Emission Quantum Yield Research Articles

Finite element analysis on the near field properties of metallic cavities with atomic sharpness

Using finite element calculations, we investigated the near field properties of two types of commonly used metal nanostructures (a tip-substrate model representing a scanning tunneling microscope type setup (TS) and a nanoparticle-on-mirror (NPoM) configuration) with atomic sharpness and extreme focusing capabilities. The spatial confinement and electric field enhancement of the local field as well as the fluorescence quantum efficiency of a model molecule (as represented by an oscillating dipole) in the cavity region of the two models were systematically studied. It was found that the TS model tends to support higher local electric field enhancement while the NPoM model can provide a more localized plasmon electric field near the nanoparticle. Calculations with the radiating model molecule indicate that both TS and NPoM can cause significant enhancements to the non-radiative decay rates at the order of 106 in the wavelength range of 500–1000 nm. The TS model shows better performance for the radiative enhancements and the resulting emission quantum yield. These results are not only helpful to improve the understanding of such important nanocavities but also supply a reference for their further applications in different areas.

Strategy for Modulating Dihedral Angle Distribution for Enhanced Anti-Kasha TADF Behavior

D–A type thermally activated delayed fluorescence (TADF) materials with aggregation-induced emission (AIE) have attracted extensive research interest for their intense emission and high quantum yield in aggregated state. Herein, TADF molecules with vertical twisted structures are achieved by the methylation strategy which effectively separated the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). With the increase of the dihedral angle, 18 times enhancement of the photoluminescence quantum yield (PLQY) is realized in the aggregated state. The density functional theory (DFT) calculations demonstrate that these TADF molecules exhibit excellent photophysical properties in violation of Kasha’s rule: fluorescence originates from the higher energy electronic excited state (S2) rather than the S1 state.

Aqueous strategy for controllable in-situ growth of high-quality perovskite nanocrystals@polymer films toward white light-emitting diodes

Perovskite nanocrystals (PNCs)@polymer films are one of the exciting candidates for fabricating high-definition display devices, owing to their universal merits such as high efficiency, superior color purity, and tunable emissions. However, the existed techniques are always based on organic solvents, of which the inevitable toxicity greatly limits their scalable applications. Herein, we report a facile strategy based on a distinctively different aqueous route for in-situ growth of MAPbBr3 (MA = CH3NH3+) PNCs in polyvinyl alcohol (PVA) matrix, enabling the environmentally-friendly and large-scale production of high-photoluminescence (PL) PNCs@polymer films. It is discovered that rapid evaporation of solvents in the precursor film is the key to separated crystallization of polymer and PNCs, thus allowing the controllable fabrication of high-quality PNCs@PVA films with tunable emissions. As a proof of concept, the as-fabricated MAPbBr3 PNCs@PVA film with typical size of 90 mm × 90 mm exhibits high transmissivity and uniformity, with a strong green emission and PL quantum yield (QY) of 95.3%. Accordingly, by using the resultant green and red films, a white light-emitting device (WLED) sized 35 mm × 40 mm is assembled, which delivers a wide color gamut (121% of NTSC standard), underscoring their very promising applications in modern display devices.

Mixed Ligand Passivation as the Origin of Near-Unity Emission Quantum Yields in CsPbBr3 Nanocrystals

Key features of syntheses, involving the quaternary ammonium passivation of CsPbBr3 nanocrystals (NCs), include stable, reproducible, and large (often near-unity) emission quantum yields (QYs). The archetypical example involves didodecyl dimethyl ammonium (DDDMA+)-passivated CsPbBr3 NCs where robust QYs stem from interactions between DDDMA+ and NC surfaces. Despite widespread adoption of this synthesis, specific ligand-NC surface interactions responsible for large DDDMA+-passivated NC QYs have not been fully established. Multidimensional nuclear magnetic resonance experiments now reveal a new DDDMA+-NC surface interaction, beyond established "tightly bound" DDDMA+ interactions, which strongly affects observed emission QYs. Depending upon the existence of this new DDDMA+ coordination, NC QYs vary broadly between 60 and 85%. More importantly, these measurements reveal surface passivation through unexpected didodecyl ammonium (DDA+) that works in concert with DDDMA+ to produce near-unity (i.e., >90%) QYs.

