Absorption Of Blue Light Research Articles

Oxidase‐Type C−H/C−H Coupling Using an Isoquinoline‐Derived Organic Photocatalyst

Oxidase-type oxidation is an attractive strategy in organic synthesis due to the use of O2 as the terminal oxidant. Organic photocatalysis can effect metal-free oxidase chemistry. Nevertheless, current methods are limited in reaction scope, possibly due to the lack of suitable photocatalysts. Here we report an isoquinoline-derived diaryl ketone-type photocatalyst, which has much enhanced absorption of blue and visible light compared to conventional diaryl ketones. This photocatalyst enables dehydrogenative cross-coupling of heteroarenes with unactivated and activated alkanes as well as aldehydes using air as the oxidant. A wide range of heterocycles with various functional groups are suitable substrates. Transient absorption and excited-state quenching experiments point to an unconventional mechanism that involves an excited state “self-quenching” process to generate the N-radical cation form of the sensitizer, which subsequently abstracts a hydrogen atom from the alkane substrate to yield a reactive alkyl radical.

Revealing the synergistic effects of cells, pigments, and light spectra on light transfer during microalgae growth: A comprehensive light attenuation model

As the sole energy for photosynthesis, light decrease rapidly with path due to absorption by pigments and scattering by cells in microalgal suspensions. By comprehensively considering cell concentrations, pigment components, and light spectra, a modified Cornet model for light transmission in microalgal suspensions is established. The developed model better fits experimental data with a higher adjusted R2, which is 5% higher than the model that is based only on cell concentration. The attenuation of blue light is the most severe, followed by red and green light. Among the three main pigments, total carotenoids contribute the most to the absorption of blue and green light (with contribution coefficients of 89.26 ± 4.53% and 46.04 ± 3.77%, respectively), and chlorophyll a contributes the most to the absorption of red light (with a contribution coefficient of 75.33 ± 5.08%). This study provides a better understanding and prediction of light transmission during microalgal cultivation.

Introduction of helical photonic crystal insulator in organic phototransistor for enhancing selective color absorption

Organic phototransistors, with their electrically adjustable photo-sensing characteristics and mechanical flexibility, are promising components of multifunctional optoelectronics. For practical applications of the optoelectronics, it is essential to develop organic phototransistors with high photo-sensing performances and wavelength selectivity. Although, several studies have been conducted on improving the photo-sensing performances of organic phototransistors through the molecular engineering of organic materials, achieving improved light absorption and stable electrical performance remains a challenge. Here, we propose a new organic phototransistor structure that improves photo-sensing performances and wavelength selectivity by introducing helical photonic crystal (HPC) insulators. To realize the HPC film acting as a reliable insulator and an effective blue-wavelength reflector, a numerical analysis is performed. In the developed device, the blue light transmitting the semiconductor medium is effectively reflected by the HPC insulator, thereby improving the absorption of blue light in the channel region. Our device exhibits higher photo-sensing performances than the reference device without HPC film in terms of photosensitivity, photoresponsivity, and blue-wavelength selectivity. This novel concept of improving the wavelength selectivity of organic phototransistors will become an effective part of the development of practical photodetectors related to next-generation light and image sensors.

Surface silicon nanostructure for enhancement of blue light absorption

To enhance blue light absorption, a nanohole-array was designed and fabricated on the surface of silicon. The absorptivity of the silicon/nanohole-array composite structure was simulated with the finite-difference time-domain method. The result showed that, when the air filling factor f = 0.45, the period P = 400 nm, and the hole depth d = 0.5 μm, the absorptivity of the silicon was greater than 0.85 in the blue band and the average light absorption gain was about 0.61. A nanohole-array was fabricated with these structural parameters. The experimental results showed that the blue absorptivity of the silicon was greater than 0.91 and the average light absorption gain was about 0.63. For incident light at an angle of 60°, the absorptivity was greater than 0.73 in the blue band. The research demonstrated that the blue light could be absorbed at the deeper position of Si through the nanohole-array. This research may serve as a reference for the design and fabrication of silicon optoelectronic devices with high blue light quantum efficiency.

