Full-spectrum Light Research Articles

Temporal Luminescence of Broadband Light-Emitting Diodes and Their Use for Generating Customizable White Light

ABSTRACT Broadband visible light-emitting diodes (LEDs) are now being used for applications where high-quality tunable light is needed. These LEDs are based on phosphors with wide emission bands (full width at half maximum, FWHM, of 70 nm or more). We describe the time-dependent characteristics of light emission from such devices. We found time lags in both luminescence buildup and decay as the broadband red, green and white LEDs are pumped by square pump photon flux. The reasons for such delays are photon percolation in phosphor/light scatterer blends and luminescence persistence due to defects in phosphors. The latter part of the paper describes a setup for combining light from phosphor-based red and green broadband LEDs with that of a band-edge emission blue LED to produce white light. It is shown that the chromaticity of white light can be changed stably by changing the frequency/duty cycle of PWM waveforms that are used for controlling red, green and blue LEDs. We also introduce a new LED drive scheme where PWM signals are converted to steady DC levels before driving LEDs. The setup described here enables the generation of full-spectrum white light with electrically controllable chromaticity.

Formation of a mixed-valence Cu(i)/Cu(ii) metal-organic framework with the full light spectrum and high selectivity of CO2 photoreduction into CH4.

Based upon the hetero-N,O ligand of pyrimidine-5-carboxylic acid (Hpmc), a new semiconductive Cu(i)/Cu(ii) mixed-valence MOF with the full light spectrum and a novel topology of {43·612·86}2{43·63}2{63}6{64·82}3, {(Cu4I4)2.5[Cu3(μ4-O) (μ3-I) (pmc)3(Dabco)3]·2.5DMF·2MeCN}∞ (NJU-Bai61, NJU-Bai for Nanjing University Bai group; Dabco = 1,4-diazabicyclo [2.2.2] octane), was synthesized stepwise. NJU-Bai61 exhibits good water/pH stabilities and a relatively large CO2 adsorption capacity (29.82 cm3 g−1 at 1 atm, 273 K) and could photocatalyze the reduction of CO2 into CH4 without additional photosensitizers and cocatalysts and with a high CH4 production rate (15.75 μmol g−1 h−1) and a CH4 selectivity of 72.8%. The CH4 selectivity is the highest among the reported MOFs in aqueous solution. Experimental data and theoretical calculations further revealed that the Cu4I4 cluster may adsorb light to generate photoelectrons and transfer them to its Cu3OI(CO2)3 cluster, and the Cu3OI(CO2)3 cluster could provide active sites to adsorb and reduce CO2 and deliver sufficient electrons for CO2 to produce CH4. This is the first time that the old Cu(i)xXyLz coordination polymers' application has been extended for the photoreduction of CO2 to CH4 and this opens up a new platform for the effective photoreduction of CO2 to CH4.

Hybrid catalysts of molybdovanadophosphoric acid and g-C3N4 with tunable bandgaps.

The integration of semiconductors and polyoxometalates provides promising benefits for the rational tuning of hybrid materials' electronic band structures; however, the intrinsic influence of certain hybridization approaches on the resulting bandgaps of their complexes has seldom been noted. Herein, graphitic carbon nitride and a series of phosphovanadomolybdates (H3+xPMo12-xVxO40, x = 0-3) have been complexed through electrostatic charge attraction, and their optical and electronic properties are fully explored to investigate the effect of minor variations of the polyoxometalate structures on the hybrid bandgaps and electronic structures. The conduction band edge of the hybrids increases along with the expansion of the number of vanadium centers in the phosphovanadomolybdate, providing potential guidance for the design of hybrid catalysts.

Three-dimensional graphene oxide cross-linked by benzidine as an efficient metal-free photocatalyst for hydrogen evolution.

