C.M Mo

ENHANCEMENT EFFECT OF PHOTOLUMINESCENCE IN ASSEMBLIES OF NANO-ZNO PARTICLES/SILICA AEROGELS

SiO2 aerogels were prepared by a sol-gel method and supercritical drying. Introduction of nano-ZnO into nanopores of the SiO2 aerogels is performed by immersion, chemical reaction, and hydrolysis. Photoluminescence of these assemblies of nano-ZnO particles/SiO2 aerogels were systematically measured. For each assembly, a very strong photoluminescence (PL) band with the peak position of about 500 nm was observed. The luminescence intensities of the assemblies of nano-ZnO particles/SiO2 aerogels are 10–50 times higher than that of nanostructured ZnO bulks. The quantum efficiency of the PL band for the assemblies is in the range of 0.2%–1%. This luminescence enhancement effect is caused by the increase of the singly ionized oxygen vacancies in nano-ZnO particles, which are located in nanopores of the SiO2 aerogel.

Luminescence in nanostructured materials

Abstract Some new photoluminescence phenomena, which have not been observed for conventional coarse grain materials, are reported for nanostructured materials,such as nanostructured η,γ-Al 2 O 8 , boehmite, TiO 2 ( anatase), and amorphous silicon nitride. In this article we discussed the mechanisms of these new luminescence phenomena appearing in nanostructured materials in terms of quantum confinement effect, impurity and defect energy levels in the energy gap and destruction of selection rules of electronic transitions.

Infrared absorption spectra of nano-alumina

Abstract The infrared absorption spectra of both nanostructured Al 2 O 3 bulk and nano-Al 2 O 3 powders with different original particle diameters after heat treatment at different temperatures were measured. The infrared absorption spectrum of nano-Al 2 O 3 (ν and γ phases) powder possesses a very broad band in the wavenumber range from 500 to 850 cm −1 and that of the nano-Al 2 O 3 powder exhibits characteristic bands of α-phase; at the same time, two strong infrared forbidden modes are observed for α-phase. The infrared spectrum of the nanostructured Al 2 O 3 bulk shows a very broad and flat band without fine structure in the wavenumber range from 400 to 1000 cm −1 , and this spectrum remains unchanged after heat treatment at different temperatures for 4 h.

Preparation and optical absorption of dispersions of nano-TiO2/MMA (methylmethacrylate) and nano-TiO2/PMMA (polymethylmethacrylate)

Dispersions of oleic acid coated nano-TiO2 particles/MMA and oleic acid coated nano-TiO2 particles/PMMA were prepared. Their optical absorption was systematically investigated. Results showed that the optical absorption is closely associated with the TiO2 concentration in the dispersion. When the TiO2 concentration (C0) ≤ 0.032 mol%, dispersions of the oleic acid coated TiO2/MMA did not precipitate after several weeks, and the diameters of TiO2 particles were very small (5–10 or 30 nm). For C0 > 0.032 mol%, the diameters of the particles ranged in two size distributions: 5–10 or 30 nm and 50–80 or 180 nm. Nano-TiO2 particles in dispersions gave rise to ultraviolet (UV) absorption. For C0 ≤ 0.032 mol%, only one UV absorption band was observed, while for C0 > 0.032 mol%, the absorption band was split into two bands. During polymerization of the dispersion of oleic acid coated nano-TiO2 particles/MMA, the absorption band showed a red shift. These red shifts were due to the oleic acid coating on the TiO2 particles. The origin of the absorption band and the mechanisms of the red shifts of the absorption band are discussed in detail.

Synthesis of “A β-SiC nanorod within a SiO2 nanorod” one dimensional composite nanostructures

Abstract “A β-SiC nanorod within a SiO 2 nanorod” one dimensional composite nanostructures were synthesized by the combination of a low temperature (1650°C) carbothermal reduction and a high temperature (1800°C) heating of sol-gel derived silica xerogels containing carbon nanoparticles. The composite nanostructures are more than 20 μm in length. The diameters of the center thinner β-SiC nanorods are typically in the range 10–30 nm, while the outside diameters of the corresponding thicker amorphous SiO 2 nanorods are between 20 and 70 nm. Large quantities of SiC rod nuclei and the nanometer-sized nucleus sites on carbon nanoparticles are both favor-able to the formation of much thinner β-SiC nanorods. The formation of the outer coaxial thicker amorphous SiO 2 nanorods is from the combination reaction of decomposed SiO vapor and O 2 during cooling.

Photoluminescence enhancement of ZnO nanocrystallites with BN capsules

This paper describes the photoluminescence (PL) properties of ZnO nanoparticles with BN capsules (ZnO/BN core/shell structure). PL enhancement of over one thousand of ZnO/BN to ZnO nanoparticles was observed, which has been attributed to the dielectric environment effects of the capsule on the interfacial structures and defect amounts of ZnO quantum dots (QDs).

Optical absorption of nanostructured Al2O3

Abstract Optical absorption of nanostructured Al 2 O 3 was investigated. Results are as follows: (1) when the annealing temperature, Ta 1100 °C, six absorption bands appear in the reflection spectrum. The appearance of the pronounced absorption bands with peak energies of 6.0 ev, ~ 55 ev, 4.8 ev, 3.75 ev and 3.05 ev, respectively, demonstrates that a large number of color centers exist in nanostructured Al 2 O 3 , including the F + center, the v-type center (V 2− , V − and V oH- centers) and the Cr 3+ impurity center and others.

A study on growth and crystallization behavior of nanostructured amorphous silicon nitride

Abstract For the first time, the growth and crystallization behavior in nanostructured amorphous silicon nitride (NASN) were systematically studied. NASN has excellent thermal stability below 1300°C, i.e. NASN does not grow below 1300°C. However, as soon as crystallization occurs the particles suddenly grow. This may be related to an interfacial effect in the NASN pellet. The relationship between growth and crystallization behavior is discussed.

β-SiC nanorods with uniform amorphous SiO2 wrappers on the outside surface

Abstract Large quantities of β-SiC nanorods with uniform amorphous SiO2 wrappers were synthesized by carbothermal reduction of silica xerogel pieces with carbon nanoparticles embedded in the network. Powder X-ray diffraction (XRD) and infrared (IR) results confirmed the formation of β-SiC and SiO2. Low-magnification transmission electron microscopy (TEM) results showed that the nanorods were typically more than 20 μm in length. High-magnification TEM and high-resolution electron microscopy (HREM) indicated that the β-SiC nanorods (with typical diameters of 14 ± 6 nm) were wrapped in amorphous SiO2 layers (with typical outside diameters of 45 ± 25 nm).

Relationship between optical transmittance and microstructure of nanostructured alumina films

Abstract Nanostructured boehmite and Al2O3 films were prepared by the sol-gel route. Microstructural features, such as phase content, grain orientation and grain diameter, were observed. The relationship between the transmittance in the visible to near infrared range and the film microstructure is discussed.