that PI-b-PEG encapsulated CdSe/CdS-QDQRs are excellent probes for studying the uptake and fate of nanoparticles by two-photon imaging techniques in vivo.Nanoscale 07/2014; · 6.74 Impact Factor
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ABSTRACT: Small semiconductor nanoclusters are important for understanding the initial formation and growth of quantum dots and also for application, for example in the tunability provided by size. However, electronic structures and effects of capping ligands have not been systematically characterized. Thus, ground and excited state calculations using coupled-cluster methods were carried out to provide benchmarks for evaluating the applicability of density functional theory (DFT) and time-dependent DFT (TDDFT) with different functionals for the ground and excited states, respectively. Our computed data suggests that the popular B3LYP functional does not deliver optimal results for the ground and excited state. While the PBE0 functional was found to provide a good description for both the ground and excited states for small bare (ZnS)n and bare and ligated (CdSe)n clusters, the results for the hydrated (ZnS)n clusters were found to deteriorate significantly. However, the errors appear to decrease with increasing cluster size. Excitation energies obtained with the long-range hybrid CAM-B3LYP and CA-B3LYP were found to provide more consistent results for both anhydrous and hydrated (ZnS)n clusters. However, their performance in spectral predictions for larger clusters requires further study. Using PBE0, electronic structures of the ground and excited states for (ZnS)n and (CdSe)n up to n = 37 using DFT and TDDFT, respectively, were re-examined. With the exception of the cage–core (ZnS)13, (CdSe)13, and (CdSe)14, small (ZnS)n and (CdSe)n are predicted to be spheroids and tubular structures (6, 8–12, 15–19) with squares and hexagons, similar to the structures of carbon single-wall nanotubes. Wurtzite (n = 23–27, 36, 37) and cage–core (n = 29–35) structures are energetically more favorable for larger clusters. We find that water and amines increase the intensities and blue shift the excitations of bare clusters. One photon absorption spectra predicted by TDDFT with the PCM solvation model for (CdSe-methylamine)13 and the larger ligated (CdSe)33 are consistent with the experimental spectra.Journal of Chemical Theory and Computation 07/2013; 9(8):3581–3596. · 5.31 Impact Factor