International Commission On Illumination Research Articles

P‐203: Highly‐Pure Color and Stable Green Hyperfluorescence Device through Host Adjustment

In this study, we report a fluorescent green emitter based on 4,4‐dfluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) backbone and its hyperfluroescence (HF) device. Our HF device shows high EQE of 20.0%, emission peak at 532 nm with narrow FWHM of 29 nm and Commission Internationale de l'Eclairage (CIE) of (0.27, 0.68). Moreover, with consideration of good host materials the device realized a long lifetime (LT90) of 210 h at an initial luminance of3,000 cd/m2.

Investigating the influence of carbon dots on β-Ca2SiO4:Ce3+ phosphors derived from agro-waste for diverse applications

A series of blue-emitting composite based on 3 wt% carbon dots in β-Ca2SiO4:Ce3+ (3 wt% CDs@β-CSO:Ce3+) was synthesized through a hydrothermal method, aiming to enhance applications in latent fingerprint (LFP) detection, anti-counterfeiting (AC) measures, and optical thermometry. The X-ray diffraction (XRD) analysis confirmed that these phosphors possess a monoclinic crystal structure. Under 356 nm excitation, the Ce3+ doped β-Ca2SiO4 phosphors (β-CSO:Ce3+) display a broad blue emission peak at 431 nm, attributed to the 5d → 4f electric dipole transition of Ce3+, while the inclusion of Carbon dots (CDs) shifts this emission to 442 nm. This shift and the improved photoluminescence (PL) intensity are thought to result from the Fӧrster Resonance Energy Transfer (FRET) mechanism. The optimal concentration of Ce3+ ions was determined to be 5 mol%, as higher concentrations led to a decrease in emission intensity due to concentration quenching (CQ). Additionally, a fabricated white light diode using these phosphors achieved chromaticity coordinates of (0.344, 0.330) according to the Commission International de L'Eclairage (CIE), with the CIE, correlated colour temperature (CCT), and colour purity (CP) metrics indicating a bright green output with values of (0.1486, 0.0433), 1759 K, and 96.4%, respectively. The optimized 3 wt% CDs@β-CSO:5Ce3+ composite demonstrated a remarkable CP of 99.9%. Notably, the phosphors maintained 85.77% of their emission intensity at 423 K, showcasing exceptional thermal stability. A novel approach utilizing sketch pen and brush mode was developed to apply the optimized AC security ink, allowing for the creation of various intricate patterns. The resulting AC tags featured high resolution and durability. These findings underscore the 3wt%CDs@β-CSO:5Ce3+ composite as superior luminescent materials for use in fields requiring LFP, AC strategies, and optical thermometry.

Pattern‐Matched Polymer Ligpands Toward Near‐Perfect Synergistic Passivation for High‐Performance and Stable Br/Cl Mixed Perovskite Light‐Emitting Diodes

Mixed Br/Cl perovskite nanocrystals (PeNCs) exhibit bright pure‐blue emission benefiting for fulfilling the Rec. 2100 standard. However, phase segregation remains a significant challenge that severely affects the stability and emission spectrum of perovskite light‐emitting diodes (PeLEDs). Here, we demonstrate the optimization of the spacing between polydentate functional groups of polymer ligands to match the surface pattern of CsPbBr1.8Cl1.2 PeNCs, resulting in effective synergistic passivation effect and significant improvements in PeLED performances. The block and alternating copolymers with different inter‐functional group spacing are facilely synthesized as ligands for PeNCs. Surprisingly, block copolymers with a higher functional group density do not match PeNCs, while alternating copolymers enable efficient PeNCs with the high photoluminescence intensity, low non‐radiative recombination rate and high exciton binding energy. Density functional theory calculations clearly confirm the almost perfect match between alternating copolymers and PeNCs. Finally, pure‐blue PeLEDs are achieved with the emission at 467 nm and Commission Internationale de l'Eclairage (CIE) coordinates of (0.131, 0.071), high external quantum efficiency (9.1%) and record spectral and operational stabilities (~ 80 mins) in mixed‐halide PeLEDs. Overall, this study contributes to designing the polymer ligands and promoting the development of high‐performance and stable pure‐color PeLEDs towards display applications.

