White Light Illumination Research Articles

Evidence for human-centric in-vehicle lighting: part 3-Illumination preferences based on subjective ratings, eye-tracking behavior, and EEG features.

Within this third part of our mini-series, searching for the best and worst automotive in-vehicle lighting settings, we aim to extend our previous finding about white light illumination preferences by adding local cortical area activity as one key indicator. Frontal electrical potential asymmetry, measured using an electroencephalogram (EEG), is a highly correlated index for identifying positive and negative emotional behavior, primarily in the alpha band. It is rarely understood to what extent this observation can be applied to the evaluation of subjective preference or dislike based on luminaire variations in hue, chroma, and lightness. Within a controlled laboratory study, we investigated eight study participants who answered this question after they were shown highly immersive 360° image renderings. By so doing, we first subjectively defined, based on four different external driving scenes varying in location and time settings, the best and worst luminaire settings by changing six unlabeled luminaire sliders. Emotional feedback was collected based on semantic differentials and an emotion wheel. Furthermore, we recorded 120 Hz gaze data to identify the most important in-vehicle area of interest during the luminaire adaptation process. In the second study session, we recorded EEG data during a binocular observation task of repeated images arbitrarily paired by previously defined best and worst lighting settings and separated between all four driving scenes. Results from gaze data showed that the central vehicle windows with the left-side orientated colorful in-vehicle fruit table were both significantly longer fixed than other image areas. Furthermore, the previously identified cortical EEG feature describing the maximum power spectral density could successfully separate positive and negative luminaire settings based only on cortical activity. Within the four driving scenes, two external monotonous scenes followed trendlines defined by highly emotionally correlated images. More interesting external scenes contradicted this trend, suggesting an external emotional bias stronger than the emotional changes created by luminaires. Therefore, we successfully extended our model to define the best and worst in-vehicle lighting with cortical features by touching the field of neuroaesthetics.

Modulation of perovskite degradation with multiple-barrier for light-heat stable perovskite solar cells

The long-term stability of perovskite solar cells remains one of the most important challenges for the commercialization of this emerging photovoltaic technology. Here, we adopt a non-noble metal/metal oxide/polymer multiple-barrier to suppress the halide consumption and gaseous perovskite decomposition products release with the chemically inert bismuth electrode and Al2O3/parylene thin-film encapsulation, as well as the tightly closed system created by the multiple-barrier to jointly suppress the degradation of perovskite solar cells, allowing the corresponding decomposition reactions to reach benign equilibria. The resulting encapsulated formamidinium cesium-based perovskite solar cells with multiple-barrier maintain 90% of their initial efficiencies after continuous operation at 45 °C for 5200 h and 93% of their initial efficiency after continuous operation at 75 °C for 1000 h under 1 sun equivalent white-light LED illumination.

Schottky-junction plasmonic nanocomposite: A non-hazardous excellent visible light photocatalyst for industrial waste management

A bio-compatible nanocomposite “Ag/Ag doped TiO2” with UV–Visible-NIR light gathering quality was synthesized by solvothermal method, followed by green synthesis method. Insertion of Ag+ ions into Ti2+ lattice sites in Ag doped TiO2 alters the n-type TiO2 semiconductor to p-type. Nanostructured doped TiO2 suffers high charge recombination loss in presence of trapped states, resulting 35 % photocatalytic efficiency. Ag decoration on p-type Ag doped TiO2 forms a Schottky barrier at metal-semiconductor junction, which reduces charge recombination loss by separating the photogenerated electron-hole (e-h) in two materials of the nanocomposite. These photogenerated charges create oxide and hydroxide super radicals in the aqueous system of photocatalyst, ensuing 80% degradation of SO dye under 50 min white light illumination. The nanocomposite also demonstrated good performance in degradation of industrial dyes like 50% Mordant Orange (MO) and 15% Direct Blue (DB) under 50 min white light irradiation. DFT analysis of the heterosystems supports absorptivity tuning of experimentally obtained nanocomposite. Moreover, the nanocomposite proved its non-toxicity to human cells, as it reveals <20% cell death with maximum dose (250 µg/ml) of the nanocomposite in cytotoxicity test. Hence, proper designing and synthesizing the nanocomposite explored an eco-friendly solar photocatalyst for industrial waste management.

