The luminescent properties of SiOx ranging in composition between x=0 and x=2 are presented. Luminescence in the SiOx system is found to be tunable across the full visible spectrum and into the near infrared. The data are used to generate an emission color map for the complete SiOx system. At the lower annealing temperatures, several lines of evidence suggest that the luminescence is due to the presence of amorphous silicon nanoclusters, whereas for higher annealing temperatures the emission is dominated by silicon nanocrystals.

We adapt a variational procedure to calculate ground-state properties of the Holstein model in the adiabatic limit. At strong coupling, this adaption leads to rapid convergence of results. The intermediate coupling regime is further handled with an adaptive algorithm. We also use semiclassically derived results for the adiabatic end point, along with weak coupling perturbation theory. These establish weak and strong coupling ͑or large and small polaron, respectively͒ regimes in two dimensions or higher. As is well known, these are connected smoothly, but the crossover becomes increasingly abrupt as the phonon frequency decreases.

Wavelength tunability is a key aspect for light-emitting materials, and is one of the critical properties driving research on semiconductor quantum dots [1] and organic microcavity devices.[2] Narrow and well-defined emission spectra are important with respect to the development of optical displays, optical amplifiers, light-emitting diodes, and ªtunableº quantum dot lasers. [3] Silicon-based light emitters, in particular, represent a key technology that may challenge the bottlenecks currently facing the microelectronics industry; [4] however, widely tunable and spectrally narrow ªquantum-dot-likeº emission has remained problematic. Here, we demonstrate that siliconrich oxide can be processed at temperatures compatible with silicon microelectronics, while at the same time, the emission wavelength can be tuned throughout the visible spectrum and extended to the fiber-optic transparency windows in the near infrared. This approach covers most of the 0.4 to 1.6 lm wavelength range needed for silicon-based photonics, [4] produces the widest spectral tunability achieved for any single material, and presents an attractive silicon-based alternative to quantum dot or microcavity organic light-emitting materials for photonic applications. Silicon nanocrystal composites are currently the focus of the intense international research efforts that may foreshadow the ªoptical age of siliconº.[5] These efforts are driven by potential photonic applications of silicon-based materials in light-emitting diodes (see, for example, the work of Valenta and co-workers [6] ), nanocrystal lasers, [7,8] and erbium-doped waveguide amplifiers (see, for example, the work of Franzò and co-workers [9] ). Silicon nanocrystal composites represent one of the best hopes for photon creation and transmission in next-generation optical interconnects.[4] Silicon nanocrystals in SiO 2 have a broad luminescence band centered in the near infrared, with a photoluminescence quantum efficiency several orders of magnitude higher than that of bulk silicon.[10]When placed within a distributed Bragg reflector (DBR) structure, the emission is intensified and spectrally narrowed, [11,12] although it is still within the 700±900 nm range characteristic of the natural emission. Nevertheless, this type of fine wavelength control is of recognized importance with respect to luminescent devices. [8] A simpler microcavity consisting of a bottom dielectric stack and a top silver mirror was recently used for a silicon nanocomposite, [13] but wavelength tunability was not demonstrated and the optical modes were broad. One of the main drawbacks with respect to device integration is the high processing temperature (generally at least 1000 C) required to form luminescent silicon nanoparticles via phase separation of a material with excess atomic silicon. Such high temperatures are incompatible with CMOS (complementary metal oxide semiconductor) technology [14] and, from the point of view of DBRs, make the fabrication of devices based on these materials more difficult, ...

We examine the impact of a complex absorbing potential on electron transport both in the continuum and on a lattice. This requires the use of non-Hermitian Hamiltonians; the required formalism is briefly outlined. The lattice formulation allows us to study the interesting problem of an electron interacting with a stationary spin and the subsequent time evolution of the electron and spin properties as the electron is absorbed after the initial interaction. Remarkably, the properties of the localized spin are affected "at a distance" by the interaction of the ͑now entangled͒ electron with a complex potential.