Anomalous photoluminescence enhancement and resonance charge transfer in type-II 2D lateral heterostructures

Type-II band alignment can realize the efficient charge transfer and separation at the semiconductor heterointerface, which results in photoluminescence (PL) quenching. Recently, several researches demonstrated great enhancement of localized PL at the interface of type-II two-dimensional (2D) heterostructure. However, the dominant physical mechanism of this enhanced PL emission has not been well understood. In this work, we symmetrically study the exciton dynamics of type-II lateral heterostructures of monolayer MoS2 and WS2 at room temperatures. The strong PL enhancement along the one-dimensional (1D) heterointerface is associated with the trion emission of the WS2 shell, while a dramatic PL quenching of neutral exciton is observed on the MoS2 core. The enhanced quantum yield of WS2 trion emission can be explained by charge-transfer-enhanced photoexcited carrier dynamics, which is facilitated by resonance hole transfer from MoS2 side to WS2 side. This work sheds light on the 1D exciton photophysics in lateral heterostructures, which has the potential to lead to new concepts and applications of optoelectronic device.

X-ray Cherenkov-luminescence tomography reconstruction with a three-component deep learning algorithm: Swin transformer, convolutional neural network, and locality module.

X-ray Cherenkov-luminescence tomography (XCLT) produces fast emission data from megavoltage (MV) x-ray scanning, in which the excitation location of molecules within tissue is reconstructed. However standard filtered backprojection (FBP) algorithms for XCLT sinogram reconstruction can suffer from insufficient data due to dose limitations, so there are limits in the reconstruction quality with some artifacts. We report a deep learning algorithm for XCLT with high image quality and improved quantitative accuracy. To directly reconstruct the distribution of emission quantum yield for x-ray Cherenkov-luminescence tomography, we proposed a three-component deep learning algorithm that includes a Swin transformer, convolution neural network, and locality module model. A data-to-image model x-ray Cherenkov-luminescence tomography is developed based on a Swin transformer, which is used to extract pixel-level prior information from the sinogram domain. Meanwhile, a convolutional neural network structure is deployed to transform the extracted pixel information from the sinogram domain to the image domain. Finally, a locality module is designed between the encoder and decoder connection structures for delivering features. Its performance was validated with simulation, physical phantom, and in vivo experiments. This approach can better deal with the limits to data than conventional FBP methods. The method was validated with numerical and physical phantom experiments, with results showing that it improved the reconstruction performance mean square error ( ), peak signal-to-noise ratio ( ), and Pearson correlation ( ) compared with the FBP algorithm. The Swin-CNN also achieved a 32.1% improvement in PSNR over the deep learning method AUTOMAP. This study shows that the three-component deep learning algorithm provides an effective reconstruction method for x-ray Cherenkov-luminescence tomography.

Synthesis and photoluminescence properties of garnet red emitting CaY2Al4SiO12:Eu3+ phosphors

Eu3+ doped CaY2Al4SiO12 garnet phosphors were synthesized by using the sol-gel method. The crystal structure of the synthesized phosphors was characterized by X-ray diffraction and Rietveld refinements. The results of X-ray diffraction and Rietveld refinements of the powders sintered at 1400 °C showed the formation of a single phase and the effective concentration of Eu3+ ions in this garnet host lattice.The composition of the substitutional solid solutions of CaY2-xEuxAl4SiO12 (x = 0.01, 0.03, 0.06, 0.09, 0.12, and 0.15) exhibit efficient red photoluminescence peaking at 596 nm, which can be assigned to the 5D0 → 7F1 intra-configurational transition of Eu3+ located at the dodecahedral site in the garnet structure. The photoluminescence properties, such as excitation and emission spectra, decay curves, and quantum yield, are presented. The thermal stability of the as-prepared phosphors was determined. Additionally, the optical bandgap for the samples was estimated with UV–visible diffuse reflectance spectra using the Tauc relation. The correlation between the structural features and luminescence properties was determined. These phosphors with high thermal stability and high color purity can be potentially used in white-light-emitting diodes.

