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Deployment Issues and Performance Study in a Relay-Assisted Indoor Visible Light Communication System
摘要： This paper investigates the deployment issues and analyzes the performance of a relay-assisted indoor visible light communications (VLC) system with dc-biased optical orthogonal frequency division modulation (DCO-OFDM). The study considers two light sources in an office environment. One light source works as the information source and is located at the ceiling while the other one works as the relay terminal, which usually is a desk light or a floor light. We analyze the general blockage in a room, discuss the path loss of the VLC channel, and compare received signal power from a line of sight (LOS) link and a non-LOS link. The constraints on the relay height in order to achieve LOS connection are investigated. Simplified optimal power allocation under illumination and blockage constraints is proposed. Bit error rate performance is analyzed and the required signal power is derived for the relay-assisted DCO-OFDM VLC system. The study shows that in a relay-assisted VLC system, the blockage of source to destination link has trivial influence on the overall system performance if relays are properly deployed.
关键词： indoor,visible light communications (VLC),dc-biased optical orthogonal frequency division modulation (DCO-OFDM),relay,Channel model,power allocation
更新于2025-09-09 09:28:46
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Fabrication of Novel ZIF-8@BiVO4 Composite with Enhanced Photocatalytic Performance
摘要： In this work, a novel metal-organic framework (MOF) and BiVO4 (BVO) composite photocatalyst was successfully synthesized by an in-situ growth method. The characterization of obtained samples was done by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, N2 adsorption, and photoluminescence spectroscopy. The photocatalytic performance of ZIF-8@BiVO4 composite was evaluated by the degradation of methylene blue (MB) under simulated visible light irradiation. Compared with the mixture of BVO and ZIF-8, the composite photocatalyst exhibited superior photodegradation ef?ciency, which could be attributed to the synergistic effect between BVO and ZIF-8. The reduced recombination of photogenerated electrons and holes was considered to be an important reason for the enhancement of photocatalytic performance. This design demonstrates a rational method to improve the photocatalytic performance by combining photocatalysts with MOFs.
关键词： photocatalyst,BiVO4,MOFs,visible light
更新于2025-09-09 09:28:46
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Photo Protection against Visible Light Induced Pigmentation
摘要： This paper presents in vivo an in vitro studies demonstrating the induction of pigmentation in human skin by visible light which can be blocked by using formulation containing the correct amount of yellow iron oxide (YIO). An in vitro absorption method was developed to determine the protection provided by a test formulation containing 4.5% YIO using an IPD UVA-VIS action spectrum. Following the development of the in vitro method and in vivo study with 10 normal healthy volunteers with Fitzpatrick skin phototypes IV to VI was conducted to verify if the predictive model. The in vitro model for visible light protection provided a protection factor of 2.5 using the in vitro absorption spectrum of 4.5% of YIO with a very similar result from the in vivo study with a protection factor of 3.0. Multiple daily exposures of visible light have shown increase in skin pigmentation and the application of YIO provide less development of pigmentation when compared to unprotected skin. In vitro testing of the absorbance of the pigmented formulation using a proposed action spectrum for immediate pigment darkening (IPD) response in the visible light range supports the in vivo protection observations for persistent pigment darkening (PPD) and can be used as predictor for skin pigmentation induced by visible light.
关键词： visible light,in vitro,in vivo,yellow iron oxide,pigmentation
更新于2025-09-09 09:28:46
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Visible Light Communications (Theory and Applications) || VLC for Indoor Positioning
摘要： As the world has become an increasingly connected ecosystem, data demand has continually pushed the limits of our wireless networks. Each generation of wireless technology has added extensive wireless capacity; however, novel use cases and technological adoption have continually raised the demand at rates previously unseen. This trend continues today as massive data downloads, video streaming, augmented reality, and the Internet of Things push the limits of 4G networks. Furthermore, increasing application complexity and demand per device is paired with an increasing number and density of wireless devices. Hence, the wireless communications industry is challenged to meet an extreme growth in data traffic in the coming years—a demand growth that is unlikely to be met with iterative modifications to the current infrastructure. With this in mind, the world mobile and wireless infrastructure community is looking toward the 5th generation of mobile telecommunications, or 5G, with the expectation that new technologies will be adopted which drastically alter the conventional view of wireless networks.
