Size-Dependent Extinction Coefficients of PbS Quantum Dots

Abstract

We report here on a detailed study on PbS colloidal quantum dots. A characterization via X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) allowed us to reliably determine the diameter and the shape of the nanocrystals. These data, together with second-derivative analysis of the absorption spectra, allowed us to determine the size dependence of seven transitions in the absorption spectrum; some of these transitions were identified on the basis of their normalized confinement energy. The size dependence of the first excitonic transition was best modeled by a four-band envelope approach which considers the anisotropy of the band edges (Andreev, A. D.; Lipovskii, A. A. Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 59, 15402-15404). The extinction coefficients were calculated using concentrations obtained from inductively coupled plasma atomic emission spectrometry (ICP-AES), and their size dependence was found to follow a power law with exponent equal to approximately 2.5. In contrast with what was expected from the effective mass approximation, the per particle absorption cross section of the lowest transition was found to be strongly dependent on the particle size.

Size-Dependent Optical Properties of Colloidal PbS Quantum Dots

“…Figure 2 shows that the data correspond well with those of Cademartiri et al 15 and Borrelli and Smith. 24 A fit to both our data and the experimental literature values yields the following result (size range fitted:…”

“…We determine the mean diam- Purity of the PbS Qdot Suspensions. In accordance with the procedure of Cademartiri et al, 15 samples are stored for several months to ensure that all traces of PbCl 2 (which is insoluble in apolar solvents) have precipitated. Hereafter, decantation separates the PbCl 2 from the suspension containing the Qdots, and a powder X-ray diffractogram is measured to determine whether PbCl 2 is still present.…”

Determination of particle size distribution of water-soluble CdTe quantum dots by optical spectroscopy

“…Actually, a prerequisite to any application of QDs is that the QD absorption, emission and size-distribution properties are quantitatively understood. In this sense, the size-dependent optical properties of CdTe, 32,33 CdSe, 32 CdS, 32 InAs, 34 and PbS 35 QDs have been previously reported. One of the most important physical features used to characterize synthesized colloidal QDs is determination of their average size and dispersion, which is generally, accomplished by high-resolution transmission electron microscopy (TEM).…”

Ultrasmall Conjugated Polymer Nanoparticles with High Specificity for Targeted Cancer Cell Imaging

“…As compared to molecular dye‐ligand conjugates, the multiple targeting ligands presented on NP surfaces allow multivalent recognition and binding to receptors on cell membrane, resulting in higher binding affinity and much improved selectivity toward targeted cells 9, 10, 11. With the rapid advances of nanotechnology, versatile NP systems including semiconducting quantum dots (QDs), gold NPs, and dye encapsulated NPs, etc., have been developed 12, 13, 14, 15, 16. Despite the fact that NPs with varied sizes have been designed for different biomedical applications,17, 18, 19 there has been limited success in highly selective cancer targeting, and only a few examples for inorganic gold NPs were reported 16, 20.…”