White Light Spectrum Research Articles

Robust structure, spectral adjustability of single-component silicate oxyapatite Sr2La8(SiO4)6O2: Ce/Tb/Sm toward phosphor-converted wLEDs application

The lack of photons in electromagnetic spectrum region of 400–450 nm, termed cyan gap among other photoluminescence (PL) coverage issues, confines the full-visible- spectrum white light's overall capability for color rendering in part of previously studied single-component phosphors. Herein, we have mechanistically investigated that a Ce3+ incorporated silicate oxyapatite Sr2La8(SiO4)6O2 (SLS) phosphor, via a facile sol-combustion synthesis under low temperature, shows efficient cyan PL with broad full width at half maxima (fwhm, ∼90 nm) and high quantum yield (QY, ∼46.3 %) as a result of tendentious dual-site occupations and parity-allowed 4f1 ↔ 5d transitions of Ce3+, based on a combination of steady/transient-state spectroscopy and theoretical calculations. According to the principle of color superposition, the color-tunable PL, including the white emission with low coordinated color temperature (CCT) and high color rendering index (CRI), is realized by further codoping the characteristic green/red line emissions from Tb3+ and Sm3+ ions in the SLS: Ce. The low PL QY (∼32.7 %) from the monodoped Tb or Sm, due to its forbidden 4f-4f transitions, is cleverly alleviated via cascade-connected energy transfer (ET) from Ce → Tb → Sm. The direct ET from Ce → Sm is hardly occurred because of the metal-mental charge transfer (MMCT) effect. Finally, a prototype pc-wLED assembled via a remote ‘capping’ packaging strategy and using only the stably composition-optimized white-emitting SLS: Ce/Tb/Sm demonstrates attractive performance of the designed device (CCT 4243 K, CRI (Ra) 87, CIE (0.365, 0.381), and LE 76 lm⋅W−1 under 120 mA) and the phosphor is promising for high-quality of light.

Luminescence and spectroscopic studies on Dy3+-Eu3+ doped SiO2-B2O3-ZnO-La2O3-BaO glass for WLED

A series of SiO2-B2O3-ZnO-La2O3-BaO (SBZLBa) glasses doped with Dy3+ and Eu3+ were synthesized using the melt-quenching technique. Their optical characteristics and potential applications in W-LED devices were investigated. The structural effects resulting from doping the glass with Dy3+ and Eu3+ ions were elucidated through infrared spectroscopy and an examination of the physical properties. The variations in emission intensity within the fluorescence spectrum validated the sensitizing effect of Dy3+ on Eu3+ within the glass matrix. By manipulating the transitions of both Dy3+ and Eu3+, the excitation wavelength was altered, enabling the realization of cool white, neutral white, and warm white luminescence, thus accommodating the diverse requirements for white light emission in lighting applications. After incorporating 1.0 mol% of Dy2O3 and 0.8 mol% of Eu2O3, respectively, the glass exhibited CIE coordinates of (0.3332, 0.3535), positioning it within the white light spectrum and in close proximity to the ideal white light coordinates of (0.33, 0.33). The SBZLBa-Dy2O3–0.8Eu2O3 glass exhibited a quantum yield of 5.98 %. It has been demonstrated through acid and alkali resistance tests that this glass possesses excellent chemical stability. Additionally, temperature-dependent emission spectra have revealed that the luminous intensity of the glass maintains over 85 % of its room temperature value at 185 °C, with Eα determined to be 0.2387 eV.

DEVELOPMENT OF AN EFFICIENT OPTICAL MODEL FOR LEDS-BASED WHITE LIGHT SPECTRUM DESIGN APPLICATIONS

We have developed an efficient optical model for simulating the white light spectrum design with high color performance. The optical model began with experimental data collection, simulation with the mathematical model using Gaussian functions, and verifying the similarity between simulation and experiment. In application, the model is applied to study the effect of red light on the optical properties of the generated white light spectrum. The obtained results indicate that the established model is helpful for the solid-state lighting application to fabricate a light source that can emit white light with high optical performance.

