Blue Light-emitting Diode Illumination Research Articles

Covalent Grafting of 5-Aminolevulinic Acid onto Polylactic Acid Films and Their Photodynamic Potency in Preserving Salmon.

A novel photodynamic inactivation (PDI)-mediated antimicrobial film of polylactic acid/5-aminolevulinic acid (PLA/ALA) was successfully fabricated by a covalent grafting method using low-temperature plasma. The chemical structure, surface morphology, hydrophilic ability, and mechanical and barrier properties of the films were characterized, and their antibacterial, anti-biofilm potency and preservation effects on ready-to-eat salmon were investigated during storage. Results showed that the amino group of ALA was covalently grafted with the carboxyl group on the surface of PLA after the plasma treatment, with the highest grafting rate reaching ∼50%. The fabricated PLA/ALA films displayed an enhanced barrier ability against water vapor and oxygen. Under blue light-emitting diode illumination, the PLA/ALA films generated massive reactive oxygen species from the endogenous porphyrins in cells induced by ALA and then fatally destroyed the cell wall of planktonic cells and the architectural structures of sessile biofilms of the pathogens (Listeria monocytogenes and Vibrio parahaemolyticus) and spoilage bacterium (Shewanella putrefaciens). More importantly, the PDI-mediated PLA/ALA films potently inhibited 99.9% native bacteria on ready-to-eat salmon and significantly suppressed the changes of its drip loss, pH, and lipid oxidation (MDA) during storage, and on this basis, the shelf life of salmon was extended by 4 days compared with that of the commercial polyethylene film. Therefore, the PDI-mediated PLA/ALA films are valid in inactivating harmful bacterial and preserving the quality of seafood.

Mesoporous Graphitic Carbon Nitride/Black Phosphorus/AgPd Alloy Nanoparticles Ternary Nanocomposite: A Highly Efficient Catalyst for the Methanolysis of Ammonia Borane.

A novel ternary nanocomposite, mesoporous graphitic carbon nitride/black phosphorus-AgPd (denoted mpg-CN/BP-AgPd), was successfully fabricated by assembling the as-prepared AgPd alloy nanoparticles (NPs) on mesoporous graphitic carbon nitride/black phosphorus (mpg-CN/BP) binary composites. This novel nanocomposite comprises a heterojunction support material formed by two distinct nonmetallic semiconductors (mpg-CN and BP) with adaptable band gaps and edge voltages, providing enhanced catalytic activity to AgPd alloy NPs in hydrogen generation from the methanolysis of ammonia borane (AB) compared to its single components under the blue light-emitting diode (LED) light illumination. The yielded mpg-CN/BP-AgPd ternary nanocomposites were characterized by many advanced analytical techniques (transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), time-resolved spectroscopy, inductively coupled plasma-mass spectroscopy (ICP-MS), and fourier transform infrared (FTIR), and then they were tested as catalysts in hydrogen generation from the methanolysis of AB at room temperature. Several parameters such as the effect of mpg-CN/BP ratio, alloy composition, and type of the light source were studied to optimize the catalytic activity of the mpg-CN/BP-AgPd nanocomposites in the methanolysis of AB. The best catalytic activity of mpg-CN/BP-AgPd nanocomposites was obtained using an mpg-CN/BP ratio of 5/1 (wt/wt) and Ag50Pd50 alloy composition under the blue LED illumination at room temperature. The activity of the ternary nanocomposites was further enhanced by the acetic acid treatment, and a high initial turnover frequency of 43.7 mol(H2) mol(catalyst)-1 min-1 was reported. Besides their high catalytic activity, the mpg-CN/BP-AgPd nanocomposites were reusable catalysts in the methanolysis of AB. This study also included detailed kinetics of AB methanolysis catalyzed by mpg-CN/BP-AgPd nanocomposites.

