White Light Source Research Articles

A lightweight network of near cotton‐coloured impurity detection method in raw cotton based on weighted feature fusion

AbstractThe objective is to improve the recognition rate of white and near cotton‐coloured impurities in raw cotton against a single white visible light source background. A lightweight detection network model without anchor boxes based on improved YOLO v4‐tiny is proposed in this paper based on weighted feature fusion (WFF). The WFF strategy was used to improve the detection accuracy of the improved YOLO v4‐tiny algorithm. Meanwhile, to address the disadvantage that the anchor boxes obtained by the K‐means algorithm clustering do not have global features, the anchor‐free and tiny decoupled head schemes are used instead of the traditional coupled detection head. The improved algorithm was validated on the PASCAL VOC2012 dataset and the self‐built raw cotton impurity dataset collected by high‐speed camera. On the raw cotton impurity test set, compared to the original YOLO v4‐tiny model, the mean average precision (mAP) and frames per second (FPS) of the improved model increased by 10.35% and 6.9%, respectively. The proposed model detects white and near cotton‐coloured impurities with an accuracy of up to 98.78% and 98.00%. The experimental results show that the proposed method can effectively detect and identify impurities in raw cotton, which is of great practical significance for foreign matter detection and identification in cotton.

Gallium-doped zinc oxide: nonlinear reflection and transmission measurements and modeling in the ENZ region

Strong nonlinear materials have been sought after for decades for applications in telecommunications, sensing, and quantum optics. Gallium-doped zinc oxide is a II–VI transparent conducting oxide that shows promising nonlinearities similar to indium tin oxide and aluminum-doped zinc oxide for the telecommunications band. Here we explore its nonlinearities in the epsilon near zero (ENZ) region and show n 2,eff values on the order of 4.5 × 10−3 cm2GW−1 for IR pumping on 200–300 nm thin films. Measuring nonlinear changes in transmission and reflection with a white light source probe in the near-IR while exciting in the near-IR provides data in both time and wavelength. Three films varying in thickness, optical loss, and ENZ crossover wavelength are numerically modeled and compared to experimental data showing agreement for both dispersion and temporal relaxation. In addition, we discuss optimal excitation and probing wavelengths occur around ENZ for thick films but are red-shifted for thin films where our model provides an additional degree of freedom to explore. Obtaining accurate nonlinear measurements is a difficult and time-consuming task where our method in this paper provides experimental and modeled data to the community for an ENZ material of interest.

User-Centric Measures of the Perceived Light Qualities of Lighting Products

Nowadays, lighting planning is predominantly determined by the need to meet physically measurable requirements that are often based on current lighting standards. However, meeting the minimum technical requirements of the standards is no guarantee for a visually appealing light environment. Instead, requirements based on perceived light qualities also need to be included to achieve better user comfort. Taking perception-based qualities into consideration when creating a light environment is, for many, not an easy task. In addition, a common terminology for perceived light qualities is currently lacking, both in industry and in research. The aim of this paper is, therefore, to explore how perceived light qualities of white light sources can be described when employing user-centric measures. The focus was on the qualities of light colour and diffuse and distinct light since these qualities have a great impact on the visual impression of light. The perception was assessed by applying analytical sensory analysis to lighting products, a method found to be promising in previous work. The methodology is based on analytical measurement by the human senses, which is particularly valuable when developing a general terminology. Since sensory analysis is still quite new to the topic of lighting, the applicability of using the methodology to assess lighting in a real context was also investigated. The results of the studies showed that the perception of light qualities can be described using further concepts in addition to those currently used. For light colour, the concepts of reddish, bluish, yellowish, and greenish light colours proved suitable for providing a richer description of the quality. The concepts of diffuse and distinct light satisfactorily captured variations in light contrast produced by shadows, reflections, and sparkles. In addition, the studies revealed that analytical sensory analysis was applicable for assessing the perception of lighting in a real-world context. The latter means that knowledge gained in the laboratory can be translated into real environments. The user-centric measures investigated in this paper have contributed to the terminology related to perceived light qualities. These can complement the physical measures in lighting planning to promote light environments that are not only energy efficient and meet technical requirements, but also cater for increased user comfort. Doi: 10.28991/ESJ-2023-07-02-022 Full Text: PDF