Pattern-Matched Polymer Ligands Toward Near-Perfect Synergistic Passivation for High-Performance and Stable Br/Cl Mixed Perovskite Light-Emitting Diodes.

Mixed Br/Cl perovskite nanocrystals (PeNCs) exhibit bright pure-blue emission benefiting for fulfilling the Rec. 2100 standard. However, phase segregation remains a significant challenge that severely affects the stability and emission spectrum of perovskite light-emitting diodes (PeLEDs). Here, we demonstrate the optimization of the spacing between polydentate functional groups of polymer ligands to match the surface pattern of CsPbBr1.8Cl1.2 PeNCs, resulting in effective synergistic passivation effect and significant improvements in PeLED performances. The block and alternating copolymers with different inter-functional group spacing are facilely synthesized as ligands for PeNCs. Surprisingly, block copolymers with a higher functional group density do not match PeNCs, while alternating copolymers enable efficient PeNCs with the high photoluminescence intensity, low non-radiative recombination rate and high exciton binding energy. Density functional theory calculations clearly confirm the almost perfect match between alternating copolymers and PeNCs. Finally, pure-blue PeLEDs are achieved with the emission at 467 nm and Commission Internationale de l'Eclairage (CIE) coordinates of (0.131, 0.071), high external quantum efficiency (9.1 %) and record spectral and operational stabilities (~80 mins) in mixed-halide PeLEDs. Overall, this study contributes to designing the polymer ligands and promoting the development of high-performance and stable pure-color PeLEDs towards display applications.

Excited-State Engineering Enables Efficient Deep-Blue Light-Emitting Diodes Exhibiting BT.2020 Color Gamut.

Organic luminescent materials that exhibit thermally activated delayed fluorescence (TADF) can convert non-emissive triplet excitons into emissive singlet states through a reverse intersystem crossing (RISC) process. Therefore, they have tremendous potential for applications in organic light-emitting diodes (OLEDs). However, with the development of ultra-high definition 4K/8K display technologies, designing efficient deep-blue TADF materials to achieve the Commission Internationale de l'Éclairage (CIE) coordinates fulfilling BT.2020 remains a significant challenge. Here, an effective approach is proposed to design deep-blue TADF molecules based on hybrid long- and short-range charge-transfer by incorporation of multiple donor moieties into organoboron multiple resonance acceptors. The resulting TADF molecule exhibits deep-blue emission at 414nm with a full width at half maximum (FWHM) of 29nm, together with a thousand-fold increase in RISC rate. OLEDs based on the champion material achieve a record maximum external quantum efficiency (EQE) of 22.8% with CIE coordinates of (0.163, 0.046), approaching the coordinates of the BT.2020 blue standard. Moreover, TADF-assisted fluorescence devices employing the designed material as a sensitizer exhibit an exceptional EQE of 33.1%. This work thus provides a blueprint for future development of efficient deep-blue TADF emitters, representing an important milestone towards meeting the blue color gamut standard of BT.2020.

Achieving Record External Quantum Efficiency of 11.5 % in Solution-Processable Deep-Blue Organic Light-Emitting Diodes Utilizing Hot Exciton Mechanism.

High performance solution-processable deep-blue emitters with a Commission International de l'Eclairage (CIE) coordinate of CIEy≤0.08 are highly desired in ultrahigh-definition display. Although, deep-blue materials with hybridized local and charge-transfer (HLCT) excited-state feature are promising candidates, their rigidity and planar molecular structures limit their application in solution-processing technique. Herein, four novel deep-blue solution-processable HLCT emitters were first proposed by attaching rigid imide aliphatic rings as functional units onto the HLCT emitting core. The functional units not only improve solubility, enhance thermal properties and morphological stability of the emitting core, but also promote photoluminescence efficiency, balance charge carrier transport, and inhibit aggregation-caused quenching effect due to the weak electron-withdrawing property as well as steric hindrance. The corresponding solution-processable organic light-emitting diodes (OLEDs) substantiate an unprecedented maximum external quantum efficiency (EQEmax) of 11.5 % with an emission peak at 456 nm and excellent colour purity (full width at half maximum=56 nm and CIEy=0.09). These efficiencies represent the state-of-the-art device performance among the solution-processable blue OLEDs based on the "hot exciton" mechanism. This simple strategy opens up a new avenue for designing highly efficient solution-processable deep-blue organic luminescent materials.