Phototoxicity of low doses of light and influence of the spectral composition on human RPE cells

Light is known to induce retinal damage affecting photoreceptors and retinal pigment epithelium. For polychromatic light, the blue part of the spectrum is thought to be the only responsible for photochemical damage, leading to the establishment of a phototoxicity threshold for blue light (445 nm). For humans it corresponds to a retinal dose of 22 J/cm2. Recent studies on rodents and non-human primates suggested that this value is overestimated. In this study, we aim at investigating the relevance of the current phototoxicity threshold and at providing new hints on the role of the different components of the white light spectrum on phototoxicity. We use an in vitro model of human induced pluripotent stem cells (hiPSC)-derived retinal pigment epithelial (iRPE) cells and exposed them to white, blue and red lights from LED devices at doses below 22 J/cm2. We show that exposure to white light at a dose of 3.6 J/cm2 induces an alteration of the global cellular structure, DNA damage and an activation of cellular stress pathways. The exposure to blue light triggers DNA damage and the activation of autophagy, while exposure to red light modulates the inflammatory response and inhibits autophagy.

Femtosecond pulse shaper built into a prism compressor.

We present a frequency domain, AOM-based pulse shaper that utilizes Brewster prisms rather than the current standard of gratings. In doing so, we demonstrate a three-fold increase in efficiency and the ability to compensate for temporal dispersion created by the acousto-optic modulator that filters the pulse spectrum. The shaper is tested between the wavelengths of 520-660 and 840-1170 nm, creating sub-50 fs pulses for each, and used to collect a 2D white-light spectrum of a thin film of semiconducting carbon nanotubes.

Mitigating modal noise in multimode circular fibres by optical agitation using a galvanometer

Abstract Modal noise appears due to the non-uniform and unstable distribution of light intensity among the finite number of modes in multimode fibres. It is an important limiting factor in measuring radial velocity precisely by fibre-fed high-resolution spectrographs. The problem can become particularly severe as the fibre’s core become smaller and the number of modes that can propagate reduces. Thus, mitigating modal noise in relatively small core fibres still remains a challenge. We present here a novel technique to suppress modal noise. Two movable mirrors in the form of a galvanometer re-image the mode-pattern of an input fibre to an output fibre. The mixing of modes coupled to the output fibre can be controlled by the movement of mirrors applying two sinusoidal signals through a voltage generator. We test the technique for four multimode circular fibres: 10 and 50 $\mu$m step-index, 50 $\mu$m graded-index, and a combination of 50 $\mu$m graded-index and 5:1 tapered fibres (GI50t). We present the results of mode suppression both in terms of the direct image of the output fibre and spectrum of white light obtained with the high-resolution spectrograph. We found that the galvanometer mitigated modal noise in all the tested fibres, but was most useful for smaller core fibres. However, there is a trade-off between the modal noise reduction and light-loss. The GI50t provides the best result with about 60 per cent mitigation of modal noise at a cost of about 5 per cent output light-loss. Our solution is easy to use and can be implemented in fibre-fed spectrographs.

High-performance warm-white OLEDs using interfacial exciplex energy transfer with external quantum efficiency exceeding 30%

To achieve energy-saving and environmentally friendly warm white lighting through the simplification of white organic light-emitting device (WOLED) structure and manufacturing process, we designed and optimized a WOLED by incorporating bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III)(FIrpic)-doped 4,4′,4′-tris(N-carbazolyl)triphenylamine(TCTA) and bis(4-phenylthieno[3,2-c]pyridinato-N,C2')(acetylacetonate)iridium(III)(PO-01)-doped 2,2',2′'-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)(TPBI) thin films as the blue and yellow emissive layer (EML), respectively, and forming an exciplex at TCTA and TPBI interface. By adjusting the doping concentration and position within the EML and the thickness of the transport layer, we achieved the optimal emission balance between the blue and yellow colors in the proposed WOLED. We successfully fabricated a highly efficient and structurally simplified WOLED without the use of light extraction coupling techniques, which exhibited high external quantum efficiency (EQE) of 32.6% and current efficiency (CE) of 80.3 cd/A, along with stable emission color with minimal CIE variation of ΔCIE(0.0027, 0.0023) from 500 cd/m² to 5000 cd/m². The experimental results revealed that the designed device structure with the triple host system (TCTA, TPBI, and interface exciplex) facilitated the widening of the recombination zone (RZ), enhanced exciton confinement and utilization, reduced triplet-triplet annihilation (TTA) effects, and achieved efficient host-guest energy transfer. Furthermore, the designed WOLED emitted warm white light spectrum suitable for healthy lighting applications. Therefore, we believe that our work contributes to the further development of ideal and simplified WOLED structure designs for achieving high-efficiency, simplified manufacturing, low-cost, energy-saving, and environmentally friendly healthy lighting.