The use of low-cost photocatalysts to split water into H2 fuel via solar energy is highly desirable for the production of clean energy and a sustainable society. Here three-dimensional graphene oxide (3DG) porous materials were prepared by cross-linking graphene oxide (GO) sheets using aromatic diamines (benzidine, 2,2′-dimethyl-4,4′-biphenyldiamine, 4,4′-diaminodiphenylmethane) that reacted with the carboxyl groups of the GO sheets at room temperature. The prepared 3DG porous materials were used as efficient metal-free photocatalysts for the production of H2via water splitting under full-spectrum light, where the photocatalytic activity was highly dependent on the cross-linker and the 3DG reduction level. It was also found that the 3DG prepared with benzidine as the linker demonstrated a significantly higher H2 evolution rate than the 3DGs prepared using 2,2′-dimethyl-4,4′-biphenyldiamine and 4,4′-diaminodiphenylmethane as the cross-linkers. The photoactivity was further tuned by varying the mass ratio of GO to benzidine. Among the prepared 3DG materials, 3DG-3, with an intermediate C/O ratio of 1.84, exhibited the highest H2 production rate (690 μmol g−1 h−1), which was significantly higher than the two-dimensional GO (45 μmol g−1 h−1) and the noncovalent 3DG synthesized by a hydrothermal method (128 μmol g−1 h−1). Moreover, this study revealed that the 3DG photocatalytic performance was favored by effective charge separation, while it could be further tuned by changing the reduction level. In addition, these results could prompt the preparation of other 3D materials and the application of new types of photocatalysts for H2 evolution.

Current Situation and Trend of the Phosphors for Full Spectrum LED Lighting

With the increase of the requirements for lighting quality, full spectrum light emitting diode (LED) lighting becomes the development hotspot. In this paper, the key materials for full spectrum LED phosphors are discussed and compared in detail. The advantages and disadvantages, research progress, and practical application of various color phosphors excited by violet and near ultraviolet light are emphasized, and then the existing problems, development trend, and industrial direction in this field are analyzed and prospected. Currently, there remain many problems in the phosphors excited by violet and near ultraviolet light, which can be applied in full spectrum. For example, the blue and cyan phosphors take on narrow emission spectrum, low light efficiency, and poor thermal stability; yellow phosphors and far-red phosphors have a low luminous efficiency due to their low absorption of violet or near ultraviolet light; and single matrix white phosphors have insufficient red light emission. Among them, luminous efficiency and thermal stability are the key factors restricting the application of the phosphors. Therefore, it is urgent to research the preparation and application technology of wide spectrum blue, cyan, yellow green, yellow, far-red, and single matrix white phosphors with high light efficiency and thermal stability, and develop the high-efficient and continuous preparation technology of the present phosphor products, to promote the further development of full spectrum LED.

Full Spectrum Phosphors for White LEDs and Virtual Windows for Light and Health Applications

Light and health is a topic of significant importance and requires fundamental studies of human interactions with light. This paper presents a review of some of the on-going studies on light and health by holistically exposing the humans to the outdoor conditions, while they are confined in indoor spaces. The designs of a new lighting-display fusion system along with examples of emerging commercial products have been presented. Full spectrum lighting is a critical component of such systems. A new simple approach for creating phosphor blends based on well known thiogallates and sulfide phosphors for designing full spectrum lighting that could replicate sunlight quality has been described. The synchronous modulation of phosphor based full spectrum light sources with electronic display playing real time outdoor videos creates a new tool for systematically studying the cognitive psycho-physiological health of human beings under different environmental conditions.

Solar-driven plasmonic tungsten oxides as catalyst enhancing ethanol dehydration for highly selective ethylene production

Non-metallic plasmonic materials, as alternatives to costly noble metals, have drawn numerous attention owning to their unique localized surface plasmon resonance (LSPR) effect. Herein, we report non-metallic plasmonic tungsten oxide (WO3−x) nanowire bundles with abundant oxygen vacancy (OVs) that gives efficient activity for ethylene production from ethanol dehydration under full spectrum light irradiation. A remarkable ethylene generation rate of 16.9 mmol g−1 h−1 was achieved with high selectivity (94.9 %) over the WO3−x-5 nanowires with maximum oxygen vacancies, which was 16 times higher than 1.0 mmol g−1 h−1 (selectivity of 90.5 %) of WO3−x-20 nanoplates with low oxygen vacancies. Such impressive performance is ascribed to the synergistic effect of plasmonic hot electrons and photothermal effect. This work is expected to provide new insights on photo-induced ethanol dehydration for highly selective ethylene production.

