Lighting Applications Research Articles

White Light Emission in Zero-Dimensional Indium Hybrid with Hydrogen Bond.

Low-dimensional organic-inorganic metal halides (OIMHs) have been explored as single-component white light emitters for applications in solid-state lighting. Herein, we report a zero-dimensional (0D) In-based OIMH (TMPDA)[InCl5(H2O)] (TMPDA = N,N,N',N'-tetramethyl-1,4-phenylenediamine), which crystallizes in the noncentrosymmetric P212121 space group and contains hydrogen bonds between the adjacent [InCl5(H2O)]2- octahedra in structure. It exhibits a large optical band gap (4.10 eV) and dual-band emission under UV light. Spectroscopic analysis and theoretical calculation indicate that the high (404 nm)- and low (513 nm)-energy emissions are attributed to the bound excitons in organic ligands and self-trapped excitons in [InCl5(H2O)]2- units, respectively. It is found that Sb doping in this 0D hybrid provides additional orange (590 nm) emission assigned to the 3P1 → 1S0 triplet radiative recombination. By adjusting the doping level, the emission color can be turned from turquoise to orange, and interestingly, a single-component white-light emission is realized by balancing the high-energy emission from organic ligand, the turquoise emission from [InCl5(H2O)]2-, and the orange one from [SbCl5(H2O)]2-. This work not only provides a new OIMH showing the single-component white light emission but also demonstrates the potential of In-based hybrids with hydrogen bonds for solid-state luminescence.

Luminescence Properties of Cs<sub>3</sub>Cu<sub>2</sub>I<sub>5</sub> Phosphors Powder with Solid State Method

The low-temperature solid-state method is utilized to prepare Cs3Cu2I5 phosphors powder by using the cesium iodide (CsI) and cuprous iodide (CuI) as the raw materials. The phase structures of samples were investigated by using X-ray spectrum and steady-state fluorescence spectrometer. The experimental results show that all of samples were crystallized in the orthorhombic structure with pnma space group at the annealing temperature of 100-400°C. Cs3Cu2I5 phosphors exhibits a strong blue photoluminescence emission with peak at 440nm under excitation at 310nm. With the increase of the annealing temperature in the range of 100-400°C, the photoluminescence quantum yield (PLQY) of Cs3Cu2I5 powder achieved the 79.95%. It is revealed that the prepared Cs3Cu2I5 powder phosphors potentially have the promising application in the blue light emitting materials.

Stretchable kirigami mechanical metamaterial with tunable dual electromagnetically induced transparency resonances

Kirigami, i.e. paper cutting is nowadays widely investigated to design the mechanical structure that can be transformed with unique and programmable performances. When it is transformed, the components of the kirigami are also reconfigured and then provide tunable polarization-sensitive electromagnetic responses. In this study, we present a design of stretchable kirigami mechanical metamaterial (SKMM) with dual electromagnetically induced transparency (EIT) resonances. The proposed two designs of SKMM show two dual EIT resonances at 0.905 THz, 0.975 THz, and 0.449 THz, 0.558 THz, which can be switched to 0.964 THz, 1.042 THz and 0.433 THz, 0.532 THz by rotating kirigami cells in predestinated orientations, respectively. During the continuous modulations of transmission spectra by increasing the stretching force, the characteristics of resonant spectra maintain excellent with their corresponding averaged Q-factors as 33.19, 21.59 and 4.87, 17.31, respectively. The EIT resonances originating from the bright-bright mode could be explained with multipole scattering theory along with the three-dimensional schematic illustrations. These results prove the proposed SKMM possesses promising applications in slow light, optical data computing, quantum information technology, and sensing fields.

Förster Resonance Energy Transfer and Enhanced Emission in Cs4PbBr6 Nanocrystals Encapsulated in Silicon Nano-Sheets for Perovskite Light Emitting Diode Applications.

