High Photoluminescence Quantum Efficiency Research Articles

Highly Efficient Near-Infrared Luminescent Radicals with Emission Peaks over 750 nm.

Purely organic molecules exhibiting near-infrared (NIR) emission possess considerable potential for applications in both biological and optoelectronic technological domains, owing to their inherent advantages such as cost-effectiveness, biocompatibility, and facile chemical modifiability. However, the repertoire of such molecules with emission peaks exceeding 750 nm and concurrently demonstrating high photoluminescence quantum efficiency (PLQE) remains relatively scarce due to the energy gap law. Herein, we report two open-shell NIR radical emitters, denoted as DMNA-Cz-BTM and DMNA-PyID-BTM, achieved through the strategic integration of a donor group (DMNA) onto the Cz-BTM and PyID-BTM frameworks, respectively. We found that the donor-acceptor molecular structure allows the two designed radical emitters to exhibit a charge-transfer excited state and spatially separated electron and hole levels with non-bonding characteristics. Thus, the high-frequency vibrations are effectively suppressed. Besides, the reduction of low-frequency vibrations is observed. Collectively, the non-radiative decay channel is significantly suppressed, leading to exceptional NIR PLQE values. Specifically, DMNA-Cz-BTM manifests an emission peak at 758 nm alongside a PLQE of 55%, whereas DMNA-PyID-BTM exhibits an emission peak at 778 nm with a PLQE of 66%. Notably, these represent the pinnacle of PLQE among metal-free organic NIR emitters with emission peaks surpassing 750 nm.

Structural Changes and Differences in Intrinsic Photoluminescence of Four Cationic Two-Dimensional Lead Halide Frameworks Modulated by Synthesis Temperature.

Luminescent hybrid organolead halide materials with cationic inorganic frameworks and high chemical inertness have demonstrated broad application prospects in the visible light region. However, the corresponding relationship between structural changes and luminescence properties in such materials needs further clarification. Here, for the first time, we have successfully synthesized [Pb2X3](PDAH)(H2O) (X = Cl or Br, PDAH = C7H4NO4) single crystals via a facile hydrothermal method and then obtained [Pb11X14](PDA)4 (X = Cl or Br, PDA = C7H3NO4) at higher temperatures. The different synthesis temperatures resulted in significant differences in the luminescence properties of the two groups of structures. X-ray crystallography revealed the different degrees of distortion of the PbII centers' coordination environment between the two structures, which would significantly affect the electron-phonon coupling process under excited states and ultimately affect the emission properties originating from self-trapped excitons (STEs) of the two materials. In addition, density functional theory (DFT) calculations indicate that the two structures have different band gap characteristics due to the different proportions of inorganic and organic components, which also affect the optoelectronic properties of the two groups of materials. It is also worth mentioning that the broadband orange-light emission of [Pb11Br14](PDA)4 with a high photoluminescence quantum efficiency (PLQE) of 86% endows it with potential applications in WLEDs.

Design and synthesis of efficient red space-confined thermally activated delayed fluorescence emitter

A novel red thermally activated delayed fluorescence (TADF) emitter, 2-(4,4″-bis(diphenylamino)-[1,1':3′,1″-terphenyl]-4′-yl) quinoxaline-6,7-dicarbonitrile (QCN-2TPA), was developed by incorporating two trianiline units into the ortho- and para-positions of the quinoxalin-6,7-dinitrile core. The adjacent trianiline unit and quinoxalin-6,7-dinitrile core interact spatially for through-space charge transfer, while the quinoxalin-6,7-dinitrile core and the para-positioned trianiline unit enable through-bond charge transfer. QCN-2TPA demonstrated high photoluminescence quantum efficiency and a small ΔEST. Organic light-emitting diodes using QCN-2TPA as the emitter achieved a maximum external quantum efficiency of 21.4 % with red emission peaking at 596 nm.

