Lingling Peng

Synthesis and Luminescence Properties of (Y, Gd) (P, V)O4:Eu3+, Bi3+Red Nano-phosphors with Enhanced Photoluminescence by Bi3+, Gd3+ Doping

A series of (Y1−y, Gdy)0.95−x(Py, V1−y)O4:0.05Eu3+, xBi3+ phosphors have been successfully prepared by a subsection method. The crystal structure, surface morphology and luminescence properties were investigated. It was found that the sintered samples crystallized in a tetragonal crystal system with space group I41/amd(a = b = 0.7119 nm, c = 0.6290 nm). The products presented rod-like morphology with length of 100–150 nm and width of 50–100 nm. A maximum peak at 619 nm (5D0 →7F2) was observed in emission spectrum of the phosphors. It was also found that co-doping of Bi3+, P5+ and Gd3+ions into YVO4:Eu3+ can not only made the right edge of the excitation band shift to the long-wavelength region, but also increased the emission intensity at 619 nm sharply and decreased the lifetime of fluorescence decay. These results may expand the application scope of the phosphors.

Improving “color rendering” of LED lighting for the growth of lettuce

Light plays a vital role on the growth and development of plant. On the base of white light with high color rendering to the benefit of human survival and life, we proposed to improve “color rendering” of LED lighting for accelerating the growth of lettuce. Seven spectral LED lights were adopted to irradiate the lettuces under 150 μmol·m−2·s−1 for a 16 hd−1 photoperiod. The leaf area and number profiles, plant biomass, and photosynthetic rate under the as-prepared LED light treatments were investigated. We let the absorption spectrum of fresh leaf be the emission spectrum of ideal light and then evaluate the “color rendering” of as-prepared LED lights by the Pearson product-moment correlation coefficient and CIE chromaticity coordinates. Under the irradiation of red-yellow-blue light with high correlation coefficient of 0.587, the dry weights and leaf growth rate are 2–3 times as high as the sharp red-blue light. The optimized LED light for lettuce growth can be presumed to be limited to the angle (about 75°) between the vectors passed through the ideal light in the CIE chromaticity coordinates. These findings open up a new idea to assess and find the optimized LED light for plant growth.

Large micro-sized K2TiF6:Mn4+ red phosphors synthesised by a simple reduction reaction for high colour-rendering white light-emitting diodes

A simple chemical method for synthesising large micro-sized K2TiF6:Mn4+ phosphors (50–100 μm) is presented, based on a direct reduction reaction with K2TiF6 particles immersed in KMnO4/HF solution. The Mn4+ concentration in K2TiF6 primarily increases as the initial KMnO4 concentration is increased, subject to the diffusion of Mn4+ ions. However, the relative emission intensity of our synthesised K2TiF6:Mn4+ is first enhanced and then declines with increasing KMnO4 concentration, with an optimum KMnO4 concentration of 0.016 g ml−1, which most likely depends on the concentration quenching effect. The synthesised K2TiF6:Mn4+ (0.35–4.4 at%) phosphors show good thermal stability and can be adopted to fabricate high CRI (Ra > 85) white LEDs for indoor lighting.

Luminescence properties of Na2SiF6:Mn4+ red phosphors for high colour-rendering white LED applications synthesized via a simple exothermic reduction reaction

Na2SiF6:Mn4+ red phosphor is reported in this paper. Na2SiF6:Mn4+ was synthesized via a simple exothermic reduction reaction approach using Na2SiF6 and NaMnO4 as raw materials. H2O2 was dropped into 0.02 mol L−1 of NaMnO4 in HF solution to reduce Mn7+ to Mn4+ at room temperature. The phosphors can produce sharp red emissions in a broad absorption range (from 500 nm to 700 nm). The white LEDs were fabricated with blue GaN chips merged with a mixture of Na2SiF6:Mn4+ and commercial YAG:Ce yellow phosphors for white light.

A novel near-ultraviolet (NUV) converting blue-violet Ca2−xAlMg0.5Si1.5O7:xCe3+ phosphor for white light-emitting-diodes (w-LEDs)

Ce3+ doped aluminosilicate phosphors (Ca2−xAlMg0.5Si1.5O7:xCe3+, x = 0.015–0.075) for white NUV w-LEDs were synthesized by a solid-state reaction method at 1250 °C. The as-prepared samples were characterized by XRD and fluorescence spectrophotometry; the obtained XRD results show that the target phase was synthesized and doping with Ce3+ did not result in an impurity phase. The as-prepared phosphors exhibit a strong blue-violet emission under the near-ultraviolet radiation excitation. Corresponding fitting results show the emission spectra contain two distinct single bands, which come from the transition of 2D3/2 → 2F7/2 and 2F5/2 of the Ce3+ ion. The colorimetric coordinates of the sample with x = 0.03 are (0.1574, 0.0359), located in the blue-violet region. In addition, the sample exhibits high external quantum efficiency (EQE = 37.3%) and excellent thermal stability (T50 = 230 °C). We obtained bright blue-violet light by pumping the sample with NUV light (λ ≈ 365 nm), which suggests that this material has the potential for application as a NUV converting blue-violet phosphor for the NUV w-LEDs.