Encapsulating Cs4PbBr6 quantum dots in silicon nano-sheets not only stabilizes the halide perovskite, but also takes advantage of the nano-sheet for a compatible integration with the traditional silicon semiconductor. Here, we report the preparation of un-passivated Cs4PbBr6 ellipsoidal nanocrystals and pseudo-spherical quantum dots in silicon nano-sheets and their enhanced photoluminescence (PL). For a sample with low concentrations of quantum dots in silicon nano-sheets, the emission from Cs4PbBr6 pseudo-spherical quantum dots is quenched and is dominated with Pb2+ ion/silicene emission, which is very stable during the whole measurement period. For a high concentration of Cs4PbBr6 ellipsoidal nanocrystals in silicon nano-sheets, we have observed Förster resonance energy transfer with up to 87% efficiency through the oscillation of two PL peaks when UV excitation switches between on and off, using recorded video and PL lifetime measurements. In an area of a non-uniform sample containing both ellipsoidal nanocrystals and pseudo-spherical quantum dots, where Pb2+ ion/silicene emissions, broadband emissions from quantum dots, and bandgap edge emissions (515 nm) appear, the 515 nm peak intensity increases five times over 30 min of UV excitation, probably due to a photon recycling effect. This irradiated sample has been stable for one year of ambient storage. Cs4PbBr6 quantum dots encapsulated in silicon nano-sheets can lead to applications of halide perovskite light emitting diodes (PeLEDs) and integration with traditional semiconductor materials.

α-Sr2SiO4:Ce3+, Dy3+, Na+ phosphors with abnormal thermal quenching properties for solid-state lighting applications

There is urgent need of thermally stable phosphors for fabricating high-performance white light emitting diodes (LEDs). In this paper, Sr2SiO4:0.02Ce3+,xDy3+, (0.02+x)Na+ phosphors were successfully synthesized by the solid-state reaction method and their luminescence properties were studied. Phase analysis shows that single-phasic α-Sr2SiO4 was prepared when x was greater than 0.006, while a mixed phase of α-Sr2SiO4 and β-Sr2SiO4 were obtained in the samples with x of 0.006 or less. When excited at 344 nm, there is a major emission band at 380–500 nm corresponding to the 5d-4f transition of Ce3+, and other emission peaks with a dominated one at 575 nm corresponding to the 4F9/2-6H13/2 transition of Dy3+. The as-developed Sr2SiO4:Ce3+,Dy3+,Na+ phosphors exhibit excellent thermal stability. To be specific, the intensity retention rate of 425 and 572 nm at 300 °C is as high as 103.6 % and 89.2 %, respectively. Furthermore, near-ultraviolet (nUV) chip-pumped white LED prototypes were assembled using the co-activated phosphor and commercial green and red phosphors, which demonstrate its great potential in high-power white LEDs for solid-state lighting applications.

Effect of Dopant Concentration on Luminescence Properties of Na3Ca2(SO4)3F: RE (RE = Eu3+, Dy3+) Phosphor for Solid-State Lighting.

A fluoride material phosphor doped with rare earth ions Eu3+ and Dy3+ was studied for its photoluminescence (PL) properties. The material was synthesized using a combustion method and characterized using X-ray diffraction (XRD) and PL techniques. The Na3Ca2(SO4)3F: Eu3+ phosphor exhibits two distinct peaks at 593 nm (orange) and 615 nm (red) at an excitation wavelength of 395 nm. The PL excitation spectrum of the Na3Ca2(SO4)3F: Dy3+ phosphor showed series of peaks, corresponding to the 4f → 4f transitions of Dy3+ ions. Under 350-nm excitation, the PL emission spectrum revealed two prominent bands one at 483 nm (blue region) due to the 4F₉/₂ → 6H₁₅/₂ transition, and another at 573 nm (yellow region) resulting from the 4F₉/₂ → 6H₁₃/₂ transition. These blue and yellow emissions suggest potential applications in solid-state lighting, particularly for mercury-free excitation sources. Rare earth-doped Eu3+/Dy3+ materials exhibit highly efficient PL properties, making them suitable candidates for white light-emitting diodes (LEDs) or other solid-state lighting phosphors.