A zero-dimensional perovskite with high-efficiency luminescence and transient response for advanced information encryption

Due to the increasingly complex network attacks and advancements in computational technology, finding new and efficient encryption techniques is an urging task. As a promising material, the application of perovskite luminescent materials in information encryption is limited to pre-planned specific scenarios or applications, lacking the ability to respond to temporary demands. In this work, we have designed a novel cadmium-based zero-dimensional perovskite, TEA2CdCl4, which presents blue luminescence centered at 413 nm originating from organic cations. Upon Sb3+ doping, it not only exhibits intense red emission at 623 nm with a high photoluminescence quantum efficiency up to 100 %, but also brings outstanding resistance to thermal quenching. Especially, an ultrafast response speed could be achieved during decryption process which has been verified by first-principles calculations. Based on the advantages, a large-area optical anti-counterfeiting paper for temporary information encryption transmission is designed, which not only verifies the potential for secure information transmission and protection, but also introduces a new concept for the application of organic–inorganic hybrid perovskites in the field of information encryption.

Highly efficient In(I) doped Cs3Cu2I5 single crystals for light-emitting diodes and gamma spectroscopy applications

High-quality Cs3Cu2I5:In single crystals with a 7 mm diameter were grown by using the vertical Bridgman method. These crystals have a high optical transmittance (>75 %) and emit a bright red-orange light under both UV and X-ray irradiation. The Cs3Cu2I5:In crystals can exhibit a high photoluminescence quantum efficiency (PLQY) of 79.5 %, thus we explored the potential applications for light-emitting diodes (LED). The fabricated LED demonstrated CIE color coordinates of (0.553, 0.431) with a color rendering index (Ra) of 77, making it suitable for supplementary light in plant growth. Moreover, we evaluated their gamma-ray spectroscopy capability by using an avalanche photodiode (APD) detector. Under 137Cs gamma-ray irradiation, the gamma scintillation yield and energy resolution gradually degraded as the In concentration increased, which can be attributed to an enhanced afterglow after In doping.

Intramolecular Hydrogen Bonding Rigidifying Flexible Bridge for Solution- and Vacuum-Processed TSCT-TADF Emitters.

To realize strong donor-acceptor face-to-face stacking for efficient through-space charge transfer-type thermally activated delayed fluorescence, a conceptually new design strategy is proposed to couple flexible bridges with adequate rigidity via built-in intramolecular hydrogen bonds (IHBs). The resulting emitter ACE-CN has a planarized benzyl methyl ether bridge self-anchored by the C-H···O IHB and shows a high photoluminescence quantum efficiency of 93%. The solution- and vacuum-processed devices exhibited high external quantum efficiencies of 11.8% and 24.7%, respectively.

Steric Control of Luminescence in Phenyl-Substituted Trityl Radicals.

Triphenylmethyl (trityl) radicals have shown potential for use in organic optoelectronic applications, but the design of practical trityl structures has been limited to donor/radical charge-transfer systems due to the poor luminescence of alternant symmetry hydrocarbons. Here, we circumvent the symmetry-forbidden transition of alternant hydrocarbons via excited-state symmetry breaking in a series of phenyl-substituted tris(2,4,6-trichlorophenyl)methyl (TTM) radicals. We show that 3-fold phenyl substitution enhances the emission of the TTM radical and that steric control modulates the optical properties in these systems. Simple ortho-methylphenyl substitution boosts the photoluminescence quantum efficiency from 1% (for TTM) to 65% at a peak wavelength of 612 nm (for 2-T3TTM) in solution. In the crystalline solid state, the neat 2-T3TTM radical shows a remarkably high photoluminescence quantum efficiency of 25% for emission peaking at 706 nm. This has implications in the design of aryl-substituted radical structures where the electronic coupling of the substituents influences variables such as emission, charge transfer, and spin interaction.

Molecular Engineering to Achieve AIE-active Fluorophore with Near-infrared (NIR) Emission and Temperature-sensitive Property.