Novel blue-emitting glass CaO-B2O3-2SiO2: Eu2+, Ce3+ with energy transfer

In this paper, CaO-B2O3-2SiO2: Eu[Formula: see text] and CaO-B2O3-2SiO2: Eu[Formula: see text], Ce[Formula: see text] fluorescent glasses have been synthesized by a conventional melt-quenching method. First, under 350[Formula: see text]nm excitation, the CaO-B2O3-2SiO2: Ce[Formula: see text] luminescent glass emits light at about 400[Formula: see text]nm, and the optimum dosage is 0.3[Formula: see text]mol%. Then, under 400[Formula: see text]nm UV excitation, the CaO-B2O3-2SiO2: Eu[Formula: see text] luminescent glasses showed a strong emission with a peak around 460[Formula: see text]nm and a half wavelength of 95[Formula: see text]nm. The results showed that the luminescence of this glass was greatest when the doping amount was 0.3[Formula: see text]mol% and gradually decreased with increase of the doping amount. After calculation and analysis, it was found that this was due to the nonradiative energy transfer between Eu[Formula: see text] ions. The mechanism of energy transfer was dipole–dipole interaction. Finally, Ce[Formula: see text]/Eu[Formula: see text] co-doped luminescent glasses were also successfully prepared with strong emission. The existence of energy transfer was demonstrated by theoretical and practical measurement data. CaO-B2O3-2SiO2: Ce[Formula: see text], Eu[Formula: see text] can be used as blue fluorescent glass for white light illumination.

Twofold optical display and encryption of binary and grayscale images with a wavelength-multiplexed metasurface

Abstract The remarkable capability in regulating light polarization or amplitude at the nanoscale makes metasurface a leading candidate in high-resolution image display and optical encryption. Diverse binary or grayscale meta-images were previously shown concealed in a single metasurface, yet they are mostly stored at same encryption level and share an identical decryption key, running the risk of exposing all images once the key is disclosed. Here, we propose a twofold optical display and encryption scheme demonstrating that binary and grayscale meta-images can be concurrently embedded in a nonspatially multiplexed silicon metasurface, and their decryptions demand for drastically different keys. Unlike previous metasurfaces relying on isolated transmission or phase manipulations upon orthogonal linear polarization incidences, this is made possible by exploiting silicon meta-atoms featuring joint transmission amplitude and polarization control at two wavelengths. In detail, the selected two meta-atoms exhibit large polarization-independent transmission difference (∼85 %) at a wavelength of 800 nm, while functioning as the nano-quarter-wave plate at wavelength of 1200 nm. Through elaborate design in simulation, a binary image can be witnessed when the metasurface is merely illuminated by an unpolarized light of wavelength 800 nm or under white light illumination. However, a distinct binary or grayscale image will come into view by inspecting the metasurface with an analyzer and when the incident light is circularly polarized at the wavelength of 1200 nm. Two metasurface samples are fabricated and successfully verified the claims experimentally. The proposed approach is expected to bring new insights to the field of optical display and encryption.

Enhancing the Photoelectrochemical Performance of a Nanoporous Silicon Photocathode through Electroless Nickel Deposition.

Renewable energy sources, particularly solar energy, are key to our efforts to decarbonize. This study investigates the photoelectrochemical (PEC) behavior of nanoporous silicon (NPSi) and its Ni-coated hybrid system. The methods involve the application of a Ni coating to NPSi, a process aimed at augmenting catalytic activity, light absorption, and carrier transport. Scanning electron microscopy was used to analyze the morphological changes on NPSi surfaces due to the Ni coating. Results demonstrate that the Ni coating creates unique structures on NPSi surfaces, with peak PEC performance observed at 15 min of coating time and 60 °C. These conditions were found to promote electron-hole pair separation and uniform Ni coverage. A continuous 50-min white light illumination experiment confirmed stable PEC fluctuations, showing the interplay of NPSi's characteristics and Ni's catalytic effect. This study provides practical guidance for the design of efficient water-splitting catalysts, contributing to the broader field of renewable energy conversion.