Measurement of ascorbic acid samples’ optical rotation via an improvised polarimeter for purity assessment

Abstract The polarization of light finds practical application in physics and chemistry through the optical activity phenomenon, where polarimeters play a crucial role. This research builds on the improvised polarimeter designed by Kvittingen and Sjursnes [1], implemented with relevant modifications, to measure optical rotations of over-the-counter ascorbic acid samples. The study aims to assess the purity of two brands of ascorbic acid through polarimetry, comparing the calculated specific rotation with the literature values and supplementing the characterization with melting point determination. The constructed polarimeter, assembled using Lego bricks, provides an affordable alternative for educational purposes, addressing the challenges observed in the accessibility of commercial polarimeters for classroom demonstrations. The methodology encompasses pre-experiment steps involving polarimeter construction, the experiment utilizing polarimetry and complementary melting point determination, and post-experiment analysis to determine specific rotation from the measured optical rotations. Results indicate that Brand X exhibited specific rotations close to theoretical values, inferring high purity. Conversely, Brand Y shows significant deviations, suggesting potential impurities. These conclusions are supported by melting point data. The comprehensive approach combining polarimetry and melting point determination enhances the reliability of purity assessments, showcasing the effectiveness of the improvised polarimeter in practical applications.

Vector angular spectrum model for light traveling in scattering media

Strongly scattering media disrupt both the wavefront distribution and the polarization state of the incident light field. Controlling and effectively utilizing depolarization effects are crucial for optical applications in highly scattering environments, such as imaging through dense fog. However, current simulation models have difficulty simulating the evolution of vector light fields within scattering media, posing challenges for studying vector light fields in strongly scattering environments. Here, we propose the Vector Angular Spectrum (VAS) model for simulating the propagation of vector light fields within scattering media. By introducing the angular spectrum distribution of vector light scattering and polarization conversion mechanisms, this model can simulate the depolarization effects of vector light propagating through strongly scattering media. The VAS model has also been used to investigate the focusing of vector scattered light through scattering media. Furthermore, the simulation results of the model have been validated through experiments. The proposed VAS model is expected to play a role in the theoretical research of vector scattered light and optical applications in strongly scattering environments.

Multifunctional BiOCl: Sm3+ nanophosphors: A luminescent platform for solid-state lighting applications, optical thermometry, photocatalytic and forensic applications

Rare-earth-activated phosphor materials have been widely used as active probes in optical materials for multidimensional applications. Here, we report a series of ultrahigh purity orange-red emitting BiOCl: xSm3+ (x = 0.5- 2.5 mol %) nanophosphors synthesized via conventional solid-state method at relatively low temperatures for various photonic and forensic applications. XRD and Rietveld refinement results confirmed the tetragonal crystal structure of the synthesized phosphor materials with space group P4/nmm. Fourier transform infrared (FT-IR) and Raman spectroscopy were used to perform the functional group analysis. The UV–Vis–NIR spectra were analyzed to determine the Judd-Ofelt (JO) intensity parameters (Ω2, Ω4, Ω6) and to identify the bonding structure and spontaneous emission properties of the samples. The prepared phosphors exhibit intense orange-red emission under 408 nm excitation and beyond 1 mol% doping of Sm3+ ions, the emission intensity decreases due to concentration quenching mechanism via, dipole-dipole interaction between the optically active Sm3+ ions in the phosphor sample. The synthesized BiOCl: Sm3+ nanophosphors possess low correlated color temperature (CCT), admirable high color purity (99.4 %) and outstanding internal quantum efficiency (IQE) of 95.27 %. The optical thermometry behavior of the optimized sample has been investigated in detail. Moreover, the optimized nanophosphor stains on porous and non-porous surfaces show clear ridge patterns with high sensitivity, efficiency, and minimal background hindrance for latent fingerprints and lip print detection in forensic applications and are used as security ink in anti-counterfeiting applications. Overall, the results revealed the potential prospects of BiOCl: Sm3+ nanophosphors in the field of display applications, optical thermometry, and forensic sciences.

