A facile method for the synthesis of crystalline and amorphous GeTe nanoparticles (NPs) using bis((trimethylsilyl)amido)germanium(II), Ge[N(SiMe3)2]2, and elemental tellurium dispersed in tri‐n‐octylphosphine (TOP) is reported. As synthesized, crystalline particles exhibit narrow dispersity at smaller sizes and tend to grow into anisotropic shapes with increasing reaction time (growth). Furthermore, crystalline GeTe NPs possess rhombohedral symmetry with absorption band energies in near IR region (0.76–0.86 eV). Amorphous GeTe particles prepared at low temperatures are nearly spherical in morphology and display amorphous‐to‐crystalline phase transition at 209–237 °C depending on their primary particle size. Detailed investigation of the local structure of the amorphous GeTe using pair distribution function (PDF) method reveals that it is closely related to that of the pressure‐ and temperature‐stabilized orthorhombic GeTe.
We demonstrate the synthesis of semiconductor Pb(2-x)Sn(x)S(2) nanocrystals with a cubic rock salt crystal structure in a composition range where this structure is unstable in the bulk. The cubic Pb(2-x)Sn(x)S(2) nanocrystals were prepared using a modified hot injection colloidal synthetic route. The x value is in the range 0.40 < x < 1. Even though these compositions lie in a region of the PbS-SnS phase diagram where no single phase exists, and despite the fact that PbSnS(2) is a distorted orthorhombic phase, the Pb(2-x)Sn(x)S(2) nanocrystals are single phase solid solutions with cubic NaCl-type structure. Experimental evidence for this derives from powder X-ray diffraction (PXRD), electron diffraction, and pair distribution function (PDF) analysis. Elemental compositions determined using scanning transmission electron microscopy/energy dispersive spectroscopy (STEM/EDS), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and electron energy loss spectroscopy (EELS) reveal a composition close to the nominal ones. The band gaps of the Pb(2-x)Sn(x)S(2) nanocrystals (0.52-0.57 eV) are blue-shifted by quantum confinement relative to that of the hypothetical cubic PbSnS(2) phase which density functional theory (DFT) calculations show to be much narrower (0.2 eV) than in the case of orthorhombic PbSnS(2) (1.1 eV). The Pb(2-x)Sn(x)S(2) nanocrystals exhibit a well-defined band gap in the near-IR region and are stable up to ~300 °C above which they phase separate into cubic PbS and orthorhombic α-SnS.
A series of novel rock-salt-type Pb(m)Sb(2n)Te(m+3n) nanocrystals (m = 2, 3, 4, 6, 8, and 10; n = 1 and 2) were successfully prepared using a colloidal synthesis route. These materials are stable only on the nanoscale and have no bulk analogues. Elemental compositions were determined using scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The nanocrystals exhibit well-defined band energies in the mid-IR region that are nearly independent of their atomic compositions. Pb(m)Sb(2n)Te(m+3n) nanocrystals behave as metastable homogeneous solid solutions at room temperature and tend to phase separate into the respective binary PbTe + Sb(2)Te(3) at 300 °C. Furthermore, pair distribution function (PDF) analysis suggests that the local structure of these Pb(m)Sb(2n)Te(m+3n) nanocrystals is distorted with respect to the rock-salt structure.
Calcination of aminopropylsilica spheres generates colloidal silica with tailorable luminescence properties depending on the calcination conditions. After calcining at 550°C for 20h, photoexcited luminescent colloidal silica exhibits a bright blue emission (λmax=375nm, 3.3eV) followed by a long-lifetime green photoluminescence centered around 500nm (2.5eV), which lasts for more than 10s at room temperature. Time resolved temperature studies indicate that the long-lifetime green photoluminescence can be fitted by a multiexponential decay function consisting of a regular exponential term and a stretched exponential term with a temperature independent beta parameter consistent with a hopping mechanism.
A series of Pb(m)Sb(2n)Se(m+3n) nanocrystals (m = 2, 4, 6 and 8; n = 1) are demonstrated that exist only as a distinct phase on the nanoscale. The nanocrystals aggregates are new compounds adopting the cubic NaCl-type structure. These materials form aggregates comprised of nanocrystallites that are attached at a preferred orientation. Elemental compositions were studied using the complementary techniques of scanning transmission electron microscopy/energy dispersive X-ray spectroscopy and inductively coupled plasma-atomic emission spectroscopy. The new ternary nanocrystal aggregates are moderately monodisperse and exhibit well-defined band gap energies in the mid-IR region. The Pb(m)Sb(2n)Se(m+3n) nanomaterials behave as homogeneous solid solutions with lattice parameter trending as a function of Sb incorporation at room temperature and tend to phase separate into PbSe and Sb2Se3 at 400 °C.
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