Synthesis, characterization and enhanced photoluminescence and temperature dependence of ZrO2:Dy3+ phosphors upon incorporation of K+ ions

This study reports the successful synthesis and comprehensive characterization of ZrO2:Dy3+ phosphors with the incorporation of K+ ions. The introduction of Dy3+ and K+ in the ZrO2 lattice as lanthanide activators demonstrates its potential as an efficient host material. The structural integrity of ZrO2 remains unaltered following the doping process. Fourier-transform infrared spectroscopy (FTIR) analysis confirms the presence of Zr-O and O-H stretching, along with H2O bending modes in the phosphor sample. The wide luminescence band seen at 460 nm is attributed to luminescence defects in the ZrO2 induced by oxygen, and the presence of water molecules. Photoluminescence (PL) spectra analysis reveals pronounced emission peaks at 491 and 578 nm, corresponding to 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions, respectively, upon excitation at 349 nm. Optimizing the Dy3+ doping concentration to 0.4 wt% and achieving a critical distance of 31.82 Å resulted in efficient energy transfer. Notably, co-doping K+ as a charge compensator significantly enhances the luminescence intensity. Moreover, at lower temperatures, direct excitation of Dy3+ ions through our pump wavelength, coupled with exciton-mediated energy transfer, leads to a remarkable increase in PL intensity. Tailoring the doping concentrations effectively shifts the emission spectrum of the phosphor mixture, aligning with the standard white light illumination coordinates (0.333, 0.333). This property positions the material as a promising candidate for applications in white light-emitting diodes (WLEDs) and various high-quality lighting applications. The enhanced photoluminescence and temperature dependence observed in ZrO2:Dy3+ phosphors upon the incorporation of K+ ions pave the way for their potential utilization in advanced luminescent devices.

UV-converted heterogeneous wettability surface for the realization of printed micro-scale conductive circuits

Achieving high precision in the fabrication of electronic circuits through additive manufacturing requires breaking the resolution limit of traditional printing processes. To address this challenge, we have developed a novel approach that involves preparing a heterogeneous wetting surface using a light-sensitive NBE-acrylate resin. By creating differences in surface energy on the substrate, we can limit the spread of the ink and surpass the limitations of conventional processes, achieving a printing resolution of 5 μm. The NBE-acrylate resin can be cross-linked under white LED light illumination (with λ > 400 nm) to yield a hydrophobic surface, which can be converted to a hydrophilic surface by UV light illumination (λ = 254 nm). The photochemical reaction of the NBE-acrylate resin under different light irradiation was confirmed by Fourier transform infrared spectroscopy (FTIR) and atomic force microscope (AFM) microforce measurements. In combination with a photomask, patterned heterogeneous wettability surfaces were prepared, which can be utilized for printing precision electronic circuits. Micrometer-scale printed circuits with a low line-to-space (L/S) of 5/50 and 10/10 μm were successfully achieved by optimizing the ink formulation, which is significantly beyond the printing resolution. In the end, fully printed thin film transistor arrays based on semi-conducting carbon nanotubes were achieved, which showed higher charge carrier mobilities of 1.89–4.31 cm2 s−1 V−1 depending on the channel width, demonstrating the application of this precision printed technique.

The Role of Alpha‐Methylbenzyl Ammonium Iodide to Reduce Defect Densities in Perovskite Devices

Hybrid organic–inorganic perovskite photovoltaic has achieved unmatched power conversion efficiency (PCE) improvement in the last decade. Nevertheless, nonradiative recombination of charge carriers due to bulk and interface defects reduces the open‐circuit voltage (V oc) and PCE of perovskite solar cells. Incorporating additives, process optimization, and interface engineering are among the effective approaches employed to reduce such issues. Herein, quasi‐2D p–i–n perovskite solar cells incorporating alpha‐methylbenzyl ammonium iodide (MBAI) cation with outstanding photovoltaic performance and stability are developed. MBAI incorporation results in films with excellent optical and electrical properties, leading to higher V OC of ≈1.15 V, fill factor of above 77%, and stability of the device. A high open‐circuit voltage and fill factor and corrected power conversion efficiencies in the range of 15% are obtained for the prepared devices. The encapsulated solar cells show excellent operational stability under white light illumination in ambient air for &gt;500 h. Due to the simple and robust preparation process, the investigated inverted perovskite solar cell can easily be combined with other solution‐processed thin film solar cells to form multijunction devices and can easily be integrated into different lightweight and flexible products.

Linker-Assisted Assembly of Ligand-Bridged CdS/MoS2 Heterostructures: Tunable Light-Harvesting Properties and Ligand-Dependent Control of Charge-Transfer Dynamics and Photocatalytic Hydrogen Evolution.

