Color Rendering Index Research Articles

Colloidal Synthesis of Blue-Emitting Cs3TmCl6 Nanocrystals via Localized Excitonic Recombination for Down-Conversion White Light-Emitting Diodes.

Lead-halide perovskite nanocrystals (NCs) have gained significant attention for their promising applications in lighting and display technologies. However, blue-emitting NCs have struggled to match the high efficiency of their red and green counterparts. Moreover, many reported blue-emitting perovskite NCs contain heavy metal lead (Pb), which poses risks to human health and the environment. In this study, we synthesized rare-earth-based Cs3TmCl6 NCs via the hot injection method, which exhibit a broadband blue emission at 440 nm. Combined experimental and theoretical studies indicate that the broadband emission in Cs3TmCl6 arises from self-trapped excitons due to the excited-state structural distortion of the [TmCl6]3- cluster. Furthermore, the ultrafast dynamics of charge carriers were analyzed using time-resolved photoluminescence and transient absorption measurements. Encouraged by the remarkable thermal, light, and water stabilities of Cs3TmCl6 NCs, as evidenced by experimental and theoretical results, a white light-emitting diode was further designed and fabricated using the Cs3TmCl6 NCs as the color converter. The device exhibits outstanding performance, achieving a long half-lifetime of 336 h and a large color-rendering index of 87.0. Combining eco-friendly features and a facile synthesis method, the rare-earth-based Cs3TmCl6 NCs mark a significant breakthrough as a reliable blue emitter, showcasing their future potential in lighting and display applications.

Defect-Enabled Superior Negative Thermal Quenching in Palmierite Ba9La(VO4)7:Eu3+ for WLED In Situ Temperature Measuring.

Negative thermal quenching (NTQ) of the phosphors is critically important for both scientific research and practical applications, but the design of efficient NTQ phosphors is still a challenging task. Herein, we report a new strategy for developing NTQ materials by cation-vacancy engineering. Specifically, a new color-tunable Ba9La1-x(VO4):xEu3+ (BLVO:xEu3+) phosphor with abundant intrinsic cation vacancy was developed, exhibiting superior NTQ behavior under 365 nm excitation. The NTQ performance can be modulated via adjusting Eu3+ doping levels, and the emission intensity of Eu3+ ions in the BLVO:0.20Eu3+ phosphor increased by 275% at 473 K compared to room temperature. Furthermore, the reported material emitting bright white light under 365 nm excitation was well-suited for use in white light-emitting diode (WLED) phosphor and fluorescent temperature sensors, exhibiting outstanding color-rendering index (90.1) in lighting and high sensitivity (Sa = 11.83% K-1, Sr = 2.33% K-1) in temperature detecting. Lastly, the operating temperature of WLED at different currents can be monitored and displayed in real time through emission spectroscopy. All of the results demonstrated that the designed NTQ BLVO:xEu3+ can be used as a single-phase white phosphor and optical thermometry. This work provides a fresh perspective for designing high-efficient NTQ phosphors and expands the application of phosphors in WLED in situ temperature detection.

High color rendering index WLEDs enabled by multi-band tuning of InP quantum dots

Quantum dots (QDs) represent a significant class of fluorescent materials, offering the potential to reduce power consumption and enhance the color rendering index (CRI) of white light-emitting diode (WLED) devices. However, the presence of toxic elements such as Cd and Pb in traditional fluorescent QDs limits their widespread commercial application. Compared to the broad emission characteristics of environmentally friendly AgInS2 and CuInS2 QDs, the narrower linewidth of InP-based core-shell QDs is advantageous for developing WLED devices with a higher CRI. In this study, we employed a multistage heating method to synthesize a series of amino-phosphine-based InP/ZnSe core-shell QDs, which exhibited emission wavelengths ranging from 535 to 650 nm, narrow emission linewidths of 43-47 nm, and high photoluminescence quantum yields of 60%-80%. Subsequently, six different color QDs are used to fabricate a WLED device. The best WLEDs show not only bright warm light (correlated color temperature = 3323 K) with a maximum luminous efficacy of 74.1 lm W-1, but also excellent color quality (CRI Ra = 93, as well as R9 = 94.8, and R13 = 97.1). These results indicate remarkable progress in InP-based WLEDs for high-quality lighting applications.

