High Color-rendering Index Research Articles

The effects of light emitting diodes on mitochondrial function and cellular viability of M-1 cell and mouse CD1 brain cortex neurons.

The invention of Light Emitting Diode (LED) revolutionized energy-efficient illumination, but concerns persist regarding the potential harm of blue light to our eyes. In this study, we scrutinized the impact of LED light characteristics on eyes using two cell types: M-1 (rich in mitochondria) and CD-1 (neuronal). Variations in color rendering index (CRI) and correlated color temperature (CCT) were investigated, alongside exposure durations ranging from 0 to 24 hours. The findings illuminated the potential benefits of high-quality LED lighting, characterized by a high CRI and low CCT, which emits a greater proportion of red light. This form of lighting was associated with enhanced cell proliferation, elevated ATP levels, and reduced oxidative stress. In contrast, LEDs with low CRI and high CCT exhibited adverse effects, diminishing cell viability and increasing oxidative stress. These results suggest that high-quality LED lighting may have neuroprotective potential as a treatment option, such as for retinal ganglion cells.

Ultra-broadband emission up to 181 nm of VO4-activated yellow phosphor for white light-emitting diodes with high color rendering index

Exploring broadband yellow phosphors capable of covering the cyan to red region is an effective approach to achieve high-performance phosphor-converted white light-emitting diodes (pc-WLEDs). Herein, we synthesized a series of VO4-activated ultra-broadband KSrP1−xVxO4 (0.1 ≤ x ≤ 1) yellow phosphors via high temperature solid-state reaction. Successive substitution of P5+ with V5+ causes a slight expansion of the lattice constant and induces several highly localized energy-levels within the forbidden band. Density functional theory calculations confirm that these newly appeared sharp-line energy-levels are attributed to the constructed VO4 anionic groups. With the optimized V5+ content, the KSrP0.7V0.3O4 phosphor exhibits an ultra-broadband yellow emission centered at 537 nm under 355 nm excitation. Impressively, its full width at half maximum is up to 181 nm, exceeding that of most reported counterparts. At 105 °C, the KSrP0.7V0.3O4 sample experiences an emission loss of 53%. A WLED device is fabricated by using phosphor blend of KSrP0.7V0.3O4 yellow phosphor and the commercial BaMgAl10O17: Eu2+ blue phosphor and a 355 nm NUV LED chip, demonstrating bright white emission with high color rendering index (CRI) of 90 and suitable correlated color temperature of 5953 K. These findings indicate that this phosphor has great potential for achieving high CRI WLEDs.

Dual emission quaternary alloyed quantum dots for white light-emitting diodes with high color-rendering index

We report the synthesis of manganese doped Ag–Zn–In–S(AZIS)/ZnS QDs for the facile fabrication of white light-emitting diodes (WLEDs). By controlling the ratio of Mn/(Zn + In), dual emission Mn:AZIS/ZnS QDs with different relative proportion of host emission and Mn2+-related emission were prepared. With proper doping, the emission of Mn: AZIS/ZnS QDs covers most of the visible spectrum. Based on the as prepared Mn:AZIS/ZnS QDs, a warm WLED device exhibited a highest color rendering index (CRI) of 92.5 companied by a correlated color temperature (CCT) of 3162 K. With the increasing of Mn2+ concentration, the corresponding WLED devices shown warmer CCT values and lower luminous efficiencies (LEs). The color-conversion efficiency of the QDs decreasing with the increasing of Mn2+ concentration may be responsible partly for the variation of device LEs. With further deep investigation on the mechanism of color-conversion between the exciting light and QDs, and the energy transfer from the host material to the manganese dopant, WLEDs based on the dual emission Mn:AZIS/ZnS QDs with better device performances are excepted to find diverse application in lighting fields.

