A detailed understanding of the photoluminescence (PL) from silicon nanocrystals (SiNCs) is convoluted by the complexity of the decay mechanism, including a stretched-exponential relaxation and the presence of both nanosecond and microsecond time scales. In this publication, we analyze the microsecond PL decay of size-resolved SiNC fractions in both full-spectrum (FS) and spectrally resolved (SR) configurations, where the stretching exponent and lifetime are used to deduce a probability distribution function (PDF) of decay rates. For the PL decay measured at peak emission, we find a systematic shift and narrowing of the PDF in comparison to the FS measurements. In a similar fashion, we resolve the PL lifetime of the ‘blue’, ‘peak’, and ‘red’ regions of the spectrum and map PL decays of different photon energy onto their corresponding location in the PDF. A general trend is observed where higher and lower photon energies are correlated with shorter and longer lifetimes, respectively, which we relate to the PL line width and electron-phonon coupling.

Rapid bulk assembly of nanoparticles into microstructures is challenging, but highly desirable for applications in controlled release, catalysis, and sensing. We report a method to form hollow microstructures via a two-stage nematic nucleation process, generating size-tunable closed-cell foams, spherical shells, and tubular networks composed of closely packed nanoparticles. Mesogen-modified nanoparticles are dispersed in liquid crystal above the nematic-isotropic transition temperature (TNI). On cooling through TNI, nanoparticles first segregate into shrinking isotropic domains where they locally depress the transition temperature. On further cooling, nematic domains nucleate inside the nanoparticle-rich isotropic domains, driving formation of hollow nanoparticle assemblies. Structural differentiation is controlled by nanoparticle density and cooling rate. Cahn-Hilliard simulations of phase separation in liquid crystal demonstrate qualitatively that partitioning of nanoparticles into isolated domains is strongly affected by cooling rate, supporting experimental observations that cooling rate controls aggregate size. Microscopy suggests the number and size of internal voids is controlled by second-stage nucleation.

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Liquid crystal (LC) phase transition dynamics can be used as a powerful tool to control the assembly of dispersed nanoparticles. Tailored mesogenic ligands can both enhance and tune particle dispersion in the liquid crystal phase to create liquid crystal nano-composites-a novel type of material. Soft nanocomposites have recently risen to prominence for their potential usage in a variety of industrial applications such as photovoltaics, photonic materials, and the liquid crystal laser. Our group has developed a novel phase-transition-templating process for the generation of micron-scale, vesicle-like nanoparticle shells stabilized by mesogenic ligand-ligand interactions. The mesogenic ligand's flexible arm structure enhances ligand alignment with the local LC director, providing control over the dispersion and stabilization of nanoparticles in liquid crystal phases. In this paper we explore the capsule formation process in detail, generating QDbased capsules over a surprisingly wide range of radii. We demonstrate that the initial nanoparticle concentration and cooling rate are important parameters influencing capsule size. By increasing particle concentration of nanoparticles and reducing the cooling rate we developed large shells up to 96±19 μm in diameter whereas decreasing concentration and increasing the cooling rate produces shells as small as 4±1 μm.

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