We used linker-assisted assembly (LAA) to tether CdS quantum dots (QDs) to MoS2 nanosheets via L-cysteine (cys) or mercaptoalkanoic acids (MAAs) of varying lengths, yielding ligand-bridged CdS/MoS2 heterostructures for redox photocatalysis. LAA afforded precise control over the light-harvesting properties of QDs within heterostructures. Photoexcited CdS QDs transferred electrons to molecularly linked MoS2 nanosheets from both band-edge and trap states; the electron-transfer dynamics was tunable with the properties of bridging ligands. Rate constants of electron transfer, estimated from time-correlated single photon counting (TCSPC) measurements, ranged from (9.8 ± 3.8) × 106 s-1 for the extraction of electrons from trap states within heterostructures incorporating the longest MAAs to >5 × 109 s-1 for the extraction of electrons from band-edge or trap states in heterostructures with cys or 3-mercaptopropionic acid (3MPA) linkers. Ultrafast transient absorption measurements revealed that electrons were transferred within 0.5-2 ps or less for CdS-cys-MoS2 and CdS-3MPA-MoS2 heterostructures, corresponding to rate constants ≥5 × 109 s-1. Photoinduced CdS-to-MoS2 electron transfer could be exploited in photocatalytic hydrogen evolution reaction (HER) via the reduction of H+ to H2 in concert with the oxidation of lactic acid. CdS-L-MoS2-functionalized FTO electrodes promoted HER under oxidative conditions wherein H2 was evolved at a Pt counter electrode with Faradaic efficiencies of 90% or higher and under reductive conditions wherein H2 was evolved at the CdS-L-MoS2-heterostructure-functionalized working electrode with Faradaic efficiencies of 25-40%. Dispersed CdS-L-MoS2 heterostructures promoted photocatalytic HER (15.1 μmol h-1) under white-light illumination, whereas free cys-capped CdS QDs produced threefold less H2 and unfunctionalized MoS2 nanosheets produced no measurable H2. Charge separation across the CdS/MoS2 interface is thus pivotal for redox photocatalysis. Our results reveal that LAA affords tunability of the properties of constituent CdS QDs and MoS2 nanosheets and precise, programmable, ligand-dependent control over the assembly, interfacial structure, charge-transfer dynamics, and photocatalytic reactivity of CdS-L-MoS2 heterostructures.

Synthesis of solid-state multicolor fluorescent calcium carbonate by controlled defect degree of (110)/(104) crystal plane and atomic order

Multicolor fluorescent calcium carbonate materials have significant applications in many fields such as papermaking, pigments, white light illumination and biological imaging, etc. In this work, blue (B-cal), yellow (Y-cal), and orange (O-cal) fluorescent calcium carbonates were synthesized using calcium gluconate and urea as substrates. The synthesis involved regulating the degree of (110)/(104) crystal plane defects and atomic order by adjusting temperature and time in the hydrothermal process. The luminescence mechanism was investigated through TEM, XRD and other characterizations. The result shows that there is an increase in atomic order and a decrease in the degree of lattice defects with red shift of the emission wavelength. The lattice defects in B-cal and Y-cal are mainly observed in the (110)/(104) crystal planes, while O-cal predominantly exhibits defects in the (104) crystal planes. Moreover, the first-principle calculation result shows that their fluorescences are caused by molecular packing or aggregation. Finally, the films were made using the different fluorescence calcium carbonates and exhibit the corresponding and favorable fluorescence and biomimetic enzyme properties.

Stabilizing formamidinium lead triiodide α-phase with diamine cations for perovskite solar cells

Bulk alkyl ammonium salt additives can significantly improve the stability of perovskite solar cells (PSCs) by forming 2D perovskite structures. However, these ammonium salts form organic interlayers impairing device efficiency. We doped the perovskite precursor with 1,4-butanediamine dihydrochloride (BDACl2) with a concentration that is low enough (BDACl2:FAI ≤ 1.0 mol %) not to form 2D perovskite. It is found that BDACl2 doping promotes grain growth and reduces the defect density, thus improving the crystalline quality of the perovskite films, resulting in an increase in PSCs device efficiency from 22.47% to 24.12%. More importantly, BDACl2 can effectively inhibit the transition from α-phase to δ-phase of FAPbI3 under operation. Therefore, PSCs retained more than 80% of their initial PCE after nearly 1500 h of operation with maximum power point tracking under simulated white light illumination in a nitrogen glove box, whereas the control cell without BDACl2 modification showed PCE decay of over 58% after aging for the same time.