Ce3+-based phosphor converter enabling laser lighting to attain both high CRI and high luminous efficacy

Eu2+ doped-CaAlSiN3 possesses broad red emission, enabling a phosphor-converted lighting device to achieve a high color rendering index (CRI) and proper color temperature. However, CaAlSiN3:Eu2+ exhibits relatively slow decay (∼1 μs) and intense re-absorption of luminescence from green/yellow emitters, thereby causing optical saturation and reducing the luminous efficacy. Here, we fabricated a novel phosphor converter comprising Lu3Al5O12:Ce3+ and Y1.3Gd1.6Al5O12:Ce3+ powders. The typical sample, when excited by a blue laser, exhibited a high luminous efficacy of 231 lm/W and a high saturation threshold of 22.2 W/mm2, resulting in a high luminous exitance of 695 lm/mm2. Importantly, the phosphor converter produced a broad emission band that included sufficient cyan and red components, resulting in a full width at half maximum (FWHM) of 134 nm and a high CRI of 81. With this excellent balance between CRI and luminous efficacy, the reported phosphor converter can significantly expand the range of laser lighting applications.

Superior white electroluminescent devices using nitrogen-doped carbon dots/TiO2 nanorods heterostructures

Nitrogen-doped carbon dots (NCDs), exhibiting strong yellow emission in aqueous solution and solid matrices, have been utilized for fabricating heterostructure white electroluminescence devices. These devices consist of nitrogen-doped carbon dots as an emissive layer sandwiched between an organic hole transport layer (PEDOT:PSS) and an array of rutile TiO2 nanorods, acting as an electron transport layer. Under an applied forward bias of 5 V, the device exhibits broadband electroluminescence covering the wavelength range of 390–900 nm, resulting in pure white light emission characteristics at room temperature. The result demonstrates the successful fabrication of all solution-processed, low-cost, eco-friendly NCDs-based LEDs with CIE (Commission Internationale d’Éclairage) coordinate of (0.31, 0.34) and color rendering index (CRI) > 90, which are close to ideal white light emission characteristics. The device functionalities are achieved based on defect-related NIR emission from TiO2 nanorods array and visible emission from nitrogen-doped carbon dots. This result paves a new opportunity to develop low-cost, solution-processed nitrogen-doped carbon dots based on warm White light emitting diodes with high CRI for large-area display and lighting applications.

Simultaneously Realizing High Efficiency and High Color Rendering Index for Hybrid White Organic Light-Emitting Diodes by Ultra-Thin Design of Delayed Fluorescence Sensitized Phosphorescent Layers.

In consideration of energy economization and light quality, concurrently attaining high external quantum efficiency (ηext ) and high color rendering index (CRI) is of high significance for the commercialization of hybrid white organic light-emitting diodes (WOLEDs) but is challenging. Herein, a blue luminescent molecule (2PCz-XT) consisting of a xanthone acceptor and two 3,6-diphenylcarbazole donors is prepared, which exhibits strong delayed fluorescence, short delayed fluorescence lifetime, and excellent electroluminescence property, and can sensitize green, orange, and red phosphorescent emitters efficiently. By employing 2PCz-XT as sensitizer and phosphorescent emitters as dopants, efficient two-color and three-color WOLED architectures with ultra-thin phosphorescent emitting layers (EMLs) are proposed and constructed. By incorporating a thin interlayer to modulate exciton recombination zone and reduce exciton loss, high-performance three-color hybrid WOLEDs are finally achieved, providing a high ηext of 26.8% and a high CRI value 83 simultaneously. Further configuration optimization realizes a long device operational lifetime. These WOLEDs with ultra-thin phosphorescent EMLs are among the state-of-the-art hybrid WOLEDs in the literature, demonstrating the success and applicability of the proposed device design for developing robust hybrid WOLEDs with superb efficiency and color quality.

Ce/Mn/Cr: (Re,Y)3Al5O12 Phosphor Ceramics (Re = Gd, Tb and Lu) for White LED Lighting with Significant Spectral Redshift and Improved Color-Rendering Index.