Unveiling the potential of Cs2AgBiBr6 perovskites for next-generation see-through photovoltaics

Lead-free perovskite solar cells are strong contenders in the race for green and sustainable energy. Among these, cesium silver bismuth bromide (Cs2AgBiBr6) stands out, but its potential was hampered by the need for high-temperature processing, hindering its transition to scalable techniques. In this work, we present the feasibility of blade-coating deposition of Cs2AgBiBr6 layer. Thanks to the temperature control of the substrate during the process, we deposited uniform films at precise thickness enabling the fabrication of fully semitransparent devices with power conversion efficiencies (PCEs) of 3.07 % and 7.7 % under 1 sun and indoor light conditions, respectively. Furthermore, we evaluated important metrics for transparent photovoltaics such as Light Utilization Efficiency (LUE) and Color Rendering Index (CRI) of the devices by varying the Cs2AgBiBr6 thicknesses and the illumination conditions. The results showed LUEs at 1 Sun illumination of 1.1 % (1.5 %) and CRI of 71 (62.5) for 200 nm-thick and 400 nm-thick perovskite films, respectively. Finally, we evaluated the process scalability fabricating 6 cm2-sized semitransparent modules suitable for low-power electronics in Internet of Things field. This study opens the door to the development of non-hazardous, scalable, lead-free perovskite solar cells and modules suitable for integration into our everyday surroundings thanks to their see-through properties.

Impact of Illuminant Metamerism on Colour Fidelity in Graphic Reproduction of Artistic Images

The aim of the research was to to evaluate the quality of illuminant metamerism by using Colour rendering index through similar paintings and half-tone reproduction images within the graphic industry. Employing the methodology of visual perception and testing conducted by standard observers, the study scrutinises how different colour techniques of paintings respond to diverse light sources under standardised conditions. This investigation is pivotal for understanding the chromatic fidelity and consistency of paintings and their reproduction with half-tone colours, by measuring the grey balance field, for all images. To find the most suitable light source and to complete the colour quality, the Osram LED light at 3000 K, 4000 K, and 6500 K is used. The resulting index could be deceptive in cases of significant disparities. The American IES TM-30-18 colour rendering index (CRI) metric, quantifies illumination metamerism's ability to faithfully depict natural colours. At every stage (R1–R15), the average colour reproduction CRI must be more than 90.

Tunable optical and photovoltaic performance in PTB7-based colored semi-transparent organic solar cells integrated MgF2/WO3 1D-photonic crystals via advanced light management.

This study explores the design, fabrication, and characterization of PTB7-based colored semi-transparent organic solar cells (ST-OSCs) with integrated MgF2/WO3 one-dimensional photonic crystals (1D-PCs). Integrating 1D-PCs enhanced light management by creating tunable photonic band gaps, leading to extraordinary color change and improved photon harvesting. For 1DPC5 - 425 the Average Visible Transmittance (AVT) values were 33.3%, and CIE x, y was 0.43, 0.52, for 1DPC3 - 650 AVT were 25.09% and CIE x, y was 0.23, 0.27, respectively. Thus, extraordinary color changes from blue to yellow could be achieved while keeping transparency. Thereupon, photovoltaic performance showed notable improvements, with Jsc increasing from 7.98mA/cm2 to 9.95mA/cm2 and 10.45mA/cm2 for 1DPC5 - 425 and 1DPC3 - 650, respectively. By 1D-PC integration, power conversion efficiency (PCE) reached from 3.93 to 4.90% and 5.08% for 1DPC5 - 425 and 1DPC3 - 650, respectively. The Color Rendering Index (CRI) indicated successful color tuning and acceptable rendering, with CRI of 52 and 87. The study demonstrates that 1D-PC integration significantly enhances ST-OSCs' optical and photovoltaic properties, paving the way for advanced energy-harvesting 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.

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.

