There has been much recent interest in the study of superluminal pulse propagation; however, all previous findings have been extremely limited, only observing superluminal group velocities for simple Gaussian-like pulses. We now report the observation of a superluminal time advance for a complex, broadband signal. Such an advance causes all frequency components and envelopes to appear to exit a circuit 0.078±0.004ms before entering it. Although this may seem counterintuitive, the results are not in conflict with relativistic causality and could lead to many useful devices.

Upconverted lasing in the nonlinear, two-photon absorption regime has been demonstrated, for the first time to the best of our knowledge in colloidal nanocrystal quantum dots (NQDs). Upon pulse excitation at sub-bandgap photon energies the radiative recombination of excitons in close-packed CdSe/CdS/ZnS core-shell NQDs was found to be sufficiently fast to compete with the intrinsic nonradiative Auger recombination, as confirmed by the presence of a fast decay (approximately 7 ps) in the time-resolved photoluminescence.

We report a derivation of the 4×4 Luttinger valence band and Bir–Pikus strain Hamiltonians valid for any [11l]-oriented epilayers. It is shown that epitaxial layers grown on substrates oriented in certain of the [11l] directions exhibit anisotropic optical transition matrix elements. This anisotropy is predicted to have its maximum for the (110) surface. For pseudomorphic epitaxial layers, calculations indicate that the zone center band gap of these structures is changed due to the effects of strain, with the largest changes occurring for those structures grown on the (111) surface.

PbSe quantum dot light emitting diodes (QD-LEDs) of a multi-layer architecture are reported in the present work to exhibit high external quantum efficiencies. In these devices, a ligand replacement technique was employed to activate PbSe QDs, and ZnO nanoparticles were used for the electron transport layer. The emission wavelength of this solution processed device is QD size tunable over a broad spectral range, and an LED efficiency of 0.73% was measured at 1412 nm. Higher efficiencies at longer wavelengths are also inferred from spectral characterization.

We present in this communication a hybrid polymer/nanocrystal photovoltaic device architecture wherein a net poly(3-hexylthiophene) (P3HT) light-absorbing film is inserted underneath the blended layer of P3HT and PbSe nanocrystal quantum dots in the active region. Such a design features the vertical integration of planar and bulk heterojunctions, which allows for the employment of a thinner bulk heterojunction for more efficient carrier collection without an excessive reduction of the overall light absorption by the photovoltaic cell. The measured device performance represents a significant improvement over previously reported hybrid cells containing bulk heterojunctions of P3HT and Pb(S,Se) nanocrystal quantum dots.