Nonthermal plasmas have emerged as a viable synthesis technique for nanocrystal materials. Inherently solvent and ligand-free, nonthermal plasmas offer the ability to synthesize high purity nanocrystals of materials that require high synthesis temperatures. The nonequilibrium environment in nonthermal plasmas has a number of attractive attributes: energetic surface reactions selectively heat the nanoparticles to temperatures that can strongly exceed the gas temperature; charging of nanoparticles through plasma electrons reduces or eliminates nanoparticle agglomeration; and the large difference between the chemical potentials of the gaseous growth species and the species bound to the nanoparticle surfaces facilitates nanocrystal doping. This paper reviews the state of the art in nonthermal plasma synthesis of nanocrystals. It discusses the fundamentals of nanocrystal formation in plasmas, reviews practical implementations of plasma reactors, surveys the materials that have been produced with nonthermal plasmas and surface chemistries that have been developed, and provides an overview of applications of plasma-synthesized nanocrystals.

This work discusses the recombination mechanisms and the chemical nature of the emitting centers subjacent to the white-light emission of sol−gel derived amine-functionalized hybrids lacking metal activator ions, such as those based on 3-aminopropyl)triethoxysilane (APTES), 3-glycidyloxypropyltrimethoxysilane (GPTES), and on urea and urethane precursors. The white-light photoluminescence (PL) results from a convolution of the emission originated in the NH (NH2) groups of the urea or urethane bridges (APTES- and GPTES-based hybrids) with electron−hole recombinations occurring in the siloxane nanoclusters. These two components reveal a radiative recombination mechanism typical of donor−acceptor pairs, mediated by some localized centers. Photoinduced proton-transfer between defects such as NH3 + and NH- (GPTES- and APTES-based hybrids) or NH2 + and N- (di-ureasils and di-urethanesils) is proposed as the mechanism responsible for the NH-related component. Electron paramagnetic resonance data suggest that the specific PL mechanism subjacent to the component associated with the siliceous nanodomains involves oxygen-related defects.

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