Photo-Switchable Sulfonylureas Binding to ATP-Sensitive Potassium Channel Reveal the Mechanism of Light-Controlled Insulin Release.

ATP-sensitive potassium (KATP) channels are present in numerous organs, including the heart, brain, and pancreas. Physiological opening and closing of KATPs present in pancreatic β-cells, in response to changes in the ATP/ADP concentration ratio, are correlated with insulin release into the bloodstream. Sulfonylurea drugs, commonly used in type 2 diabetes mellitus treatment, bind to the octamer KATP channels composed of four pore-forming Kir6.2 and four SUR1 subunits and increase the probability of insulin release. Azobenzene-based derivatives of sulfonylureas, such as JB253 inspired by well-established antidiabetic drug glimepiride, allow for control of this process by light. The mechanism of that phenomenon was not known until now. In this paper, we use molecular docking, molecular dynamics, and metadynamics to reveal structural determinants explaining light-controlled insulin release. We show that both trans- and cis-JB253 bind to the same SUR1 cavity as antidiabetic sulfonylurea glibenclamide (GBM). Simulations indicate that, in contrast to trans-JB253, the cis-JB253 structure generated by blue light absorption promotes open structures of SUR1, in close similarity to the GBM effect. We postulate that in the open SUR1 structures, the N-terminal tail from Kir6.2 protruding into the SUR1 pocket is stabilized by flexible enough sulfonylureas. Therefore, the adjacent Kir6.2 pore is more often closed, which in turn facilitates insulin release. Thus, KATP conductance is regulated by peptide linkers between its Kir6.2 and SUR1 subunits, a phenomenon present in other biological signaling pathways. Our data explain the observed light-modulated activity of photoactive sulfonylureas and widen a way to develop new antidiabetic drugs having reduced adverse effects.

Monolithic RGB Micro-Light-Emitting Diodes Fabricated with Quantum Dots Embedded inside Nanoporous GaN

We report the use of colloidal quantum dots (QDs) embedded in nanoporous (NP) gallium nitride (GaN) as a color converter to achieve different emission colors and fabricate micro-light-emitting diodes (micro-LEDs). The optical property of NP-GaN has been studied by analyzing the light transmittance propagating in NP-GaN. A strong light scattering effect can be induced by NP-GaN, resulting in a dramatically increased optical transmission path for blue light and high light absorption by QDs loaded inside NP-GaN. A 4 in. color converter has been achieved with a wavelength deviation of 1 nm across the entire wafer. Monolithic red, green, and blue micro-LEDs have been fabricated with a pixel size of around 35 × 35 μm2.

Effect of Na3AlF6 on the chroma and mineral compositions of the interstitial phase in white Portland cement clinker

With the reduction of high quality raw materials, white Portland cement (WPC) manufacturers are faced with the problem of lack of resources. In this paper, it is found that adding Na3AlF6 can increase the whiteness of WPC, which is helpful to alleviate the scarcity of resources in WPC manufacture. The effect of Na3AlF6 on the mineral compositions, chroma and hydration of the interstitial phase in clinker was studied by the Rietveld method, scanning electron microscope-energy dispersive spectrometer (SEM-EDS), Raman spectrum, spectrophotometer and calorimeter. The whitening mechanism of Na3AlF6 to WPC was revealed in our work. The results showed adding Na3AlF6 increased the C12A7 content and reduced the C3A content in the interstitial phase. This was beneficial to improve the reflectivity of the sample to visible light, which increased the brightness (L*) of the interstitial phase. Part of Al2O3 of C4AF was captured to form C12A7 in the samples with Na3AlF6, resulting in the decrease of the C4AF content. This weakened the blue light absorption of the samples with Na3AlF6, thereby reducing the yellowness (b*) of the interstitial phase. Therefore, the addition of 1.0 % Na3AlF6 increased the whiteness of WPC clinker. Moreover, adding Na3AlF6 increased the accumulated heat of WPC hydration but prolonged the induction period.