Highly efficient red emission of CsPbBrI2 quantum dots glasses modified by Nb5+ for light-emitting application

Red-emitting perovskite quantum dots (QDs) have significant potential for application in optoelectronic devices. However, their application is hindered by preparation challenges and low photoluminescence quantum yield (PLQY). In this study, CsPbBrI2 red-emitting QDs with a PLQY of up to 58.73 % were synthesized in germanium borate glass. The experimental results indicated that the addition of Nb5+ can not only partially replace the Pb2+ sites but also passivate halogen defects in QDs, enhance radiative transitions, and significantly improve the lattice ordering of CsPbBrI2 QDs glass. Additionally, the incorporation of Nb2O5 supplies free oxygen, facilitating the conversion of [BO4] to [BO3] in the glass network, which results in a looser structure conducive to crystallization. Moreover, the Nb5+-doped CsPbBrI2 QDs glass demonstrated excellent hydrothermal stability. The QDs glass exhibiting the highest luminescent performance was subsequently combined with an InGaN blue chip to create a WLED with a color rendering index (CRI) of 82.7. This study offers an innovative methodology for synthesizing perovskite QDs glass materials with enhanced red emission efficiency through transition metal doping, highlighting their significant potential for practical applications in WLEDs.

A yellow-green-emitting phosphor K3LaSi2O7:Eu2+ with superior thermal stability for solid-state lighting

Yellow-green-emitting phosphors with good thermal stability when excited by ultraviolet (UV) light are relatively less common compared to blue and red phosphors. In this study, a serial of K3LaSi2O7:xEu2+ (KLSO: xEu2+) phosphors with hexagonal structure (P63/mcm space group) were successfully synthesized. Under 360 nm excitation, KLSO: xEu2+ exhibits yellow-green luminescence peaked at 540 nm. Additionally, sharp emission peaks at 592 and 614 nm are observed when excited at 390 nm, indicating a small amount of Eu3+ ions still exist. The Eu2+ ions are found to occupy both La3+ and K+ sites in the KLSO host, resulting in two luminescent centers at 535 and 592 nm based on Gaussian fitting of the emission spectrum. The optimal Eu2+-doping concentration is verified at KLSO:0.05Eu2+. The thermal stability tests indicate that its luminescence intensity at 150 °C maintains 90.01 % of that at room-temperature. Meanwhile, the component substitution of Na+ ions for K+ ones is beneficial for the enhancement of luminescence, achieving a quantum efficiency of 40.62 %. Finally, this phosphor is applied to white LED, which shows a correlated color temperature (CCT) of 4164 K, a color rendering index (CRI) of 86.6, and CIE color coordinate of (0.3604,0.3174). It indicates that K3LaSi2O7:xEu2+ is a promising candidate for solid-state lighting.

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.

Comparative investigation on carbon dots and chloride fluxes modified ZnAl2O4:Cr3+ nanophosphors for temperature sensing, cutting-edge forensic, anti-counterfeiting and w-LEDs applications

A novel Cr3+ doped ZnAl2O4 is synthesized by grafting carbon dots (CDs) and chloride fluxes (NaCl, KCl, NH4Cl) through the solid-state reaction method. Upon excitation at 530 nm wavelength, the Cr3+ ions in the ZAO NPs emit red light due to the influence of a strong crystal field. This red emission arises from the electric dipole 2Eg→4A2g of the Cr3+ ions. Among the chloride fluxes examined, NH4Cl had a significant impact on the PL intensity. Notably, when CDs are incorporated into the ZAO:7Cr3+/NH4Cl NPs, a remarkable increase of 17.25-folds in photoluminescence (PL) intensity is observed. This enhancement is substantially higher than that of CDs alone (11.23-folds) and NH4Cl alone (3.82-folds). The increased PL intensity is attributed to the Förster resonance energy transfer (FRET) mechanism. Furthermore, the addition of CDs (5 wt.%) enhanced the colour purity (CP) of ZAO:7Cr3+/NH4Cl NCs to 99.8%, achieving a high Internal quantum efficiency (IQE) of 93.4 %. Notably, the CDs (5 wt.%)@ZAO:7Cr3+/NH4Cl NCs maintained 92.43 % of their emission intensity even at 420 K, demonstrating exceptional thermal stability compared to ZAO:7Cr3+ NPs. Moreover, the NPs holds promise for optical thermometry, boasting a high relative sensitivity (Sr) of 6.74 × 10-2 %K-1 across a temperature range spanning from 300 to 480 K. Moreover, the latent fingerprints (LFPs) developed using CDs(5 wt.%)@ZAO:7Cr3+/NH4Cl NCs demonstrate remarkable selectivity and high contrast. Under UV irradiation, the structural features of LFPs at levels I–III are clearly visible. In addition, the strong red fluorescence emitted by CDs(5 wt.%)@ZAO:7Cr3+/NH4Cl NCs makes them suitable for applications in AC. CDs(5 wt.%)@ZAO:7Cr3+ NCs exhibit significant potential for w-LED fabrication, achieving a correlated colour temperature (CCT) of 5517 K, a CIE coordinate of (0.332, 0.331), and a high colour rendering index (CRI) of Ra = 94, outperforming ZAO:7Cr3+/NH4Cl NPs. Overall results clearly demonstrates that, CDs(5 wt.%)@ZAO:7Cr3+/NH4Cl NCs are effective for applications in optical thermometry, dactyloscopy, w-LEDs, and AC.