In order to attain phosphor ceramics with a high Color-Rendering Index (CRI), samples with the composition of Y0.997-xRexCe0.003)3(Al0.9748 Mn2+0.024Cr3+0.0012)5O12(Rex = 0, Gd0.333, Gd0.666, Gd0.997, Tb0.333, Tb0.666, Tb0.997 and Lu0.997 were prepared by solid-state reaction and vacuum sintering, and exhibited potential for high-quality, solid-state lighting. Doping with Cr3+ and Mn2+ effectively enhanced the red component of Ce3+ spectra through the intense energy transfer from Ce3+ ions to Mn2+/Cr3+ ions. The crystal field splitting of [GdO8] and [TbO8] was more extensive than that of [YO8], causing a massive redshift in the Ce3+ emission peaks from 542 to 561 and 595 nm, while [LuO8] had an opposite effect and caused a blueshift with a peak position at 512 nm. White LED devices incorporating Ce/Mn/Cr: (Gd0.333Y0.664)3Al5O12 phosphor ceramic exhibited a high CRI of 83.97, highlighting the potential for enhancing the red-light component of white LED lighting.

Simultaneous enhancement of red luminescence and thermal stability of a novel red phosphor: A Li+-Eu3+ co-occupied site strategy in BaAl2Ge2O8 lattices

The rapid development of phosphor-converted white light emitting diodes (pc-WLEDs) requires new red phosphors with efficient and thermally stable luminescence for high-quality warm-white lighting. However, it is still a challenge to discover red phosphors with facile synthesis, high internal quantum efficiency (IQE), excellent thermal stability and high color purity. Herein, a novel red-emitting Eu3+ activated barium dialuminum digermanate (BaAl2Ge2O8, BAGO) phosphor showing strong red emission at 610 nm was prepared. The IQE is improved from 32.91% to 78.84% by employing a charge compensation strategy. The lithium-ion co-doped BAGO:Eu3+ phosphor exhibits a nearly twofold increase in integral photoluminescence (PL) intensity and the high color purity reaches 94.17%. Impressively, the PL intensity of the BAGO:Eu3+,Li+ phosphor drops by only 2.6% at 150 °C of that at room temperature. Finally, the pc-WLED using the red BAGO:Eu3+,Li+ phosphor exhibits white light with the chromaticity coordinate of (0.3515, 0.3495), a high color-rendering index of 92 and a low correlated color temperature of 4746 K. All these results manifest that BAGO:Eu3+,Li+ phosphor is a suitable red phosphor for near-ultraviolet (NUV) chip-based pc-WLEDs.

Triple-layer remote phosphor geometry: an excellent selection to improve the optical properties of white light-emitted diodes

High performance white-light-emitting diodes (WLEDs) have been the goal of recent research on phosphor-in-glass (PiG) devices. In this paper, we introduce a configuration of WLED that achieves high color rendering index (CRI), and correlated color temperature with the addition of Zn<sub>2</sub>SiO<sub>4</sub>:Mn<sup>2+</sup>, As<sup>5+</sup> and YAl<sub>3</sub>O<sub>4</sub>B<sub>12</sub>:Eu<sup>3+</sup><sub>. </sub>The technique is lower the temperature during the creation process of phosphor in glass and control the consistent thickness in between 0.5 to 0.7 mm to yield high color quality PiG, high CRI above 80 WLEDs, and extend the color temperature range to 3,900 to 5,300 K. The consistent heat generation combined with extraordinary CRI for PiG prove that low temperature sintering has the potential to create WLEDs with advanced quality. The improved WLEDs can be utilized in many high-demand lighting fields such as chromatic examination, medical analysis, and aesthetic lighting.

Color Rendering Index over 95 Achieved by Using Light Recycling Process Based on Hybrid Remote-Type Red Quantum-Dot Components Applied to Conventional LED Lighting Devices.

Red color conversion materials have often been used in conventional white LEDs (light-emitting diodes) to enhance the insufficient deep-red component and thus improve the color-rendering property. Quantum dots (QDs) are one of the candidates for this due to their flexibility in controlling the emission wavelength, which is attributed to the quantum confinement effect. Two types of remote QD components, i.e., QD films and QD caps, were prepared and applied to conventional white LED illumination to improve the color-rendering properties. Thanks to the red component near 630 nm caused by the QD components, the color rendering indices (CRIs) of both Ra and R9 could be increased to over 95. It was found that both the diffusing nature of the reflector and the light recycling process in the vertical cavity between the bottom reflector and the top optical films play important roles in improving the color conversion efficiency of remote QD components. The present study showed that the proper application of remote QDs combined with a suitable optical cavity can control the correlated color temperature of the illumination over a wide range, thus realizing different color appearances of white LED illumination. In addition, a high CRI of over 95 could be achieved due to the sufficient excitation from fewer QDs, due to the strong optical cavity effect.

Thermal and Optical Analysis of Quantum-Dot-Converted White LEDs in Harsh Environments

Quantum-dot-converted white LEDs (QD-WLEDs) are promising in both lighting and display applications owing to their high luminous efficiency (LE) and high color-rendering index (CRI). However, their working lifetime is severely limited by the poor reliability of QDs and the LED package. In this work, the variation in photothermal parameters in QD-WLEDs during aging was investigated, and the effect of QDs and the LED package on the optical performance of QD-WLEDs was analyzed. First, the optical properties of phosphor–silicone, QD–silicone, and silicone were measured during the 524 h aging process at 80 °C and 100 °C, respectively. QD-WLEDs with high optical performance were packaged and aged under the same conditions to investigate the variation in their optical parameters and analyze the trends of their CRIs and correlated color temperatures (CCTs). According to the experimental results and the calculation models of the spectra, it was found that the changes in optical parameters are mainly caused by the degradation of QDs, and the aging of QDs has different effects on the CRI and CCT. The analysis of the energy-transfer process shows that the decrease in luminous flux of QD-WLEDs during the aging process is mainly caused by the aging of silicone. Based on optical and thermal analysis, this study proposed different optimization strategies for optical quality and lifetime in the LED design process.

Efficient Semitransparent Organic Solar Cells with CRI over 90% Enabled by an Ultralow‐Bandgap A‐DA'D‐A Small Molecule Acceptor

AbstractSemitransparent organic solar cells (ST‐OSCs) can function as power‐generating windows due to their ability to allow visible light go‐through for human eyesight while absorbing low‐energy photons in the near‐infrared region for photocurrent generation. In this regard, effective ST‐OSCs with high light utilization efficiency (LUE) and color rendering index (CRI) can be developed via a synergistic material and device engineering strategy. Herein, an A‐DA'D‐A acceptor BZO‐4Cl is synthesized with an ultralow optical bandgap of 1.26 eV and bathochromically shifted absorption of roughly 60 nm with respect to Y6. Initially, the opaque devices using PTB7‐Th as the donor show a high power conversion efficiency (PCE) of 14.12% , which can be listed as one of the highest efficiencies for the PTB7‐Th‐based OSCs so far. Then, through these efforts of optimizations in the bulk‐heterojunction(BHJ) composition, top electrodes and anti‐reflection layer, the cutting‐edge ST‐OSC demonstrates a high LUE of 4.02%, and a CRI of 90.67%, making it one of the best‐performing ST‐OSCs with both high LUE and CRI values. These results indicate that the ST‐OSCs presented in this study have significant potential for use in applications that possess transparent visible light and energy‐generation functions.

Efficient blue-light-excited cyan-emitting CaLu2HfScAl3O12:Ce3+ phosphors for full-visible-spectrum warm-white LEDs

Bright cyan-emitting phosphor is indispensable to fill the cyan gap for the fabrication of full-visible-spectrum warm-white light-emitting diodes (LEDs) with high color rendering index (CRI). In this study, we demonstrate a novel efficient cyan-emitting Ce3+-activated CaLu2HfScAl3O12 (CLHSA) garnet phosphor for application in blue-light-excited full-spectrum warm-white LEDs. CLHSA:Ce3+ phosphors show broadband excitation spectra in the 300–470 nm spectral range with a maximum peak at 408 nm, indicating they can be efficiently pumped by the blue LED chips. The optimal doping concentration of Ce3+ ions is found to be 1 mol%. Upon 408 nm excitation, the optimal CLHSA:1%Ce3+ phosphor gives rise to a bright broadband cyan emission (peak position: 498 nm; bandwidth: 97.5 nm) with CIE chromaticity coordinates of (0.2196, 0.4265) and high photoluminescence quantum yield of 64.5%. Finally, we have fabricated a blue-light-excited high-CRI warm-white LED device by employing the CLHSA:1%Ce3+ cyan phosphor, commercial YAG:Ce3+ yellow phosphor and commercial CaAlSiN3:Eu2+ red phosphor as well as a 450 nm LED chip, which demonstrates a bright warm-white light emission with a high CRI (Ra = 92.6), a low correlated color temperature (3660 K), and good CIE chromaticity coordinates of (0.3993, 0.3939) as well as a high luminous efficacy of 45 lmW−1. Therefore, this newly discovered efficient cyan-emitting CLHSA:1%Ce3+ phosphor is promising for application in blue-chip-pumped full-visible-spectrum warm-white LEDs with high CRI values.

Towards efficient blue Eu2+ activated pyrophosphate phosphor for warm white LED applications

A blue-emitting LiCsBaP2O7:Eu2+(LCBPO:Eu2+) pyrophosphate phosphor prepared by solid-state synthesis that emits bright blue light with a first-rate internal quantum efficiency and high color purity is reported. Furthermore, when heated from 298 K to 473 K, LCBPO:0.015Eu2+ phosphor exhibits excellent color stability. Impressively, LCBPO:0.015Eu2+ blue phosphor exhibits exceptional stability against air exposure over a month. Fabricating a near-ultraviolet (n-UV) pumped pc-wLED using LCBPO:0.015Eu2+ along with green (Sr,Ba)2SiO4:Eu2+ and red (Ca,Sr)AlSiN3:Eu2+ phosphors demonstrates a well distributed warm white light with a high color-rendering index (Ra) of 91.7, a low correlated color temperature (CCT) of 3382 K and a high luminous efficiency (LE) of 26.1 l m/W. The high-performance optical characteristics, straightforward synthesis procedures and economical initial materials cost of LCBPO:Eu2+ support the potential of this material for usage in warm white LED-based lighting systems.

Facile preparation of highly efficient Te4+-doped Rb2SnCl6 perovskites for white light-emitting diodes

Lead-free vacancy‐ordered halide double perovskite microcrystals are new alternatives to lead-based halide perovskite materials for lighting applications; however, they are limited by harsh synthesis conditions and low quantum efficiency. Hence, a facile solution recrystallization method was used to synthesize Te4+-doped Rb2SnCl6 phosphors. Via Te4+ doping, the phosphors show a yellow–green emission at 550 nm and a broadband emission line width of approximately 97 nm, achieving a high photoluminescence quantum yield of 74.2%, arising from the Te4+ 1S0 →3P1 self-trapping exciton transition. The Te4+-doped Rb2SnCl6 microcrystals are subsequently used to fabricate a white light-emitting diode device, which shows a high color-rendering index of 97.1 and a correlated color temperature of 4739 K. This work reports a facile method to synthesize alloy double perovskite phosphors, opening up new avenues for the development of environment-friendly lighting applications.

Anti‐Solvent Synthesis of Three‐Color Indium‐Based Halide Perovskite Microplate/Microcrystal Phosphors for High Color Rendering WLEDs

AbstractLead‐free halide perovskites are emerging as promising eco‐friendly candidates for next‐generation solid‐state lighting because of their nontoxicity and availability for broad emission. Herein, a modified room‐temperature anti‐solvent precipitation method is developed to synthesize the Sb3+‐doped, In‐based, lead‐free halide perovskites in microplate/microcrystal structure with different emission colors. The layered structure of InCl3 serves as the template for the growth of Cs2InCl5(H2O):Sb3+ microplate phosphors. Moreover, the presence of HCl not only improves the solubility of precursors, but also provides the acid etching effect. The resultant Sb3+‐doped Cs2InCl5(H2O) microplate phosphors show bright yellow emission with photoluminescence quantum yield up to 92.4%. Furthermore, Cs3InCl6:Sb3+ and Cs2NaInCl6:Sb3+ are synthesized through the similar method, which displays the bright green and deep‐blue emission, respectively. Subsequently, the proof‐of‐concept white light‐emitting diodes (WLEDs) are fabricated based on Cs2NaInCl6:Sb3+ + Cs2InCl5(H2O):Sb3+ and Cs2NaInCl6:Sb3+ + Cs3InCl6:Sb3+ + Cs2InCl5(H2O):Sb3+ phosphors, which achieves high‐quality white light with the color rendering index (CRI) of 91.6 and 95.4, respectively. The results greatly advance the development of lead‐free halide perovskite phosphors synthesis, which may offer new possibilities for high CRI WLEDs fabrication.

(Sr,Ca)AlSiN3:Eu2+ phosphor-in-glass and YAG ceramic composites for high CRI and high-power white LEDs

A series of red-emitting (Sr,Ca)AlSiN3:Eu2+ phosphor-in-glasses (SCASN PiGs) were successfully prepared by spin coating. The optical, thermal and luminescence performance of the SCASN PiGs with different ratios of phosphor to glass (P1G4, P1G3, P1G2 and P1G1) were investigated systematically. The thermal stabilities of SCASN PiGs are superior to (Sr,Ca)AlSiN3:Eu2+ phosphor. As the P1G2 sample was coupled with blue LED chips, warm white light with luminous efficacy (LE) of 115.60 lm/W, color rendering index (CRI) of 73.6 and correlated color temperature (CCT) of 2750 K was achieved running in 100 W COB model. In addition, the CRI of YAG-P1G2 sample was improved to 81.7 when a YAG ceramic was added. These results suggested that the YAG-SCASN PiG is a promising candidate for high CRI and high-power (hp) WLEDs.

Toward Ultra‐Broadband Absorption and High Quantum Efficiency Red Emission via Fluoride Single Crystals with Heavy Mn4+ Doping

AbstractOwing to the avoidance of device reabsorption and improvement in the color rendering index (CRI), Mn4+‐activated fluorides have potential applications in full‐spectrum lighting. However, it is still challenging to improve the external quantum efficiency (EQE) and adapt it to the excitation of violet‐light chips used for increasing the CRI and reducing the blue‐light hazard. Here, red‐light single crystals Rb2Si1−xMnxF6 (RSMF) with an ultrahigh optimal Mn4+ content of 32.4 mol% are obtained through structural and morphological design. Breaking through the limitation of low quenching concentration (<10 mol%) of Mn4+‐activated fluorides, the as‐grown heavy Mn4+‐doped RSMF crystal not only exhibits a record EQE of 80.2% but also has a broad excitation band of full width at half maxima = 86 nm, which can be efficiently excited by both blue (460 nm) and violet (437 nm) light. The white light‐emitting diodes fabricated by violet/blue dual‐chips, commercial green phosphor, and the optimized RSMF crystal can realize a high luminous efficacy of 161.8 lm W−1 and high CRI of Ra = 95.5. Additionally, laser diode devices with high luminous flux of 198.2 lm are also presented. This study provides new insights into heavy Mn4+‐doped materials and promotes the application of full‐spectrum lighting.

One-Step Synthesis of White-Light-Emitting Carbon Dots for White LEDs with a High Color Rendering Index of 97.

White-light-emitting carbon dots (WCDs) show innate advantages as phosphors in white light-emitting diodes (WLEDs). For WLEDs, the color rendering index (CRI) is the most important metric to evaluate its performance. Herein, WCDs are prepared by a facile one-step solvothermal reaction of trimellitic acid and o-phenylenediamine. It consists of four CDs identified by column chromatography as blue, green, yellow, red, and thus white light is a superposition of these four types of light. The mixture of the four CDs undergoes Förster resonance energy transfer to induce the generation of white light. The photoluminescence of WCDs originates from the synergistic effect of carbon core and surface states. Thereinto, the carbon core states dominate in RCDs, and the increase of amide contents and degree of conjugation promote the redshift of the emission spectra, which is further confirmed by theoretical calculations. In addition, a high CRI of 97 is achieved when the WCDs are used as phosphors to fabricate WLEDs, which is almost the highest value up to now. The multicolor LEDs can also be fabricated by using the four multicolor CDs as phosphors, respectively. This work provides a novel approach to explore the rapid preparation of low-cost, high-performance WCDs and CDs-based WLEDs.

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

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