Stable CsPbX3 (X = Cl, Br, I) Nanocrystal‐in‐Glass Composite (NGC) for Solid‐State Laser‐Driven White Light Generation

AbstractPerovskite CsPbX3 (X = Cl, Br, I) nanocrystals with advantages of high quantum yield, narrow emission peaks, and tunable fluorescence are considered as the next generation of light‐emitting sources. However, fluorescence degradation due to the poor stability of perovskite nanocrystals in moisture, high temperature, and illumination remains one of the greatest challenges in their further development. In this work, a fully dense coating strategy is proposed to improve the overall stability of perovskite nanocrystals, especially under high‐density laser irradiation. A mesoporous silica SiO2 layer is introduced to construct a stable coating for isolating the perovskite from external environment. To eliminate the pores of the CsPbX3@SiO2, an inorganic glass is also employed via solution‐combustion technique to generate a fully compact encapsulation for further stability promotion. The as‐prepared nanocrystal‐in‐glass composite exhibits efficient and stable fluorescence performance in luminous efficiency, chromaticity, and long‐term reliability in the conditions of thermal shock, humidity, and blue laser irradiation. With the integration of red/green/blue emitting nanocrystals, the color gamut of the white laser lighting source covers 134% of the National Television Standards Committee standard, providing exciting opportunity for high performance laser‐driven white light generation.

A Study on the Development of a White Light Source Module for a Large-Capacity Searchlight Using a Blue Laser Diode

In this paper, a large-capacity white light source module using a high-power blue laser diode and a reflective spaced phosphor was designed. The reflective spacing phosphor ensured thermal stability. The proposed white light module is a reflective phosphor structure with a bi-directional optical system based on a rhombus prism lens. The rhombus prism optical system can greatly narrow the blue laser beam width and a long-wavelength band-pass filter of 500 nm or more is applied to change the movement path of the laser beam and transmit white light excited by the phosphor. A dichroic filter was applied to the fold mirror part and a planar convex lens was designed to focus the blue laser beam so that the phosphor was irradiated. Finally, a high-power white light source is obtained from the pre-optics unit to which the dichroic filter is applied. In order to use the proposed white light source as a searchlight, a divergence angle of 4° or less is required. For this implementation, a large-area collimating lens combining an aspheric condensing lens and an achromatic lens was applied. It was confirmed that the divergence angle of 4 degrees or less was satisfied at the focal length (FL) of 38.5 to 42.5 mm of the optical lens of the laser white light module emitter and the collimating optical system.

Visible DC approach by controlling the UV light in (Eu3+/Tb3+) co-activated TBZN glasses for w-LEDs and a-Si solar cells

Borotellurite (TBZN: TeO2–B2O3–ZnO–Na2O) glasses co-activated with Eu3+ and Tb3+ ions were fabricated by a melt quenching method to know their ability for white light sources and solar converters. Amorphous nature, morphology, elemental mapping of the chemical composition, and functional groups of glasses were investigated. The down conversion (DC) process was studied on the luminescence characteristics of Eu3+/Tb3+ co-activated TBZN glasses by ultraviolet light (UV:351 & 378 nm) conversion and these glasses exhibit the characteristic red (5D0→7F1,2,3,4) luminescence of Eu3+ along with green (5D4→7F5) and blue (5D4→7F6) luminescence of Tb3+ ions in the visible region. Upon 378 nm of UV radiation, the co-activating of Tb3+ with Eu3+ ions improves the green and red DC emissions by 2 and 4 orders of magnitude due to energy transfer (ET) from Eu3+ to Tb3+, respectively. The evidence of ET: Eu3+ → Tb3+ is stated by the declining of red emission (%) and decay times from the 5D0 level of Eu3+ ions, and the reduction in decay times was confirmed to be dipole-dipole interaction in the means of Reisfeld and Dexter's ET process. The solar spectral performance of the excitation and de-excitation spectra of (Eu3+/Tb3+):TBZN glass system is imparted with the standard solar spectrum. Results are also discussed in terms of integrated intensity of red to green emission in (%), critical transfer distance (Rc), (x, y) color coordinates, correlated color temperatures (CCT), color purity (CP), and quantum efficiency (ηQE) values to discriminate the potentiality of (Eu3+/Tb3+):TBZN glass system in white light emitting diodes and solar cells.