A Study on the Effect of Microlens Arrays on the Correlated Color Temperature and Color Rendering Index of Quantum Dot Lighting

A Study on the Effect of Microlens Arrays on the Correlated Color Temperature and Color Rendering Index of Quantum Dot Lighting

Pure white emission full thermally activated delayed fluorescence organic light emitting diode with a supplementary emission layer

In addition to efficiency and lifetime, spectral stability, high color rendering index (CRI), and the Commission Internationale de l’Eclairag (CIE) coordinate close to the equi-energy white point (0.33, 0.33) are also important parameters for the development of white organic light emitting diodes (WOLEDs). However, how to realize these advantages at the same time is a challenge. In this paper, a series of white devices based on complementary color full thermally activated delayed fluorescence (full-TADF) emitters were fabricated with the aim to obtain WOLEDs with high color rendering index and CIE coordinate near the equi-energy white point. Through optimizing the doping concentration of the emitters, adding a supplementary emission layer, modifying the thickness of the main emission layer and the supplementary emission layer, the best device displays the CIE coordinates of (0.34, 0.35) and the CRI of 86, exhibiting good white emission. The results in this paper may provide a feasible method for realizing complementary color full-TADF WOLEDs with pure white emission.

Optimization for Spectral and Power Characteristics of Bicolour LED Driver

LED-powered luminaires have the ability to offer cutting-edge features like temperature adjustment and color management. Color shift creates discomfort in human eyes. So it is essential to design a LED driver which will precisely control the color parameters of the LED driver. Precise control of color parameters like CRI, CCT, color intensity is very complex and challenging. This paper describes the nonlinear optimization methodology for the design of blended LED light sources. This paper presents the methodology that enables LED strings regarding various parameters, e.g. high color rendering index (CRI) and high luminous efficacy of a blended bi-color (namely red CCT-2500K and blue CCT-9000K) LED driving system. Due to the applied optimization, the obtained CRI is maintained 98.03%. The overall luminous intensity depends upon the combined luminous flux which depends upon the current control of both LED sources. These optimized LED currents ensure the desired CCT. The achieved luminous efficacy is 90% at two optimal peak wavelengths 601 nm and 426 nm respectively. Power loss is minimized by frequency optimization. At the same time power parameters i.e. low THD and high P. F. is also maintained. The nonlinear optimization is verified in Ltspice simulations and experimentally for two different luminaire strings.

Designing a high-efficiency broadband cyan phosphor for low-blue full-spectrum LED lighting

Efficient cyan-emitting phosphor plays an important role in the development of solid-state lighting, which is indispensable to filling the cyan gap for full-spectrum warm-white light-emitting diodes (WLEDs) with high color rendering index (CRI). Herein, a novel highly efficient broadband cyan phosphor Ce3+-doped Ca3HfAl2Si2O12 (CHASO: Ce3+) garnet compound was developed by the substitution of Lu3+-Al3+ with Ca2+-Hf4+/Si4+ in Lu3Al5O12. The crystal structure and photoluminescence (PL) properties of CHASO: Ce3+ were investigated in detail. Notably, CHASO: Ce3+ phosphor can be effectively excited by violet light (390 – 430 nm) and exhibited bright cyan emissions around 490 nm with high PL internal quantum yields of 89.2 %. Moreover, the integrated PL intensity of the phosphor at 423 K was 66.3 % of that at room temperature. Finally, by incorporating CHASO: 11 %Ce3+ with commercial blue/yellow/red phosphor onto a violet LED chip (400 nm), the prototype full-spectrum WLEDs device exhibits warm white light with high color rendering index (CRI, Ra and R9 > 90) and low correlated color temperature 3301 K. These results suggest the highly efficient phosphor CHASO: Ce3+ is promising for low-blue full-spectrum healthy lighting.

High-efficiency RbASiF6:Mn4+ (A = K, Cs) phosphors obtained by one-step green synthesis method

Red-emitting Mn4+-doped fluoride phosphors are recognized as promising materials for high-performance warm white light-emitting diodes (WLEDs). However, the extensive use of toxic hydrofluoric acid in traditional synthesis methods hinders their development and commercialization. Furthermore, the traditional solid-phase method often has cumbersome sintering steps, high temperature, long holding time, and certain safety hazards, so it is very necessary to develop a green synthesis method with simple steps and low energy consumption. In this study, a low-temperature solid-state method is proposed to synthesize RbASiF6:Mn4+ (A = K, Cs) phosphors by one step. Optimal emission intensities were observed at Mn4+ concentrations of 1.2 % in RbKSiF6 and 2.1 % in RbCsSiF6. These phosphors demonstrated high thermal stability. At 423 K, the photoluminescence intensities of RbKSiF6:1.2 %Mn4+ and RbCsSiF6:2.1 %Mn4+ reached 114 % and 87 % of their respective values at room temperature. Meanwhile, the chromaticity shifts were almost negligible, and high color purity was achieved for both phosphors. The electro-optical performance of WLED devices utilizing these phosphors, in combination with YAG:Ce3+ and GaN chips, showed high color rendering indices (CRI) and low correlated color temperatures (CCT) across varying currents. Specifically, under a driving current of 20 mA, the device incorporating RbKSiF6:1.2 %Mn4+ exhibited a CRI of 94 and a CCT of 3732 K, with a luminous efficacy of 61 lm/W. These findings highlight the potential of green-synthesized RASFM phosphors in advancing the application of warm WLEDs.

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

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

Advances in High-Efficiency Blue OLED Materials

Organic light-emitting diode (OLED) technology has rapidly emerged in the display and lighting sectors due to its high contrast ratio, wide viewing angle, and sleek design. Beyond these attributes, OLEDs have also demonstrated crucial applications in medicine, fashion, sports, and more, leveraging their emissive properties and flexible design. As the cornerstone of full-color displays, blue OLEDs, whose performance directly impacts color rendition and saturation, have garnered significant attention from both scientific researchers and industrial practitioners. Despite the numerous advantages of OLED technology, blue OLEDs still confront formidable challenges in terms of luminous efficiency, durability, and material stability. This review examines the evolution of blue OLED materials over recent years, specifically focusing on three generations: fluorescent, phosphorescent, and thermally activated delayed fluorescence (TADF). Through molecular design, device structure optimization, and the application of innovative technologies, remarkable advancements have been achieved in enhancing the luminous efficiency, lifetime, and color purity of blue OLEDs. However, to advance commercialization, future efforts must not only ensure high efficiency and long lifetime but also improve material stability, environmental sustainability, and reduce development costs. Emerging materials such as thermally activated exciton materials and the application of hyperfluorescent (HF) OLED technology represent vital driving forces for the continuous advancement of blue OLED technology. It is anticipated that significant milestones will continue to be achieved in the development of highly efficient blue OLEDs in the future.

Rational design of narrowband deep blue MR-TADF dendrimers for high performance solution-processed all fluorescence white OLEDs

Developing solution-processable deep-blue multiple resonances thermally activated delayed fluorescence (MR-TADF) is a formidable challenge. Here, we using a convergent synthesis process successfully developed a series of MR-TADF dendrimers based on C=O/N resonant core (QAO). The alkyl chain alternate-linked functional dendrons not only ensure the narrow-band deep-blue emission but also enable the dendrimers with aggregation-induced emission enhancement (AIEE) properties, which efficiently mitigate the aggregation-induced exciton quenching (ACQ) and obnoxious spectral redshift broadening effect. Notably, the solution-processed deep blue MR-TADF OLEDs achieved a maximum external quantum efficiency (EQE) of 13.5 % and CIE of (0.15, 0.12) with an electroluminescence peak below 450 nm. Further using such dendrimer as a sensitizer for white OLEDs resulted in an optimized high EQE of 18.9 % and a high color-rendering index (CIR) of 81.1 for two and three optical components of white emissions, which are among the highest values of previously reported solution-processed all-fluorescence white OLEDs. This is the first attempt to construct white OLED based on an MR-TADF emitter and the satisfactory results indicate that the flexible dendron engineering strategy can effectively develop high-performance narrow band deep-blue MR-TADF for wide-color gamut display and high CIR white OLEDs.