All-Inorganic Zero-Dimensional Sb3+-Doped Rb2ScCl5(H2O) Perovskite Single Crystals: Efficient Self-Trapped Exciton Emission and X-ray Detection

Zero-dimensional (0D) halide perovskites have attracted extensive attention for their potential applications in solid-state lighting and X-ray detection due to their fascinating optoelectronic properties and convenient solution processability. Herein, we report the synthesis and photophysical properties of high-quality Sb3+-doped 0D Rb2ScCl5(H2O) perovskite single crystals. The pristine crystals exhibit weak yellow self-trapped exciton (STE) emission peaking at 632 nm. The emission quantum yield can be dramatically enhanced from less than 1% to about 53% via Sb3+ doping. Spectroscopic characterizations indicate that the photoluminescence enhancement is a result of the efficient energy transfer from Sb3+ to the emissive STEs. Additionally, 0.2%Sb3+:Rb2ScCl5(H2O) single crystals exhibit potential application in direct X-ray detection with a high sensitivity of 58.5 μC Gy-1 cm-2.

Protonated organic cations enhance the luminescence performance and thermal stability of fluoride red phosphor K2TiF6:Mn4+

The application of red luminescent phosphors composed of Mn4+-activated fluoride in WLEDs has aroused great interest. However, most of the fluoride phosphors doped with Mn4+ have poor luminescent thermostability. In order to improve their luminescent thermostability, a new type of organic-inorganic hybrid red luminescent phosphor K2TiF6:PIPH22+,Mn4+ (PIPH22+ = protonated piperazine) was synthesized by a simple cation exchange method in this work. Protonated piperazine was incorporated into K2TiF6 lattice, and the strong hydrogen bond between H- and F- enabled the organic group to exist stably in the inorganic lattice. Compared with K2TiF6:Mn4+, the addition of PIPH22+ increases distance between adjacent [TiF6]2- and inhibits the energy migration of Mn4+ ions between [MnF6]2- to reduce nonradiative transitions. Therefore, the hybrid sample K2TiF6:PIPH22+,Mn4+ has higher emission intensity and quantum yield. Under the excitation of 467 nm blue light, K2TiF6:PIPH22+, Mn4+ exhibits sharp red emission near 631 nm, and the luminescence intensity is 2.14 times that of K2TiF6:Mn4+. K2TiF6:PIPH22+,Mn4+ has significant negative thermal quenching and higher luminescence thermostability, which can be attributed to electron-phonon interaction mechanism at high temperature. The prototype WLED prepared with YAG:Ce3+, K2TiF6:PIPH22+,Mn4+ and InGaN blue LED chip can emit warm white light (CCT = 2795 K, CRI = 91.1) under 20 mA current, and the luminescence efficiency was 105.8 Lm/W. The prototype WLED was tested under 20–120 mA current, and the results showed that the changes of CCT and CRI were stable. These results indicate the potential of K2TiF6:PIPH22+,Mn4+ in WLED applications.

Chitosan Composites Containing Boron-Dipyrromethene Derivatives for Biomedical Applications.

The work is devoted to preparing and characterizing the properties of photosensitive composites, based on chitosan proposed for photodynamic therapy. Chitosan films with a 5% addition of two BODIPY dyes were prepared by solution casting. These dyes are dipyrromethene boron derivatives with N-alkyl phthalimide substituent, differing in the presence of iodine atoms in positions 2 and 6 of the BODIPY core. The spectral properties of the obtained materials have been studied by infrared and UV-vis absorption spectroscopy and fluorescence, both in solutions and in a solid state. Surface properties were investigated using the contact angle measurement. The morphology of the sample has been characterized by Scanning Electron and Atomic Force Microscopy. Particular attention was paid to studying the protein absorption and kinetics of the dye release from the chitosan. Adding BODIPY to the chitosan matrix leads to a slight increase in hydrophilicity, higher structure heterogeneity, and roughness, than pure chitosan. The presence of iodine atoms in the BODIPY structure caused the bathochromic effect, but the emission quantum yield decreased in the composites. It has been found that BODIPY-doped chitosan interacts better with human serum albumin and acidic α-glycoprotein than unmodified chitosan. The release rate of dyes from films immersed in methanol depends on the iodine present in the structure.