High photostability and luminescent efficiency of quantum dots: ultrathin epitaxial Al self-passivation layer with a homogeneous ligand

Semiconductor quantum dots (QDs) have aroused extensive interest in various applications because of their excellent optical and electronic properties. However, long-term photostability of the CdSe QDs has always posed application challenges. This study discusses the high-quality QDs synthesized using an uncomplicated coating method. The ultrathin epitaxial Al self-passivation layer is coated with a homogeneous ligand to maintain high luminescent efficiency and photostability of the QDs. The time-dependent intensity responses of the CdSe/CdS, CdSe/CdS/Al, and CdSe/CdS/CdS/Al QDs were verified under continuous irradiation using a single-particle one-watt blue light-emitting diode (LED). The CdSe/CdS photoluminescence (PL) intensity rapidly decreased under the blue LED illumination, whereas that of the CdSe/CdS/CdS/Al QDs remained almost unchanged for 300 min. The PL spectra of the three samples in 10–300 K were verified by comparing the temperature-dependent full-width at half-maximum of their emission energies and luminescent intensities. The mechanism of the temperature-dependent non-radiative relaxation of CdSe QDs coated with CdS layers of different thicknesses evolved from the thermal activation of carrier trapping by surface defects/traps in the CdSe QDs to the thermal escape of carriers in the core/shell QDs, assisted by multiple longitudinal–optical phonons. The luminescence mechanism was almost independent of the Al epitaxial growth layer.

Activated Sludge Growth under LED Illumination

The excess activated sludge production is the main problem of activated sludge method in waste water treatment plants. Several researches are being carried out to control the excess sludge production. Sludge growth process is a major factor to control the sludge production. Several observations are carried out to learn the information of sludge growth under several circumstances. One of the process was to observe the effect of light on sludge production performed by other researchers. Recently, the light emitting diode (LED) illumination is being used in different purposes including vegetable plantation. Here, we have observed sludge growth under LED illumination process with aerobic SBR plants. The white, blue and red LED illumination (each of 2 types) were used and the activated sludge growth and their waste water treatment abilities were investigated. We did not find any difference in pH, chemical oxygen demand (COD) removal in the activated sludge under LED illumination. But significant differences were found in sludge growth and sedimentation properties of activated sludge. Floc construction was disturbed by red/ blue LED illumination. It degraded the SV30 characteristics of the activated sludge. We have found that the growth of activated sludge was effected due to the different frequencies of LED illumination.

The impact of red and blue light-emitting diode illumination on radish physiological indices

Abstract The objective was to evaluate the effect of different combinations of red (638 nm) and blue (455 nm) light produced by solid-state light-emitting diodes (LEDs) on physiological indices (net assimilation rate, hypocotyl-to-leaf ratio, leaf area, leaf dry weight, hypocotyl length and diameter, plant length, developed leaves), variation of photosynthetic pigments and non-structural carbohydrates in radish (Raphanus sativus L., var. ‘Faraon’). Lighting experiments were performed under controlled conditions (total PPFD - 200 μmol m−2 s−1; 16 h photoperiod; 14/18°C night/day temperature). The LED conditions: 638 nm; 638 + 5% 455 nm; 638 + 10% 455 nm; 638 + 10% 455 + 731 nm; 638 + 10% 455 + 731 + 669 nm. Our results showed that radishes grown under red (638 nm) alone were elongated, and the formation of hypocotyl was weak. The net assimilation rate, hypocotyl-to-leaf ratio, and leaf dry weight also were low due to the low accumulation of photosynthetic pigments and non-structural carbohydrates in leaves. The supplemented blue (455 nm) light was necessary for the non-structural carbohydrates distribution between radish storage organs and leaves which resulted in hypocotyl thickening. Red alone (638 nm) or in combination with far-red (731 nm), or red669 for radish generative development was required.

Large negative persistent photoconductivity in InAs∕AlSb quantum wells

Negative persistent photoconductivity in backgated InAs∕AlSb quantum wells under red and blue light emitting diode illumination is observed to depend on both illumination energy and intensity. During these experiments the electron sheet density is varied by one order of magnitude from 5.6×1011 to 5.8×1010cm−2. This behavior is attributed to the role of optically excited holes in the AlSb barrier layers near the InAs quantum well. Furthermore, a long relaxation time in the electron sheet density is observed and attributed to the slow movement of electrons from the InAs quantum well to ionized deep levels in the AlSb barriers.

Organic heterojunction phototransistor

We propose an organic heterojunction phototransistor stacked with organic layers of electron and hole transport materials. The materials used in this study are perylene derivative (td-PTC) as the ultrathin base layer and triphenylamine derivative (TPD) as the emitter and collector layers. The current versus voltage characteristics as a function of incident optical intensity are typical of a phototransistor with current saturation. The bipolar transistor operation is confirmed by a comparison with the diode structure of the TPD/td-PTC device and because of the base thickness dependence of the current. External quantum efficiency is 2.9% under blue light-emitting diode illumination. In the current response, the initial displacement current is superimposed. Obtained response times are 600 μs for both transient turn-on and turn-off currents.