Optimal Laboratory Cultivation Conditions of Limnospira maxima for Large-Scale Production.

Cultivating Limnospira maxima, renowned for its abundant proteins and valuable pigments, faces substantial challenges rooted in the limited understanding of its optimal growth parameters, associated high costs, and constraints in the procurement of traditional nitrogen sources, particularly NaNO3. To overcome these challenges, we conducted a comprehensive 4 × 3 factorial design study. Factors considered included white, red, blue, and yellow light spectra, along with nitrogen sources NaNO3 and KNO3, as well as a nitrogen-free control, for large-scale implementation. Optimal growth, measured by Optical Density, occurred with white and yellow light combined with KNO3 as the nitrogen source. These conditions also increased dry weight and Chl-a content. Cultures with nitrogen deprivation exhibited high values for these variables, attributed to carbon accumulation in response to nitrogen scarcity. Phycocyanin, a crucial pigment for nutrition and industry, reached its highest levels in cultures exposed to white light and supplemented with KNO3, with an impressive content of 384.11 g kg-1 of dry weight. These results highlight the efficacy and cost-efficiency of using a combination of white light and KNO3 for large-scale L. maxima cultivation. This strategy offers promising opportunities to address global food security challenges and enhance the production of industrially relevant pigments.

Growth, photosynthetic function, and stomatal characteristics of Persian walnut explants in vitro under different light spectra.

Light plays a crucial role in photosynthesis, which is an essential process for plantlets produced during in vitro tissue culture practices and ex vitro acclimatization. LED lights are an appropriate technology for in vitro lighting but their effect on propagation and photosynthesis under in vitro condition is not well understood. This study aimed to investigate the impact of different light spectra on growth, photosynthetic functionality, and stomatal characteristics of micropropagated shoots of Persian walnut (cv. Chandler). Tissue-cultured walnut nodal shoots were grown under different light qualities including white, blue, red, far-red, green, combination of red and blue (70:30), combination of red and far-red (70:30), and fluorescent light as the control. Results showed that the best growth and vegetative characteristics of in vitro explants of Persian walnut were achieved under combination of red and blue light. The biggest size of stomata was detected under white and blue lights. Red light stimulated stomatal closure, while stomatal opening was induced under blue and white lights. Although the red and far-red light spectra resulted in the formation of elongated explants with more lateral shoots and anthocyanin content, they significantly reduced the photosynthetic functionality. Highest soluble carbohydrate content and maximum quantum yield of photosystem II were detected in explants grown under blue and white light spectra. In conclusion, growing walnut explants under combination of red and blue lights leads to better growth, photosynthesis functionality, and the emergence of functional stomata in in vitro explants of Persian walnuts.

Synthesis and cis-trans kinetics of an azobenzene-based molecular switch for light-responsive silica surfaces

Light-responsive materials design is an attractive research field that stimulates demand for the synthesis of novel molecular photoswitches. The novel photoswitches should be capable of being attached to a desired surface in order to provide it with light-responsive properties. The switchback to its ground state is expected to be gradual, with the possibility of acceleration. This study presents a comprehensive description of a chemical route to a molecular photoswitch based on an azobenzene derivative with a trifluoromethoxy group and a long alkyl chain. The photoswitch is capable of modifying submicrometer silica particles and silicon wafers as models of curved and flat surfaces, respectively. The thermal relaxation times of the synthesized azobenzene were studied in three different solvents: ethanol, chloroform, and toluene. The results reveal a significantly delayed relaxation process lasting for several days. This observation is found to be related to the polarity of the solvents used. To characterize the extensive thermal relaxation process, a methodology including the use of white-light pulses to accelerate cis-trans isomerization is suggested. The white light spectrum used in pulses affects thermal relaxation but does not alter the relaxation time extrapolated to zero. The density of the photoswitch molecules attached to particles varies from 0.7 to 1.7 molecules/nm2 as the initial amount of azobenzene in the reaction increases. Surface-attached photoswitches demonstrate reversible cis-trans isomerization behavior when exposed to UV and white light irradiation. A 14° contact angle change is observed when flat surfaces modified with photoswitches are irradiated with UV light.

