Spectra Of Light-emitting Diodes Research Articles

Highly thermally stable CaLaMgSbO6: Sm3+ double perovskite phosphors for optical thermometer and plant growth

A series of CaLaMgSbO6: Sm3+ orange-red phosphors were synthesized using a high-temperature solid-state method. These phosphors' phase, luminescence properties, and thermal stability were thoroughly investigated. Under 405 nm excitation, the CaLaMgSbO6: Sm3+ phosphor exhibit a broadband orange-red emission with the maximum emission peak positioned at 598 nm. The optimal CaLaMgSbO6: 0.025Sm3+ phosphor features CIE chromaticity coordinates of (0.5902, 0.4085) with an orange-red hue. Impressively, the emission intensity at 423 K remains at 78.7 % of its room temperature intensity, which shows its outstanding thermal stability. The emission spectra of light-emitting diodes (LEDs) fabricated with CaLaMgSbO6: 0.025Sm3+ phosphor possess a large overlap with the absorption band of phytochromes. Meanwhile, the temperature-sensing properties of CaLaMgSbO6: Sm3+ phosphors were studied across various wavelength bands using the fluorescence intensity ratio (FIR) technique. The relative sensitivity of FIR (I598/I563) was found to be highest at 298 K, measuring 0.15 % K−1. The above research results suggest that CaLaMgSbO6: Sm3+ phosphors have potential applications in plant growth and optical temperature sensing.

(Invited) Non-Fullerene Acceptor in Organic Solar Cells Toward Improving Performance as Indoor Light Energy Harvester

Research in organic solar cells aims to develop new materials that improve efficiency. The inception of emerging non-fullerene acceptors (NFAs) by replacing the fullerene counterpart in organic solar cells (OSCs) has pushed the bulk-heterojunction based photovoltaics to achieve efficiencies around 18% [1-6]. In order to produce efficient OSCs, it is required to have donor and acceptor materials with matching absorption bands in the Vis-NIR range, high charge-carrier mobility, and a small energy offset to minimize voltage losses. Mainly, the development of Y7 NFA molecule has improved power conversion efficiencies by pairing selected polymer donors, such as PM6 [7, 8]. Nowadays, OSCs have attracted great attention for being used as indoor light energy harvesters. The organic materials in the active layer can have tuned optical band gaps, providing an absorption spectrum that matches with emission spectra of several indoor lights, e.g., halogen lights, LED (light-emitting diodes), and FLs (fluorescent lamp), which have different emitting spectra [9, 10].The use of OSCs for indoor light harvesting applications is promising for integration into low-power indoor electronic devices from microwatts to milliwatts, such as data transfer systems, alarm systems and distributed controls. Moreover, the OSCs have the possibility to be used with power wireless sensor nodes connected to the Internet of Things. At present, LEDs are the most popular low-light level sources which can be found in offices and homes. The intensity of the light emitted by an artificial light source, per unit area of a surface is called illuminance and measured in units of lux (lx). A level 500 lx is typically recommended for office environments and 200 lx for living room environments.In this research, we have been aiming at the performance and stability over time of organic solar cells under LED illumination using fullerene and non-fullerene acceptors. We have chosen as the indoor illumination source an LED lamp with a color temperature of 3000 K and color rendering index (CRI) > 80 following the protocols ISOS [11]. The LED lamp output illuminances were varied in the range from 200 to 1500 lx. We have used PM6 as polymer donor material due to their absorption spectrum and energy band gaps well-matched to the incident LED spectrum. In order to research the improvement of the performance of OSCs under indoor illumination we have compared PC70BM fullerene acceptor with ITIC-M, Y6-O, and Y7 non-fullerene acceptors. As a result, under 1000 lx illumination we achieved PCEs from ~ 12% using Y6-O, ~ 15% using PC70BM, ~16% using Y7 up to more than 18% efficiency using ITIC-M. The study is performed including optical and electrical characterization with the purpose of understanding the behavior and the transport processes taking place in the device. In future work, we focus on the stability of the encapsulated OSCs under continuous LED illumination following the agreed stability testing protocols to study which active layer turns out to be more stable under these conditions. Acknowledgements: This work was supported by the Ministerio de Ciencia, Innovación y Universidades (MICINN/FEDER) PDI2021-128342OB-I00, by the Agency for Management of University and Research Grants (AGAUR) ref. 2021-SGR-00739, and by the Catalan Institution for Research and Advanced Studies (ICREA) under the ICREA Academia Award. M. Ramírez-Como acknowledge to CONAHCYT ref. BPPA-20220624083033039-2364083.