Synthesis, structure, and luminescence properties of a 0D organic-inorganic cadmium iodide: Combined experimental and theoretical approach

Hybrid organic-inorganic metal halide materials with zero-dimensional (0D) structures have emerged as a captivating field of research due to their distinctive electronic properties and remarkable broadband emission characteristics. In this study, we successfully synthesized a novel hybrid cadmium iodide compound, (BZA)2CdI4.H2O (BZA+: benzylammonium), in the form of single crystals employing the solvent-evaporation method. The room temperature single-crystal X-ray diffraction analysis revealed that (BZA)2CdI4.H2O possesses a typical 0D crystal structure, where (CdI4)2− anions are spatially isolated and surrounded by (BZA)+ cations and H2O molecules. The crystal packing is intricately governed by various non-covalent intermolecular interactions, including π–π stacking interactions, NH…I, NH…O, and OH…I hydrogen bonds, quantified through Hirshfeld surface analysis. Thermal analysis further demonstrated that the removal of water molecules in the crystal lattice yields a dehydrated phase of (BZA)2(CdI4). Upon 330 nm irradiation, the title compound displayed a broad bluish-white light emission, featuring a primary band at 430 nm and a secondary band at 500 nm. Based on photoluminescence spectra measurements and density functional theory (DFT) calculations, the dual-band emission is assigned to the emission of (BZA)+ organic cations and to excitons confined in the [CdI4]2– isolated inorganic tetrahedron, respectively. Interestingly, the presence of isolated molecular units in the 0-D structure results in strongly localized charges and bluish-white light emission with Commission International de l'Eclairage (CIE) colour coordinates (0.23, 0.28). These results confirm the promise of 0D metal-halide hybrids with dual-band emission as luminescent materials for solid-state lighting.

Fine tuning of excited states by trifluoromethylphenyl for blue-shifted color and enhanced EQEs in thermally activated delayed fluorescence emitters

3,6-di-tert-butyl-9H-carbazole and 3,6-diphenyl-9H-carbazole have been widely used to construct blue thermally activated delayed fluorescence (TADF) emitters. However, it is difficult for related emitters to achieve maximum external quantum efficiency (EQEmax) above 20 % with the Commission Internationale de l'Eclairage (CIE) y ≤ 0.12. A new type of donor was developed to construct blue TADF molecules, namely CF3P-BuCz-TRZ and CF3P-PhCz-TRZ. The weak electron-withdrawing trifluoromethylphenyl (CF3P) with moderate steric hindrance was introduced into the 1-site of carbazole donor for improving the color purity for blue TADF emitters. More importantly, the introduction of CF3P tightly compacts the energy levels for the significant excited states in RISC process. The energy gap between the lowest singlet excited (S1) state and the lowest triplet (T1) state (Δ E(S1−T1)), as well as between T1 and the higher triplet (Tn, n ≥ 2) states (Δ E(Tn−T1)) were reduced, so that Tn (n ≥ 2) could be effectively harvested to further promote reverse intersystem crossing (RISC). As a result, the OLEDs based on CF3P-BuCz-TRZ and CF3P-PhCz-TRZ displayed blue electroluminescence with CIE coordinates of (0.156, 0.107) and (0.155, 0.115). In particular, the maximum EQEs of the CF3P-PhCz-TRZ device reached 20.43 % without employing any light out-coupling enhancement or TADF-sensitized structure. This strategy should be valuable for designing more pure-blue and deep-blue TADF emitters.

Structure Engineering of Acridine Donor to Optimize Color Purity of Blue Thermally Activated Delayed Fluorescence Emitters.