Rapid single-photon color imaging of moving objects.

This paper outlines an experimental demonstration of a Bayesian image reconstruction approach to achieve rapid single-photon color imaging of moving objects. The capacity to extract the color of objects is important in a variety of target identification and computer vision applications. Nonetheless, it remains challenging to achieve high-speed color imaging of moving objects in low-photon flux environments. The low-photon regime presents particular challenges for efficient spectral separation and identification, while unsupervised image reconstruction algorithms are often slow and computationally expensive. In this paper, we address both of these difficulties using a combination of hardware and computational solutions. We demonstrate color imaging using a Single-Photon Avalanche Diode (SPAD) detector array for rapid, low-light-level data acquisition, with an integrated color filter array (CFA) for efficient spectral unmixing. High-speed image reconstruction is achieved using a bespoke Bayesian algorithm to produce high-fidelity color videos. The analysis is conducted first on simulated data allowing different pixel formats and photon flux scenarios to be investigated. Experiments are then performed using a plasmonic metasurface-based CFA, integrated with a 64 × 64 pixel format SPAD array. Passive imaging is conducted using white-light illumination of multi-colored, moving targets. Intensity information is recorded in a series of 2D photon-counting SPAD frames, from which accurate color information is extracted using the fast Bayesian method introduced herein. The per-frame reconstruction rate proves to be hundreds of times faster than the previous computational method. Furthermore, this approach yields additional information in the form of uncertainty measures, which can be used to assist with imaging system optimization and decision-making in real-world applications. The techniques demonstrated point the way towards rapid video-rate single-photon color imaging. The developed Bayesian algorithm, along with more advanced SPAD technology and utilization of time-correlated single-photon counting (TCSPC) will permit live 3D, color videography in extremely low-photon flux environments.

Efficient 1D ZnO/Cu2S heterostructure photocatalyst on topological Ag molded PVDF polymer fiber matrix for photoelectrochemical hydrogen evolution applications

A heterostructure semiconductor photo-electrocatalyst ZnO/Cu2S-loaded PVDF polymer matrix is used for solar water splitting. Herein, Ag nanoparticle-casted electrospun PVDF polymer matrix fibers have been used as a platform to fabricate the 1D ZnO nanorods as a photo-electrocatalyst. The Cu2S nanoparticles passivated on the 1D ZnO nanoarray show a two-fold enhancement of the photoelectrochemical hydrogen evolution. The conducting Ag nanoparticles sensitized PVDF, enhancing the conductance, and synergistically contributed to the water splitting under white light illumination. The PVDF/Ag/ZnO/Cu2S photoanode demonstrated photoelectrochemical water splitting. Ag nanoparticles (Ag NP), 1D nanostructures, and Cu2S narrowband gap semiconductors integrated into the photoanode accelerate the oxidation of the water through more visible absorption and high charge carrier transport. The PVDF/Ag/ZnO/Cu2S photoanode generates a stable saturated photocurrent density of 0.62 mA/cm2 in the −0.2 to 0.4 V vs. Ag/AgCl potential window. The chemically inert PVDF fibers with an Ag metal surface show a low onset potential and a charge transfer resistance of 844 Ohm/cm2 with a 0.42% photon to electron conversion efficiency for solar water splitting. Solar water oxidation has been demonstrated under unbiased conditions.

Demonstration of iodide-dependent UVA-triggered growth inhibition in Saccharomyces cerevisiae cells and identification of its suppressive molecules

Upon white light illumination, the growth of the budding yeast Saccharomyces cerevisiae was extremely impaired only in the presence of iodide ions, but not fluoride, chloride and bromide ions. Action spectroscopy revealed that the maximum wavelength of the light is around at 373 nm, corresponding to the UVA region. Using a genetic approach, several genes, including OPY1, HEM1, and PAU11, were identified as suppressors of this growth inhibition. This iodide-dependent UVA-triggered growth inhibition method, along with its suppressive molecules, would be beneficial for understanding cell growth processes in eukaryotes and can be utilized for medium sterilization using UVA light.