Effect of light spectra on in vitro multiplication, elongation and adventitious rooting stages of Bambusa vulgaris Schrad. ex J. C. Wendl.

Bamboos occur throughout much of the temperate and tropical world, have rapid growth, and have various commercial and environmental applications. Clonal production of selected plants on a industrial scale is an important strategy for the bamboo sector. This study aimed to evaluate the effects of the light spectrum on in vitro multiplication, elongation, adventitious rooting, and anatomical features of the leaf surface of Bambusa vulgaris. In the multiplication and elongation stages, in vitro–established explants were transferred to a culture medium supplemented with 8.88 µmol of 6-benzylaminopurine (BAP) and 2.69 µmol of α-naphthalene acetic acid (NAA), and subjected to four light spectra (i.e., white, blue, green, and red). At the adventitious rooting stage, the culture medium was supplemented with 9.84 µmol of indole-3-butyric acid (IBA), 5.37 µmol NAA, and 2.22 µmol BAP under identical light spectra. Explant survival was not influenced by light spectra in the multiplication and elongation stages. White (2.2 shoots) and blue (1.8 shoots) light spectra were the most suitable for the number of shoots per explant. The white spectrum was associated with the highest average length of shoots (7.4 cm) and number of leaves per explant (3.0 leaves). The white light spectrum resulted in the highest average chlorophyll a contents (12.60 µg mg−1), total chlorophyll (16.60 µg mg−1), and carotenoids (10.10 µg mg−1). White and blue light spectra resulted in the best responses for vigor, and least senescence and tissue oxidation. White and blue light spectra favored the chlorophyll b content, resulting in 4.60 and 3.60 µg mg−1, respectively. Survival (80.0 %), adventitious rooting (50.0 %), vigor, senescence, and tissue oxidation were favored in the white light spectrum in the adventitious rooting stage. Scanning electron microscopy of leaves exposed to the white light spectrum revealed microtrichomes and spines on the adaxial surface of the leaf blade, papillae and stomata; on the abaxial surface, there were many unicellular trichomes arranged in rows, denoting normal growth and development. These results may help the production of micropropagated plants of Bambusa vulgaris on an industrial scale.

Effect Of Light Spectrum LED Lettuce on IOT-Based Indoor Farming

Lettuce (Lactuca sativa L.) is an economically important crop worldwide and one of the most popular species grown in indoor farming. Lettuce's fast growth and growing cycle make lettuce a model plant to study the interaction between plants and light. The influence of light is one of the fundamental environmental factors for plant growth and development. Light-emitting diodes (LEDs) have higher light efficiency and higher wear efficacy, leading to a reduction in associated heating compared to other artificial lighting sources, such as fluorescent lamps or sodium vapor lamps. This research aimed to determine different responses of the morphological response of lettuce by giving LED light spectrum with a single color spectrum difference and IOT-based temperature and humidity monitoring. This research used a t-student test with a level of 5% on the mean value of the white light spectrum with a yellow light on lettuce plants. The addition of the LED light spectrum produces a different response to the morphological parameters. The addition of the LED spectrum gave a response to the plant height variable, where the provision of a yellow LED light spectrum resulted in plant height which affected lettuce plants

Far-Red Light Mediated Carbohydrate Concentration Changes in Leaves of Sweet Basil, a Stachyose Translocating Plant.

Photosynthetic active radiation (PAR) refers to photons between 400 and 700 nm. These photons drive photosynthesis, providing carbohydrates for plant metabolism and development. Far-red radiation (FR, 701-750 nm) is excluded in this definition because no FR is absorbed by the plant photosynthetic pigments. However, including FR in the light spectrum provides substantial benefits for biomass production and resource-use efficiency. We investigated the effects of continuous FR addition and end-of-day additional FR to a broad white light spectrum (BW) on carbohydrate concentrations in the top and bottom leaves of sweet basil (Ocimum basilicum L.), a species that produces the raffinose family oligosaccharides raffinose and stachyose and preferentially uses the latter as transport sugar. Glucose, fructose, sucrose, raffinose, and starch concentrations increased significantly in top and bottom leaves with the addition of FR light. The increased carbohydrate pools under FR light treatments are associated with more efficient stachyose production and potentially improved phloem loading through increased sucrose homeostasis in intermediary cells. The combination of a high biomass yield, increased resource-use efficiency, and increased carbohydrate concentration in leaves in response to the addition of FR light offers opportunities for commercial plant production in controlled growth environments.

