•Bound-free transitions determine the binding energy of the {1,1}He2···I35Cl complex.•The He atom dissociates more rapidly from a delocalized state than a T-shaped state.•When {1,1}He2···ICl dissociates, 3.5% of the energy goes into ICl rotation.The dissociation dynamics of He2···I35Cl complexes prepared with varying amounts of intermolecular vibrational excitation within the 2He + I35Cl(B,v′ = 3) potential energy surface are reported. For the intermolecular level associated with one He atom in an energetically excited, delocalized state and the other localized in the lowest-energy, T-shaped potential minimum, the higher-energy He atom dissociates preferentially. The binding energy of the ground-state He2···I35Cl(X,v″ = 0) conformer with a police nightstick geometry (one He atom in the T-shaped minimum and the second in the linear well) is measured to be 38.6(9) cm–1.

The photoluminescence (PL) intensity of semiconductor quantum dots (QDs) is routinely monitored to track the chemical and physical properties within a sample or device incorporating the QDs. A dependence of the PL quantum yields (QYs) on the excitation energy could lead to erroneous conclusions but is commonly not considered. We summarize previous evidence and present results from two methodologies that confirm the possibility of a dependence of the PL QYs on the excitation energy. The data presented indicate that PL QYs of CdSe and CdSe/ZnS QDs suspended in toluene are highest for excitation just above the band gap, Eg, of each. The PL QYs decrease with increasing excitation energies up to 1 eV above Eg. The PL intensity decay profiles recorded for these samples at varying emission and excitation energies indicate that the changes in the PL QYs result from the nonradiative relaxation pathways sampled as the charge carriers relax down to the band edge.

Colloidal CdTe quantum wires are reported having ensemble photoluminescence efficiencies as high as 25% under low excitation-power densities. High photoluminescence efficiencies are achieved by formation of a monolayer CdS shell on the CdTe quantum wires. Like other semiconductor nanowires, the CdTe quantum wires may contain frequent wurtzite–zinc-blende structural alternations along their lengths. The present results demonstrate that the optical properties, emission-peak shape and photoluminescence efficiencies, are independent of the presence or absence of such structural alternations.

Photogenerated electron–hole pairs are observed to be bound as 1D excitons in CdSe quantum wires (QWs) at room temperature. Microscopy experiments performed on dilute samples of CdSe QWs prepared on coverslips with patterned electrodes reveal that there is no change in either the overall photoluminescence (PL) intensity or the distribution of the PL intensity with the application of an external electric field. Changes in the PL intensity, and thus evidence for separate charge carriers within the QWs, are observed only for concentrated samples. In these concentrated samples, a thin film of other compounds, including trioctylphosphine oxide and a bismuth salt formed in the synthesis, is observed to encompass the QWs. The separate charge carriers that influence the PL intensity are attributed to the other compounds in the sample.Keywords: 1D excitons; bound electron−hole pairs; CdSe; excitons; quantum wires; semiconductor nanomaterials;

Two-laser, action spectroscopy experiments have been performed in the I2B–X, υ′–0 spectral region on H2···I2 and D2···I2 complexes to investigate the dependence of the H2/D2 + I2 intermolecular interactions on orientation. The spectra contain features associated with at least two different conformers of the ground-state H2/D2···I2(X,υ′′ = 0) complexes; one conformer has a preferred T-shaped geometry with the H2/D2 moiety localized in a potential minimum that is orthogonal to the I—I bond axis, and the second conformer has a linear geometry with the H2/D2 moiety positioned in minima at either end of the I2 molecule, along the bond axis. Those features associated with complexes containing para-H2(j = 0), ortho-H2(j = 1), ortho-D2(j = 0), and para-D2(j = 1) are also assigned. The linear conformers are found to be more strongly bound than the T-shaped conformers with binding energies of 118.9(1.9) cm–1 versus 91.3–93.3 cm–1 for the ortho-H2···I2 complexes and 144.2(2.1) cm–1 versus 107.9 cm–1 for the para-D2···I2 complexes, respectively. Electronic structure calculations of the complexes containing ICl and I2 with H2, He, Ne, and Ar were performed to reveal the nature of the interactions and to shed insight into the origins of the different binding energies. The most stable minima in the H2/D2 + I2(B,υ′) excited-state potentials have T-shaped geometries. Calculated energies and probability amplitudes of the excited-state levels provide insight into the different excited-state intermolecular vibrational levels accessed by transitions of the two ground-state conformers.

CdSe quantum belts (QBs) having lengths of 0.5−1.5 μm and thicknesses of 1.5−2.0 nm exhibit high photoluminescence (PL) efficiencies of ∼30%. Epifluorescence studies establish the PL spectra to be uniform along single QBs, and nearly the same from QB to QB. Photogenerated excitons are shown to be effectively delocalized over the entire QBs by position-selective excitation. Decoration of the QBs with gold nanoparticles indicates a low density of surface-trap sites, located primarily on the thin belt edges. The high PL efficiencies and effective exciton delocalization are attributed to the minimization of defective {11̅00} edge surface area or edge-top/bottom (face) line junctions in QBs relative to quantum wires having roughly isotropic cross sections, for which very low PL quantum efficiencies have been reported. The results suggest that trap sites can be minimized in pseudo-one-dimensional nanocrystals, such that the facile transport of energy and charge along their long axes becomes possible.

Laser-induced fluorescence and action spectroscopy experiments have identified multiple conformers of the D2···ICl van der Waals complex for both ortho-D2 (o-D2) and para-D2 (p-D2). As with the analogous H2···ICl van der Waals complexes [Darr, J. P.; Crowther, A. C.; Loomis, R. A.; Ray, S. E.; McCoy, A. B. J. Phys. Chem. A2007, 111, 13387], the C2v conformer with the deuterium molecule localized at the iodine atom end of the dihalogen is significantly more stable than the asymmetric conformer that has the deuterium positioned orthogonally to the ICl bond axis, D0′′ = 223.9(2.4) versus 97.3(8)−103.9(3) cm−1 for p-D2···I35Cl(X,v′′=0). For both conformers, complexes containing p-D2 are found to be more strongly bound than those with o-D2. The electronically excited D2···ICl(A,v′) and D2···ICl(B,v′) complexes are found to have equilibrium geometries that are nearly the same as those of the ground-state asymmetric structures. Calculated D2···ICl(B,v′=3) energies and probability amplitudes obtained using a simple scaled He + ICl(B,v′=3) potential provide clues to the nature of the different excited-state levels accessed.

Rovibronic transitions of multiple conformers of the He2···79Br2(X, v′′ = 0), He3···79Br2(X, v′′ = 0), He2···I35Cl(X, v′′ = 0), and He3···I35Cl(X, v′′ = 0) complexes stabilized in a pulsed, supersonic expansion are observed in action spectra recorded in the B−X region of the dihalogens. In addition to features associated with He2···79Br2 and He2···I35Cl complexes with the rare gas atoms localized in the toroidal potential well lying in a plane perpendicular to the dihalogen bond, those associated with a ground-state conformer that has one He atom localized in the toroidal potential and the other He atom localized in the linear well at the end of the dihalogen moiety are also identified. Transitions of at least three conformers of the He3···Br2 complex and two conformers of the He3···ICl complex are also observed. The relative populations of the different conformers are found to depend on where along the supersonic expansion the spectra are recorded, and thus on the local temperature regime sampled. The He2···79Br2 and He2···I35Cl conformers with one He atom in each well are found to be the more stable conformers.