Inside Cover Picture

This work reports an anthrazoline‐based photocatalyst, which features strong visible light absorption, high emission quantum yield and a long excited‐state lifetime. With the irradiation of visible light, our photocatalyst combination with Ni(II) complex can efficiently promote C—O bond formations, including esterification and etherification with a wide range of scope. The newly developed dual photocatalytic system with this conception is just like the Chinese philosophical concept “Yin and yang”. More details are discussed in the article by Zhu et al. on page 411—416.image

Molecular design and properties of near-infrared emitting Cr(III) complexes

<p indent="0mm">The development of highly-emissive nonprecious metal complexes is an effective strategy toward low-cost photochemistry and efficient utilization of natural resources. Among them, near-infrared emitting Cr(III) complexes possess the potential as an excellent photofunctional material with high emission quantum yield and long lifetime. In recent years, significant development has been made in the development of photofunctional Cr(III) complexes by the use of tridentate ligands with a large bite angle. In this manner, highly-efficient spin-flip near-infrared emission and circularly polarized luminescence of chiral Cr(III) complexes have been achieved. The molecular design and near-infrared emissions of these Cr(III) complexes are discussed in this review, together with their current research state and remaining issues. Finally, potential strategies to improve the luminescent properties of achiral and chiral Cr(III) complexes are proposed.

Circularly Polarized Luminescent Bis(Boron Difluoride) Complexes with Chiral Schiff‐base Ligands

AbstractThe syntheses, structures, and circularly polarized luminescence (CPL) properties of bis(boron difluoride) complexes with chiral Schiff‐base ligands are described herein. A series of chiral Schiff‐base bis(boron difluoride) complexes based on the naphthalene backbone were prepared by reacting BF3⋅OEt2with the corresponding precursors, and the molecular structures were identified by NMR spectroscopy and X‐ray diffraction (XRD) analysis. These complexes exhibited efficient photoluminescence in dilute solution with high emission quantum yields (Φ) up to 0.99. The circularly polarized luminescence properties of the molecules were also investigated. Compared to solution, in the KBr dispersed pellet state the absolute value of the luminescence dissymmetry factor (glum) was significantly increased up to 1.2×10−2. The photophysical properties were further investigated by means of DFT calculations.

Symmetry-breaking host–guest assembly in a hydrogen-bonded supramolecular system

Bio-inspired self-assembly is invaluable to create well-defined giant structures from small molecular units. Owing to a large entropy loss in the self-assembly process, highly symmetric structures are typically obtained as thermodynamic products while formation of low symmetric assemblies is still challenging. In this study, we report the symmetry-breaking self-assembly of a defined C1-symmetric supramolecular structure from an Oh-symmetric hydrogen-bonded resorcin[4]arene capsule and C2-symmetric cationic bis-cyclometalated Ir complexes, carrying sterically demanding tertiary butyl (tBu) groups, on the basis of synergistic effects of weak binding forces. The flexible capsule framework shows a large structural change upon guest binding to form a distorted resorcin[4]arene hexameric capsule, providing an asymmetric cavity. Location of the chiral guest inside the anisotropic environment leads to modulation of its Electric Dipole (ED) and Magnetic Dipole (MD) transition moments in the excited state, causing an increased emission quantum yield, longer emission lifetime, and enhancement of the dissymmetry factor (glum) in the circularly polarized luminescence.

Elastic and bright assembly-induced luminescent crystals of platinum(II) complexes with near-unity emission quantum yield.

