Size-dependent optical properties of SnO2 nanoparticles prepared by soft chemical technique.

SnO2 nanoparticles with uniform size and well crystallinity were prepared by using soft chemical technique. Surfactant was used to control the growth and agglomeration of the SnO2 nanoparticles. X-ray diffraction patterns and transmission electron microscopy were used to characterize the structures of SnO2 nanoparticles before and after thermal annealing. It is found that the size of SnO2 nanoparticles can be controlled by changing the preparation parameters and post-thermal annealing temperatures (400 degrees C-1000 degrees C). The optical band gap of SnO2 particles was enlarged compared to its bulk counterpart and the red-shift of the optical band gap with the particle size was observed which can be attributed to quantum size effect. A broad photoluminescence band in a range of 350-550 nm associating with the defect states on the SnO2 particle surface was detected and the intensity was significantly enhanced after the thermal annealing while the size-dependent luminescence excitation spectra were also observed.

Large-scale synthesis of single-crystalline RE2O3 (RE=Y, Dy, Ho, Er) nanobelts by a solid-liquid-phase chemical route.

Yttrium-group heavy rare-earth sesquioxide (RE(2)O(3), RE=Y, Dy, Ho, Er) nanobelts were successfully fabricated by thermolysis of solid RE(NO(3))(3)x H(2)O in a dodecylamine/1-octadecene mixed solvent system. The synthetic principle is based on separating the nucleation and growth processes by utilizing the poor solubility of RE(NO(3))(3)chi H(2)O in the solvent mixture and the heat-transportation difference between the liquid and solid. By using dodecylamine, RE(2)O(3) nanobelts can be readily obtained. X-ray diffraction (XRD) analysis shows that the synthesized RE(2)O(3) nanobelts are body-centered cubic and crystalline. Field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), selective-area electron diffraction (SAED), and high-resolution transmission electron microscopy (HR-TEM) demonstrate that the synthesized RE(2)O(3) compounds possess regular geometric structure (beltlike) with perfect crystallinity. Preliminary experimental results prove that the dodecylamine plays a key role in the formation of RE(2)O(3) nanobelts and cannot be replaced by other surfactants. Furthermore, this method can be extended to the synthesis of RE(2)O(3) nanobelt/metal nanocrystal nanocomposites and ABO(3) (A=Y, Dy, Ho, Er; B=Al) and A(3)B(5)O(12) (A=Y, Dy, Ho, Er; B=Al)-type ternary oxide nanobelts, using mixed-metal nitrate salts in the correct stoichiometry instead of single rare-earth nitrates.