Near-infrared organic small molecule luminescent materials have the advantages of easy modification, high quantum efficiency, good biological affinity, and color adjustability; thus, have promising application prospects in the fields of photoelectric devices, sensitive detection, photodynamic therapy, and biomedical imaging. However, traditional organic luminescent molecules have the problems of short emission wavelength, aggregation-causing emission quenching, and low quantum yield. Herein, we successfully synthesized four D-π-A-D light-emitting molecules based on electron-withdrawing malonitrile group and different electron-donating arylamine groups. These compounds showed satisfactory solvatochromism, aggregation-induced emission, red and near-infrared fluorescence, high photoluminescence quantum efficiency and temperature response properties. This successful example of molecular engineering provides a valuable reference for the development of advanced NIR materials with AIE and temperature-sensitive properties.

High-Brightness Blue Polariton Organic Light-Emitting Diodes.

Polariton organic light-emitting diodes (POLEDs) use strong light-matter coupling as an additional degree of freedom to tailor device characteristics, thus making them ideal candidates for many applications, such as room temperature laser diodes and high-color purity displays. However, achieving efficient formation of and emission from exciton-polaritons in an electrically driven device remains challenging due to the need for strong absorption, which often induces significant nonradiative recombination. Here, we investigate a novel POLED architecture to achieve polariton formation and high-brightness light emission. We utilize the blue-fluorescent emitter material 4,4'-Bis(4-(9H-carbazol-9-yl)styryl)biphenyl (BSBCz), which exhibits strong absorption and a highly horizontal transition-dipole orientation as well as a high photoluminescence quantum efficiency, even at high doping concentrations. We achieve a peak luminance of over 20,000 cd/m2 and external quantum efficiencies of more than 2%. To the best of our knowledge, these values represent the highest reported so far for electrically driven polariton emission from an organic semiconductor emitting in the blue region of the spectrum. Our work therefore paves the way for a new generation of efficient and powerful optoelectronic devices based on POLEDs.

Performance-improved narrowband near-ultraviolet emission from a simple butyl and cyanogen substituted indolocarbazole

High-efficiency narrowband near-ultraviolet (NUV) organic light-emitting diodes with high color purity have currently encountered great challenges. Here, using butyl (Bu) and cyanogen (CN) substituted strategy in the simplest polycyclic aromatic hydrocarbons of indolocarbazole (ICz), two simple emitters of BuICz and BuICzCN were demonstrated. This simple strategy was observed to enable both emitters to realize NUV emission at 380–381 nm with a small full width at half maximum (FWHM) of 21–23 nm and high photoluminescent quantum efficiency of 50%–59% in toluene solution. Furthermore, the BuICzCN doped devices exhibited a slightly blueshifted narrowband NUV electroluminescence at 388 nm with a small FWHM of 32.3 nm but a higher external quantum efficiency of 3.92% in comparison with the BuICz doped devices. This work provides a path to realize high-performance narrow-band NUV emission.

Enhancing Light Out-coupling in Perovskite Light-Emitting Diodes through Plasmonic Nanostructures.

Perovskite light-emitting diodes (PeLEDs) have emerged as promising candidates for lighting and display technologies owing to their high photoluminescence quantum efficiency and high carrier mobility. However, the performance of planar PeLEDs is limited by the out-coupling efficiency, predominantly governed by photonic losses at device interfaces. Most notably, the plasmonic loss at the metal electrode interfaces can account for up to 60% of the total loss. Here, we investigate the use of plasmonic nanostructures to improve the light out-coupling in PeLEDs. By integrating these nanostructures with PeLEDs, we have demonstrated an effectively reduced plasmonic loss and enhanced light out-coupling. As a result, the nanostructured PeLEDs exhibit an average 1.5-fold increase in external quantum efficiency and an ∼20-fold improvement in device lifetime. This finding offers a generic approach for enhancing light out-coupling, promising great potential to go beyond existing performance limitations.