关键词： Visible Light Communications,Software Defined VLC,RF/VLC HetNets,VLC,5G
更新于2025-09-09 09:28:46
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Visible Light Communications (Theory and Applications) || Lighting and Communications: Devices and Systems
摘要： An important step in the design of a visible light communications (VLC) system is to comprehend the limitations arising from the optical wireless channel. Accurate channel characterization is an important prerequisite to set the system parameters appropriately in order to establish a high-quality link since it permits better exploitation of the available energy and spectral resources in view of optimizing the system design. An accurate channel model is also necessary to precisely predict the performance of VLC systems. In this chapter, we address channel modeling for VLC systems mainly focusing on indoor systems. We introduce different sources of impairment in VLC systems arising from beam propagation or transmitter (Tx)/receiver (Rx) devices. Indeed, the latter could be attributed to the “global channel” comprising the blocks between the signal Tx and signal detection at the Rx. After this introduction, we give an overview of different propagation modes in Section 3.2. In addition, we explain methods for numerical channel simulation. Analytical channel modeling for the cases of single- and multiple-source systems is presented in Section 3.3. Then, in Section 3.4, we outline the limitations arising from the aggregate channel while focusing on the problem of intersymbol interference (ISI) and how it affects the link performance particularly in the absence of a line of sight (LOS). This could be due to multipath-induced channel time dispersion, that is, multiple reflections from people and objects within an indoor environment, the lack of sufficient bandwidth of the transmitting device, most commonly a light-emitting diode (LED), the photodetector (PD), and the cabling used for lighting installations. Limitations due to the LED nonlinear characteristics could also be considered as an impairment of the global channel, which is the subject of Section 3.5 where channel distortion modeling is investigated. Finally, channel modeling for multiple-input multiple-output (MIMO) VLC systems will be presented next in Section 3.6.
关键词： Channel Modeling,Intersymbol Interference,Multiple-Input Multiple-Output,Optical Wireless Channel,Visible Light Communications
更新于2025-09-09 09:28:46
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Photoelectrocatalytic Reduction of Carbon Dioxide to Methanol using CuFe2O4 Modified with Graphene Oxide under Visible Light Irradiation
摘要： Photoelectrocatalytic reduction of CO2 into valuable products can provide energy in a sustainable way with levelling off the concentration of CO2 in our environment. In this study, graphene oxide (GO) incorporated with copper ferrite (CuFe2O4) has been employed to enhance photoelectrocatalytic CO2 reduction under visible light. The TEM and XPS characterization indicated a strong interaction between the CuFe2O4 and GO in the hybrid catalyst. The GO incorporation reduced the e-/h+ recombination in the hybrid catalyst by trapping the photoexcited electrons from CuFe2O4 leading to high methanol yield of 28.8 μmole/Lcm-2 at 20.5% quantum efficiency. The incident photon current efficiency (IPCE) and Faradaic efficiency for methanol formation were observed 8.02% and 87% respectively. The results showed that the photoelectrocatalytic activity for CO2 reduction can be improved by incorporating GO with CuFe2O4 and it provides a universal platform to fabricate GO-CuFe2O4 based hybrid photocatalyst with promising applications in CO2 reduction.
关键词： Visible light irradiation,CuFe2O4,CO2,Graphene oxide,Photoelectrocatalytic reduction,Methanol
更新于2025-09-09 09:28:46
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Visible-Light Photocatalyzed Deoxygenation of N-Heterocyclic <i>N</i> -Oxides
摘要： A scalable and operationally simple method is described that allows for the chemoselective deoxygenation of a wide range of N-heterocyclic N-oxides (a total of 36 examples). This visible-light-induced protocol features the use of only commercially available reagents, room-temperature conditions, and unprecedented chemoselective removal of the oxygen atom in a quinoline N-oxide in the presence of a pyridine N-oxide in the same molecule through the judicious selection of a photocatalyst.