Molecular crystals of Pt(II) complexes with metallophilic interactions can provide bright assembly-induced luminescence with colour tunability. However, the brittleness of many of these crystals makes their application in flexible optical materials difficult. Herein, we have achieved the elastic deformation of crystals of polyhalogenated Pt(II) complexes exhibiting bright assembly-induced luminescence. A crystal of [Pt(bpic)(dFppy)] (Hbpic = 5-bromopicolinic acid, HdFppy = 2-(2,4-difluorophenyl)pyridine) and a co-crystal of [Pt(bpic)(dFppy)] and [Pt(bpic)(ppy)] (Hppy = 2-phenylpyridine) were found to exhibit significant elastic deformation due to their highly anisotropic interaction topologies. While the crystal of [Pt(bpic)(dFppy)] exhibited monomer-based ligand-centred 3ππ* emission with an emission quantum yield of 0.40, the co-crystal exhibited bright, triplet metal-metal-to-ligand charge transfer (3MMLCT) emission owing to Pt⋯Pt interactions, thereby achieving a significantly higher emission quantum yield of 0.94.

Effect of bromine substitution on blue phosphorescent trans-(N-heterocyclic carbene)Pt(II) acetylide complexes.

N-heterocyclic carbene complexes of the type trans-(NHC)2PtII(CC-Ar)2 (where Ar = phenyl or substituted phenyl) are of interest as violet and blue phosphors. These complexes emit efficient phosphorescence in solution and in the solid state, and they have been applied as phosphors in organic light emitting diodes. This study explores the effect of bromine substitution on the trans-(NHC)2PtII(CC-Ar)2 chromophore through photophysical studies of a pair of complexes in which the phenyl groups feature either 3,5-dibromo- or 4-monobromo-substituents (IPt-DB and IPt-MB, respectively). The Br atoms were introduced as heavy atom(s) with the aim to enhance spin-orbit coupling and increase the radiative and non-radiative decay rates of the phosphorescent triplet state. Both IPt-MB and IPt-DB exhibit sky-blue phosphorescence in solution and in PMMA matrix. Interestingly, the emission quantum yield and lifetime of IPt-MB are substantially lower compared to IPt-DB in solution. This effect is attributed to a substantially larger non-radiative decay rate in the mono-bromo complex. Analysis of the photophysical data, combined with DFT and TD-DFT calculations, suggest that the difference in photophysical properties of the two complexes is related to the position of the Br-substituents on the phenyl acetylide rings. In short, in IPt-MB, the Br-substituents are located para-to the Pt-CC-unit, and this gives rise to stronger electron-vibrational coupling in the excited state, enhancing the rate of non-radiative decay.

Turn-off luminescence sensing, white light emission and magnetic studies of two-dimensional lanthanide MOFs.

The lanthanide metal organic framework compounds [Ln(BPTA)1.5(Bpy)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1a-5a) and [Ln(BPTA)1.5(Phen)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1b-5b) were prepared by employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as the primary ligand and 2,2'-bipyridine (1a-5a) and 1,10-phenanthroline (1b-5b) as the secondary ligands. Single-crystal structural studies on [Gd(BPTA)1.5(Bpy)]·0.5DMF (3a) and [Dy(BPTA)1.5(Phen)]·0.5DMF (5b) indicated that the compounds have a two-dimensional structure. The Y compound exhibits blue emission, and the other compounds exhibit emission in the expected regions (λex = 350 nm). White light emission was achieved by careful mixing of the red (Eu3+) and green (Tb3+) components in the blue emitting Y compound. Thus, Y0.96Tb0.02Eu0.02 (bpy) and Y0.939Tb0.06Eu0.001 (phen) were found to show white emission when excited using a wavelength of 350 nm. The introduction of N-N-containing ancillary ligands (i.e., bpy and phen) increased the overall quantum yield (QY) of white light emission to 31% and 43%, respectively. The high QY observed for the Tb and Eu compounds was found to be sensitive and selective for the fluorometric detection of azinphos-methyl pesticide and trinitrophenol (TNP) in an aqueous medium at the ppb level. The same behaviour was observed when utilising the compounds as onsite paper strip sensors. Their magnetic properties were also studied, revealing for the Tb and Dy derivatives slow relaxation of the magnetisation at low temperature. The present study highlights the usefulness of rigid π-conjugated molecules such as 2,2'-bipyridine and 1,10-phenanthroline in enhancing the many utilities of rare-earth-containing MOFs towards white light emission, the sensing of harmful and dangerous substances and magnetic properties.