Planar Chiral Thermally Activated Delayed Fluorescence Materials Based on Di[2.2]paracyclophane for Circularly Polarized Electroluminescence

AbstractIn this study, featuring di[2.2]paracyclophane (DpCp) amine derivatives as electron donors and 4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl (Trz) as the electron acceptor, four thermally activated delayed fluorescence (TADF) molecules are disclosed. The C2 symmetric molecules, DpCpN‐Trz and DpCpCz‐Trz, bearing a chair‐like planar chiral di[2.2]paracyclophane moiety, are obtained as optically pure enantiomers (R/S)‐C‐DpCpN‐Trz and (R/S)‐C‐DpCpCz‐Trz. And the compounds B‐DpCpN‐Trz and B‐DpCpCz‐Trz with a bridge‐like di[2.2]paracyclophane skeleton are meso‐compounds, thus without optically activity. All emitters show blue emissions peaking from 464 to 485 nm, accompanied by high photoluminescence quantum efficiency (up to 93%). The enantiomers (R/S)‐C‐DpCpN‐Trz and (R/S)‐C‐DpCpCz‐Trz exhibit symmetric circularly polarized photoluminescence spectra with dissymmetry factors (|gPL|) ranging from 3.8 × 10−4 to 6.7 × 10−4 in toluene and films. The organic light‐emitting diodes (OLEDs) fabricated with these emitters achieve maximum external quantum efficiencies of up to 19.5%. Notably, the circularly polarized OLEDs (CP‐OLEDs) with (R/S)‐C‐DpCpN‐Trz and (R/S)‐C‐DpCpCz‐Trz demonstrate |gEL| factors of up to 7.6 × 10−4. This study demonstrates a feasible way to design TADF materials and enantiomers by incorporating DpCp derivatives for CP‐OLEDs.

Enabling Broadband Solar-Blind UV Photodetection by a Rare-Earth Doped Oxyfluoride Transparent Glass-Ceramic.

Oxyfluoride transparent glass-ceramics (GC) are widely used as the matrix for rare-earth (RE) ions due to their unique properties such as low phonon energy, high transmittance, and high solubility for RE ions. Tb3+ doped oxyfluoride glasses exhibit a large absorption cross section for ultraviolet (UV) excitation, high stability, high photoluminescence quantum efficiency, and sensitive spectral conversion characteristics, making them promising candidate materials for use as the spectral converter in UV photodetectors. Herein, a Tb3+ doped oxyfluoride GC isdeveloped by using the melt-quenching method, and the microstructure and optical properties of the GC sample are carefully investigated. By combining with a Si-based photo-resistor,a solar-blind UV detector is fabricated, which exhibits a significant photoelectric response with a broad detection range from 188 to 400nm. The results indicate that the designed UV photodetector is of great significance for the development of solar-blind UV detectors.

High-performance CsSnBr<sub>3</sub>/Si PN heterojunction photodetectors prepared by pulsed laser deposition epitaxy

Halide perovskite semiconductors have outstanding physical properties such as high light absorption coefficient, large carrier diffusion length, and high photoluminescence quantum efficiency, and demonstrate significant potential applications in optoelectronic devices such as photodetectors and solar cells. However, the toxicity and environmental instability associated with lead-based perovskites significantly limit their applications. An attractive solution is substituting tin for lead in perovskites and growing high-quality tin-based perovskite films. In this study, we adopt the pulsed laser deposition method to achieve the epitaxial growth of CsSnBr<sub>3</sub> films on silicon substrates. The morphologies, optical and electrical properties of the CsSnBr<sub>3</sub> films, as well as the CsSnBr<sub>3</sub>/Si heterojunction detectors, are comprehensively investigated with various characterization techniques, including XRD 2<i>θ</i>-<i>ω</i> and <i>φ</i> scans, atomic force microscope, scanning electron microscope, photoluminescence and time-resolved photoluminescence spectroscopy, and Hall electrical measurements. The results indicate that such a CsSnBr<sub>3</sub> film grows epitaxially onto the silicon substrate via a face-to-face mode. Interestingly, an unusual temperature-dependent bandgap increase is found to be due to the high electron effective mass of CsSnBr<sub>3</sub>. The CsSnBr<sub>3</sub> film shows the P-type semiconductor behavior with a high mobility of 122 cm²/(V·s), enabling the formation of an ideal Type-II heterojunction with the silicon substrate. The CsSnBr<sub>3</sub>/Si semiconductor heterojunction detector exhibits distinctive heterojunction PN diode characteristics in the dark and a pronounced photoresponse under illumination. At zero bias, the detector displays a switch ratio exceeding 10<sup>4</sup>, responsivity of 0.125 mA/W, external quantum efficiency of 0.0238%, detectivity (<inline-formula><tex-math id="Z-20240301150440">\begin{document}$D^* $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231645_Z-20240301150440.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231645_Z-20240301150440.png"/></alternatives></inline-formula>) of 2.1×10<sup>9</sup> Jones, response time 3.23 ms, and recovery time of 4.87 ms. Under a small bias of –1 V, the switch ratio decreases to 50, but responsivity and external quantum efficiency increase by 568 times. The detectors can maintain self-powered operation state with a high switch ratio of 10<sup>4</sup>, millisecond-level response time and millisecond-level recovery time. In conclusion, this work presents a self-powering, high-performance photodetector based on CsSnBr<sub>3</sub> epitaxial films integrated with silicon substrates.