Study of structural and spectroscopic properties of Dy3+ ions doped potassium magnesium molybdate single phase phosphor for white lighting applications

Study of structural and spectroscopic properties of Dy3+ ions doped potassium magnesium molybdate single phase phosphor for white lighting applications

A Survey on Schwarz Lemma and Kobayashi Metrics for Harmonic and Holomorphic Functions

M. Mateljević [34] mainly consider various version of Schwarz lemma and its relatives related to harmonic and holomorphic functions including several variables. His methods (results) unify very recent approaches. This considerations include domains on which he can compute Kobayashi-Finsler norm. We intend do to a light application on the methods of [34].

Vehicle Detection and Counting for Traffic Congestion Estimation Using YOLOv5 and DeepSORT in Smart Traffic Light Application

The escalating number of vehicles on the roads has exacerbated trafficcongestion, presenting a significant and inevitable challenge for roadusers.Trafficcongestionnotonlyincreasesthetraveltimeofroadusers;it also causes air pollution since more vehicles are stuck on theroad. To address this issue, deep learning algorithms, including YOLOv5and DeepSORT, have been leveraged to enable vehicle detection and estimate the number of vehicles through image processing. This study focuses on training a custom YOLOv5 dataset of vehicles and compares its performance with a pretrained YOLOv5 dataset in terms of feasibility for detecting and estimating the number of vehicles. In the proposed approach, YOLOv5 is employed to detect vehicles in video streams, DeepSORT is used for vehicle tracking and counting as they pass through the detection zone, and the number of vehicles in each lane is estimated with the aid of Supervision. The custom dataset's validation demonstrates promising results, with the precision curve indicating convergence for all classes at 97.4% precision and an 87% accuracy in predicting vehicle classes. Additionally, the precision-recall curve assesses the ability to detect individual vehicle categories, such as bus, car, motorcycle, and truck, with accuracies of 68.2%, 95.2%, 79.9%, and 70.1%, respectively. Furthermore, the overall accuracy for detecting all vehicle classes combined is 78.3%. The F1 curve indicates that the system achieves a confidence level of 30.9% F1 score, ensuring 78% confidence in accurately predicting all classes. Both the pretrained and custom datasets exhibit similar accuracy in counting the total number of vehicles passing through the detection zone as well as estimating the number of vehicles in each lane. However, it is evident that the custom dataset's performance can be further improved by incorporating more extensive and diverse datasets during the training process to enhance the accuracy of vehicle detection and estimation. In conclusion, the integration of deep learning algorithms, specificallyYOLOv5 and DeepSORT, offers a promising solution for addressing traffic congestion byefficiently detecting and estimating vehicle numbers, which allow traffic systems to identify which lane is congested and prioritise ensuring the congested lane has a smooth traffic flow. Continued research with larger datasets can lead to further advancements and refined results in the field of traffic management and optimization.

Charge compensation-driven downconverted luminescence enhancement in Er3+-doped SrTiO3 phosphors by co-doping with alkali ions (M+ = Li, Na, K) for solid-state lighting applications

Charge compensation-driven downconverted luminescence enhancement in Er3+-doped SrTiO3 phosphors by co-doping with alkali ions (M+ = Li, Na, K) for solid-state lighting applications

Harvesting the tuning mechanism of strategic polychrome and white light emission in NapH dye based on excited state intermolecular proton transfer