A highly efficient red emitting phosphor with enhanced blue-light absorption through a local crystal field regulation strategy

Mn4+-doped oxide phosphors with emission in deep-red region are promising for the application of plant cultivation lighting. However, it remains a great challenge to synthesize these phosphors with high blue-light absorption efficiency, which is pivotal for their practical commercial applications. Herein, we conducted a local crystal field regulation strategy to notably improve the luminescent property of the Mg14Ge5O24:Mn4+ phosphor. For instance, by introducing F- ions into the host, the absorption efficiency in blue-light region increased remarkably from 13% to 28%. By further substitution of Ti4+ for Ge4+ ions, the absorption efficiency further increased to 50%. Meanwhile, the achieved internal photoluminescence quantum yield is up to 92% for the Mg28Ge5.42Ti2O38F10:Mn4+ phosphor under 422 nm blue-light excitation. Besides, the phosphor exhibits excellent photoluminecence thermal stability, i. e., the emission intensity at 423 K retained 96% of that at room temperature. By means of X-ray absorption near-edge structure and extended X-ray absorption fine structure analysis, the effect of introducing F- and Ti4+ ions on the local coordination and valence of Mn ions in the hosts and the luminescent property of the phosphors are discussed in detail. Finally, LEDs were packaged by combining blue diode chips and Mg28Ge5.42Ti2O38F10:Mn4+ phosphor, and their validity for promoting growth of plants were successfully demonstrated.

Enhancing blue light absorption by Sm3+ Co-doing in Ca9Nd(PO4)7: Eu3+ for white light-emitting diodes

White light-emitting diodes (WLEDs) is widely concerned as the next-generation source of displays and lighting on account of many advantages. In this work, Sm3+ ions were introduced into Ca9Nd(PO4)7: Eu3+ (CNPO: Eu3+) red phosphors as a co-dopant to boost the blue-light excitation. X-ray diffraction (XRD) data confirm the successful preparation of the materials. Rietveld refinements were employed to investigate the site occupation and lattice parameter variation. All obtained materials have showed red emission under blue light or near-ultraviolet light excitation. The photoluminescence (PL) emission spectra features both signals from the two dopants, and the introduction of Sm3+ could effectively boost the red-light emission and blue-light excitation. Theoretical simulations help evidence the capability of the CNPO materials as host matrix of luminescent centers. Finally, a blue LED chip-based WLED was assembled in demonstration of their potential applications. Compared to the controlling device made with Eu3+ single-doped samples, the co-doped one has stronger blue light excitation and red light emission that guarantees a high luminous efficacy of over 90 lm W−1. The device also shows a superb long-term stability under continuous working. All in all, the CNPO: Eu3+, Sm3+ phosphors have shown many promising aspects in blue chip-based WLED applications.

Characteristics of Porous YAG:Ce Nano-Powders Phosphor Fabricated by a Solution Combustion Synthesis.

A cerium-doped YAG (Y₃Al5O12) phosphor is used as a rare-earth element phosphor for blue light absorption and yellow light emission for a white light source. A solution combustion synthesis, which is a method for producing nano-powder, is a reaction that is spontaneous ignition by reaction heat released through oxidation/reduction reaction between metal nitrate and fuel. Since the reaction speed is fast and it does not go through a separate firing process, it is a method of easily synthesizing nano-powder by simple process. In this study, YAG:Ce nano-powders were prepared by using various fuels in the combustion synthesis method. Depending on the kind of the additive fuel, the reaction of the combustion synthesis process was different, and the shape of the powder particles according to the fuels was also different. The agglomerated particles of nanoparticles were observed and the characteristics of YAG:Ce powders synthesized under various conditions were analyzed.