Luminescent carbene-copper(i)-amide polymers for efficient host-free solution-processed OLEDs.

Luminescent metallopolymers have attracted broad interest in the fields of healthcare and organic electronics. However, polymeric emitters based on earth-abundant metal complexes are scarce. Here, two series of Cu(i) polymers, PMAC-x and PCAAC-x (x = 1-3) have been developed using two kinds of Cu(i)-based carbene-metal-amide (CMA) complexes as side-chain emitter units to combine with a nonconjugated polystyrene backbone. These Cu(i) polymers emit via distinct thermally activated delayed fluorescence or dominant phosphorescence, inherited from the grafted Cu(i)-based CMA units. Particularly, the PMAC-x polymers exhibit high photoluminescence quantum efficiencies of up to 0.78, short emission lifetimes of down to 0.66 μs, and fast radiative rates of up to 106 s-1 in neat films. Thanks to the good encapsulation effect of the polystyrene backbone, these Cu(i) polymers not only demonstrate favorable moisture stability but also show significant aggregation-induced emission. The resultant host-free solution-processed organic light-emitting diodes (OLEDs) achieve outstanding electroluminescence performance with a record external quantum efficiency of 13.8% at a practical luminance of ∼100 nits, representing state-of-the-art device efficiency for metallopolymer-based OLEDs. This work not only presents the first example of CMA polymers but also provides the future direction of polymeric emitters from earth-abundant metal complexes for the OLED application.

Anion exchange as an excellent tool to obtain highly efficient blue-emitting all-inorganic perovskite quantum dots

In this study, we examined the dynamic photoluminescence (PL) characteristics of all-inorganic perovskite quantum dots (QDs) during the anion-exchange process between bromide and chloride ions. CsPbBr3 QDs were synthesized using an ultrasound-induced hot-injection route. These QDs were then treated with TMS-Cl solutions, resulting in the formation of blue-emitting CsPb(Br/Cl)3 QDs with high quantum efficiencies. Even the addition of a small amount of TMS-Cl to the CsPbBr3 solution led to a noticeable blue shift of the emission. Moreover, surface treatment with a small amount of TMS-Cl also resulted in an enhanced PL quantum efficiency (PLQE) owing to surface trap removal. Exposure of the CsPbBr3 perovskite QDs solution to a higher amount of TMS-Cl yielded deep-blue-emitting QDs (412 nm) with a very high PLQE of 57 %.

Centimeter-Sized Single Crystals of Tetrahedral Manganese (II) Halide Hybrids for Wide-Color Gamut Backlighting Displays.

