Xl L. Wu

Tunable photoluminescence from sheet-like black phosphorus crystal by electrochemical oxidation

An electrochemical method to prepare two-dimensional (2D) layered black phosphorus oxide with an inhomogeneous and non-stoichiometric structure is developed and described. The localized oxygen-related electronic states induce tunable photoluminescence (PL) between 620 and 670u2009nm. After oxidation, several new Raman modes with frequencies below 300u2009cm−1 emerge and the Ag1 mode splits into two sub-bands. The frequency difference between the two sub-bands (Δ) exhibits a monotonic dependence on the emission wavelength suggesting that PL is determined by the degree of oxidation. Similar to graphene oxide, phosphorene oxide is a promising 2D structure with many potential applications.

Resonant Raman scattering from CdS nanocrystals enhanced by interstitial Mn

Different Raman scattering effects are observed from CdS and Mn-doped CdS nanocrystals (NCs) with an average size of 5.1u2009nm synthesized by the reverse-micelle method. The intensity of the longitudinal optical (LO) phonon spectrum acquired from the Mn-doped CdS NCs is more than 20 times larger than that from the undoped CdS NCs. Spectroscopic and theoretical analyses reveal that the enhancement is caused by the interstitial Mn dopants, which decrease the NC surface deformation potential due to the small dielectric constant of the metal resulting in enhanced coupling between the LO phonon and surface plasmon.

Electronic states and photoluminescence of TiO2 nanotubes with adsorbed surface oxygen

The electronic states associated with enhanced photocatalytic activity of anodic anatase TiO2 nanotubes (NTs) annealed in N2 and O2 are investigated by photoluminescence (PL). The NTs annealed in N2 show a green peak related to oxygen vacancies and its position blueshifts with deceasing temperature, whereas those annealed in O2 show a double peak at 475–600 nm and the energy separation increases with decreasing temperature. Spectral analysis and density function theory calculation disclose that the double peak results from residual oxygen vacancies and oxygen atoms on the NT wall and the increased energy separation arises from the larger difference between the inner and outer NT stress at low temperature.

Electronic structure and magnetism in g-C4N3 controlled by strain engineering

Regulation of magnetism and half-metallicity has attracted much attention because of its potential in spintronics. The magnetic properties and electronic structure of graphitic carbon nitride (g-C4N3) with external strain are determined theoretically based on the density function theory and many-body perturbation theory (G0W0). Asymmetric deformation induced by uniaxial strain not only regulates the magnetic characteristics but also leads to a transformation from half-metallicity to metallicity. However, this transition cannot occur in the structure with symmetric deformation induced by biaxial strain. Our results suggest the use of strain engineering in metal-free spintronics applications.

3C-SiC nanocrystals/TiO2 nanotube heterostructures with enhanced photocatalytic performance

p-type ultrathin 3C-SiC nanocrystals are coated on heat-treated n-type TiO2 nanotube arrays formed by electrochemical etching of Ti sheets to produce heterostructured photocatalysts. Depending on the amounts of 3C-SiC nanocrystals on the TiO2 nanotubes, photocatalytic degradation of organic species can be enhanced. The intrinsic electric field induced by the heterojunction promotes separation of the photoexcited electrons-holes in both the TiO2 nanotubes and 3C-SiC nanocrystals. Hence, holes can more effectively travel to the surface of 3C-SiC nanocrystals and there are more electrons on the surface of TiO2 nanotubes consequently forming more •O2− and •OH species to degrade organic molecules.

Enhanced fluorescence from dye molecules by Au nanoparticles on asymmetric double-stranded DNA and mechanism

Gold nanoparticles (NPs) prepared on asymmetric DNA double helical structures show some twinning structures and sharp corners because of the low processing temperature. The distance between individual NPs varies between 2 and 4u2009nm, and these NPs form clusters with a size of ∼40u2009nm. The DNA structures also provide docking sites for the fluorescent dye. The dependence of the fluorescence enhancement on the distance between the NPs and dye molecules is investigated. The maximum enhancement factor is 5.8 when the distance between the dye and Au NP surface is 3.4u2009nm and the results are consistent with theoretical simulation.

Partial pressure-induced growth of silicon nitride belts with tunable width and photoluminescence properties

α- and β-Si3N4 belts with tunable width were synthesized by regulating the partial pressure of NH3/N2 in gaseous mixtures of Ar and NH3/N2 during the nitridation of silicon powders, which demonstrated tunable photoluminescence properties.