9,9-Dimethyl-9,10-dihydroacridine (DMAC) is one of the most widely used electron donor for constructing high-performance thermally activated delayed fluorescence (TADF) emitters. However, DMAC-based emitters often suffer from the imperfect color purity, particularly in blue emitters, due to its strong electron-donating capability. To modulate donor strength, 2,7-F-Ph-DMAC and 2,7-CF3-Ph-DMAC were designed by introducing the electron-withdrawing 2-fluorophenyl and 2-(trifluoromethyl)phenyl at the 2,7-positions of DMAC. These donors were used, in combination with 2,4,6-triphenyl-1,3,5-triazine (TRZ) acceptor, to develop novel TADF emitters 2,7-F-Ph-DMAC-TRZ and 2,7-CF3-Ph-DMAC-TRZ. Compared to the F- or CF3-free reference emitter, both two emitters showed hypsochromic effect in fluorescence and comparable photoluminescence quantum yields without sacrificing the reverse intersystem crossing rate constants. In particular, 2,7-CF3-Ph-DMAC-TRZ based OLED exhibited a blue shift by up to 39 nm and significantly improved Commission International de l'Éclairage (CIE) coordinates from (0.36, 0.55) to (0.22, 0.41), while the external quantum efficiency kept stable at about 22.5 %. This donor engineering strategy should be valid for improving the color purity of large amount of acridine based TADF emitters. It can be predicted that pure blue TADF emitters should be feasible if these F- or CF3-modifed acridine donors are combined with other weaker electron acceptors.

Achieving Deep‐Blue Through‐Space Charge‐Transfer Emitter by Designing the Donor‐π‐Donor‐σ‐Acceptor Molecular Structure

AbstractIn the realm of organic light‐emitting diode (OLED), through‐space charge transfer (TSCT) thermally activated delayed fluorescence (TADF) emitters have demonstrated remarkable achievements. Nevertheless, realizing both deep‐blue emission and high efficiency by the TSCT strategy remains a persistent challenge. Here, the novel donor‐π‐donor‐σ‐acceptor (D‐π‐D‐σ‐A) type deep‐blue TSCT emitter, namely D‐tCz‐BO, is formulated to investigate its performance in OLED. D‐tCz‐BO show a narrow deep‐blue emission and efficient TADF character (λPL = 448, FWHM = 54 nm, ΦPL = 82%, and ΔEST = 0.09 eV). More importantly, the OLED based on D‐tCz‐BO as the emitter showed a maximum external quantum efficiency (EQEmax) of 20.5%, with a Commission Internationale de l'Eclairage (CIE) coordinate of (0.14, 0.12). This represents one of the best deep‐blue TSCT‐TADF emitters to date.

Graphene nanosheet reinforcement of polyurethane nanocomposite for green and sustainable photoluminescence, superhydrophobic, and anticorrosive paint.

A simple and environmentally friendly method was developed for smart and efficient waterborne polyurethane (PUR) paint. Sugarcane bagasse was recycled into reduced graphene oxide nanosheets (rGONSs). Both lanthanide-doped aluminate nanoparticles (LAN; photoluminescent agent, 7-9nm) and rGONSs (reinforcement agent) were integrated into a waterborne polyurethane to produce a novel photoluminescent, hydrophobic, and anticorrosive nanocomposite coating. Using ferrocene-based oxidation under masked circumstances, graphene oxide nanosheets were produced from sugarcane bagasse. The oxidized semicarbazide (SCB) nanostructures were integrated into polyurethane coatings as a drying, anticorrosion, and crosslinking agent. Polyurethane coatings with varying amounts of phosphor pigment were prepared and subsequently applied to mild steel. The produced paints (LAN/rGONSs@PUR) were tested for their hydrophobicity, hardness, and scratch resistance. Commission Internationale de l'éclairage (CIE) Laboratory parameters and photoluminescence analysis established the opacity and colourimetric properties of the nanocomposite coatings. When excited at 365 nm, the luminescent transparent paints emitted a strong greenish light at 517 nm. The anticorrosion characteristics of the coated steel were investigated. The phosphor-containing (11% w/w) polyurethane coatings displayed the most pronounced anticorrosion capability and long-persistent luminosity. The prepared waterborne polyurethane paints were very photostable and durable.