Organic white light emitting (WLE) materials have sparked a research boom due to their promising applications in display devices, artificial lighting, and molecular sensors. However, the complex luminescence mechanism of full-spectra emitting materials has limited the development of white light materials with high stability and reproducibility. In this study, building on the full-spectra luminescent naphthimide dye (NapH) introduced by Xu et al., (Chin. Chem. Lett. 35(2024), 108348), we report the solvent-sensitive excited state proton transfer (ESPT) properties and white light emission mechanism in NapH. Our theoretical research results show that the ESPT process of NapH molecule is hindered in the low-polar solvent tetrahydrofuran (THF), so only the blue fluorescence from the Enol* is observed in the experiment. In contrast, in polar solvents such as water (H2O) and methanol (MeOH), the formation of strong intermolecular hydrogen bonds successfully initiates the ESPT process, leading to the dual fluorescence observed in experiments, with blue emission from the Enol* and red emission from the Nap anion. In essence, different solvent environments can adjust several emission colors. Furthermore, we theoretically verify that the optimal white light emission can be achieved when the mixed solvent ratio of dimethyl sulfoxide (DMSO) and dioxane (DIOX) is 5:5, which aligns well with experimental results. More importantly, we elucidate the specific WLE mechanism from multiple perspectives, including potential energy curves and electron spectra. Our work not only displays the interaction models of NapH molecule in various solvents, but also reveals the underlying luminescence mechanism, thus providing a valuable theoretical reference for the development and advancement of new white light materials.

Unveiling the power of Haar frequency domain: Advancing small target motion detection in dim light

Visual small target motion detection finds successful applications in varied scenarios. However, dim-light conditions, such as the tunnel scenes and nighttime environments, present significant challenges to existing detection methods which mainly operate within the spatiotemporal domain. This is because the transmission of small target motion information suffers from the inevitable interference of image noise caused by dim light in the spatiotemporal domain, resulting in the detriment of extracting essential spatiotemporal features of the target motion. Given the significant obstacles posed by dim-light imaging to small target motion detection within the spatiotemporal domain, the exploration of an alternative observation domain for small target motion, alongside the development of a corresponding detection method, emerges as a viable solution. To address this, in this paper, we discovered the remarkable potential of the Haar frequency domain in characterizing the small target motion in dim light. To investigate the advantages of integrating Haar frequency processing in small target motion detection, we introduce a Haar-windowed summation mechanism into an existing bio-inspired small target motion detection model. The proposed mechanism integrates visual information in spatiotemporal windows regulated by frequency parameters of Haar wavelets and effectively discriminates the small target motion from the disturbance of random noise caused by dim light. Theoretical analysis and numerical experiments confirm the superior performance of integrating the Haar frequency processing. This study provides a new vision of small target motion detection through the lens of the frequency domain and extends the limits of existing bio-inspired models for practical applications in dim light.

Light Disturbance Analysis and Applications

Light Disturbance Analysis and Applications

White light emission in Bi3+/Te4+ co‐doped Cs2SnCl6 for adjustable daily lighting and visible light communication

Abstractns2 ions‐doped lead‐free perovskites have garnered significant attention for their potential in diverse optoelectronic applications, owing to their broad emission characteristics arising from self‐trapped excitons (STEs). Herein, high‐performance white light‐emitting diodes (WLEDs) for intelligent lighting are developed by Bi3+/Te4+co‐doped Cs2SnCl6. Effective energy transfer between the dual STE emissions results in tunable broadband emissions covering the full‐color region. Adjustable WLEDs containing cold‐ and warm‐white lighting are fabricated. The WLEDs have excellent luminescent performances coupled with adjustable correlated color temperatures of 6417 and 3829 K. This versatility allows them to meet lighting demand for different scenarios, which is essential for future WLEDs to achieve healthy lighting. In addition, the excellent white light emission characteristics can also be applied in the visible light communication (VLC) system, achieving a −3 dB bandwidth of 13.3 MHz and opening eye diagrams in the data rate range of 10–60 Mbps. This work represents a significant advancement toward building intelligent health lighting applications and achieving high‐quality light sources for VLC based on lead‐free perovskites.