Effects of Light Spectrum on Survival, Growth, Physiological, and Biochemical Indices of Redclaw Crayfish (Cherax quadricarinatus) Juveniles

The spectrum is a key environmental factor, and light-emitting diodes (LEDs) can influence the growth and development of crustaceans by altering the composition of the spectrum. This study conducted a 30-day experiment to investigate the effects of five LED spectra (red, yellow, blue, green, and white light) on the growth, antioxidant and immune enzyme activities, stress hormone levels, and the expression of α-amylase (α-AMY), ecdysone receptor (EcR) and retinoid X receptor (RXR) genes in juvenile redclaw crayfish (Cherax quadricarinatus). The results show that the survival rate of juveniles is markedly higher in the yellow and red-light groups than in the other three groups (P<0.05). The green light group exhibits the lowest survival rate, yet it demonstrates the highest weight gain rate and specific growth rate. Regarding enzyme activity and hormone levels, the yellow light group shows the lowest malondialdehyde content, with higher superoxide dismutase and acid phosphatase activity than the other groups; no significant differences are observed in lysozyme activity among the groups (P>0.05). The melatonin content in the green and blue light groups is significantly higher than that in the other three groups (P<0.01). In terms of growth gene expression, the expression of α-AMY, EcR, and RXR in juvenile C. quadricarinatus is regulated by the spectrum. In conclusion, when raised under the yellow light spectrum, juvenile C. quadricarinatus displays elevated survival rates, rapid growth, and robust antioxidant and immune defenses. This study provides important technical parameters for optimizing and enhancing the industrial cultivation of juvenile C. quadricarinatus.

High‐Bandgap Perovskites for Efficient Indoor Light Harvesting

The use of metal‐halide perovskites in photovoltaic applications has become increasingly attractive due to their low‐temperature manufacturing processes and long charge‐carrier lifetimes. High‐bandgap perovskite solar cells have potential for indoor applications due to their efficient absorption of the spectrum of light‐emitting diodes (LEDs). This study investigates the performance of high‐bandgap perovskite solar cells under a wide range of lighting conditions, including a commercially available white LED lamp with a 5–40 000 lx illuminance range and a standard 1 sun reference. The performance of CH3NH3PbI3‐based perovskite solar cells to CH3NH3Pb(I0.8,Br0.2)3 solar cells with varying electron transport layers (ETL), including PCBM, PCBM:CMC, and CMC:ICBA fullerene combinations, is compared. Because the spectral response of perovskite solar cells covers the white LED spectrum very well, the major performance difference is related to the open‐circuit voltage and fill factor. The cells with the CH3NH3Pb(I0.8,Br0.2)3 absorber layer and the CMC:ICBA ETL demonstrate superior open‐circuit voltage and therefore a high efficiency above 29% at 200–500 lx, typical for indoor lighting.

Biochemical repercussions of light spectra on nitrogen metabolism in spinach (Spinacia oleracea) under a controlled environment.