A Breakthrough in Color‐Tunable All‐Fluorescent White OLEDs through the Cooperation Between a New Blue HLCT Fluorophore and a Long‐Wavelength TADF Emitter

AbstractIt is a vitally important and challenging task to achieve high efficiency and wide color‐tunable white organic light emitting diodes (CT‐WOLEDs) meeting the needs of various decoration and lighting applications. Here, a high‐performance single‐cell all‐fluorescent CT‐WOLED with a single‐doped single‐emissive‐layer structure has been developed employing a multi‐functional hybrid local and charge transfer (HLCT) fluorophore 2‐(4‐(9H‐carbazol‐9‐yl)−2′,5′‐difluoro‐[1,1′:4′,1′'‐terphenyl]−4‐yl)−1‐phenyl‐1H‐phenanthro[9,10‐d]imidazole (PICZ2F) as a deep‐blue emitter as well as an effective host for a yellow thermally activated delayed fluorescence emitter. The record‐breaking power efficiency of 89.50 lm W‒1 and correlated color temperature (CCT) span from 3749 to 18 279 K are achieved simultaneously, which is not only one of the state‐of‐the‐art CT‐WOLEDs reported so far, but also comparable to the best values from all‐fluorescent white devices with a single‐emissive‐layer. Moreover, by using PICZ2F as an emitter, an external quantum efficiency (EQE) of 7.10% with the Commission Internationale de lEclairage (CIE) coordinates of (0.155, 0.068) is achieved in the doped device, and a low‐efficiency roll‐off even at a high luminance of 15 000 cd m−2 (EQE15000: 5.80%) is achieved in the non‐doped device. Overall, the findings provide a promising strategy to develop simple but efficient CT‐WOLEDs.

Enhancing Light-Emitting Efficiency of Blue Through-Space Charge Transfer Emitters via Fixing Configuration Induced by Intramolecular Hydrogen Bonding.

Closely aligned configuration of the donor (D) and acceptor (A) is crucial for the light-emitting efficiency of thermally activated delayed fluorescence (TADF) materials with through-space charge transfer (TSCT) characteristics. However, precisely controlling the D-A distance of blue TSCT-TADF emitters is still challenging. Herein, an extra donor (D*) located on the side of the primary donor (D) is introduced to construct the hydrogen bonding with A and thus modulate the distance of D and A units to prepare high-efficiency blue TSCT emitters. The obtained "V"-shaped TSCT emitter presents a minimal D-A distance of 2.890 Å with a highly parallel D-A configuration. As a result, a high rate of radiative decay (>107 s-1) and photoluminescence quantum yield (nearly 90%) are achieved. The corresponding blue organic light-emitting diodes show maximum external quantum efficiencies (EQEmax) of 27.9% with a Commission Internationale de L'Eclairage (CIE) coordinate of (0.16, 0.21), which is the highest device efficiency of fluorene-based blue TSCT-TADF emitters. In addition, the TSCT-TADF emitter-sensitized OLEDs also achieve a high EQEmax of 29.3% with a CIE coordinate of (0.12, 0.16) and a narrow emission.

1,1,1-Trifluoro-5,5-dimethyl-2,4-hexanedione based ternary complexes of Eu(III): Synthesis, structural and luminescence investigations

In this current study, we have synthesized four europium(III) complexes utilizing a tri-fluorinated β-diketone moiety: 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione (TFDH) with auxiliary ligand: 2,2′- bipyridine and its derivatives. FTIR, UV–Vis and luminescence spectroscopic characterizations were implemented for evaluation of the bonding and luminous characteristics in synthesized europium(III) complexes. Eight-coordination environment around Eu3+ ion has been demonstrated by 1H NMR spectral data. Photoluminescence (PL) study of these complexes has been carried out in powdered form. Characteristic red emitting behavior of Eu(III) ion was observed corresponds to the transition of 5D0→7F2 in PL spectra of Eu(III) complexes. The CIE (Commission Internationale de l'Eclairage) chroma coordinates 1931 and CCT (Correlated Color Temperature) values were derived from the information obtained from the emission spectra. The Judd-Ofelt intensity parameters (Ωτ) and excited state deactivation time (τ) in solid state have also been estimated. In the synthesized Eu(III) complexes, the europium ion was present in a highly polarizable ligand field, as demonstrated by the higher values of Ω2. Values of band gap i.e. optical and electronic as well as the red luminous nature of prepared complexes showed up their utilization in display devices.