Phosphors with narrow-band green emissions and high photoluminescent quantum efficiency (PLQY) are significantly required for backlighting displays with wider color gamut. In this work, two centimeter-sized manganese (II) halide single crystals TMG2MnCl4 and TMG2MnBr4 (TMG = 1,1,3,3-tetramethylguanidine) are synthesized, exhibiting bright narrow-band green emissions with high PLQYs up to 62% and 90%, respectively. The narrow-band green light emission is located at 520nm with a full-width at half-maximum (FWHM) of only 57nm. The photoluminescence mechanisms of two single crystals are elaborated. Two white-light-emitting diodes for backlighting displays (BD-WLEDs) based on them are fabricated, exhibiting the widest color gamut of 122% National Television Standards Committee (NTSC), and a luminous efficacy reached ≈93lmW-1 with excellent luminescence stability at high temperatures. These properties indicate the potential applications of tetrahedral manganese (II) hybrids in wide-color gamut backlighting displays.

Advances and future perspectives in polycrystalline halide perovskite light-emitting diodes

Metal halide perovskites (MHPs) have emerged as a highly promising candidate for next-generation light-emitting materials due to their exceptional optoelectronic properties. These properties include superior color purity, high photoluminescence quantum efficiency (PLQY), and the facile tunability of bandgap through compositional and dimensional control. Particularly, polycrystalline perovskites have been introduced as the first perovskite light-emitting diodes (PeLEDs) with superior charge mobility. However, the development of efficient and stable PeLEDs, crucial for commercialization, has proven to be a significant challenge due to the low exciton binding energy (E b) and inherent defects. Nevertheless, recent achievements have demonstrated polycrystalline PeLEDs with an external quantum efficiency (EQE) surpassing 28% and a half-lifetime (T 50) exceeding 30,000 h. In this review, we present the progress of polycrystalline PeLEDs with improved efficiency (PLQY, EQE) and stability by focusing on grain size regulation, defect passivation, and dimensional control. This review offers promising strategies for realizing polycrystalline perovskite material as a light emitter, highlights limitations and provides future perspectives for advancing PeLEDs.

Valence conversion and site reconstruction in near-infrared-emitting chromium-activated garnet for simultaneous enhancement of quantum efficiency and thermal stability

Achievement of high photoluminescence quantum efficiency and thermal stability is challenging for near-infrared (NIR)-emitting phosphors. Here, we designed a “kill two birds with one stone” strategy to simultaneously improve quantum efficiency and thermal stability of the NIR-emitting Ca3Y2-2x(ZnZr)xGe3O12:Cr garnet system by chemical unit cosubstitution, and revealed universal structure-property relationship and the luminescence optimization mechanism. The cosubstitution of [Zn2+–Zr4+] for [Y3+–Y3+] played a critical role as reductant to promote the valence transformation from Cr4+ to Cr3+, resulting from the reconstruction of octahedral sites for Cr3+. The introduction of [Zn2+–Zr4+] unit also contributed to a rigid crystal structure. These two aspects together realized the high internal quantum efficiency of 96% and excellent thermal stability of 89%@423 K. Moreover, information encryption with “burning after reading” was achieved based on different chemical resistance of the phosphors to acid. The developed NIR-emitting phosphor-converted light-emitting diode demonstrated promising applications in bio-tissue imaging and night vision. This work provides a new perspective for developing high-performance NIR-emitting phosphor materials.

8-Phenylquinoline-Based Tetradentate 6/6/6 Platinum(II) Complexes for Near-Infrared Emitters.

A series of novel tetradentate 6/6/6 Pt(II) complexes containing an 8-phenylquinoline-benzo[d]imidazole-carbazole ligand was designed; the Pt(II) complexes could be synthesized by metalizing the corresponding ligand with K2PtCl4 in high isolated yields of 60-90%. Experimental and theoretical studies suggested that the ligand modification of the quinoline moieties of the Pt(II) complexes could tune their electrochemical, photophysical, and excited-state properties. Notably, all the Pt(II) complexes exhibited highly electrochemical stabilities with reversible redox processes except the quasi-reversible reduction of PtYL3. The large π-conjugation of the ligand together with increased metal-to-ligand charge-transfer (3MLCT) characters in T1 states enabled the Pt(II) complexes to show broad Gaussian-type NIR emission spectra with high photoluminescence quantum efficiencies of 1.2-1.5% and short τ of 0.8-1.5 μs in dichloromethane at room temperature. This work should provide a valuable reference for the design and development of monomer NIR emitters.