Achieving white light emission by modulating the degree of ring opening of a diphenyl imidazole derivative

The white light emission arises from a single organic molecule, which is significant for simplifying the device preparation process and obtaining a stable white light spectrum. Unfortunately, white light emission from most single organic molecules is achieved by controlling molecules in the ground or excited state to produce a new generation of luminescent species (complementary color mode). Such newly generated species are difficult to obtain individually. Herein, a new compound named (E)-N,N-diphenyl-4-(4-(1,4,5-triphenyl-1H-imidazole-2-yl)styryl)aniline (TPASt-PIM) was synthesized in this paper. The organic/inorganic hybrid LED device was prepared by placing TPASt-PIM in silica gel and covering it on a UV chip. A part of TPASt-PIM was used to generate N-((Z)-(benzoylimino)(4-((E)-4-(diphenylamino)styryl)phenyl)methyl)-N-phenylbenzamide (TPASt-PYZ) by photo-oxidation in the device to achieve white light emission. In addition, TPASt-PYZ was prepared and isolated. The mechanism by which TPASt-PIM can emit white light emission in the device was explored. The results show that the photo-oxygenation process of TPASt-PIM in the device can be used to obtain white light emission and achieve energy saving and green utilization because the additional synthesis of TPASt-PYZ is avoided.

Audio Transmission Using Visible Light Communication Technology with Pre-Equalization Technique

Abstract: The Visible Light Communication (VLC) is the emerging technology that aims to offer high speed internet access in indoor environment. This technology basically uses intensity modulation of current lighting infrastructure, which is provided by Light Emitting Diodes. During the implementation of this technology there may be Inter Symbol Interference (ISI) and power loss in free space channel, in order to overcome this problem and to utilize white light spectrum fully for effective transmission of data several techniques are followed. In this paper, the pre-equalization technique is chosen and implemented for audio transmission. The Pre-equalization of data is performed using MATLAB 2022a Graphical User Interface (GUI) and then feed to designed real-time VLC system. Pre-equalization of audio data improves sound quality and maintained it throughout the transmitting distance which is in Line Of Sight. The optical power distribution of the signal at an indoor environment for chosen white LED for audio transmission is also observed.

Exposure to cyan or red light inhibits the axial growth of zebrafish eyes

Myopia, or nearsightedness, is the most common type of refractive error and is characterized by a mismatch between the optical power and ocular axial length. Light, and more specifically the spectral composition of light, has been known to influence myopic axial growth. In this pilot study, we exposed zebrafish to illuminations that vary in spectral composition and screened for changes in axial length. The illumination spectra included narrow band ultra-violet A (UVA) (peak wavelength 369 nm), violet (425 nm), cyan (483 nm), green/yellow (557 nm), and red (633 nm) light, as well as broad band white light (2700 K and 6500 K), dim white light and broad spectrum (day) light. We found that rearing zebrafish in cyan or red light leads to a reduction of the ocular axial length. The results of this pilot study may contribute to new perspectives on the role of light and lighting as an intervention strategy for myopia control.

The influence of LED lighting on the development of Monarda L. in the conditions of hydroponics

The article presents the results of a study of the significance of the influence of the white and combined (red-blue-white) light spectrum on the growth and productivity of plants of the genus Monarda L. in the conditions of hydroponics. The optimal lighting mode has been found for the highest productivity of the monarda. A quantitative analysis of the content of photosynthetic pigments was carried out. The yield, leaf size and content of photosynthetic pigments in monarda leaves when grown under white LED lamps turned out to be higher than under colored ones.