Cr3+ Activated Garnet Phosphor with Efficient Blue to Far‐Red Conversion for pc‐LED

AbstractFar‐red (FR) phosphor‐converted light‐emitting diodes (pc‐LEDs) driven by blue LED chips are novel light sources for applications in phototherapy, photosynthesis, natural light simulation, and so on but still bear low electricity‐to‐FR light conversion efficiency (≤ 23%) due to deficiency of phosphors that have both high blue light absorptance and high FR internal quantum efficiency (IQE) for the realization of efficient blue to FR conversion. FR Ca3Sc2Si3O12 (CSSG):Cr3+ garnet phosphor has ultra‐high IQE (> 90%) but low blue light absorption. Here, a twofold increase of blue light absorption cross‐section is reported with still high FR IQE via Lu3+−Mg2+ substitution for Ca2+−Sc3+ in CSSG:Cr3+ to form Ca3–xLuxMgxSc2–xSi3O12:Cr3+ garnet solid solution, which is attributed to enhanced mixing of odd‐parity configuration into 3d configuration of Cr3+ induced by the cations substitution. Optical properties, crystal field strengths, and thermal stabilities of the solid solution phosphors are studied as a function of x. After complete replacement of Sc3+, the as‐fabricated FR pc‐LED emits at 750 nm with 65.7% blue‐to‐FR quantum conversion efficiency and consequently offers an electricity‐to‐FR light conversion efficiency over 30%. Moreover, the solid solution phosphors show high quenching temperatures in the range of 580–610 K. The results can advance the development of efficient FR phosphors and pc‐LEDs for various applications.

Crystal growth, structure and optical properties of Pr3+-doped yttria-stabilized zirconia single crystals* *Project supported by the National Natural Science Foundation of China (Grant No. 11975004) and the Key Research and Development Plan Project of Guangxi, China (Grant No. Guike AB18281007).

The development of blue semiconductor light-emitting diodes (LEDs) has produced potential applications for Pr-doped materials that can absorb blue light, especially crystals, and we now report structure and optical properties for high-quality Pr-doped single crystals of yttria-stabilized zirconia (YSZ) grown by the optical floating zone (FZ) method. X-ray diffraction (XRD) and Raman spectroscopy showed that all of the single crystal samples were in the cubic phase, whereas the corresponding ceramic samples contained a mixture of monoclinic and cubic phases. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy showed that Pr was present as the Pr3+ ion in ceramic rods and single crystals after heating to high temperatures. The absorption and photoluminescence excitation (PLE) spectra of the Pr-doped YSZ crystals measured at room temperature showed strong absorption of blue light, while their photoluminescence (PL) spectra showed five emission peaks at 565 nm, 588 nm, 614 nm, 638 nm, and 716 nm under 450 nm excitation. The optimum luminescence properties were obtained with the crystal prepared using 0.15 mol% Pr6O11, and those with higher concentrations showed evidence of quenching of the luminescence properties. In addition, the color purity of Pr-doped YSZ single crystal reached 98.9% in the orange–red region.

Structural design enables highly-efficient green emission with preferable blue light excitation from zero-dimensional manganese (II) hybrids

• Two new zero-dimensional Mn 2+ bromide hybrids are reported. • Both show preferable blue light excitation and high photoluminescence efficiency. • The orbital-mixing for Mn-Br bond play a significant role. • A WLED with ~130 lm/W and superb long-term stability is achieved. Manganese (II) compounds are promising luminescent candidates for white light-emitting diodes (WLEDs) applications. However, the forbidden d - d transition of Mn 2+ ion makes the absorption of blue light and emission relatively weak without a sensitizer. The strategy of isolating MnX n (X is the ligand) with some ionic liquids is used to design two new hybrid compounds in this study, focusing on the orbital hybridization to relax the parity selection rule of the d - d transition. A large hindrance of the organic cations in the two new Manganese (II) hybrids enables a large Mn-Mn distance (up to ~ 10 Å) to form zero-dimensional (0D) structures, and the Mn sites in both compounds have a low site symmetry ( C 2 or C 1 ). The 0D structure of MnX n polyhedral is beneficial to isolatedly investigate the orbital hybridization of the ligand and Mn 2+ ion. A higher orbital hybridization extent for Mn-Br bond is evidenced by Density Functional Theory (DFT) simulation. This conclusion leads to the strong and stable green light emissions under preferable blue light (460 nm) excitations, giving photoluminescence quantum yields (PLQYs) as high as 76%. The WLEDs fabricated with these compounds have presented high luminous efficiency up to ~130 lm/W and survived multiple stability tests. The research favors the discovery of ideal Mn compounds for displays and lighting applications.