ZnO nanowire broadband ultra-wide-angle optical diffusers grown by aqueous chemical bath deposition

Light traveling path management is one of the key technologies to improve the performance of lighting, displays, and solar cells. Here we report broadband ultra-wide-angle optical diffusers using ZnO nanowires grown on flexible substrates by aqueous chemical bath deposition. The growth behavior of ZnO nanostructures strongly influences the degree of light scattering and is mainly governed by the molecular complexes present in the chemical bath, their relative concentration, and their interactions, which were efficiently controlled by the ammonia concentration in this work. Our ZnO nanowires grown at optimal ammonia concentrations exhibit higher optical transmission haze values than previously reported ZnO nanostructures over broadband (400 – 800 nm). In addition, our ZnO nanowires exhibit larger values in the key parameters of total transmittance and light scattering angle than commercial 3 M™ optical diffusers 3635–30/3635–70. Therefore, our chemical bath deposited ZnO nanowires are expected to be a compelling solution for optical diffusers in display and lighting applications.

New phase-construction phosphors ceramics for warm-white solid-state lighting: Orange-yellow-emitting (Lu,Gd)3(Sc,Al)5O12: Ce3+

Phosphor-converted white light-emitting diodes (pc-wLEDs) and phosphor-converted white laser diodes (pc-wLDs) are extensively utilized in lighting applications, with their quality and reliability heavily dependent on color converters. Recent progress in all-inorganic color converters, particularly phosphor ceramics (PCs), have markedly enhanced performance. However, due to the difficulty of managing emissive components, achieving warm white light with substantial red emission still remains challenging. In this work, a series of pure-phase Ce3+-activated garnet-structured solid-solution PCs, (Lu,Gd)3(Sc,Al)5O12: Ce (LGSAG: Ce), were fabricated using vacuum sintering technology for the first time. Through systematic analysis, it can be revealed that the addition of Gd3+ leads to a red shift in emission through changes in crystal-field splitting, whereas the inclusion of Sc3+ primarily focuses on improving the microstructure of the developed PCs. Particularly, the pc-wLED constructed from typical LGSAG: Ce PC generated significantly warmer light with a correlated color temperature (CCT) of 2916 K, compared to the 9557 K from LuAG: Ce PC. Meanwhile, under 40.0 W (15.7 W/mm2) blue laser excitation, the maximum luminous flux and luminescence efficiency of one typical LGSAG: Ce PG are 1172 lm and 29.3 lm/W, respectively. Therefore, the developed LGSAG: Ce PCs can show notable potential as color converters for future high-power warm-white solid-state lighting applications.

Comparative investigation of structural, morphological and temperature-dependent photoluminescence characteristics of trivalent rare-earth-activated NaCaPO4 phosphors for solid-state lighting applications

This study explores the synthesis, structure, morphology, and photoluminescence features of trivalent RE3+-activated NaCaPO4 phosphors, aiming to develop phosphor materials for white-light-emitting diode (WLED) applications. Single-phase polycrystalline NaCa(1-x) REx3+ PO4 (REx3+ = Sm, Eu, Dy, and Tb) phosphor materials with various REx3+-doping percentiles were produced by a solid-state reaction process, which were analyzed using various characterization techniques. The FullProf Suite software program was used for phase evidence and crystalline structure analysis, confirming the composition of orthorhombic materials as a single phase. FE-SEM micrographs revealed asymmetrically stacked morphologies across all the compositions. This study reveals that trivalent RE3+-activated phosphors produced exceptional PL outcomes. Dexter's and Blasse's approaches were used to establish the interaction mechanisms and critical energy transfer ranges as dipole-dipole. Lifetime decay patterns were used to fit a bi-exponential function and the resulting values were approximated in milliseconds. This study reveals that trivalent RE3+-activated NaCaPO4 phosphors, with their thermal resilience and color integrity, have potential applications in solid-state lighting (SSL) technology.