We report an investigation into the formation of Si x Ge 1−x alloy nanocrystals (64 < x < 100) synthesized from mixing GeI 2 :PR 3 adducts with hydrogen silsesquioxane (HSQ). The use of trialkylphosphine adducts allows GeI 2 and HSQ to be homogeneously coprecipitated, improving control over the size and composition of the resulting Si x Ge 1−x nanocrystals. This approach yields oxide-embedded and freestanding materials with near-infrared photoluminescence (PL) comparable in quantum efficiency to similarly prepared Si nanocrystals. The formation of bimodal populations of Si-rich and Gerich nanocrystals was observed, with homogeneous distribution of Ge within each population. Through changes to precursor stoichiometry and annealing temperature and time, control over particle size and composition was demonstrated. The impact of these factors on the near-IR PL was evaluated. We propose a multistep formation mechanism to account for the formation of separate Si-rich and Ge-rich populations and present indirect evidence for the participation of Ge in the emission process. Materials were analyzed using Fourier transform infrared spectroscopy, Raman spectroscopy, powder X-ray diffraction, PL spectroscopy, high-resolution transmission electron microscopy and spatially resolved energy-dispersive X-ray spectroscopy.

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Ge-Er):Stabilization of the β-Yb5Sb3-Type Structure Through Tetrel Substitution. -The title compounds are prepared by arc-melting stoichiometric mixtures of the elements with a 5-7 wt.% excess of Bi followed by annealing at 800°C for at least two weeks. Although none of the binary bismuthides Ln5Bi3 adopt the β-Yb5Sb3-type structure the title compounds crystallize with this structure type in the space group Pnma with Z = 4 (single crystal XRD on Ce5Si0.87Bi2.13 and powder XRD for Ce5GeBi2). Despite the partial mixing of Si or Ge and Bi atoms, the structure is essentially ordered. The Ce and Pr compounds undergo magnetic transitions at low temperatures, possibly involving ferromagnetic interactions. -(BARRY, S. D.; TKACHUK, A. V.; BIE, H.; BLANCHARD, P. E. R.; MAR*, A.; J. Solid State Chem. 184 (2011) 1, 21-29, http://dx.