Synthesis and photoluminescence properties of cerium-doped terbium-yttrium aluminum garnet phosphor for white light-emitting diodes applications

Abstract. Cerium-doped terbium–yttrium aluminum garnet phosphors were synthesized using the solid-state reaction method. The crystalline phase, morphology, and photoluminescence properties were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), and fluorescence spectrophotometer, respectively. The XRD results indicate that with an increase of the amount of x (Tb3+), all of the samples have a pure garnet crystal structure without secondary phases. The SEM images reveal that the samples are composed of sphere-like crystallites, which exhibit different degrees of agglomeration. The luminescent properties of Ce3+ ions in (TbxY1−x)2.9Al5O12∶Ce0.1 have been studied, and it was found that the emission band shifted toward a longer wavelength. The redshift is attributed to the lowering of the 5d energy level centroid of Ce3+, which can be explained by the nephelauxetic effect and compression effect. These phosphors were coated on blue light-emitting diode (LED) chips to fabricate white light-emitting diodes (WLEDs), and their color-rendering indices, color temperatures, and luminous efficiencies were measured. As a consequence of the addition of Tb3+, the blue LED pumped (Tb0.4Y0.6)2.9Al5O12∶Ce0.1 phosphors WLEDs showed good optical properties.

Oxalic acid assisted hydrothermal synthesis and optical absorption property of WO3/TiO2 nanocomposites

The WO3/TiO2 nanocomposites were successfully prepared via a facile oxalic acid assisted hydrothermal process. The oxalic acid played a vital role on the preparation of WO3/TiO2 nanocomposites. Notably, it has been observed that the nanocomposites exhibited the wider absorption edge, and the higher photocatalytic activity, compared with pure TiO2. In addition, the photocatalytic mechanism was proposed, and it elaborated that WO3/TiO2 nanocomposite promoted the separation of the photoproduction carriers, and improved photocatalytic activity. The WO3/TiO2 nanocomposite may have a potential application as a UV–visible photocatalyst.

Effect of sintering temperature on the emission-spectrum-shape-evolution of Sr 2 SiO 4 :Eu 2+ phosphor

Color rendering index and color temperature are the key factors for the LEDs application. The two points are closely related to the emission spectrum shape of phosphors. As the key factors for the LEDs application, both the above aspects are closely dependent on the emission spectrum shape of phosphors. In this study, the emission spectrum shape has been adjusted via a home designed route. A combination of structural, morphological, and optical characterization techniques has been used to study the shape evolution mechanism. The structural results show that the Sr2SiO4 phase has not been changed with the sintering temperature increasing, but the emission spectrum shape has changed dramatically, meanwhile, the colorimetric coordinate moves from blue-green to green region. Gaussian fitting method has been used to treat the emission spectrum, and the as-obtained results indicate the emission spectrum contains two single bands, which come from the 4f7(7S7/2)–4f6(7FJ)5d1 transition of Eu2+ on the different Sr sites in the Sr2SiO4 crystal. The intensity of the two single bands is driven by sintering temperature, because of the difference between the energy barrier of the Eu2+ occupying the different Sr sites in the matrix crystal. Moreover, the mechanism of the above phenomenon has also been studied by means of first principles method, and the obtained results agree well with the former deduction.

Synthesis of Cubic Phase-Co Microspheres by Mechanical Solid-State Reaction-Thermal Decomposition and Research on Its Growth Kinetics

Cubic phase cobalt (Co), which can be used as a key component for composite materials given its excellent ductility and internal structure, is not easy to obtain at room temperature. In this study, oxalic acid and cobalt nitrate are used as raw materials to synthesize the cobalt oxalate precursor, which has a stable structure with a five-membered chelate ring. Cobalt oxalate microspheres, having a high internal energy content, were prepared by using mechanical solid-state reaction in the presence of a surfactant, which can produce spherical micelles. The thermal decomposition of the precursor was carried out by maintaining it in a nitrogen atmosphere at 450°C for 3 h. At the end of the procedure, 100 nm cubic phase-Co microspheres, stable at room temperature, were obtained. Isothermal and nonisothermal kinetic mechanisms of cobalt grain growth were investigated. The cubic-Co grain growth activation energy, , was calculated in this study to be 71.47 kJ/mol. The required reaction temperature was low, making the production process simple and suitable for industrial applications.