Shixiu Cao

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.

Highly ordered Ag–TiO 2 nanocomposited arrays with high visible-light photocatalytic activity

TiO2 is active only in the ultraviolet region. To enhance the active ability, a combined method consisting of the anodic oxidation method and the hydrothermal method was developed to prepare highly ordered Ag-TiO2 nanocomposited arrays. The anodic oxidation was used to synthesize amorphous nanotubes with high chemical activity that subsequently served as highly ordered templates in preparing the final sample. The amorphous nanotubes got converted to highly ordered Ag-TiO2 (anatase) arrays in the silver nitrate & glucose aqueous solution via hydrothermal treatment. SEM and TEM results show that the Ag-TiO2 nanocomposite was composed of a large number of Ag nanoparticles and anatase TiO2 nanoparticles, and the morphology of those at the top of the arrays was found different from that of its trunk. The morphology evolution mechanism of the obtained sample was discussed. It is also revealed that the Ag-TiO2 nanocomposite has high visible-light photocatalytic activity.

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.

Color-tunable photoluminescence and energy transfer of (Tb1−xMnx)3Al2(Al1−xSix)3O12:Ce3+ solid solutions for white light emitting diodes

(Tb1−xMnx)3Al2(Al1−xSix)3O12:Ce3+ solid solution phosphors were synthesized by introducing the isostructural Mn3Al2(SiO4)3 (MAS) into Tb3Al5O12:Ce3+ (TbAG). Under 456 nm excitation, (Tb1−xMnx)3Al2(Al1−xSix)3O12:Ce3+ shows energy transfers (ET) in the host, which can be obtained from the red emission components to enhance color rendering. Moreover, (Tb1−xMnx)3Al2(Al1−xSix)3O12:Ce3+ (x = 0–0.2) exhibits substantial spectral broadening (68 → 86 nm) due to the 5d → 4f transition of Ce3+ and the 4T1 → 6A1 transition of Mn2+. The efficiency of energy transfer (ηT, Ce3+ → Mn2+) gradually increases with increasing Mn2+ content, and the value reach approximately 32% at x = 0.2. Namely, the different characteristics of luminescence evolution based on the effect of structural variation by substituting the (MnSi)6+ pair for the larger (TbAl)6+ pair. Therefore, with structural evolution, the luminescence of the solid solution phosphors could be tuned from yellow to orange-red, tunable by increasing the content of MAS for the applications of white light emitting diodes (wLED).

Mn^4+-doped fluoride phosphors rapidly synthesized by ball milling

In this paper, we present a rapid approach for synthesizing highly efficient emitting K2TiF6:Mn4+ red phosphors by ball milling. K2TiF6:Mn4+ can be obtained via cation exchange by reacting K2TiF6 and KMnO4. The synthesized time is reduced to 15 min, which is 5 times as fast as that of the simple chemical method, but the photoluminescence intensity of the obtained K2TiF6:Mn4+ increases by 34.6%. With the increase of the milling speed, the size of phosphor decreases, but the reaction of Ti4+ substituted by Mn4+ in K2TiF6 is accelerated. This is a new approach for preparing luminescent Mn4+-doped fluoride phosphors.

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.