Moving object detection under different weather conditions using full-spectrum light sources

The moving object detection always remains an active field of research given the variety of challenges related to this topic. In fact, most of the challenges related to the low illumination and weather conditions (fog, snow, rain, etc.) remain unresolved and require more developments. In this paper, our intrinsic objective is to overcome these challenges using an effective moving object detection method. Unlike most works in the literature that use one of the two infrared or visible spectra independently, we proposed a Moving Object Detection method based on background modeling using the Full-Spectrum Light Sources (FSLS-MOD). To better ensure the adaptability and independence of the moving object speeds and sizes, the principle of the inter-frame differences’ methods is introduced in the background modeling stage. Furthermore, we applied a new strategy to switch between the spectra allowing us to benefit from the advantages of each spectrum and carry out a better moving object detection even in bad weather conditions. An experimental study by quantitative and qualitative evaluations proved the robustness and effectiveness of our proposed method of moving object detection using the switching strategy between full-spectrum light sources under different illuminations and weather conditions.

Plasmonic W18O49/attapulgite nanocomposite with enhanced photofixation of nitrogen under full-spectrum light

Ammonia (NH3) obtained by traditional Haber–Bosch technique under extreme conditions stimulates the exploration of sustainable approach via nitrogen photofixation process, however, efficient utilization of solar energy remains a great challenge. Herein, a novel plasmonic W18O49 supported on acid modified attapulgite (H-ATP) composite was prepared by microwave hydrothermal method. The impact of the loading fraction of W18O49 on the ammonia production rate was investigated. Results indicate that ATP possesses abundant adsorption sites after modified by phosphoric acid which facilitates the immobilization of W18O49. The 40% W18O49/H-ATP achieves the highest ammonia production rate of 138.76 μmol g−1 h−1 under solar light irradiation, even 78.76 μmol g−1 h−1 under NIR light (λ > 780 nm). The formed Z-scheme heterostructure improves the separation of charge-carriers, and the localized surface plasmon resonance (LSPR) effect of W18O49 broadens the light response range, both of which contribute to the enhanced nitrogen photofixation performance.

Photocatalytic degradation of ofloxacin by ZnO/CsxWO3composite synthesized by two-step method: A kinetic study

The composite of ZnO/CsxWO3with heterojunction was prepared by a two-step solvothermal method and the degradation of ofloxacin solution under full-spectrum light irradiation was carried out to evaluate the performance. The composites were characterized by XRD, SEM, EDS and UV-Vis-NIR reflectance. The result shows that the prepared composite has an ideal optical absorption in the spectral region of 200–2500[Formula: see text]nm and higher photocatalytic performance compared with ZnO and CsxWO3. Moreover, [Formula: see text], [Formula: see text]OH and [Formula: see text][Formula: see text] radicals are determined to be the active species. It is suggested that the heterojunction between ZnO and CsxWO3for ZnO/CsxWO3composite is important for improving the charge separation and thus restraining the recombination of photogenerated electrons and holes. Photodegradation of ofloxacin catalyzed by ZnO/CsxWO3followed the first-order kinetics and the degradation rate of ZnO/2CsxWO3was about two times higher than those of CsxWO3and ZnO.