Selecting appropriate light spectra of light-emitting diodes (LEDs) and optimal nutrient composition fertilizers has become integral to commercial controlled environment agriculture (CEA) platforms. This study explored the impact of three LED light regimes (BR: Blue17%, Green 4%, Red 63%, Far-Red 13% and infrared 3%, BGR; Blue 20%, Green 23%, Red 47%, Far-Red 8% and infrared 2%; and GR; Blue 25%, Green 41%, Red 32%, and Far-Red 2%) and nitrogen levels (3.6 and 14.3 mM N) on spinach (Spinacea oleracea). Under limited nitrogen (3.6 mM), BGR light increased the fresh shoot (32%) and root (39%) biomass than BR, suggesting additional green light's impact on assimilating photosynthates under suboptimal nitrogen availability. Reduced chlorophyll (a and b) and carotenoid accumulation, electron transport rate (ETR), and higher oxalates under limited nitrogen availability highlighted the adverse effects of red light (BR) on spinach productivity. Increased activities of nitrogen-associated enzymes (GOGAT; Glutamate synthase, GDH; NADH-Glutamate dehydrogenase, NR; Nitrate reductase, and GS; Glutamine synthetase) in spinach plants under BGR light further validated the significance of green light in nitrogen assimilation. Amino acid distributions remained unchanged across the light spectra, although limited nitrogen availability significantly decreased the percent distribution of glutamine and aspartic acid. Overall, this study demonstrated the favorable impacts of additional green light on spinach productivity, as demonstrated under BGR, than GR alone in response to nitrogen perturbation. However, the exact mechanisms underlying these impacts still need to be unveiled. Nevertheless, these outcomes provided new insights into our understanding of light spectra on spinach nitrogen metabolism.

Responses of kecapi (Sandoricum koetjape Merr.) seedlings under different spectrum and intensity of light emitting diode

Kecapi (Sandoricum koetjape Merr.) is a local fruit belonging to the Meliaceae family. The market price of this fruit is unstable due to inconsistent production and fruit quality. Kecapi’s cultivation system can be improved by modifying the environment in which LED (Light Emitting Diode) is used as artificial light. This study aims to determine changes in morphological, physiological, and anatomical responses to LED light’s different spectrum and intensity levels. The research used a two-factor, completely randomized design (CRD) consisting of an LED spectrum (purple and white) and two light intensities. The results showed the changes in morphological and physiological responses in high-intensity treatment with the white spectrum of LED (WH). The low intensity with the white spectrum of LED (WL) increased leaf chlorophyll content and photosynthesis rate. The anatomical response has in the low-intensity purple LED (PL) treatment. Increased leaf width occurred in high intensity with the purple LED spectrum (PH). Glucose content in the leaf decreased in all treatments, and increased fructose content in the leaf only occurred in the low-intensity purple spectrum of LED treatment.

Spectral composition of LED light differentially affects biomass, photosynthesis, nutrient profile, and foliar nitrate accumulation of lettuce grown under various replacement methods of nutrient solution.

To enhance crop yield and quality, plant cultivation in controlled-growing systems is an alternative to traditional open-field farming. The use of light-emitting diode (LED) as an adjustable light source represents a promising approach to improve plant growth, metabolism, and function. The objective of this study was to assess the impact of different light spectra (red, red/blue (3:1), blue, and white) with an emission peak of around 656, 656, 450, and 449 nm, respectively, under various replacement methods of nutrient solution (complete replacement (CR), EC-based replacement (ECBR), and replacing based on plant needs (RBPN)), on biomass, physiological traits, and macro- and micronutrient contents of two best-known lettuce varieties, Lollo Rossa (LR) and Lollo Bionda (LB), in the nutrient film technique (NFT) hydroponic system. The results indicated that mix of red and blue LED spectra under RBPN method is the most effective treatment to enhance fresh and dry weights of lettuce plants. In addition, red LED spectrum under RBPN, and red and blue light under ECBR nutrient solution significantly increased leaf stomatal conductance, net photosynthesis and transpiration rate, and intercellular CO2 concentration of LR variety. Phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mn) content in LR variety, and iron (Fe), zinc (Zn), copper (Cu), and manganese (Mn) content in both varieties increased upon exposure to blue and red LED light spectrum with RBPN method. Our results suggest that exposure to combination of red and blue light along with feeding plants using RBPN and ECBR methods can increase absorption of macro- and micronutrient elements and improve photosynthetic properties, and eventually increase lettuce yield with lower nitrate accumulation.

