Identification of a Telecom Wavelength Single Photon Emitter in Silicon.

We identify the exact microscopic structure of the G photoluminescence center in silicon by first-principles calculations with including a self-consistent many-body perturbation method, which is a telecommunication wavelength single photon source. The defect constitutes of C_{s}C_{i} carbon impurities in its C_{s}─Si_{i}─C_{s} configuration in the neutral charge state, where s and i stand for the respective substitutional and interstitial positions in the Si lattice. We reveal that the observed fine structure of its optical signals originates from the athermal rotational reorientation of the defect. We attribute the monoclinic symmetry reported in optically detected magnetic resonance measurements to the reduced tunneling rate at very low temperatures. We discuss the thermally activated motional averaging of the defect properties and the nature of the qubit state.

Photoluminescence, infrared, and Raman spectra of co-doped Si nanoparticles from first principles.

Co-doped silicon nanoparticles (NPs) are promising for the realization of novel biological and optoelectronic applications. Despite the scientific and technological interest, the structure of heavily co-doped Si NPs is still not very well understood. By means of first principles simulations, various spectroscopic quantities can be computed and compared to the corresponding experimental data. In this paper, we demonstrate that the calculated infrared spectra, photoluminescence spectra, and Raman spectra can provide valuable insights into the atomistic structure of co-doped Si NPs.

Computational design of in vivo biomarkers.

Fluorescent semiconductor nanocrystals (or quantum dots) are very promising agents for bioimaging applications because their optical properties are superior compared to those of conventional organic dyes. However, not all the properties of these quantum dots suit the stringent criteria of in vivo applications, i.e. their employment in living organisms that might be of importance in therapy and medicine. In our review, we first summarize the properties of an 'ideal' biomarker needed for in vivo applications. Despite recent efforts, no such hand-made fluorescent quantum dot exists that may be considered as 'ideal' in this respect. We propose that ab initio atomistic simulations with predictive power can be used to design 'ideal' in vivo fluorescent semiconductor nanoparticles. We briefly review such ab initio methods that can be applied to calculate the electronic and optical properties of very small nanocrystals, with extra emphasis on density functional theory (DFT) and time-dependent DFT which are the most suitable approaches for the description of these systems. Finally, we present our recent results on this topic where we investigated the applicability of nanodiamonds and silicon carbide nanocrystals for in vivo bioimaging.

Near-infrared luminescent cubic silicon carbide nanocrystals for in vivo biomarker applications: an ab initio study.

Molecule-sized fluorescent emitters are much sought-after to probe biomolecules in living cells. We demonstrate here by time-dependent density functional calculations that the experimentally achievable 1-2 nm sized silicon carbide nanocrystals can emit light in the near-infrared region after introducing appropriate color centers in them. These near-infrared luminescent silicon carbide nanocrystals may act as ideal fluorophores for in vivo bioimaging.