Oxygen vacancy rich Bi2O4-Bi4O7-BiO2-x composites for UV–vis-NIR activated high efficient photocatalytic degradation of bisphenol A

To fully utilize the solar light, photocatalyst with broad spectrum response from UV to near-infrared (NIR) is desirable. In this work, ternary mixed valent Bi2O4-Bi4O7-BiO2-x with rich oxygen vacancy has been synthesized through one-pot hydrothermal treatment of NaBiO3. The results showed that through adjusting the hydrothermal conditions, oxygen vacancy-rich Bi2O4-Bi4O7-BiO2-x nanocomposites with much higher efficiency than single or mixed bismuth oxides (Bi2O4, Bi4O7, BiO2-x and Bi4O7-BiO2-x,) can be synthesized for photocatalytic degradation of bisphenol A (BPA) under UV, visible, and NIR light irradiation. In addition, the liquid chromatography-mass spectrometer (LC–MS) characterization demonstrated that BPA was oxidized to 4-isopropenyphenol first and the rings were opened sequentially under NIR light irradiation. Further detection of reactive species indicated that holes, O2−, and OH were the main oxidizing species in the degradation system. The experimental observations and density functional theory (DFT) calculations suggested that both type-II and the Z-scheme charge transfer with oxygen vacancies as electrons and holes mediators were formed at the interfaces of Bi2O4, Bi4O7, and BiO2-x, resulting in a very efficient separation of photogenerated charge carriers in the composite. This work adds to the growing potential of mixed valent bismuth oxides based photocatalysts and is expected to accelerate the pace of the development of new-generation photocatalysts with high efficiency utilizing full-spectrum solar light.

Distinct Morphological, Physiological, and Biochemical Responses to Light Quality in Barley Leaves and Roots.

Light quality modulates plant growth, development, physiology, and metabolism through a series of photoreceptors perceiving light signal and related signaling pathways. Although the partial mechanisms of the responses to light quality are well understood, how plants orchestrate these impacts on the levels of above- and below-ground tissues and molecular, physiological, and morphological processes remains unclear. However, the re-allocation of plant resources can substantially adjust plant tolerance to stress conditions such as reduced water availability. In this study, we investigated in two spring barley genotypes the effect of ultraviolet-A (UV-A), blue, red, and far-red light on morphological, physiological, and metabolic responses in leaves and roots. The plants were grown in growth units where the root system develops on black filter paper, placed in growth chambers. While the growth of above-ground biomass and photosynthetic performance were enhanced mainly by the combined action of red, blue, far-red, and UV-A light, the root growth was stimulated particularly by supplementary far-red light to red light. Exposure of plants to the full light spectrum also stimulates the accumulation of numerous compounds related to stress tolerance such as proline, secondary metabolites with antioxidative functions or jasmonic acid. On the other hand, full light spectrum reduces the accumulation of abscisic acid, which is closely associated with stress responses. Addition of blue light induced accumulation of γ-aminobutyric acid (GABA), sorgolactone, or several secondary metabolites. Because these compounds play important roles as osmolytes, antioxidants, UV screening compounds, or growth regulators, the importance of light quality in stress tolerance is unequivocal.

Placental scaffolds support osteogenic and chondrogenic differentiation of bovine adipose-derived cells

Green phosphor Lu2Si4N6C:Ce3+ (LSNC:Ce3+) shows an ideal feasibility to the near ultraviolet LED (n-UV LED) for “Full-Spectrum Lighting” (FSL). However, it is complex to synthesize pure Lu2Si4N6C phase. Herein, we prepared LSNC:Ce3+ via a novel dehydrogenation-driven high temperature solid-state reaction method, which distinctly optimized the morphology, and then significantly enhanced the photoluminescent performance of LSNC:Ce3+. The improving mechanism ascribed to the stepwise dehydrogenation of LuH3 which was beneficial to further shear LuH3 particles. The LSNC:Ce3+ phosphor obtained by the optimized process exhibits excellent thermal stability, and its external quantum efficiency is 57.3%. Interestingly, the intensities of excitation peaks decrease at 375 nm while it increases at 425 nm gradually with the Ce3+ concentration. It is reasonably ascribed to the different ability of photo-ionization in different 5d levels. Finally, the constructed w-LED with the titled phosphor exhibits a well-distributed warm white light with high color rendering index (Ra = 96.6, R9 = 96, R12 = 82). It indicates that the LSNC:Ce3+ gives assistance to compensation for the “spectrum chasm” in blue-green region, as well as contributes to the improvement of Ra and R9, that is beneficial for full-spectrum lighting.