Stable All‐Fluorescence White Organic Light‐Emitting Diodes with High Efficiency and High CRI

AbstractWhite organic light‐emitting diodes (WOLEDs) have been regarded as the candidates for next‐generation flat‐panel displays and solid‐state lighting due to their low cost. However, it is still challenging to achieve two‐component WOLEDs with high efficiency, high color index (CRI), and long lifetime. Here, high‐performance all‐fluorescence WOLEDs based on a blue fluorescent emitter and an orange thermally activated delayed fluorescent (TADF) emitter are demonstrated. The optimized all‐fluorescence WOLED with two EMLs presents the maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 23.4%, 40.2 cd A−1, and 33.2 lm W−1, corresponding to a maximum CRI value of 83.1 and Commission Internationale de L'Eclairage (CIE) coordinate of (0.30, 0.31). To further improve the device stability, the all‐fluorescence WOLEDs with three EMLs and tandem structure are constructed, respectively. Under the premise of ensuring efficiency, in going from the two‐EMLs to the three‐EMLs and the tandem structure, the LT50 (time to 50% of the initial luminance) of all‐fluorescence WOLEDs increase from 601 to 714 h and 1622 h at an initial luminance of 1000 cd m−2. These strategies and results present new insight into the design of all‐fluorescence WOLEDs with high efficiency, high CRI, and extended lifetime.

Tetravalent manganese-doped lithium meta-silicate red-emitting phosphors for LED applications: structural and luminescence properties

In this paper, different concentrations of tetravalent manganese-activated lithium meta-silicate red-emitting phosphors, namely Li2SiO3:xMn4+ (x = 0.01, 0.02, 0.03, 0.04 and 0.05 mol), have been prepared by the solid-state reaction method at 950 °C. The structural, thermal, morphological, and optical properties of the sintered phosphors were characterized by powder X-ray diffractometry (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), raman, UV-Visible and photoluminescence (PL) spectra. Excitation and emission spectra are used to study optical characteristics, which match well with the commercially visible region. The red emission bands for Li2SiO3:0.02Mn4+ peak at approximately 642 nm (λex = 425 nm) and 717 nm (λex = 475 nm), respectively due to the spin-forbidden 2E → 4A2 transition. The doping concentrations of xMn4+ in the Li2SiO3 host were investigated, and the correlations between Mn4+ doping concentration and luminescence intensity were examined. The Commission Internationale de l'Eclairage (CIE) chromatic coordinate graph confirmed the emission color observation in the red region, showed an excellent color purity (CP). In addition, the quantum efficiency (QE) of Li2SiO3:Mn4+ phosphors reached up to 70.51%. The investigation shows that synthesized Li2SiO3:Mn4+ phosphors are beneficial for red Light-Emitting Diodes (LEDs) used in solid-state lighting.

Highly efficient multi-resonance thermally activated delayed fluorescence material toward a BT.2020 deep-blue emitter

An ultrapure deep-blue multi-resonance-induced thermally activated delayed fluorescence material (DOB2-DABNA-A) is designed and synthesized. Benefiting from a fully resonating extended helical π-conjugated system, this compound has a small ΔEST value of 3.6 meV and sufficient spin–orbit coupling to exhibit a high-rate constant for reverse intersystem crossing (kRISC = 1.1 × 106 s–1). Furthermore, an organic light-emitting diode employing DOB2-DABNA-A as an emitter is fabricated; it exhibits ultrapure deep-blue emission at 452 nm with a small full width at half maximum of 24 nm, corresponding to Commission Internationale de l’Éclairage (CIE) coordinates of (0.145, 0.049). The high kRISC value reduces the efficiency roll-off, resulting in a high external quantum efficiency (EQE) of 21.6% at 1000 cd m–2.