Active Area Temperature Measurement of Medium-Power LEDs by Dynamics Changes in Forward Voltage during Current Heating and Cooling

The most common non-destructive methods of measuring the temperature of the active area of light emitting diodes (LEDs) are briefly analysed and their disadvantages are pointed out. Measurements of the temperature of the active area of medium-power LEDs by the dynamics of change in the direct voltage during heating by currents of different densities and in the process of cooling in the mode of flow of small, so-called measuring current, which not cause heating of LEDs, are presented. An electrical scheme realising the used method is given. The results of measurements show that the thermal resistance of LED, determined by the results of measuring the temperature of the active area by the proposed method, is greater than the reference value. The comparison of the results of temperature measurements using traditional methods of analysing the radiation spectra of LEDs and the temperature dependence of direct voltage is carried out.

Discrete nutrient utilizations in two Bauhinia species exposed to supplemental light-emitting diode spectra and exponential fertilization

Bauhinia is a widely planted urban tree plant in tropical cities, which are frequently dwelling in a habitat exposed to inevitable streetlamp lighting. It is of practical meaning to figure out the lighting spectra that benefit nutrient utilization in corporation with a proper exponential fertilization regime. In this study, Bauhinia brachycarpa and B. variegata seedlings were cultured with exponential fertilization at the rate of 80 mg nitrogen (N) plant-1 (N-phosphorus-potassium, 10-7-9) with an unfertilized control, and both were exposed to light-emitting diode spectra of R1BG5 (13.9% red, 77.0% green, 9.2% blue), R2BG3 (26.2% red, 70.2% green, 3.5% blue), and R3BG1 (42.3% red, 57.3% green, 0.4% blue). The R3BG1 spectrum resulted in smaller growing size and dry mass but higher nutrient concentration and root water content compared to the other two spectra. Exponential fertilization increased fresh mass for two Bauhinia species but only increased dry mass in B. brachycarpa. Compared to B. variegata, B. brachycarpa was verified to have a higher capacity to accommodate exogeneous nutrient input through exponential fertilization. The R3BG1 spectrum was recommended for the illumination in streetlamps for Bauhinia because this spectrum can promote nutrient uptake without too fast rate of growth relative to other spectra with lower red-light proportions.

Origins of the high-energy electroluminescence peaks in long-wavelength (∼495–685 nm) InGaN light-emitting diodes

We investigate the unexpected high-energy electroluminescence (EL) peaks observed in long-wavelength InGaN light-emitting diodes (LEDs) with ground state emission peaks between ∼495 and 685 nm by studying the EL spectra of LEDs with varying quantum well (QW) thicknesses and indium compositions. In addition to the ground state emission, two high-energy emission peaks were observed in the LEDs with thick QWs and high indium compositions. The less energetic high-energy emission peak (2.4–2.6 eV) is attributed to the optical transitions involving excited states. Factors influencing the excited state transitions, such as the QW thickness and indium compositions, were also examined by simulations to better understand the occurrence of these transitions. The more energetic high-energy emission peak (2.8–3.1 eV) originates from V-defect sidewalls and was verified through micro-photoluminescence measurements. Identification of the high-energy emission peaks is essential as it enables targeted epitaxial or growth optimizations to minimize or eliminate these undesirable emission peaks. This work demonstrates the importance of using thin QWs to suppress the unwanted high-energy emissions due to excited state transitions and V-defect sidewalls for long-wavelength InGaN LEDs.