关键词： chemoselective,deoxygenation,room-temperature,N-heterocyclic N-oxides,visible-light photocatalysis
更新于2025-09-09 09:28:46
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A Mixed-Ligand Metal-Organic Framework for Two-Photon Responsive Photocatalytic C-N and C-C Coupling Reactions
摘要： Multiple-photon photochemical process breaks the existing energy limitation of visible-light photocatalysis. Through careful incorporation of both bis(3,5-dicarboxyphenyl)-pyridine and bis(3,5-dicarboxyphenyl)methylpyridinium ligands into a single metal?organic framework, we reported herein photocatalytic C?N and C?C oxidative coupling reactions that evidenced the direct two-photon response process. Time-dependent luminescence decays studies demonstrated that the framework reached the same excited state by a two-photon absorption process as that reached via a single-photon absorption process, and the excited state could activate substrates even under NIR light irradiation. Under a 660 nm LEDs irradiation, both the photooxidative C?N coupling reaction of benzylamine to form benzylidene-1-phenylmethanamine, and the C?C coupling reaction between nitromethane and N-phenyl-trtrahydroisoquinoline were accelerated directly in a heterogeneous manner. Control experiments suggested that the minimal by-products were formed under the NIR light irradiation comparing to those of the UV light catalytic reactions. Importantly, photon intensity-dependent studies exhibited a nonlinear correlation between catalytic efficiency of MTV-MOFs and photon power intensity, verifying the two-photon responsive nature, which indicated that metal?organic framework with high-density and ordered photoactive motifs could enhance the two-photon absorption ability, thereby improve photocatalytic efficiency even under LEDs irradiation.
关键词： coupling reactions,two-photon photocatalysis,metal?organic framework,nonlinear optics,visible-light
更新于2025-09-09 09:28:46
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Synthesis of nanocrystalline bismuth oxide and its visible photocatalytic activity in the degradation of an organic dye
摘要： Bismuth oxide powder was synthesized, characterized and employed as a visible light photocatalyst for the degradation of aqueous solutions of Orange G (OG), a mono azo dye that is a commonly used colouring agent in various industrial applications. A simple combustion method using urea as fuel was employed to synthesize the metal oxide nanopowders. The prepared material was found to be nanocrystalline in nature as confirmed by XRD analysis. The band gap energy of the material is calculated by plotting (Ah(cid:1))2 vs. h(cid:1) from the UV-DRS spectrum and it is found to be 2.7 eV. The surface morphology and roughness of the material was studied by FE-SEM and AFM techniques. XPS and EDAX studies confirmed the elemental purity and presence in the nanomaterial. Preliminary studies were carried out in order to optimize the solution pH, catalyst dosage and initial dye concentration. As the catalyst possessed good activity at all pH values, thereafter all the photocatalytic reactions were carried out at neutral pH to make the process less cumbersome and cost effective. An optimum catalyst dosage of 1.5 g/L was fixed for a dye solution of 5 mg/L concentration. Kinetic studies showed the photo-degradation to follow pseudo-first order kinetics. Studies on the effect of electrolytes in solution showed that there was a decrease in the efficiency of the catalyst in the presence of the electrolytes. Reusability studies were performed on the catalyst to estimate the economic viability of the system.
关键词： visible light,combustion method,Bismuth oxide,Orange G,photocatalysis
更新于2025-09-09 09:28:46
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Fabrication of flexible MIL-100(Fe) supported SiO2 nanofibrous membrane for visible light photocatalysis
摘要： Core/shell structured SiO2/MIL-100(Fe) fibrous membrane was prepared for photocatalytic degradation of dyes. The metal organic framework shells of MIL-100(Fe) were decorated on electrospun SiO2 nanofiber surface through layer-by-layer assembly. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy tests confirmed the successful synthesis of the MIL-100(Fe) nanoparticles. The formed SiO2/MIL-100(Fe) catalysts exhibited high catalytic activity towards degradation of Rhodamine B under visible light irradiation. The photocatalytic activity remained above 80% within 90 min illumination after three cycles. Due to the easy preparation and high photocatalytic performance, as well as convenient collection for reuse, the obtained SiO2/MIL-100(Fe) membranes are promising catalysts for practical application.
关键词： Layer-by-layer assembly,Visible light,SiO2/MIL-100(Fe),Dye degradation,Photocatalysis
更新于2025-09-09 09:28:46