Photo-induced oxygen vacancy formation and anomalous photoconductivity in solution-processed CoFe2O4 thin films

Designing an optoelectronic device requires adequate information about the photo-response of the active material. Here, we have studied the optical and optoelectrical properties of the solution-processed inverse spinel structured CoFe2O4 (CFO) thin film and correlated it with the photovoltaic performance of CFO active material-based all-oxide solar cell. The optical absorption spectra of spin-coated CFO films show the existence of a direct bandgap of 2.64 eV with a maximum absorption coefficient &amp;gt;105/cm. A simple spin-coated CFO/TiO2p–n heterojunction shows an open circuit voltage of over 0.95 V under 1 sun illumination. However, photo-induced oxygen vacancy formation and the desorption of surface oxygen lead to additional electron generation and hole capture, respectively, in the p-type CFO, resulting in an anomalous photocurrent decay under white light illumination, resulting in a low short-circuit current density. This study provides a fundamental understanding of photo-carrier dynamics in solution-processed CFO thin films and apprehends the photophysics of designing spinel-ferrite-based optoelectronic devices.

Phthalocyanine-Blue Nanoparticles for the Direct Visualization of Tumors with White Light Illumination.

The current standard of care for colon cancer surveillance relies heavily on white light endoscopy (WLE). However, dysplastic lesions that are not visible to the naked eye are often missed when conventional WLE equipment is used. Although dye-based chromoendoscopy shows promise, current dyes cannot delineate tumor tissues from surrounding healthy tissues accurately. The goal of the present study was to screen various phthalocyanine (PC) dye-loaded micelles for their ability to improve the direct visualization of tumor tissues under white light following intravenous administration. Zinc PC (tetra-tert-butyl)-loaded micelles were identified as the optimal formulation. Their accumulation within syngeneic breast tumors led the tumors to turn dark blue in color, making them clearly visible to the naked eye. These micelles were similarly able to turn spontaneous colorectal adenomas in Apc+/Min mice a dark blue color for easy identification and could enable clinicians to more effectively detect and remove colonic polyps.

AL-aided AMC in a multi-user white-light OFDMA VLC system over a light-diffusing fiber loop.

To develop an adaptive modulation scheme for flexible high-speed multi-user visible light communication (VLC), automatic modulation classification (AMC) is adopted for monitoring the modulation formats of different subcarrier groups. An AMC scheme based on a joint convolutional neural network (CNN), active learning (AL), and data augmentation (DA) is demonstrated over an orthogonal frequency division multiplexing access (OFDMA) VLC system. The configuration of the diffuse white-light VLC system is combined with a pair integrated transceiver module, a light-diffusing fiber (LDF), and a wireless channel, which can provide white-light illumination and ubiquitous access. Within the forward error correction (FEC) threshold, the data rates of the white-light VLC links can reach 325.5 Mbps with a bit error rate (BER) of 2.163 × 10-3. An experiment with two-user access via the proposed VLC link with an unequal bandwidth allocation was demonstrated. The performance of the AL-aided CNN AMC scheme also shows a classification accuracy rate of 95.48% for the constellation diagrams of different subcarriers of the OFDMA signal over 240 training samples and faster convergence than a CNN-based AMC.

Athena: Specialty Certificate Examination case for general dermatology and dermatology in primary healthcare.

A 75-year-old woman presented to the dermatology clinic with a 6-month history of painful oral erosions. Clinical examination of the oral cavity revealed two intact tense bullae at the right retromolar trigone, the features of which were accentuated by white light illumination using a dermoscope. We discuss further assays, diagnosis and treatment.

Broadband omnidirectional visible spectral metamaterials

Optical metamaterials offer the possibility of controlling the behavior of photons similarly to what has been done about electrons in semiconductors. However, most optical metamaterials are narrowband, and they achieve negative refraction within a small window of incident angles, making them impractical for common visible light systems that operate effectively over a wide range of frequencies and directions. Considerable resistive loss at the resonant frequency of these metamaterials further prevents them from being deployed in the real world. Here, we develop a novel metamaterial randomly assembled by a list of narrowband, omnidirectional, and ultralow-loss meta-cluster systems using a bottom-up approach. Weak interactions among numerous meta-cluster sets greatly broaden the effective bandwidth of the overall structure, exhibiting frequency selectivity and spatial modulation when responding to white-light illumination. We observe negative refraction in the 490–730 nm band, and observe an inverse Doppler effect at green, yellow, and red frequencies, across most of the visible spectrum. Our method allows for low-cost fabrication of sizable broadband omnidirectional three-dimensional metamaterial samples, which opens the door to the rapid development of optical metamaterials, micro–nano assembly and preparation, tunable optical device engineering, etc.