The Thermodynamic Limit of Indoor Photovoltaics Based on Energetically‐Disordered Molecular Semiconductors

Due to their tailorable optical properties, organic semiconductors show considerable promise for use in indoor photovoltaics (IPVs), which present a sustainable route for powering ubiquitous “Internet‐of‐Things” devices in the coming decades. However, owing to their excitonic and energetically disordered nature, organic semiconductors generally display considerable sub‐gap absorption and relatively large non‐radiative losses in solar cells. To optimize organic semiconductor‐based photovoltaics, it is therefore vital to understand how energetic disorder and non‐radiative recombination limit the performance of these devices under indoor light sources. In this work, we explore how energetic disorder, sub‐optical gap absorption, and non‐radiative open‐circuit voltage losses detrimentally affect the upper performance limits of organic semiconductor‐based IPVs. Based on these considerations, we provide realistic upper estimates for the power conversion efficiency. Energetic disorder, inherently present in molecular semiconductors, is generally found to shift the optimal optical gap from 1.83 to ≈1.9 eV for devices operating under light emitting diode spectra. Finally, we also describe a methodology (accompanied by a computational tool with a graphical user interface) for predicting IPV performance under arbitrary illumination conditions. Using this methodology, we estimate the indoor power conversion efficiencies of several photovoltaic materials, including the state‐of‐the‐art systems PM6:Y6 and PM6:BTP‐eC9.

Effect of mixed light emitting diode spectrum on antioxidants content and antioxidant activity of red lettuce grown in a closed soilless system

BackgroundLight spectra have been demonstrated to result in different levels of comfort or stress, which affect plant growth and the availability of health-promoting compounds in ways that sometimes contradict one another. To determine the optimal light conditions, it is necessary to weigh the vegetable’s mass against the amount of nutrients it contains, as vegetables tend to grow poorly in environments where nutrient synthesis is optimal. This study investigates the effects of varying light conditions on the growth of red lettuce and its occurring nutrients in terms of productivities, which were determined by multiplying the total weight of the harvested vegetables by their nutrient content, particularly phenolics. Three different light-emitting diode (LED) spectral mixes, including blue, green, and red, which were all supplemented by white, denoted as BW, GW, and RW, respectively, as well as the standard white as the control, were equipped in grow tents with soilless cultivation systems for such purposes.ResultsResults demonstrated that the biomass and fiber content did not differ substantially across treatments. This could be due to the use of a modest amount of broad-spectrum white LEDs, which could help retain the lettuce’s core qualities. However, the concentrations of total phenolics and antioxidant capacity in lettuce grown with the BW treatment were the highest (1.3 and 1.4-fold higher than those obtained from the control, respectively), with chlorogenic acid accumulation (8.4 ± 1.5 mg g− 1 DW) being particularly notable. Meanwhile, the study observed a high glutathione reductase (GR) activity in the plant achieved from the RW treatment, which in this study was deemed the poorest treatment in terms of phenolics accumulation.ConclusionIn this study, the BW treatment provided the most efficient mixed light spectrum to stimulate phenolics productivity in red lettuce without a significant detrimental effect on other key properties.

Effects of Different Spectrum of LEDs on Retinal Degeneration Through Regulating Endoplasmic Reticulum Stress.

To evaluate the impact of full-spectrum light-emitting diodes (LEDs) on albino guinea pigs' retina and investigate the roles of short-wavelength opsin (S-opsin) and endoplasmic reticulum (ER) stress in light-induced retinal degeneration (LIRD). Three-week-old albino guinea pigs (n = 30) were distributed into five groups under 12/12 light/dark cycles with indoor natural light (NC; 300-500 lux, n = 6), full-spectrum LEDs (FL; 300 lux, n = 6; 3000 lux, n = 6), and commercial cold-white LEDs (CL; 300 lux, n = 6; 3000 lux, n = 6) and raised for 28 days. Hematoxylin and eosin staining and transmission electron microscopy evaluated the morphological changes of retinas. The immunofluorescence and real-time quantitative polymerase chain reaction (RT-qPCR) measured the expression and content of S-opsin and ER stress-related genes and proteins. We found that albino guinea pigs exposed to FL at either 300 lux or 3000 lux developed less severe retinal morphological damage than animals exposed to the CL light, which emerged as a significant characteristic of LIRD. Meanwhile, the damage on the ventral retina was more serious, mainly due to its ability to absorb the blue light in the LEDs more easily. Compared to the FL-exposed groups, the CL light increased the aggregation of S-opsin and the expression of ER stress-related factors. Commercial cold-white LEDs can induce ER stress and unfolded protein response in LIRD, and full-spectrum LED attenuates LIRD by regulating ER stress in albino guinea pig retinas in vivo. Full-spectrum LEDs offer specific eye protection and eye adaptability that can well replace commercial cold-white LEDs in both clinical practice and research. It should be further developed for lighting used in health care facilities.

