Carbon nanotube (CNT) forests are known to be among the darkest materials on earth. They can absorb the entire visible range of electromagnetic wave more efficiently than any other known black material. We have attempted controlled mechanical processing of the CNTs and, surprisingly, observed mirror-like reflection from the processed area with 10%-15% reflectivity, a level higher than typical reflectivity of pure forests by over two orders of magnitude, for a wide range of the spectrum (570-1100 nm). Patterning of micro mirrors in the forest is demonstrated to show its potential application for producing monolithically integrated reflector-absorber arrays in the material. V

We report coupling of the excitonic photon emission from photoexcited PbSe colloidal quantum dots (QDs) into an optical circuit that was fabricated in a silicon-on-insulator wafer using a CMOS-compatible process. The coupling between excitons and sub-μm sized silicon channel waveguides was mediated by a photonic crystal microcavity. The intensity of the coupled light saturates rapidly with the optical excitation power. The saturation behaviour was quantitatively studied using an isolated photonic crystal cavity with PbSe QDs site-selectively located at the cavity mode antinode position. Saturation occurs when a few μW of continuous wave HeNe pump power excites the QDs with a Gaussian spot size of 2 μm. By comparing the results with a master equation analysis that rigorously accounts for the complex dielectric environment of the QD excitons, the saturation is attributed to ground state depletion due to a non-radiative exciton decay channel with a trap state lifetime ~ 3 μs.

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We consider a one dimensional model of an electron in a doubly (or nearly) degenerate band that interacts with elastic distortions. We show that the electron equations of motion reduce to a set of coupled non-linear Schrödinger equations. For the case of interband electron-phonon coupling stemming from local Jahn-Teller interactions, new multicomponent self-localized polaron solutions -vector polarons-are described and classified. The phase diagram for the different types of vector polarons in this model is presented. By interpreting the components of the orbital doublet as those of spin-1 2 , our results can also be used to describe bound magnetic polarons.

A kinetic model is derived and used to analyze recently published works and new data on the temperature dependence of the spectrally integrated photoluminescence (PL) from thick-film formulations of PbSe colloidal quantum dots (QDs), with particular attention to the effects of air exposure. The model assumes that the excitons thermalize within a ground-state manifold of states and treats the distribution of radiative and nonradiative decay rates within the distribution as generally as possible, while using a minimal number of free parameters. By adjusting the parameters of the model, good fits are obtained for the wide range of integrated PL behaviors reported in [J. Phys. Chem. Lett. 2, 889 (2011); ACS Nano 6, 5498 (2012); Phys. Rev. B 82, 165435 (2010)] and the new data presented in this manuscript. By comparing the extracted parameters we deduce the following: (i) All of the samples in the first two references emit from two distinct clusters of states separated by an energy of 55 to 80 meV regardless of air exposure, while there is only one cluster of emissive states that contributes to the emission reported in the third reference. (ii) In the absence of intentional air exposure, the nonradiative decay from all samples can be described by a single Arrhenius-like process. (iii) Although air-exposure effects are reversible in some samples and irreversible in others, the changes in integrated PL behavior brought about by air-exposure forces the introduction of a common, low-activation-energy nonradiative pathway in all cases.(iv) The low-lying emissive cluster of the two-emissive-cluster samples exhibits behavior similar to the single emissive cluster of the other samples. (v) Many hours of air exposure do not trend either the radiative or nonradiative behavior of the dual-emissive-cluster samples towards the behavior of the single-emissive-cluster samples.