Huidong Tang

It is well known that trees grown on roadsides suffer from stressful environments, including poor soils, bad weather, and harmful gases from automobile exhaust. Improving the adaptability of roadside trees to adverse environments is important for urban management. An experiment was carried out with six-year-old Buxus megistophylla Levl. hedgerows, where 20 mg/L 5-aminolevulinic acids (5-ALA) solution was sprayed on the blade surface at the end of April. Three months later, plant morphology, chlorophyll fast fluorescence characteristics, antioxidant enzyme activities and the mineral element content were investigated. The results showed that leaf size and thickness were significantly greater with 5-ALA treatment, and the leaf color was also greener than those of the control. 5-ALA treatment significantly promoted the electron transfer activity of the PSII reaction center on the donor side, the reaction center itself and the receptor side. It reduced energy dissipation through the heat with increased photochemical quantum yields. The activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in leaves and roots, were stimulated by 5-ALA treatment. The content of soluble sugars and free proline in leaves was significantly increased by 5-ALA treatment, as were the absorption and accumulation of several kinds of mineral nutrient elements, such as nitrogen, phosphate, calcium, magnesium, iron, copper and boron. Additionally, 5-ALA application significantly increased the content of cadmium, mercury, chromium and lead in the roots but decreased them in the leaves. This implies that 5-ALA may induce a mechanism in B. megistophylla in which toxic elements were intercepted in roots to avoid accumulation in leaves, which ensured healthy growth of the aboveground tissues. 5-ALA may regulate the absorption and utilization of mineral nutrient elements in soil with the interception of toxic heavy metal elements in roots, promote leaf photosynthetic performance, induce the accumulation of soluble sugars and free proline, and improve the antioxidant enzyme systems for plants to adapt to the stressful environment of urban roads. These results provide a basis for 5-ALA applications alongside city roads.

Eu ²⁺ /Ga ³⁺ co-doped Na ₂ ZrSi ₂ O ₇ phosphors were prepared via a facile solid-state reaction route. The structural characteristics, photoluminescence spectra, and application performances of Na _{2- x} Eu _x Zr _{1- x} Ga _x Si ₂ O ₇ ( x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) were investigated. The main motivation of Ga ³⁺ co-doping on Zr ⁴⁺ is to eliminate the charge imbalance created by the aliovalent substitution of Eu ²⁺ on Na ⁺ sites in the lattices. The results indicated that the Eu ²⁺ /Ga ³⁺ co-doped Na ₂ ZrSi ₂ O ₇ kept a good esseneite-like structure with a triclinic space group of P-1. The phosphor presents a narrow cyan-emitting band centered at 485 nm under near-UV light excitation. The luminescence efficiency of Eu ²⁺ activator was significantly improved through the co-doping of Ga ³⁺ for Zr ⁴⁺ ions in Na ₂ ZrSi ₂ O ₇ . The maximum luminescence absolute quantum efficiency of 43% was observed in Na _{2- x} Eu _x Zr _{1- x} Ga _x Si ₂ O ₇ (x = 0.1) under the excitation of the near-UV light. The phosphor has good thermal stability with an activation energy of 0.31 eV. To realize charge compensation via cation co-substitution could be a practical strategy to improve luminescence in Eu ²⁺ -activated phosphors on aliovalent sites.

A novel phosphor, K₂MgSiO₄:Eu[Formula: see text], was synthesized by a solid-state reaction method. The phase formation was checked by X-ray powder diffraction. The photoluminescence excitation, emission spectra, decay curve and CIE coordinates of samples with different Eu[Formula: see text] ion concentrations were investigated in detail. The excitation spectra show a broad wavelength range of 225–470 nm. The K₂MgSiO₄:Eu[Formula: see text] phosphors exhibit highly red emission peaking at about 616 nm which is assigned to the ⁵D[Formula: see text]F₂ transition of Eu[Formula: see text]ions under the excitation of near-ultraviolet (NUV) (394 nm) light. The critical quenching concentration of Eu[Formula: see text] doped in the K₂MgSiO₄: Eu[Formula: see text] phosphors was about 10 mol.% and the concentration quenching mechanism was dipole–dipole interactions between Eu[Formula: see text] ions. The results indicate that K₂MgSiO₄:Eu[Formula: see text] is a potential red phosphor candidate for NUV-pumped white light emitting diodes.

Recently, RB SiC as a two-phase mirror material has taken particularly attraction because of its readily formable to near-net-shape. But it is difficult to obtain high quality optical surface due to the polish rate differences between SiC and Si components. Typical defects, such as polishing scratches, pores and surface irregularities which are mostly caused by the inhomogeneity of SiC and Si phase distributions are easily detected. The solution is the addition of a thick coating to cover these surface defects which may be polished to improve the quality of optical surface. Two thick coatings, PVD Si and PVD SiC, were applied by RF magnetron sputtering in this paper. After a series of sputtering parameters optimization, both the coatings' surfaces show fewer defects than that of RB SiC after polished. Results from this PVD progress, the surface morphologies' changes in optimization and the surface defects after polished are presented.