Under 980 nm excitation, unusual 3P2-->3H6 (approximately 264 nm) and 3P2-->3F4 (approximately 309 nm) emissions from Tm3+ ions were observed in hexagonal NaYF4:Yb3+ (20%)/Tm3+ (1.5%) microcrystals. In comparison with the strong emissions from 1D2 and 1I6, the emissions from 1G4 and 3H4 almost vanished due to the efficient cross-relaxation of 1G4 + 3H4-->3F4 + 1D2(Tm3+). Double logarithmic plots of the upconversion emission intensity versus the excitation power are neither straight lines nor typical saturation curves. Theoretical analysis indicated that the complicated dependent relationships were mainly caused by phonon-assisted energy transfers and nonradiative relaxation.

SiC/SiO 2 one-dimensional nanochains and SiC/SiO 2 two-dimensional X-junction and Y-junction nanochains were synthesized by using a simple and low-cost microwave method. Structural, morphological, and elemental analysis revealed that the SiC/SiO 2 nanochains consisted of 3C-SiC strings with diameters of 20-80 nm and periodic SiO 2 beads with diameters of 100-400 nm. Spectral analysis indicated that both SiC strings and SiO 2 beads produced significant photoluminescence, and the presence of SiO 2 beads enhanced the emissions from SiC strings. On the basis of experimental characterizations, a two-step growth mechanism of the nanochains was proposed to elucidate the growth process.

A growth mechanism was proposed for YF 3 nanocrystals forming in the quaternary reverse microemulsion system with water/cetyltrimethylammonium bromide/cyclohexane/1-pentanol. In the proposed mechanism, primary particles are formed by constant collision, fusion, and fission of micelles. These primary particles can further self-organize to one-dimensional nanostructure at room temperature. Results of X-ray diffraction and transmission electron microscopy reveal that each nanobundle consists of numerous nanowhiskers with a mean length of ∼700 nm and a mean diameter of ∼2 nm. Under 980 nm excitation, blue (