Mn-doped Ca14Al10(Zn,Mg)6O35: A deep-red oxide phosphor with high photoluminescence quantum yield and thermal stability

Mn-activated oxides have been widely regarded as a new class of red phosphors, while the weak absorption of blue light, low quantum yield (QY), and insufficient thermal quenching performance limit their applications. In this study, a series of deep-red emitting Ca14Al9.8Zn6−xMg0.1+xMn0.1O35 phosphors with outstanding luminescence performances are fabricated, and their optical and vibrational properties, as well as the thermal quenching mechanism, are investigated. The partial substitution of Mg for Zn not only greatly improves the absorption capability of blue light, but also suppresses the crystal defects, resulting in high QY (85.9% with excitation at 460 nm) and low thermal quenching effect (the emission intensity remains ~99.2% at 460 K and ~60.8% at 580 K relative to that at 300 K). This work demonstrates the great potential applications of Ca14Al9.8Zn6−xMg0.1+xMn0.1O35 phosphors in LED devices.

Tunable YAG:Ce3+ ceramic phosphors for white laser-diode lighting in transmissive/reflective models

Y3Al5O12:Ce3+ (YAG:Ce3+) transparent ceramic phosphor (TCP) is one of the most promising converters for the laser-diode (LD) lighting because it has good capacity for absorbing blue light and prominent luminous efficiency (LE). A challenge is how to achieve a high-quality YAG:Ce3+ TCP to realize a high LE value. We propose a strategy to depress the defects by using the charge-balanced Mg2+-Si4+ to substitute the Al3+-Al3+. Benefiting from the flux effect of MgO and SiO2, the transmittance of the YAG:Ce3+ TCP (thickness of 1 mm) increases from 13 % to 70 % by controlling the pores in the TCP. By introducing Al2O3 to be one kind of light scatters to enhance the blue light absorption, the LE reaches 185.7 lm/W, which is much higher than the value (137 lm/W) of the same TCP previously reported. These results evidence that the optimized YAG:Ce3+ TCP has an excellent performance in LD lighting. Prototype white LD devices are demonstrated in both the transmissive and the reflective models.

A Di-Carbazole-Based Dye as a Potential Sensitizer for Greenhouse-Integrated Dye-Sensitized Solar Cells

For the first time in dye-sensitized solar cell (DSSC) technology, a di-carbazole-based dye was synthesized and evaluated for its usage as a potential sensitizer for the development of wavelength selective semi-transparent DSSCs for greenhouses-oriented applications. The dye was designed to demonstrate a blue light absorption, allowing a high transmittance in the red region of the visible light, even after its adsorption on the anode semiconductor, which is the most important one for the photosynthetic action of the plants. The application of the new dye to DSSCs was examined using either a high-performance iodide-based electrolyte or a highly transparent iodine-free electrolyte to determine a good balance between electric power generation and device transparency. The spectral engineered DSSCs demonstrated quite promising characteristics, providing a high external quantum efficiency (higher than 70%) in the whole blue–green region of the visible light, while allowing high transparency (up to 55%) in the red region, where the second peak in the absorbance spectrum of chlorophyll is located. Finally, the derived results were discussed under the consideration of important metrics for this niche application, including the transparency of the solar cells in the region of photosynthetic active radiation and the attained crop growth factor. The present work constitutes one of the few comprehensive studies carried out up to now in the direction of the development of 3rd generation “agrivoltaics” for their possible integration as cladding materials in energy-autonomous greenhouses.

Silicon dots films deposited by spin-coating as a generated carrier addition layer of third generation photovoltaics