Effects of Various LED Light Spectra on Growth, Gonadal Development, and Growth-/Reproduction-Related Hormones in the Juvenile Red Spotted Grouper, Epinephelus akaara.

The light spectrum is a key environmental cue involved in growth and reproduction in teleosts. This study investigated the effects of exposure on juvenile red spotted grouper exposed to white (control), red (590 nm), blue (480 nm), and green (520 nm) light-emitting diodes (LEDs) (12 h light:12 h dark) for two months. The body weight (BW), total length (TL), condition factor (CF), weight gain rate (WGR), gonadosomatic index (GSI), and hepatosomatic index (HSI) were assessed. Gonadal development was observed. The gene expression of growth-related hormones, such as growth hormone (GH), pre-pro-somatostatin-I (PSS-I), neuropeptide Y (NPY), and CCK, and of reproduction-related hormones, such as Kiss1, Kiss2, GPR54, sbGnRH, FSHβ, and LHβ, was analyzed. The results showed that the fish in the white LED group exhibited the best BW, TL, CF, WGR, and HSI after one or two months. The fish exposed to white LEDs showed the best growth after two months, but no significant differences in GH levels were detected. Contrarily, the expression levels of the PSS-I significantly increased (p < 0.05) in fish from the white group, suggesting the complex regulation of GH production and the limited effects of PSS-I on the inhibition of GH synthesis and somatic growth. The significantly increased NPY levels in the four LED groups (p < 0.05) indicated that these four LED spectra were effective in stimulating food intake and energy homeostasis. After two months, the gonads developed from chromatin nucleolar-stage oocytes to perinucleolar-stage oocytes in the four LED groups. The gene expression of Kiss2 and GPR54 in the four LED groups and of sbGnRH in the white and blue LED groups significantly increased when compared to that in the initial group (p < 0.05), while there were no significant differences in FSHβ and LHβ expression in the four LED groups. These results suggest that FSH and LH may not play important roles in gonadal development in juvenile red spotted grouper that are exposed to these four LED spectra.

The effect of LED light quality on the carotenoid metabolism and related gene expression in the genus Brassica

BackgroundNew vegetable production systems, such as vertical farming, but also well-established in-door production methods led to the implementation of light emitting diodes (LEDs). LEDs are the most important light sources in modern indoor-production systems and offer the possibility for enhancing growth and specific metabolites in planta. Even though the number of studies investigating the effects of LED lighting on vegetable quality has increased, the knowledge about genus variability is limited. In the present study, the effect of different LED spectra on the metabolic and transcriptional level of the carotenoid metabolism in five different Brassica sprouts was investigated. Cruciferous vegetables are one of the main food crops worldwide. Pak choi (Brassica rapa ssp. chinensis), cauliflower (Brassica oleracea var. botrytis), Chinese cabbage (Brassica rapa ssp. pekinensis), green kale (Brassica oleracea ssp. sabellica) and turnip cabbage (Brassica oleracea spp. gongylodes) sprouts were grown under a combination of blue & white LEDs, red & white LEDs or only white LEDs to elucidate the genus-specific carotenoid metabolism.ResultsGenus-specific changes in plant weight and on the photosynthetic pigment levels as well as transcript levels have been detected. Interestingly, the transcript levels of the three investigated carotenoid biosynthesis genes phytoene synthase (PSY), β-cyclase (βLCY) and β-carotene hydroxylase (βOHASE1) were increased under the combination of blue & white LEDs in the majority of the Brassica sprouts. However, only in pak choi, the combination of blue & white LEDs enhanced the carotenoid levels by 14% in comparison to only white LEDs and by ~ 19% in comparison to red & white LEDs.ConclusionsThe effects of light quality differ within a genus which leads to the conclusion that production strategies have to be developed for individual species and cultivars to fully benefit from LED technology.

60Co γ-irradiation of AlGaN UVC light-emitting diodes

270 nm AlGaN UV Light-Emitting Diodes (LEDs) were exposed to 1–5 Mrad fluences of Co-60 γ-rays. The effect of the exposure to radiation was a ∼40% reduction in optical output after the highest fluence. No significant midgap emission was induced in the electro-luminescence spectra of the irradiated LEDs. We ascribe the decrease in optical output to creation of non-radiative states within the active regions. There were small (5–10%) increases in forward and reverse current as a result of irradiation with an effective carrier removal rate of <1 cm−1. The irradiation did not produce any increase in degradation rate of the LEDs output power under high drive current (95 mA) compared to unirradiated devices, which is consistent with the lack of midgap emission. The relatively small changes in electrical and optical properties, along with the resistance of the AlxGa1-xN/AlN to displacement damage effects indicate these devices may be well-suited to harsh terrestrial and space radiation applications.

Realizing full-spectrum LED lighting with a bright broadband cyan-green-emitting CaY2ZrGaAl3O12:Ce3+ garnet phosphor

Full-visible-spectrum white light-emitting diodes (LEDs) with ultrahigh color rendering index (CRI), which are capable of offering a light source that mimics natural sunlight, have great application potentials in healthy lighting, high-resolution displays, and plant growth lighting. However, cyan gap in the 480–520 nm wavelength range is commonly existed in the emission spectra of traditional phosphor-converted white LEDs, and thus it is urgent to develop high-performance cyan-emitting phosphors to close this spectral gap for realizing full-visible-spectrum LED lighting. Herein, we demonstrate a new efficient cyan-green-emitting Ce3+-activated CaY2ZrGaAl3O12 garnet phosphor for near-ultraviolet (near-UV) pumped full-visible-spectrum warm-white LEDs. The CaY2ZrGaAl3O12:Ce3+ cyan-green phosphor has a cubic structure with the space group Ia3‾d and lattice parameters of a = b = c = 12.39645(8) Å and V = 1886.08(6) Å3. Ce3+ doping concentration dependent luminescence properties have been studied, and the highest emission intensity is obtained at 1 mol%. The optimal CaY2ZrGaAl3O12:1%Ce3+ sample shows a broad excitation band in the 300–490 nm wavelength range with peak at 409 nm due to the 4f→5d transition of Ce3+ ions. Upon 409 nm excitation, CaY2ZrGaAl3O12:1%Ce3+ produces a wide cyan-green emission band in the 425–750 nm spectral range with a peak at 514 nm and a full width at half-maximum of 110 nm owing to the 5d→4f transition of Ce3+ ions, and the corresponding CIE color coordinates and internal quantum efficiency are determined to be (0.2802, 0.4856) and 56%, respectively. Furthermore, the resulting CaY2ZrGaAl3O12:1%Ce3+ phosphor exhibits good thermal stability, and its emission intensity at 423 K is about 58% of that at 303 K. Finally, a white LED device is fabricated by employing a 395 nm near-UV chip with the phosphor blend of commercial BaMgAl10O17:Eu2+ blue phosphor, as-prepared CaY2ZrGaAl3O12:1%Ce3+ cyan-green phosphor, commercial (Ba,Sr)2SiO4:Eu2+ green phosphor and commercial CaAlSiN3:Eu2+ red phosphor, which exhibits a bright full-spectrum warm-white light with low color correlated temperature of 3334 K and ultrahigh CRI values (Ra = 97, R9 = 95.3, R12 = 90.1) for 20 mA driving current. This work provides a new perspective in designing luminescent materials for high-color-quality full-visible-spectrum LED lighting.

Calculation and Selection of Spectral Characteristics of Radiation of LED Luminaires for Operation Rooms

Many researchers considered improvement of colour discrimination an important factor of surgery illumination, but none of them provided data on colour contrast estimation. The article describes the results of an extensive search of spectrum that are the most preferable for application in surgery equipment using selected light emitting diodes (LED) of different types. The search was not also based on the qualitative characteristics recommended by the standard, but also on a previously non-considered parameter: colour contrast between human tissues K estimated in uniform-chromaticity systems. The programme developed in MATLAB environment allows to model the cumulative spectrum of a LED light source, to determine the proportions of LED radiation or crystals in LED providing the maximum value of LED general colour rendering index Ra at the set correlated colour temperature or the maximum value of averaged K in uniform-chromaticity systems both in presence of the limited Ra value of 85 and if there are no limitations. Such options of spectrum search allowed to evaluate the probability of K change and its maximum, as well as to identify three possible operating modes of surgery equipment when using the said LEDs. The first of them is following the existing recommendations for Ra with possible insignificant change of K, the second one is the priority of K assuming violation of the Ra recommendations to increase K, and the third option assumes switching between the modes if necessary. LED spectra are selected for such different modes. Other colour rendering indexes are also estimated, and the authors recommend using the new standard TM‑30–15 for standardisation of the colour rendering quality of light sources used in surgery luminaires. It is based on 99 samples and some of the tests have reflective properties close to those of human tissues.

Choosing a Method for Approximating the Spectral Distribution of Colour LEDs and Comparing their Parameters and Characteristics in Nominal Mode

New technologies and new light sources make it possible to create fundamentally new approaches in the design and construction of lighting devices. Light emitting diodes (LEDs) are a relatively new, promising and energy-efficient light source with a few unique properties: long lifetime, high luminous efficiency, aesthetics, environmental friendliness, reliability, high durability, and possibility to create a variety of spectra easily. During the lighting devices development, it is convenient to use mathematical approximations of the spectral distributions of the used LEDs in the composition of the product to calculate the final spectrum of the device in the visible range. These calculation methods are particularly interesting in architectural lighting. They are also applicable to the development of modern LED greenhouse irradiators. The article considers two main methods for approximating the emission spectra of colour LEDs: via symmetric and asymmetric distribution. The spectral distributions of four main types of LEDs that are used in the lighting devices design based on colour LEDs were measured in a wide range of currents from 100 mA to 1000 mA: red, amber, green, and blue. The results were also compared with a model that considers the two-dimensional density of states and potential fluctuations in the active region of the heterostructure of LED. Based on the carried-out measurements and calculations, the optimal approximation method via the asymmetric spectral distribution of LED radiation was determined.

Manipulation of light spectrum is an effective tool to regulate biochemical traits and gene expression in lettuce under different replacement methods of nutrient solution

The use of light-emitting diode (LED) technology represents a promising approach to improve plant growth and metabolic activities. The aim of this study was to investigate the effect of different light spectra: red (656 nm), blue (450 nm), red/blue (3:1), and white (peak at 449 nm) on biochemical properties, photosynthesis and gene expression in two lettuce cultivars (Lollo Rossa and Lollo Bionda) grown under different methods of nutrient solution replacement in hydroponics. Complete replacement and EC-based replacement of nutrient solution increased content of proline and soluble sugars and activity of antioxidant enzymes (CAT, GPX and SOD) under the red/blue LED and red LED light treatments in both cultivars. In addition, the red/blue and the monochromatic red light increased the soluble protein content and the antioxidant activity in the Lollo Rosa cultivar under the replacement method according to the needs of the plant. An increase in flavonoid content in the EC-based method in the Lollo Rosa variety treated with a combination of red and blue light was also observed. The red/blue light had the greatest induction effect on anthocyanin content, expression of the UFGT, CHS, and Rubisco small subunit genes, and the net photosynthetic rate. Data presented here will directly contribute to the development of nutrient solution and LED spectrum management strategies to significantly improve plant growth and metabolism, while avoiding water and nutrient waste, and environmental pollution.