A low-cost hyperspectral scanner for natural imaging and the study of animal colour vision above and under water

Hyperspectral imaging is a widely used technology for industrial and scientific purposes, but the high cost and large size of commercial setups have made them impractical for most basic research. Here, we designed and implemented a fully open source and low-cost hyperspectral scanner based on a commercial spectrometer coupled to custom optical, mechanical and electronic components. We demonstrate our scanner’s utility for natural imaging in both terrestrial and underwater environments. Our design provides sub-nm spectral resolution between 350–950 nm, including the UV part of the light spectrum which has been mostly absent from commercial solutions and previous natural imaging studies. By comparing the full light spectra from natural scenes to the spectral sensitivity of animals, we show how our system can be used to identify subtle variations in chromatic details detectable by different species. In addition, we have created an open access database for hyperspectral datasets collected from natural scenes in the UK and India. Together with comprehensive online build- and use-instructions, our setup provides an inexpensive and customisable solution to gather and share hyperspectral imaging data.

Optically Modulated Ultra-Broad-Band Warm White Emission in Mn2+-Doped (C6H18N2O2)PbBr4 Hybrid Metal Halide Phosphor

Finding new low-dimensional metal halides with broad-band emission is attracting interest in single-component phosphor for white light-emitting diodes (WLEDs). The full-spectrum white light still r...

Piezotronics enhanced photocatalytic activities of Ag-BaTiO3 plasmonic photocatalysts

Ag-BaTiO3 piezo-photocatalysts were fabricated by precipitating Ag nanoparticles on BaTiO3 nano-piezoelectric through a photochemical reducing approach. The mechanism of piezo-photocatalysis and the effect of the size and distribution of Ag nanoparticles on the properties of the photocatalyst were investigated. The surface plasmon resonance (SPR) of Ag nanoparticles endows the catalyst an absorption in the visible light region. The piezoelectric field originated from the deformation of BaTiO3 can further enhance the separation of the photogenerated carriers of SPR and promote the formation of oxidizing radicals that could accelerate the degradation of organic dyes. The 1mAg-BaTiO3 showed an excellent photocatalytic performance of degrading 83% Rh B in 75 min under full-spectrum light irradiation with ultrasonic excitation. The piezoelectric charges on the surfaces of the BaTiO3 and formed piezoelectric potential in the nanocrystal have been confirmed to express an increment of the catalytic activity more than 20% (compared with the sole photocatalysis). This work provides an effective technology for environment purification and could be extended to other piezoelectric materials.

TiO2 @ MoSe2 line-to-face heterostructure: An advanced photocatalyst for highly efficient reduction of Cr (VI)

Developing photocatalysts with rapid charge separation and transfer is an effective strategy for improving photocatalytic performance. Herein, a composite heterostructure with line-to-face contact made of few-layer MoSe 2 in situ tightly grown on TiO 2 nanoribbons (TiO 2 @MoSe 2 ) is synthesized via a facile hydrothermal route. In contrast to alone MoSe 2 , the growing MoSe 2 array obviously avoid the aggregation and face-to-face self-restacking phenomenon, making it a reality of the transmission of photo-generated carriers mainly in basal plane rather than between the interlamination. The line-to-face heterointerface could significantly facilitate the photo-generated electron-hole pair fast separation and transport, which is verified by the analysis of photoelectrochemical performance tests. The Cr (VI) photoreduction experiments under full spectrum or visible light further demonstrated the photocatalytic capability of TiO 2 @MoSe 2 was superior to both MoSe 2 and TiO 2 .