Single-component and white-emitting garnet-type phosphors Li3Y3Te2O12: Dy3+, Eu3+ with tunable color and high thermostability: Synthesis, luminescence and energy transfer

The discovery of novel Dy3+- activated and Dy3+/Eu3+ co- activated Li3Y3Te2O12 phosphors with garnet-type was successfully achieved by high temperature solid-state sintering method. The phase purity, effects of the doping concentration of sensitizer and activator on the phase structure, as well as morphology characterization were ascertained using X-ray powder diffraction, the Rietveld refinement method, Fourier transform infrared spectrum and scanning electron microscope. Morphology and detailed photoluminescence behavior were examined via chromaticity coordinate of International Commission on illumination, steady-state and dynamic fluorescence spectra. The absorption spectrum of phosphors mentioned above possess strong response in the range of 350–400 nm, and the white-light emission spectrum consisting of two comparable intensities of blue- and yellow-emitting. The yellow one belongs to the hypersensitive forced dipole transition of 4F9/2–6H13/2, originated from inversion asymmetry of Dy3+ occupied sites in Li3Y3Te2O12 matrix. The concentration quenching mechanism of Dy3+ were identified to be the interactions between dipoles. Dy3+ → Eu3+ energy transfer phenomenon in Li3Y3Te2O12 host were observed and evaluated via PL curves and decay process. The Dexter’s theory and Reisfeld’s approximation are employed to reveal the energy transfer mechanism between sensitizers and activators and energy transfer efficiency in depth. The results indicate that utilizing Dy3+ → Eu3+ energy transfer was conducive to promote white → red tunable color emission. Furthermore, the as-prepared phosphors have been proved to own excellent thermal stability, indicating that it can be used as a promising single-component and white-emitting candidate in the design of ultraviolet-pumped white solid-state lighting.

The Effect of White Light Spectrum Modifications by Excess of Blue Light on the Frost Tolerance, Lipid- and Hormone Composition of Barley in the Early Pre-Hardening Phase.

It is well established that cold acclimation processes are highly influenced, apart from cold ambient temperatures, by light-dependent environmental factors. In this study we investigated whether an extra blue (B) light supplementation would be able to further improve the well-documented freezing tolerance enhancing effect of far-red (FR) enriched white (W) light. The impact of B and FR light supplementation to white light (WFRB) on hormone levels and lipid contents were determined in winter barley at moderate (15 °C) and low (5 °C) temperatures. Low R:FR ratio effectively induced frost tolerance in barley plantlets, but additional B light further enhanced frost hardiness at both temperatures. Supplementation of WFR (white light enriched with FR light) with B had a strong positive effect on abscisic acid accumulation while the suppression of salicylic acid and jasmonic acid levels were observed at low temperature which resembles the shade avoidance syndrome. We also observed clear lipidomic differences between the individual light and temperature treatments. WFRB light changed the total lipid content negatively, but monogalactosyldiacylglycerol (MGDG) content was increased, nonetheless. Our results prove that WFRB light can greatly influence phytohormone dynamics and lipid contents, which eventually leads to more efficient pre-hardening to avoid frost damage.

Insights into molecular cluster materials with adamantane-like core structures by considering dimer interactions.

A class of adamantane-like molecular materials attracts attention because they exhibit an extreme non-linear optical response and emit a broad white-light spectrum after illumination with a continuous-wave infrared laser source. According to recent studies, not only the nature of the cluster molecules, but also the macroscopic structure of the materials determines their non-linear optical properties. Here we present a systematic study of cluster dimers of the compounds AdR4 and [(RT)4 S6 ] (T=Si, Ge, Sn) with R=methyl, phenyl or 1-naphthyl to gain fundamental knowledge about the interactions in the materials. For all compounds, a similar type of dimer structures with a staggered arrangement of substituents was determined as the energetically most favorable configuration. The binding energy between the dimers, determined by including London dispersion interactions, increases with the size of the core and the substituents. The cluster interactions can be classified as substituent-substituent-dominated (small cores, large substituents) or core-core-dominated (large cores, small substituents). Among various possible dimer conformers, those with small core-core distances are energetically preferred. Trimer and tetramer clusters display similar trends regarding the minimal core-core distances and binding energies. The much lower energy barrier determined for the rotation of substituents as compared to the rotation of the cluster dimers past each other indicates that the rotation of substituents more easily leads to different conformers in the material. Thus, understanding the interaction of the cluster dimers allows an initial assessment of the interactions in the materials.