Modulation of ground and excited state properties of ruthenium complexes through sequential incorporation of metal into a polypyridyl-imidazole bridging ligand.

A polypyridyl-imidazole-based bridging ligand, 2-(4-(4,5-di(pyridine-2-yl)-1H-imidazole-2-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (phen-H2PhImz-bpy), possessing three bidentate coordinating sites, has been designed in this work. The bridging ligand is employed to synthesize mono-, bi-, and trimetallic Ru(II) complexes in combination with terminal bipyridine units for the systematic modulation of photophysical and redox properties upon sequential incorporation of the metal unit into the bridge. All the compounds are characterized via NMR spectroscopy and electrospray ionization mass spectrometry. Absorption and both steady-state and time-resolved emission spectroscopic investigations of the ligand as well as Ru(II) complexes are thoroughly conducted in different solvents. The redox behaviors of the complexes are examined through cyclic voltammetry (CV) in acetonitrile. The focus of the investigation is centered on the systematic modulation of MLCT absorption and emission as well as the redox behavior of the complex entity upon the gradual incorporation of the Ru2+ unit into the complex backbone. The emission energy, quantum yield and lifetime are found to decrease systematically with an increase in the Ru2+ unit in the complex backbone and a linear relationship is observed in each case. A good correlation is also observed between the emission energies of complexes with their respective ΔE1/2 values (the difference between the first oxidation and first reduction potential).

BINOL-like atropisomeric chiral nanographene.

Interest in making chiral polycyclic aromatic hydrocarbons (PAHs) or nanographenes (NGs) has greatly increased recently. To date, a majority of chiral nanocarbons have been designed based on helical chirality. Here, we describe a novel atropisomeric chiral oxa-NG 1 by the selective dimerization of naphthalene-containing, hexa-peri-hexabenzocoronene (HBC)-based PAH 6. The photophysical properties of the oxa-NG 1 and monomer 6 were investigated, including UV-vis absorption (λ max = 358 nm for 1 and 6), fluorescence emission (λ em = 475 nm for 1 and 6), fluorescence decay (15 vs. 16 ns), and fluorescence quantum yield, and it was found that the photophysical properties of the monomer are nearly maintained in the NG dimer due to its perpendicular conformation. Single-crystal X-ray diffraction analysis shows that both enantiomers cocrystallize in a single crystal, and the racemic mixture can be resolved by chiral high-performance liquid chromatography (HPLC). The circular dichroism (CD) spectra and circularly polarized luminescence (CPL) of the enantiomers of 1-S and 1-R were studied and the CD and CPL spectra exhibited opposite Cotton effects and fluorescence signals. Density functional theory (DFT) calculations and HPLC-based thermal isomerization results showed that the racemic barrier is as high as 35 kcal mol-1, suggesting a rigid chiral nanographene structure. Meanwhile, in vitro studies indicated that oxa-NG 1 is an efficient photosensitizer for white-light-induced singlet oxygen generation.

Bright near-infrared circularly polarized electrochemiluminescence from Au9Ag4 nanoclusters.

Metal nanoclusters are excellent electrochemiluminescent luminophores owing to their rich electrochemical and optical properties. However, the optical activity of their electrochemiluminescence (ECL) is unknown. Herein, we achieved, for the first time, the integration of optical activity and ECL, i.e., circularly polarized electrochemiluminescence (CPECL), in a pair of chiral Au9Ag4 metal nanocluster enantiomers. