White Light-emitting Diodes Research Articles

Solid-State Fluorescent Carbon Dots with Hydrophobic Modification Induced Red Emission for White Light-Emitting Diodes.

Herein, we developed red solid-state fluorescent carbon dots (SSF-CDs) through a one-step solvothermal method, utilizing acetone as the carbonization solvent. Optical and structural characterization revealed that the sp2 domains in the core of the R-CDs were consistently interrupted and that the oxygen-containing groups on the surface were replaced by alkyl groups. This substitution mitigates excessive π-π interactions, thereby preventing quenching of fluorescence in the solid state. Adjusting the molar ratio of citric acid (CA) and urea yielded solid fluorescent carbon dots (CDs) with panchromatic luminescence, indicating enhanced π-π interactions and more pronounced red shifts in the emission peaks. Furthermore, we found that this strategy is applicable to other carbon sources, including phenylenediamine, salicylic acid, and lignin. This research presents an innovative strategy for the fabrication of solid-state luminescent CDs.

Up-conversion materials for solid-state lighting

AbstractConventional phosphor-converted white LEDs (WLEDs), using (Stokes) down-conversion light emission, suffer from a red deficiency that increases the Color Temperature towards “cool white light” above 5000 K. The present work describes a phosphor-Up-converted WLED approach that wishes to overcome this issue by achieving white light generation (WLG) through Up-conversion photoluminescence (UCPL), without energy losses due to Stokes shift and excited by a 980 nm LED instead of the more expensive blue LEDs. The UC materials include thin films of lanthanide (Ln)-doped aluminosilicate glass multilayers, alternating (Ln)-doped aluminosilicate and titania films in the form of 1-D photonic crystals and Ln ion-implanted materials. Sol-gel (SG) processing has been used as a low-cost high purity processing method to prepare titania, as well as aluminosilicate films containing Er3+, Tm3+ and Yb3+, for WLG and possible application as WLED materials. The total Ln content varied from a high of 22 mol% to as low as 5.8 mol%. The materials prepared have been characterized by UV-Vis-NIR (using a variable angle specular reflection accessory), plus FTIR and UCPL spectroscopies. The UC light emission was analyzed with the help of CIE chromaticity diagrams. Graphical abstract

Bacterial Hybrid Light-Emitting Diodes.

Photon down-converting filters with fluorescent proteins (FPs) are a new frontier in the quest for rare-earth-free and non-toxic color filters for white light-emitting diodes. There are, however, concerns related to the FP purification costs and lack of FP recyclability/reuse. Here, the direct use of bacteria in photon down-converting filters can be of utmost relevance, eliminating purification and allowing in situ production of new FPs. However, their high background autofluorescence/scattering and low stability in polymer coatings have traditionally hampered the application of Engineering Living Materials (ELMs) for photon manipulation. Indeed, there are no examples of ELMs in lighting systems. This work discloses the first protocol to prepare living spheroplasts with > 90% scattering reduction, high FP expression fairly keeping their photoluminescence figures-of-merit, and excellent resilience in polymer films over 1 year under ambient storage. This unlocked the preparation of the first bacteria hybrid light-emitting diodes integrating ELMs for photon conversion. These devices feature similar stabilities to those using purified FPs, while enabling a cost-effective strategy and active FP recycling by the simple recultivation of spheroplasts. Overall, this work introduces a successful case toward bacteria-polymer photon manipulation, in general, and a new living lighting concept, in particular.

Effects of nickel substitution on structural, magnetic and optical properties of Sillenite bismuth ferrite nanoparticles

The Ni-doped Bi25FeO40 nanoparticles [Bi25 NixFe(1-x)O40, x = 0.1, 0.3, and 0.5] were synthesized by the hydrothermal method at a temperature of 180 °C. The effects of the Ni substitute on the structural, optical, magnetic, and photocatalytic performance have been investigated. The successful synthesis of the materials was confirmed by Rietveld's refined powder X-ray diffraction and Fourier transform infrared spectroscopy. Scanning electron microscopy together with energy dispersive X-ray spectroscopy (EDS) revealed the morphology of the synthesized nanomaterials as well as its chemical composition. The studied materials exhibited anomalous magnetic properties as evident from the vibrating sample magnetometry (VSM) analysis. These features display a weak ferromagnetic nature and demonstrate increased magnetization when doping elements are incorporated. Furthermore, Optical analysis revealed that bandgaps of Bi25NixFe(1-x)O40 were found to be increased from 2.06 eV to 2.31 eV with increasing Ni content. Additionally, the expansion of sillenite bismuth nickel ferrite's optical bandgap was further confirmed by the photocatalytic degradation of methylene blue as a model dye under the low-power white LED illumination. Lower bandgap undoped nanoparticles showed the highest photocatalytic efficiency, with a degradation rate of ∼43.11 % compared to higher bandgap doped nanoparticles, without adjustment of any reaction conditions such as pH or catalyst amount. The kinetic reaction rate of undoped Bi25FeO40 was roughly twice as fast as that of the material doped with 50 % Ni.

Reconstructing the Surface of K2SiF6:Mn4+ Phosphors toward Enhanced Moisture Resistance for White LED Applications.

The K2SiF6:Mn4+ (KSFM) phosphor featuring efficient ultranarrow red emissions is an outstanding candidate for white light-emitting diode (WLED) applications. However, poor moisture resistance seriously affects its application performance. In this study, a two-step surface reconstruction strategy is proposed to dramatically enhance the moisture resistance of commercially available KSFM phosphors, involving treatment with H2NbF7 and subsequent hydrothermal treatment. The modified KSFM phosphor exhibits a high internal quantum efficiency (IQE) of 98.9% after the two-step surface treatment. Meanwhile, nearly 100% of the initial emission intensity is retained for the modified KSFM phosphor even after aging in high temperature (85 °C) and high relative humidity (85% RH) environments for 6 days, in sharp contrast to only 18.6% retention for the original KSFM phosphor. The relative emission intensity of the modified KSFM remains at 98.9% even after being immersed in water for 6 h. Additionally, the phosphor-converted LED fabricated with the modified KSFM phosphor demonstrated excellent long-term stability, retaining up to 97.9% of initial luminous efficacy after aging under 85 °C and 85% RH conditions for 500 h. The moisture-resistance mechanism is elucidated on the basis of spectroscopic analysis as well as structural and compositional characterization of the phosphor surface layer, which can be attributed to the formation of a robust Mn4+-rare shell with high crystalline quality following this two-step surface treatment. The findings contribute to the performance improvements of KSFM phosphors for industrial applications.

A Novel Broadband Green Phosphor La2W2O9: Bi3+, and Its Application in High Color-Rendering Index pc-WLED

Broadband green phosphors have important applications in overcoming the blue-green (cyan) 470–510[Formula: see text]nm gap of phosphor-converted white LED (pc-WLED) and achieving high color rendering index (CRI) white lighting. In this work, a broadband green phosphor La2W2O9: [Formula: see text]Bi[Formula: see text] was synthesized by solid-state method. The phase, morphology and luminescence properties of the series of phosphors were systematically studied. The results showed the La2W2O9: [Formula: see text]Bi[Formula: see text] green phosphor exhibits a wide emission band in the range of 400–800[Formula: see text]nm with full width at half-maximum (FWHM) of 164[Formula: see text]nm, filling the cyan gap and reaching its peak at 550[Formula: see text]nm. The phosphor exhibits broadband excitation, and the excitation range covers the wavelength region of 200–500[Formula: see text]nm, and matches well with commercial ultraviolet LED. With the obtained broadband green phosphor, commercial CaAlSiN3:Eu[Formula: see text] red phosphor, commercial BaMgAl[Formula: see text]O17:Eu[Formula: see text] blue phosphor, and a 365[Formula: see text]nm commercial chip, a warm white pc-WLED device with a high color-rendering index (Ra[Formula: see text]97.4, R1–R15[Formula: see text]90) and low correlated color temperature (CCT[Formula: see text]3610[Formula: see text]K) was fabricated. The results demonstrate the wide range of applications for La2W2O9:Bi[Formula: see text] phosphor in the field of premium warm white LED lighting.

Reducing red light proportion in full-spectrum LEDs enhances runner plant propagation by promoting the growth and development of mother plants in strawberry.

Full-spectrum light-emitting diodes (LEDs) have gradually replaced narrow-spectrum LEDs and are widely used in plant factories with artificial lighting (PFALs). However, the specific effect of LED light quality on dry mass allocation in runner plant propagation remains unclear. Hence, we cultivated "Akihime" strawberries as mother plants for 115 days to conduct runner plant propagation experiment under white LEDs (W100), white and red LEDs (W84R16 and W55R45), red and blue LEDs (RB100), and red, blue and green LEDs (RB80G20) in PFALs, and determined key factors affecting dry mass accumulation and allocation among mother plants and runner plants based on growth component analysis. The results showed that the net photosynthetic rate and total leaf area in mother plants in W100 increased by 11% and 31%, respectively, compared with W55R45. In comparison to W84R16 and W55R45, W100 increased the dry mass (23%-30%) of runner plants mainly by increasing the total dry mass (TDM) (23%) of strawberry plants, without significantly affecting the fraction of dry mass partitioning to runner plants. However, the number of runners in W55R45 was 5.1 per plant, representing only 78% of that in W100. Compared with RB100, RB80G20 significantly increased the number of runner plants and runner numbers by 16% and 19% to 13.0 per plant and 5.8 per plant, respectively. The partial replacement of blue light with green light in RB80G20 induced a shade avoidance response in runner plants, resulting in a 55% increase in the total leaf area of runner plants compared with RB100. Data from growth component analysis showed that compared with red and blue LEDs, white LEDs increased the TDM of runner plants by 83% by increasing the plant TDM accumulation (44%) and the fraction of dry mass partitioning to runner plants (37%). Additionally, the dry mass (g) of runner plants per mol and per kilowatt-hour under in W100 were 0.11 and 0.75, respectively, significantly higher than other treatments. Therefore, reducing red light proportion in full-spectrum LEDs is beneficial for strawberry runner plant propagation in PFALs.

Influence of UV irradiation on the luminescence properties of CsPbBr3 perovskite quantum dots and CsPbBr3 perovskite quantum dots/PVDF composite film—for white LED application

Perovskite quantum dots (QDs) have been widely investigated for their excellent properties such as high color purity in displays, tunable emission wavelength, and high photoluminescence quantum yield. For device applications, improving the stability is an area of interest. In this study, the effects of UV irradiation on the structural and luminescence properties of CsPbBr3 perovskite quantum dots (CPB QDs) excited at 365 nm were investigated. To overcome the effects of UV irradiation, a CPB QDs/PVDF composite flexible film was prepared. It exhibits high structural and optical stability under UV irradiation and emits a highly intense green color. The emission wavelength and intensity were observed for three years, and the stability of the temperature-dependent emission intensity up to 400 K has been reported. In addition, it is stable in water. A white LED, fabricated by integrating a blue LED with CPB QDs/PVDF composite film and red phosphor, produces bright natural white light [(CIE x, CIE y) = (0.3704, 0.3611), and CCT = 4177 K] with a color gamut area coverage of 86.4% of the standard NTSC (1953) color space.&#xD.

Mg2+‐Doped Cesium Copper Halide for Bright Electroluminescent White Light‐Emitting Diodes

AbstractLead‐based perovskite nanocrystals (NCs) as one of the most promising materials in the fields of display and lighting, have outstanding optical performance and simple solution preparation process. However, the toxicity of lead and poor stability limit their commercialization. Meanwhile, as a key component of display and lighting, white light‐emitting diodes (WLEDs) still faces challenges such as low luminance and complex preparation process. A method is proposed for preparing nontoxic and stable Cs3Cu2I5 NCs by doping Mg2+ ions, achieved broadband blue light emission with a high PLQY of 96.2% and excellent thermal cycling stability and air stability. Then, the Mg2+ ions doped Cs3Cu2I5 NCs are used as emissive layer, while the 1,3,5‐Tri (m‐pyridine‐3‐ylphenyl) benzene (TmPyPb) is selected as electron transport layer to interact with Cs3Cu2I5 thin films for the formation of Cu‐I complex with broadband yellow light emission. This approach obviated the need for multi‐layer sedimentary emission layers, resulting in WLEDs featuring a high color rendering index (CRI) of 91, a peak external quantum efficiency (EQE) of 0.71% and maximum luminance of 2116 cd m−2 that is the highest values of lead‐free perovskite WLEDs at present. Therefore, Cs3Cu2I5 NCs have good application prospects in WLEDs.

Cutting-edge applications of oleic acid-modified CdSiO3: Ce3+ phosphors: Artificial intelligence enhanced latent fingerprint detection, anti-counterfeiting and optical thermometry

A series of (1–11 mol%) Ce³⁺ doped CdSiO₃ phosphors are synthesized via a solution combustion method, and the sample with the optimal doping concentration underwent surface modification with oleic acid (OA). X-ray diffraction (XRD) analysis confirmed the formation of high-purity, well-crystallized CdSiO3:Ce3+ phosphors. Upon 347 nm UV excitation, the phosphor exhibited intense blue emission at 400 nm, with an optimized Ce³⁺ concentration of 5 mol%, attributed to dipole-dipole interactions. The OA-modified phosphor demonstrated significantly enhanced properties, achieving a color purity (CP) of 97.2% and Internal quantum efficiency (IQE) of 82.5%. The phosphor also exhibited excellent thermal stability, retaining 93.0% of its emission intensity at 423 K and a thermal quenching temperature exceeding 483 K, with a high activation energy (Eₐ) of 0.384 eV. In practical applications, the OA modified phosphor showed exceptional performance in latent fingerprints (LFPs) detection and anti-counterfeiting (AC) across different substrates, offering high resolution, contrast, and minimal background interference. MATLAB based analysis yielded a matching score of 94.52%, surpassing conventional benchmarks, underscoring the phosphor's potential for advanced fingerprint identification. These results demonstrate that the CdSiO₃:5Ce³⁺ phosphor is a promising candidate for applications in white light-emitting diodes (w-LEDs), optical thermometry, forensic analysis and AC technologies.

Photoluminescence properties of Mn2+-activated red-emitting phosphors with superior thermal stability for backlighting display applications

The red-emitting phosphors, Na2Mg1-x(PO3)4:xMn2+ with concentrations ranging from 0.01 to 0.11, have been successfully synthesized using a simple solid-state method. The as-synthesized phosphors are crystallized in an orthorhombic structure. The luminescence mechanism of Mn2+ ions in Na2Mg(PO3)4 lattice has been deeply explained using the Tanabe-Sugano (T-S) energy level diagram for the d5 electron configuration. The typical photoluminescent emission (PL) and photoluminescent excitation (PLE) spectra were measured. Several excitation peaks in the spectral range of 250–550 nm on the PLE spectrum and a strong emission peak at 613 nm indicate that the as-synthesized phosphors can be effectively excited using ultraviolet (UV) and near-UV LED chips. Several photometric characteristics were measured, such as the Commission International de'LEclarirage (CIE) chromaticity coordinate (x, y), color purity (CP), and correlated color temperature (CCT), corresponding to the concentration-dependent PL spectra. Furthermore, the thermal stability of the Na2Mg1-x(PO3)4:xMn2+ phosphors was investigated through temperature-dependent PL spectra and decay curves from 10 to 500 K. All results confirm that the as-synthesized red-emitting phosphors exhibit excellent thermal stability, which are attractive characteristics for white light emitting diodes (W-LEDs) applications.

Loading Dyes into Chiral Cd/Zn-Metal-Organic Frameworks for Efficient Full-Color Circularly Polarized Luminescence.

Host-guest chemistry of chiral metal-organic frameworks (MOFs) has endowed them with circularly polarized luminescence (CPL), it is still limited for MOFs to systematically tune full-color CPL emissions and sizes. This work directionally assembles the chiral ligands, metal sites and organic dyes to prepare a series of crystalline enantiomeric D/L-Cd/Zn-n MOFs (n=1~5, representing the adding amount of dyes), where D/L-Cd/Zn with the formula of Cd2(D/L-Cam)2(TPyPE) and Zn2(D/L-Cam)2(TPyPE) (D/L-Cam=D/L-camphoric acid, TPyPE=4,4',4'',4'''-(1,2-henediidenetetra-4,1-phenylene)tetrakis[pyridine]) were used as the chiral platforms. The framework-dye-enabled emission and through-space chirality transfer facilitate D/L-Cd/Zn-n bright full-color CPL activity. The ideal yellow CPL of D-Cd-5 and D-Zn-4, with |glum| as 4.9 × 10-3 and 1.3×10-3 and relatively high photoluminescence quantum yield of 40.79 % and 45.40 %, are further assembled into a white CPL light-emitting diode. The crystal sizes of D/L-Cd/Zn-n were found to be strongly correlated to the types and additional amounts of organic dyes, that the positive organic dyes allow for the preparation of > 7 mm bulks and negative dyes account for sub-20 μm particles. This work opens a new avenue to fabricate full-color emissive CPL composites and provides a potentially universal method for controlling the size of optical platforms.

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

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

Artificial light at night alters foraging behavior of freshwater amphipods depending on the light spectrum and the presence of predation cues

Abstract Artificial light at night (ALAN) is a common anthropogenic disturbance, which alters animal behavior. However, little is known about the impact of the spectral composition of ALAN and co-occurring predation risk on the behavior of aquatic organisms. We experimentally investigated how ALAN of different spectra (cool white LED and HPS light) affects the behavior and foraging of Gammarus jazdzewskii (Amphipoda) on chironomid prey, both as a single stressor and in combination with an olfactory predation cue. Gammarids exposed to ALAN in the absence of predation cues consumed less, compared with darkness, mainly due to their lower activity. Moreover, gammarids showed a stronger response to LED light, spending more time in the shelter and increasing prey handling time in this treatment. The addition of predation cues did not enhance the negative impact of ALAN on the foraging success. Gammarids maintained similar consumption levels as in the ALAN treatment without predation cues and in darkness with predation cues. However, gammarids in LED light altered their behavior in response to predation threat: they decreased prey handling time and consumed prey faster, which may have compensated for the higher food demand in stressful conditions. They also tended to exhibit risky behavior, leaving the shelter and moving towards the lit area, presumably to escape and avoid the combined effects of light and predation cues. Therefore, when assessing the effects of ALAN on organisms, light quality and co-occurring biotic factors should be considered, as predator pressure is common in natural environments.

Additive engineering for Sb2S3 indoor photovoltaics with efficiency exceeding 17%

Indoor photovoltaics (IPVs) have attracted increasing attention for sustainably powering Internet of Things (IoT) electronics. Sb2S3 is a promising IPV candidate material with a bandgap of ~1.75 eV, which is near the optimal value for indoor energy harvesting. However, the performance of Sb2S3 solar cells is limited by nonradiative recombination, which is dependent on the quality of the absorber films. Additive engineering is an effective strategy to fine tune the properties of solution-processed films. This work shows that the addition of monoethanolamine (MEA) into the precursor solution allows the nucleation and growth of Sb2S3 films to be controlled, enabling the deposition of high-quality Sb2S3 absorbers with reduced grain boundary density, optimized band positions, and increased carrier concentration. Complemented with computations, it is revealed that the incorporation of MEA leads to a more efficient and energetically favorable deposition for enhanced heterogeneous nucleation on the substrate, which increases the grain size and accelerates the deposition rate of Sb2S3 films. Due to suppressed carrier recombination and improved charge-carrier transport in Sb2S3 absorber films, the MEA-modulated Sb2S3 solar cell yields a power conversion efficiency (PCE) of 7.22% under AM1.5 G illumination, and an IPV PCE of 17.55% under 1000 lux white light emitting diode (WLED) illumination, which is the highest yet reported for Sb2S3 IPVs. Furthermore, we construct high performance large-area Sb2S3 IPV minimodules to power IoT wireless sensors, and realize the long-term continuous recording of environmental parameters under WLED illumination in an office. This work highlights the great prospect of Sb2S3 photovoltaics for indoor energy harvesting.

The spectral mismatch correction factor estimation using broadband photometer measurements and catalog parameters for tested white LED sources

Using a modeled look-up chart developed in this work, we show that accurate photometric measurements of characteristics like illuminance or luminous intensity of test LED sources can be measured in one step. This is a simple broadband measurement that may substitute for complicated and costly spectral measurements currently in place. To develop the look-up chart, the typical minimum and maximum of the Spectral Mismatch Correction Factor (SMCF) for a given photometers was estimated in relation to catalog parameters of the LEDs such as correlated color temperature (CCT) and melanopic daylight efficacy ratio (mDER). This research was based on the unique and large dataset of real photometers spectral response srel(λ) collected and measured at accredited laboratories located at America, Asia and Europe and modeled LED's spectral power distribution (SPD) data. Independent look-up tables were developed for color-mixed LEDs (cm-LEDs) and white phosphor-converted LEDs (pc-LEDs), two common LED types.

First-Principles Linear Combination of Atomic Orbitals Calculations of K2SiF6 Crystal: Structural, Electronic, Elastic, Vibrational and Dielectric Properties.

The results of first-principles calculations of the structural, electronic, elastic, vibrational, dielectric and optical properties, as well as the Raman and infrared (IR) spectra, of potassium hexafluorosilicate (K2SiF6; KSF) crystal are discussed. KSF doped with manganese atoms (KSF:Mn4+) is known for its ability to function as a phosphor in white LED applications due to the efficient red emission from Mn⁴⁺ activator ions. The simulations were performed using the CRYSTAL23 computer code within the linear combination of atomic orbitals (LCAO) approximation of the density functional theory (DFT). For the study of KSF, we have applied and compared several DFT functionals (with emphasis on hybrid functionals) in combination with Gaussian-type basis sets. In order to determine the optimal combination for computation, two types of basis sets and four different functionals (three advanced hybrid-B3LYP, B1WC, and PBE0-and one LDA functional) were used, and the obtained results were compared with available experimental data. For the selected basis set and functional, the above-mentioned properties of KSF were calculated. In particular, the B1WC functional provides us with a band gap of 9.73 eV. The dependencies of structural, electronic and elastic parameters, as well as the Debye temperature, on external pressure (0-20 GPa) were also evaluated and compared with previous calculations. A comprehensive analysis of vibrational properties was performed for the first time, and the influence of isotopic substitution on the vibrational frequencies was analyzed. IR and Raman spectra were simulated, and the calculated Raman spectrum is in excellent agreement with the experimental one.

High correlated color temperature white light-emitting diodes disrupt refractive development in guinea pigs

Ubiquitous white light-emitting diodes (LEDs) possess optical properties that differ from those of natural light. This difference can impact visual perception and biological functions, thus potentially affecting eye health. Myopia, which leads to visual impairments and potentially irreversible vision loss or blindness, is the most prevalent refractive error worldwide. Ambient light has been found to be a significant factor in refractive development. The overlap between the commonly utilized of white LEDs and the rapid increase in the prevalence of myopia raises suspicions that white LEDs may represent hidden visual cues. To clarify the potential effects of white LEDs on refractive development, we exposed guinea pigs to different forms of artificial lighting over a period of eight weeks. We found that exposure to white LEDs with a high correlated color temperature (CCT) of approximately 5000 K can induce significant myopic shifts in guinea pigs, along with a decrease in collagen accumulation in the sclera. Additionally, this exposure was found to significantly reduce choroidal tissue thickness in guinea pigs. Our study findings indicate that high CCT white LEDs disrupt refractive development in guinea pigs. These results suggest that high CCT white LEDs might similarly affect refractive development in humans, highlighting the need for further clinical investigation.

Algae derived carbon dots and its polymeric composites for white light emission

Nanomaterials with multicolor emission have been of great interest due to their versatility. Recently, environmentally friendly carbon dots (CDs) with excitation wavelength/solvent/dopant dependent emission have been used for designing different types of white light emitting diodes (W-LED). In this work, single-green precursor (Arthrospira platensis) derived CDs from a one-step hydro/solvothermal synthesis, have been implemented in the elaboration of W-LEDs. The white emission of CDs was modulated by the solvent engineering and doping strategies. A CDs/PVA composite based W-LED with a color render index (CRI) upper to ∼90 %, Commission Internationale Eclairage (CIE) coordinates of (0.31, 0.33) and correlated color temperature (CCT) of 6500 K is demonstrated. These findings suggest that white CDs derived from A. platensis possess promising potential in the field of optoelectronic devices, especially in the production of efficient and high-quality white illumination.

Efficient and tunable emission of Na5Lu(WO4)4:Tb3+,Eu3+ phosphors for warm white LEDs with high color rendering index

Phosphors with high luminescence efficiency, tunable emission and high color rendering index (CRI) are vital importance for the quality of white light emitting diodes (w-LEDs) in real application. In this work, a new single phase color-tunable Na5Lu(WO4)4:Tb3+,Eu3+ phosphor with outstanding luminescent properties was designed and synthesized. Its crystal structure, electronic structure, and luminescence features were studied in detail. The band gap of the host was calculated to be at about 4.68 eV. The differential charge distribution after Tb, Eu doping through density functional theory simulation theoretically proved the electron redistribution in the W-O bond upon substitution of Tb3+/Eu3+. The energy transfer of Tb3+→Eu3+ enabled tunable emission of luminescent colors from green to orange-red due to the quadrupole-quadrupole interaction. The optimal Na5Lu(WO4)4:60%Tb3+,20%Eu3+ phosphor exhibited excellent photoluminescence quantum yield of 84.19% and good luminescent thermal stability (I423K/298K = 75.90%) with an activation energy of 0.1976 eV. Finally, a white LED device with color coordinates of (0.3371, 0.3636), color rendering index of 89.4 and correlated color temperature of 5334 K was fabricated. These findings demonstrated that Na5Lu(WO4)4:60%Tb3+,20%Eu3+ phosphor could be a potential orange-red-emitting color converter for white LEDs. This work not only assisted in the understanding of experimental observations but also provided a theoretical basis for the rational design of phosphors.