Shiliang Qu

Photoluminescence properties of Eu3+-doped ZnS nanocrystals prepared in a water/methanol solution

Monodispersed ZnS and Eu3+-doped ZnS nanocrystals have been prepared through the co-precipitation reaction of inorganic precursors ZnCl2, EuCl3, and Na2S in a water/methanol binary solution. The mean particle sizes are about 3-5 nm. The structures of the as-prepared ZnS nanoparticles are cubic (zinc blende) as demonstrated by an x-ray powder diffraction. Photoluminescence studies showed a stable room temperature emission in the visible spectrum region for all the samples, with a broadening in the emission band and, in particular, a partially overlapped twin peak in the Eu3+-doped ZnS nanocrystals. The experimental results also indicated that Eu3+-doped ZnS nanocrystals, prepared by controlling synthetic conditions, were stable

Nonlinear absorption and optical limiting in gold-precipitated glasses induced by a femtosecond laser

Nonlinear absorptions of Au nanoparticles precipitated silicate glasses by irradiation of a focused femtosecond pulsed laser were investigated using Z-scan technique with 8 ns pulses at 532 nm. Optical limiting (OL) effects in such glasses have been also measured. It is observed that the behaviors of transition from saturable absorption to reverse saturable absorption and the OL performances for different samples are significantly different, which depend drastically on the irradiation power density of the femtosecond laser used for the Au nanoparticles precipitation in the glass. Strong nonlinear absorptions in these samples are mainly attributed to the surface plasmon resonance (SPR) and free carrier absorptions of the precipitated Au nanoparticles.

Optical nonlinearities of space selectively precipitated Au nanoparticles inside glasses

Optical nonlinearities of Au nanoparticles precipitated inside glasses induced by irradiation of a focused femtosecond laser were investigated using Z-scan technique with 8 ns pulses at 532 nm. The transformation behaviors both from self-defocusing to self-focusing and from saturable absorption to reverse saturable absorption were observed in the glass samples, which depend drastically on the irradiation power density of the femtosecond laser used. The optical nonlinearities were analyzed in detail and proved numerically by the excited-state theory of conduction band electrons.

Metal nanoparticle precipitation in periodic arrays in Au2O-doped glass by two interfered femtosecond laser pulses

We report on the precipitation control of Au nanoparticles in periodic arrays in silicate glass. Au2O-doped glass samples were first irradiated by two 800 nm interfered femtosecond laser pulses at room temperature and then heat treated at 550 °C for the Au nanoparticle precipitation in the laser irradiation areas. One-dimensional periodic arrays of the Au nanoparticles were controlled by changing the pulse energy and the incident angle between the interfered laser pulses. The smallest dimension in the obtained arrays was a width of 300 nm. The mechanism of the metal nanoparticle precipitation by this technique was discussed. Only two pulses are required to encode these periodic microstructures, which are applicable to emerging nanostructure devices such as optical memory with ultrahigh storage density, micrograting with high diffractive efficiency and integrative micro-optical switches.

Synthesis and temperature-dependent near-band-edge emission of chain-like Mg-doped ZnO nanoparticles

Chain-like Mg-doped ZnO nanoparticles were prepared using a wet chemical method combined with subsequent heat treatment. The blueshifted near-band-edge emission of the doped ZnO sample with respect to the undoped one was investigated by temperature-dependent photoluminescence. Based on the energy shift of the free-exciton transition, a band gap enlargement of similar to 83 meV was estimated, which seems to result in the equivalent shift of the bound-exciton transition. At 50 K, the transformation from the donor-acceptor-pair to free-to-acceptor emissions was observed for both the undoped and doped samples. The results show that Mg doping leads to the decrease of the acceptor binding energy. (c) 2006 American Institute of Physics.

Photoinduced formation of colloidal Au by a near-infrared femtosecond laser

A Au colloid was prepared in a 5 mM HAuCl 4 solution through irradiation with a focused infrared femtosecond laser at 800 nm. The Au colloid was characterized by absorption spectra, transmission electron microscopy, and x-ray diffraction analysis. The appearance of absorption peak around 526 nm in the absorption spectra and the wine-red color of sample solution HAuCl 4 under focused laser irradiation verified the formation of Au colloid. The solution color changed in the order of yellow → orange → wine-red due to the local formation of Au nanoparticles near the focus. The pulse energy, focus position of laser beam, and solvent composite play important roles in formation, grain size, and stability of the Au colloid. A mechanism for the precipitate of Au nanoparticles was proposed, and a multiphoton process of femtosecond laser was involved.

Optical limiting properties in phthalocyanines with different substituent groups

The optical limiting (OL) properties of free-base phthalocyanines and nickel metallophthalocyanines with the same structure but, with different substituent groups, octa-dodecaoxyl long chains, were investigated by using nanosecond pulses at 532 nm. The experimental results show that the OL capabilities in the two kinds of phthalocyanines depend nonmonotonically on lengths of the side chains.

One-off writing of multimicrogratings on glass by two interfered femtosecond laser pulses

Multimicrogratings are one-off written on silicate glass by two interfered femtosecond pulsed laser beams with the aid of a mask. The period and depth of the multimicrogratings are revealed by optical microscopy and atomic force microscopy. The depth is dependent on both the colliding angle between the two interfered laser beams and the laser pulse energy, but the period relies on the colliding angle only. We also observe a series of grooves formed at the middle of each bulge of the multimicrogratings and attribute it to the higher-order modulation arising from second-harmonic generation of the femtosecond laser pulse during the one-off writing processes.

Low-cycle fatigue-cracking mechanisms in fcc crystalline materials

The low-cycle fatigue (LCF) cracking behavior in various face-centered-cubic (fcc) crystalline materials, including Cu single crystals, bicrystals and polycrystals, Cu–Al and Cu–Zn alloys, ultrafine-grained (UFG) Al–Cu and Cu–Zn alloys, was systematically investigated and reviewed. In Cu single crystals, fatigue cracking always nucleates along slip bands and deformation bands. The large-angle grain boundary (GB) becomes the preferential site in bicrystals and polycrystals. In addition, fatigue cracking can also nucleate along slip bands and twin boundaries (TBs) in polycrystalline materials. However, shear bands and coarse deformation bands are observed to the preferential sites for fatigue cracking in UFG materials with a large number of GBs. Based on numerous observations on fatigue-cracking behavior, the fatigue-cracking mechanisms along slip bands, GBs, TBs, shear bands and deformation bands were systematically compared and classified into two types, i.e. shear crack and impingement crack. Finally, these fatigue-cracking behaviors are discussed in depth for a better understanding of their physical nature and the transition from intergranular to transgranular cracking in various fcc crystalline materials. These comprehensive results for fatigue damage mechanisms should significantly aid in obtaining the optimum design to further strengthen and toughen metallic materials in practice.