In this work, silicon ink composing of silicon powder and zinc oxide solution was formulated and spin-coated on quartz and n/p-Si substrates followed by drying the films under atmosphere at the temperature of 550 ​°C. The results showed that this top-addition layer could be the highly promising layer for photo-generating carriers in third-generation photovoltaics to enhance blue-light absorption. X-ray diffraction and scanning electron microscopy techniques were used to study the presence of silicon and zinc oxide nano-crystallites. The thin films consisting of different energy bandgap of Si nanocrystals (~100 ​nm) with narrow bandgap and spherical ZnO:Bi nanocrystal (~20 ​nm) with wider bandgap could be obtained from the evidence of bandgap enlargement. The band gaps of the thin films were tunable by adjusting silicon dots density in ZnO:Bi film. Energy upshift of light absorption edge depended on the silicon dots density was observed in the range 1.6–3.3 ​eV related band gap enlargement by Tauc plot. Under illumination, a high photocurrent gain of the thin film comprised of low Si dots density coated on a quartz substrate was about 103 times higher compared with its dark current. This result is agreeably explained in terms of its lower superficial trap states at the interface between silicon and zinc oxide matrix. The composite layer can be applied to a third-generation solar cell with the efficiency 1.50% higher than that with a typical crystalline-Si solar cell.

Blue light absorbing pigment in Streptococcus agalactiae does not potentiate the antimicrobial effect of pulsed 450 nm light

IntroductionRecently, it was shown that Group B Streptococcus (GBS) COH1 strain, which has granadaene—an endogenous chromophore known to absorb blue light—is not susceptible to 450 nm pulsed blue light (PBL) inactivation unless the bacterium is co-cultured with exogenous porphyrin. PurposeTo confirm or refute the finding, we studied the effect of blue light on NCTC, another strain of GBS with more granadaene than COH1, to determine if the abundance of granadaene—and by implication more absorption of blue light—fosters GBS susceptibility to PBL. MethodsWe irradiated cultures of the bacterium with or without protoporphyrin, coproporphyrin, flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide (NAD) or NADH. After 24-h incubation, bacterial colonies were enumerated, log10 CFU/mL computed, and descriptive and inferential data analyzed and compared. Results: (1) The rich amount of granadaene in NCTC did not enhance its susceptibility to antimicrobial pulsed blue light (PBL). (2) Adding exogenous porphyrin fostered NCTC susceptibility to irradiation, resulting in 100% bacterial suppression. (3) Exogenous FMN or FAD, which strongly absorb 450 nm light, did not promote the antimicrobial effect of PBL, neither did exogenous NAD or NADH, two weak blue light-absorbing photosensitizers. ConclusionThese results strengthen our previous assertion that an endogenous chromophore with the capacity to absorb and transform light energy into a biochemical process that engenders bacterial cell death, is essential for 450 nm PBL to suppress GBS.

Chlorophyll does not reflect green light – how to correct a misconception

ABSTRACT Plant leaves are green because they contain the green photosynthetic pigments, chlorophylls a and b. Popular science literature, and sometimes even textbooks, state that the greenness is caused by reflection of green light by chlorophyll. In the present study, we compared the reflectance spectra of green leaves to yellow or white leaves of the same species. Chlorophyll-deficient leaves reflected green light more efficiently than green leaves of the same species, which conclusively refutes the misconception. The data show that the green colour of leaves is caused by preferential absorption of blue and red light by chlorophyll, not by reflection of green light by chlorophyll. The data suggest that the cellulose of the cell walls is the main component that diffusely reflects visible light within plant leaves.

Visible-Light-Enabled C-H Functionalization by a Direct Hydrogen Atom Transfer Uranyl Photocatalyst.

The development of the uranyl cation as a powerful photocatalyst is seriously delayed in comparison with the advances in its fundamental and structural chemistry. However, its characteristic high oxidative capability in the excited state ([UO2 ]2+ * (+2.6 V vs. SHE; SHE=standard hydrogen electrode) combined with blue-light absorption (hv=380-500 nm) and a long-lived fluorescence lifetime up to microseconds have reveals that the uranyl cation approaches an ideal photocatalyst for visible-light-driven organic transformations. Described herein is the successful use of uranyl nitrate as a photocatalyst to enable C(sp3 )-H activation and C-C bond formation through hydrogen atom transfer (HAT) under blue-light irradiation. In particular, this operationally simple strategy provides an appropriate approach to the synthesis of diverse and valuable diarylmethane motifs. Mechanistic studies and DFT calculations have provided insights into the detailed mechanism of the photoinduced HAT pathway. This research suggests a general platform that could popularize promising uranyl photocatalytic performance.