Silicon nanocrystals (NCs) represent one of the most promising material systems for light emission applications in microphotonics. In recent years, several groups have reported on the observation of optical gain or stimulated emission in silicon NCs or in porous silicon (PSi). These results suggest that silicon-NC-based waveguide amplifiers or silicon lasers are achievable. However, in order to obtain clear and reproducible evidence of stimulated emission, it is necessary to understand the physical mechanisms at work in the light emission process. In this paper, we report on the detailed theoretical aspects of the energy levels and recombination rates in doped and undoped Si NCs, and we discuss the effects of energy transfer mechanisms. The theoretical calculations are extended toward computational simulations of ensembles of interacting nanocrystals. We will show that inhomogeneous broadening and energy transfer remain significant problems that must be overcome in order to improve the gain profile and to minimize nonradiative effects. Finally, we suggest means by which these objectives may be achieved.

Luminescent silicon nanocrystals (Si-NCs) surface functionalized with dodecyl groups were exposed to solutions of nitroaromatic compounds including nitrobenzene, nitrotoluene, and dinitrotoluene. It was found that Si-NC luminescence was quenched upon exposure to nitroaromatics via an electron transfer mechanism as indicated by Stern-Volmer analysis. This quenching was exploited and a straightforward paper-based Si-NC sensor was developed. This paper motif was found to be sensitive to solution, vapor, and solid phase nitroaromatics, as well as solution borne RDX and PETN.

Silicon nanocrystals (SiNCs) have received much attention because of their exquisitely tunable photoluminescent response, biocompatibility, and the promise that they may supplant their CdSe quantum dot counterparts in many practical applications. One attractive strategy that promises to extend and even enhance the utility of SiNCs is their incorporation into NC/polymer hybrids. Unfortunately, methods employed to prepare hybrid materials of this type from traditional compound semiconductor (e.g., CdSe) quantum dots are not directly transferable to SiNCs because of stark differences in surface chemistry. Herein, the preparation of chemically resistant SiNC/polystyrene hybrids exhibiting exquisitely tunable photoluminescence is reported and material processability is demonstrated by preparing micro and nanoscale architectures.

Silicon nanocrystals are of interest in the nascent field of silicon microphotonics, with potential applications as waveguide amplifiers, light-emitting diodes, and silicon-based lasers. Comparing computational simulations and experiment, it is shown that nonresonant carrier tunneling in ensembles of silicon nanocrystals is a controlling factor in the luminescence. In thin film silicon nanocrystal composites, only the larger particles can be luminescent as a result of rapid carrier tunneling, suggesting that these applications may only be achieved for well-isolated nanocrystals or for arrays with a narrow distribution of sizes.

Silicon quantum dots (Si-QDs) represent a well-known QD fluorophore that can emit throughout the visible spectrum depending on the interface structure and surface functional group. Detection of nitroaromatic compounds by monitoring the luminescence response of the sensor material (typically fluorescent polymers) currently forms the basis of new explosives sensing technologies. Freestanding silicon QDs may represent a benign alternative with a high degree of chemical and physical versatility. Here, we investigate dodecyl and amine-terminated Si-QD luminescence response to the presence of nitrobenzene and dinitrotoluene (DNT) in various solid, solution, and vapor forms. For dinitrotoluene vapor the 3σ detection limit was 6 ppb for monomer-terminated QDs. For nitroaromatics dissolved in toluene the detection limit was on the order of 400 nM, corresponding to ∼100 pg of material distributed over ∼1 cm(2) on the sensor surface. Solid traces of nitroaromatics were also easily detectable via a simple 'touch test'. The samples showed minimal interference effects from common contaminants such as water, ethanol, and acetonitrile. The sensor can be as simple and inexpensive as a small circle of filter paper dipped into a QD solution, with a single vial of QDs able to make hundreds of these sensors. Additionally, a trial fiber-optic sensor device was tested by applying the QDs to one end of a 2 × 2 fiber coupler and exposing them to controlled DNT vapor. Finally, the quenching mechanism was explored via luminescence dynamics measurements and is different for blue (amine) and red (dodecyl) fluorescent silicon QDs.