Ultrafine Si nanowires/Sn3O4 nanosheets 3D hierarchical heterostructured array as a photoanode with high-efficient photoelectrocatalytic performance

Constructing a high performance three-dimensional (3D) semiconductor photoelectrode for photoelectrocatalytic hydrogen (H2) production by water splitting is a promising method to resolve the current energy and environmental issues. Here, a ultrafine Si nanowires/Sn3O4 nanosheet (SiNWs/Sn3O4) 3D hierarchical heterostructured photoanode was synthesized via a facile approach with a metal-assisted chemical etching step following an in situ hydrothermal synthesis process. The ultrafine SiNWs/Sn3O4 3D hierarchical heterostructured photoanode exhibits significantly enhanced photoelectrochemical activity, and its photocurrent density is 8 times higher than that of single phase structures of SiNWs. This increase of catalytic activity may be attributed to the enhancement of the full-spectrum light absorption, decrease of the photocarrier recombination rate and a low transmission resistance at the catalyst/electrolyte interface. This work provides a novel design for preparing highly efficient Si based 3D heterostructured catalysts for the production of clean energy.

Enhanced photocatalytic N2 fixation by promoting N2 adsorption with a co-catalyst

Photocatalytic N2 fixation involves a nitrogen reduction reaction on the surface of the photocatalyst to convert N2 into ammonia. Currently, the adsorption of N2 is the limiting step for the N2 reduction reaction on the surface of the catalyst. Based on the concept of photocatalytic water splitting, the photocatalytic efficiency can be greatly enhanced by introducing a co-catalyst. In this report, we proposed a new strategy, namely, the loading of a NiS co-catalyst on CdS nanorods for photocatalytic N2 fixation. Theoretical calculation results indicated that N2 was effectively adsorbed onto the NiS/CdS surface. Temperature programmed desorption studies confirmed that the N2 molecules preferred to adsorb onto the NiS/CdS surface. Linear sweep voltammetry results revealed that the overpotential of the N2 reduction reaction was reduced by loading NiS. Furthermore, transient photocurrent and electrochemical impedance spectroscopy indicated that the charge separation was enhanced by introducing NiS. Photocatalytic N2 fixation was carried out in the presence of the catalyst dispersed in water without any sacrificial agent. As a result, 1.0 wt% NiS/CdS achieved an ammonia production rate of 2.8 and 1.7 mg L−1 for the first hour under full spectrum and visible light (λ > 420 nm), respectively. The catalyst demonstrated apparent quantum efficiencies of 0.76%, 0.39% and 0.09% at 420, 475 and 520 nm, respectively. This study provides a new method to promote the photocatalytic efficiency of N2 fixation.

Controllable Fabrication of Heterogeneous p-TiO2 QDs@g-C3N4 p-n Junction for Efficient Photocatalysis

Photocatalytic technology has been considered to be an ideal approach to solve the energy and environmental crises, and TiO2 is regarded as the most promising photocatalyst. Compared with bare TiO2, TiO2 based p-n heterojunction exhibits a much better performance in charge separation, light absorption and photocatalytic activity. Herein, we developed an efficient method to prepare p-type TiO2 quantum dots (QDs) and decorated graphitic carbonitrile (g-C3N4) nanocomposites, while the composition and structure of the TiO2@g-C3N4 were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-visible diffuse reflectance spectroscopy characterizations. The characterization results reveal the surface decorated TiO2 quantum dots is decomposed by titanium glycerolate, which exhibits p-type conductivity. The presence of p-n heterojunction over interface is confirmed, and photoluminescence results indicate a better performance in transfer and separation of photo-generated charge carriers than pure semiconductors and type-II heterojunction. Moreover, the synergy of p-n heterojunction over interface, strong interface interaction, and quantum-size effect significantly contributes to the promoted performance of TiO2 QDs@g-C3N4 composites. As a result, the as-fabricated TiO2 QDs@g-C3N4 composite with a p/n mass ratio of 0.15 exhibits improved photo-reactivity of 4.3-fold and 5.4-fold compared to pure g-C3N4 in degradation of organic pollutant under full solar spectrum and visible light irradiation, respectively.