Optimizing hexafluoro-2,4-pentanedione based Eu(III) complexes: A comprehensive study on the synthesis, spectroscopic characterization with Judd-Ofelt calculation

Utilizing Europium(III), compounds having eight-coordination geometry of the type [Eu(hfpd)3L2] and [Eu(hfpd)3Lʹ] were synthesized [hfpd = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, L = tri-octyl-phosphine oxide (TOPO) and Lʹ = 1,10-phenanthroline (phen), Neocuproine (neoc) and bathocuproine (bathoc)] and characterized through elemental, FTIR, CV and Proton-NMR techniques. Photoluminescent studies and quantum yield helped to understand the role of coordination environment and ligands on the emission intensity. Luminescence decay curves served as the basis for calculating the excited-state lifetimes of the synthesized complexes. JO parameters (Ω2, Ω4) and asymmetry ratio were also evaluated to study the coordination environment around the central metal ion. Solid-state complexes exhibited an intense, monochromatic bright red emission, as characterized by its Commission International de l’Eclairage (CIE) color coordinates. Owing to red luminescence and semi-conducting properties, these Eu(III) complexes can be employed as red-emitting material for fabricating lighting devices.

Constructing multifunctional deep-blue emitters with weak charge transfer excited state for high-performance non-doped blue OLEDs and single-emissive-layer hybrid white OLEDs

Deep-blue emitter with high photoluminescence efficiency (PLQY) is highly desirable in ultra-high definition displays and white solid-state lightings. In this work, two deep-blue phenanthro[9,10]imidazole derivatives, PPIS and PPPIS, with hot exciton property are successfully developed. Compared to PPIS, the embedded phenyl bridge in PPPIS is able to effectively increase the overlap of frontier molecular orbitals. In consequence, PPPIS shows higher oscillator strength and significantly enhanced PLQY. PPPIS also achieves better electroluminescence performance in non-doped device, showing deep-blue emission with Commission International de l'Eclairage (CIE) coordinates of (0.153, 0.087) and the maximum external quantum efficiency (EQEmax) of 8.5% with minuscule efficiency roll-off. Meanwhile, when PPPIS serves as the host for phosphor PO-01, high-efficiency orange phosphorescent device is obtained with high EQEmax of 29.8% and negligible efficiency roll-off at 1000 cd/m2. Further, efficient single-emissive-layer white device is assembled via utilizing PPPIS as a blue emitter as well as the host for PO-01 simultaneously, providing warm-white emission with CIE coordinates of (0.429, 0.433) at 1000 cd/m2, the forward-viewing EQEmax of 27.2% and maximum power efficiency (PEmax) of 80.1 lm/W, respectively. Our studies can establish a viable design strategy for deep-blue emitters in high-performance non-doped blue OLEDs and hybrid WOLEDs.

Dual-Emissive γ-[Cu4I8]4- Enables Luminescent Thermochromism in an Organic-Inorganic Hybrid Copper(I) Halide.

A highly luminescent (C13H28N2)2Cu4I8 single crystal containing isolated γ-[Cu4I8]4- anionic cluster was synthesized without the use of unsaturated cations. To the best of our knowledge, compounds bearing such like anions are not dual-emitting under UV excitation. However, dual emission does occur in (C13H28N2)2Cu4I8. Moreover, the emission bands were found to be temperature-sensitive, allowing tuning of the emission colors from blue (0.19, 0.20) to green (0.33, 0.47) in the Commission International de L' Eclairage (CIE) chromaticity coordinates. Remarkably, the color could be restored on returning to the initial temperature, confirming an efficient and reversible luminescent thermochromic effect in (C13H28N2)2Cu4I8. The origin of this excellent optical performance is discussed, and the difference in the mechanism with the dual-emissive Cu(I) halide complexes is also elucidated. Overall, our work provides a promising way to achieve efficient luminescent thermochromism. The developed (C13H28N2)2Cu4I8 represents one of the viable alternatives for eco-friendly luminescent thermochromic materials.