Synthesis of Efficient and Stable Tetrabutylammonium Copper Halides with Dual Emissions for Warm White Light-Emitting Diodes.

In order to achieve high color rendering index (CRI) and low correlated color temperature (CCT) indoor lighting, single component phosphors with broadband dual emission emission are high demanded for white light emitting diodes (WLEDs). However, phosphors with such fluorescent properties are rare at present. Herein, we report a facile solid-state chemical method for the synthesis of single-component phosphor with broadband emission and large Stokes shift that can meet the requirements of future white light sources. These new tetrabutylammonium copper halides phosphors have excellent warm white emission characteristics, and their luminescence peaks located at 494 nm and 654 nm, respectively. The optimized photoluminescence (PL) quantum yield can reach 93.7%. The typical CIE coordinate of the as-fabricated WLED is at (0.3620, 0.3731) with CRI of 89 and low CCT of 4516 K.

The neglected influence of zinc oxide light‐soaking on stability measurements of inverted organic solar cells

AbstractAlthough zinc oxide (ZnO) is one of the most commonly used materials for electron transport layers in organic solar cells (OSCs), it also comes with disadvantages such as the so‐called light‐soaking issues, i.e., its need for exposure to UV light to reach its full potential in OSCs. Here, the impact of ZnO light‐soaking issues on stability measurements of OSCs is investigated. It is found that in the absence of UV light a reversible degradation occurs, which is independent of the used active layer material and accelerates at higher temperatures but can be undone with a short UV exposure. This reversible aging is attributed to the re‐adsorption of oxygen, which for manufacturing reasons is trapped at the interface of ZnO, even in an oxygen‐free environment. This oxygen can be removed with a UV pretreatment of the ZnO but at the expense of device efficiency and production that has to take place in an oxygen‐free environment. This study establishes that stability measurements of ZnO‐containing OSCs must be performed exclusively with a light source including a UV part since the usage of a simple white light source – as often reported in the literature – can lead to erroneous results.

The Impact of Trap-Assisted Tunneling and Poole–Frenkel Emission on Synaptic Potentiation in an α-Fe2O3/p-Si Memristive Device

A signature of synaptic potentiation conductance has been observed in an α-Fe2O3/p-Si device fabricated using spin coating. The conductance of the device in dark conditions and illumination with a white light source was characterized as a function of the application of a periodic bias (voltage) with a triangular profile. The conductance of the device increases with the number of voltage cycles applied and plateaus to its maximum value of 0.70 μS under dark conditions and 12.00 μS under illumination, and this mimics the analog synaptic weight change with the action potential of a neuron. In the range of applied voltage from 0 V to 0.7 V, the conduction mechanism corresponds to trap-assisted tunneling (TAT) and in the range of 0.7–5 V it corresponds to the Poole–Frenkel emission (PFE). The conductance as a function of electrical pulses was fitted with a Hill function, which is a measure of cooperation in biological systems. In this case, it allows one to determine the turn-on threshold (K) of the device in terms of the number of voltage pulses, which are found to be 3 and 166 under dark and illumination conditions, respectively. The gradual conductance change and activation after a certain number of pulses perfectly mimics the synaptic potentiation of neurons. In addition, the threshold parameter extracted from the Hill equation fit, acting as the number of pulses for synaptic activation, is found to have programmability with the intensity of the light illumination.

Evaluation of Growth and Photosynthetic Rate of Cucumber Seedlings Affected by Far-Red Light Using a Semi-Open Chamber and Imaging System

Far-red light was excluded in photosynthetic photon flux; however, recent studies have shown that it increases photosynthetic capacity. In addition, there were few studies on the whole canopy photosynthetic rate and continuous changes of morphology on cucumber seedlings affected by far-red light. This study evaluated the effect of conventional white LEDs adding far-red light on cucumber seedlings using a semi-open chamber system for the measurement of the whole canopy gas exchange rate, and the Raspberry Pi-based imaging system for the analysis of a continuous image. In the image, through the imaging system, it was confirmed that far-red light promoted the germination rate of cucumber seedlings and enhanced early growth. However, the dry weight of the shoot and root did not increase. The measured net apparent CO2 assimilation rate was improved by an increasing leaf area during the cultivation period. The conventional white LED light source with added far-red light increased the photosynthetic rate of cucumber seedlings’ whole canopy. However, at the early seedling stage, plant height and leaf area of the whole canopy was increased by far-red light, and it was revealed that the image data saturated faster. It was considered that the photosynthetic efficiency decreased due to a shading effect of the limited planting density of the cell tray. The results found that using appropriate far-red light, considering planting density, could increase the photosynthetic rate of the whole canopy of crops, thereby promoting crop growth, but it was judged that the use of far-red light in the early growth stage of cucumber seedlings should be considered carefully.

Self-powered photodetectors based on InxMo1-xS2 crystals

Transition metal dichalcogenides (TMDCs) have attracted global interest in recent years due to their optoelectronic characteristics and tunable bandgap energies. Due to their potential use in photovoltaic devices, photodetectors, and field effect transistor (FET) recording systems, single crystalline semiconductors of TMDC family have attracted a lot of attention. In the present article, the direct vapour transport technique was used to synthesis the InxMo1-xS2 (x = 0, 0.05, and 0.1) crystals. The purity and distribution of all the elements were investigated by EDAX mapping. The power X-ray diffraction technique examine the grown crystals have hexagonal lattice structure. The structure of all the crystals was investigated by scanning electron microscopy (SEM). The in-plane E2g and outer-plane A1g vibration modes were studied through Raman spectra. Photodetectors based on InxMo1-xS2(x = 0, 0.05, and 0.1) crystals show the self-powered photoresponse under white light source at 100 mW/cm2power intensity.

Programmable freeform optics with extended white light sources: possibilities and limitations.

Freeform optics can be used in lighting applications to generate accurate prescribed illumination patterns from compact light sources such as LEDs. When targeting dynamic illumination systems, a time-variable optical functionality is needed. Phase-only spatial light modulators (SLMs) have been used in the past for various dynamic beam shaping applications with monochromatic, zero-étendue illumination under paraxial conditions. Such limitations can no longer hold when considering lighting applications. In this paper, a novel algorithm for the calculation of smooth phase shift patterns is presented in order to generate arbitrary target patterns from arbitrary incident wave fronts for non-paraxial conditions. When applying such phase shift patterns to SLMs, these devices can be considered as programmable freeform optics. The experimental performance of the calculated phase patterns is analyzed on a real SLM, with a maximal phase shift of 6π, for collimated laser beams and white LEDs. The possibilities and limitations of generating accurate prescribed target patterns are critically discussed in terms of the angular extent of the target pattern, the consider spectrum of the light source and the étendue of the incident light beam.

A super-high brightness and excellent colour quality laser-driven white light source enables miniaturized endoscopy.

A laser-driven white light source promises intrinsic advantages for miniaturized endoscopic illumination. However, it remains a great challenge to simultaneously achieve high brightness and excellent colour rendition due to the shortage of highly efficient and thermally robust red-emitting laser phosphor converters. Here, we designed CaAlSiN3:Eu@Al (CASN@Al) converters with neglectable efficiency loss by tightly bonding all-inorganic phosphor films on an aluminium substrate. A layer-by-layer phosphor converter (LuAG/CASN@Al), i.e., stacking a green-emitting Lu3Al5O12:Ce (LuAG) layer on CASN@Al, was constructed to enhance light conversion efficiency and reduce reabsorption loss under blue laser excitation, which thus produces an excellent white light source with a luminous efficacy of 258 lm W-1 and a colour rendering index of 91. A miniaturized endoscopy with a coupling efficiency twice that of the commercial white LEDs was demonstrated by using the laser-driven white light and showed a central illuminance as high as 52 730 lx, more vivid images and long-term reliability.

The first evidence of antibiofilm action of Proteus mirabilis with tetra-cationic porphyrins containing cisplatin by antimicrobial photodynamic therapy.

Biofilms are responsible for up to 80% of antimicrobial-resistant nosocomial infections. Most of these infections are associated with medical devices such as urinary catheters, and in this context, it is estimated that 90-100% of patients who undergo long-term catheterization develop infections. Proteus mirabilis, the most prevalent microorganism, is responsible for 20-45% of these infections. Thus, this study aimed to evaluate, for the first time, the antimicrobial and antibiofilm effects of cationic porphyrins on P. mirabilis. Neutral porphyrins 3-H2TPyP and 4-H2TpyP and tetra-cationic derivatives 3-cis-PtTPyP and 4-cis-PtTPyP were evaluated in broth microdilution tests to determine the minimum inhibitory and bactericidal concentrations. Time-kill curves, checkerboard test, reactive oxygen species (ROS) scavenger assays, conventional biofilm formation, and biofilm assay with catheters were also performed. The microdilution tests showed greater efficacy against P. mirabilis when 3-cis-PtTPyP was exposed to white-light conditions; this also occurred when the microbial time-kill curve was performed at 0, 2, 6, and 12h. The radical superoxide species was possibly responsible for photoinactivation in the ROS scavenger assays. In biofilm assays (conventional and catheter), 3-cis-PtTPyP obtained better results when irradiated with a white-light source. In the checkerboard assay, the same compound showed no differences when tested in association with ciprofloxacin hydrochloride. Our findings lead us to conclude that antimicrobial photodynamic therapy and cationic porphyrins obtained positive results and are promising alternatives to treat P. mirabilis biofilms.

New glass ceramics: an effective conjunction of wet chemistry synthesis and sintering

A glass with CdS nanoparticles was used simultaneously as a matrix for Ce-doped garnet and a yellow-red phosphor to prepare luminescent glass ceramics for the sources of white light. CdS nanoparticles compensate for the unbalanced Ce3+ emission spectrum of the composite material due to the addition of a red component. The synthesized composite material can be a tunable light converter due to altered luminescence spectra by changing the sintering conditions and excitation wavelength

Expanding the color palette of bicolor-emitting nanocrystals.

Owing to their bright and tunable luminescence spectra, nanocrystals appear as a unique playground for light source design. Displays and lighting require white light sources that combine several narrow lines. As Kasha's rule prevents the emission of hot carriers, blends of multiple nanocrystal populations are currently the obvious strategy for broad-band source design. However, a few reports suggest that bicolor emission can also be obtained from a single particle even under weak excitation if a careful design of the exciton scattering mechanism sufficiently slows down its relaxation pathways. A key challenge remains to maintain quantum confinement for color tunability in the same structure, while simultaneously achieving a large size to leverage the critical, slower exciton diffusion or relaxation down to the ground state. Herein, we demonstrate that 2D nanoplatelets offer an original opportunity for the design of confined and large heterostructures. We demonstrate that bicolor emission is not limited to green-red pair and show that blue-yellow and purple-green emissions can be obtained from CdSe/CdTe/CdSe core/crown/crown and CdSe/CdS core/crown heterostructures, respectively.

High color rendering and high-luminance laser lighting using all inorganic nitride phosphor films.

Despite the huge advances that have been made in the development of ultra-high luminance laser lighting, achieving high color rendering properties in such systems at the same time remains a challenge. Recent studies show that in most cases, the luminous efficacy (LE) of laser lighting is compromised to improve the color rendering index (CRI). In this study, a possible solution to this problem has been proposed by preparing phosphor-in-glass (PiG) films comprised of the yellow-emitting phosphor (LSN:Ce3+) and the red-emitting phosphor (CASN:Eu2+). The composite material synthesized in this study exhibited outstanding optical and thermal properties. A uniform white light with a high CRI of 80.0 and a high LE of 185.9 lm W-1 was achieved by optimizing the yellow/red ratio and the emission peak position of the blue laser. Furthermore, it was found that this design enabled the phosphor to restrict the light emission area effectively, thus attaining a high luminous exitance of 1302 lm mm-2. With their superior optical performance, the PiG films can be regarded as promising color converter candidates for future high-quality laser-based white light sources.

Tunable Emission Wavelength and Chromaticity Electroluminescence Realized in Ho Doped ZnO Microspheres Heterojunction

Tunable white light sources have huge potential applications in the scope of intelligent lighting or high-quality display system, but it is still a challenge to tune the emission wavelength and chromaticity in a simple structure. Herein, the Ho3+ doped ZnO microsphere was bonded onto the p-GaN substrate to form a heterojunctional light-emitting diode. Through a combination of the light confinement effect in the ZnO microsphere and multilevel emission system in rare earth materials, the device demonstrates tunable electroluminescence (EL) both in wavelength and chromaticity. The device shows broadband emission peak at 400 nm with full width at half maximum (FWHM) of 34 nm under forward pulsed driven bias. While it shows a series of sharp emissions from rare earth ions Ho3+ with peaks at 427 nm, 492 nm, 567 nm, 592 nm and 654 nm and FWHM less than 1.3 nm under reverse pulsed driven bias. More meaningful, the wavelength and chromaticity can be controlled with duty cycle or the rate of forward and reverse driven bias under intelligent programmable alternating current (AC) driven. Finally, the gradient from blueviolet light to white light can be realized.

High-efficiency all fluorescence white OLEDs with high color rendering index by manipulating excitons in co-host recombination layers.

All fluorescence white organic light-emitting diodes (WOLEDs) based on thermally activated delayed fluorescence (TADF) emitters are an attractive route to realize highly efficient and high color quality white light sources. However, harvesting triplet excitons in these devices remains a formidable challenge, particularly for WOLEDs involving conventional fluorescent emitters. Herein, we report a universal design strategy based on a co-host system and a cascaded exciton transfer configuration. The co-host system furnishes a broad and charge-balanced exciton generation zone, which simultaneously endows the devices with low efficiency roll-off and good color stability. A yellow TADF layer is put forward as an intermediate sensitizer layer between the blue TADF light-emitting layer (EML) and the red fluorescence EML, which not only constructs an efficient cascaded Förster energy transfer route but also blocks the triplet exciton loss channel through Dexter energy transfer. With the proposed design strategy, three-color all fluorescence WOLEDs reach a maximum external quantum efficiency (EQE) of 22.4% with a remarkable color rendering index (CRI) of 92 and CIE coordinates of (0.37, 0.40). Detailed optical simulation confirms the high exciton utilization efficiency. Finally, by introducing an efficient blue emitter 5Cz-TRZ, a maximum EQE of 30.1% is achieved with CIE coordinates of (0.42, 0.42) and a CRI of 84 at 1000 cd m-2. These outstanding results demonstrate the great potential of all fluorescence WOLEDs in solid-state lighting and display panels.

Efficient second- and higher-order harmonic generation from LiNbO3 metasurfaces.

Lithium niobate (LiNbO3) is a material that has drawn great interest in nonlinear optics because of its large nonlinear susceptibility and wide transparency window. However, for complex nonlinear processes such as high-harmonic generation (HHG), which involves frequency conversion over a wide frequency range, it can be extremely challenging for a bulk LiNbO3 crystal to fulfill the phase-matching conditions. LiNbO3 metasurfaces with resonantly enhanced nonlinear light-matter interaction at the nanoscale may circumvent such an issue. Here, we experimentally demonstrate efficient second-harmonic generation (SHG) and HHG from a LiNbO3 metasurface enhanced by guided-mode resonance. We observe a high normalized SHG efficiency of 5.1 × 10-5 cm2 GW-1. Moreover, with the alleviated above-gap absorption of the material, we demonstrate HHG up to the 7th order with the shortest generated wavelength of 226 nm. This work may provide a pathway towards compact coherent white-light sources with frequency spanning into the deep ultraviolet region for applications in spectroscopy and imaging.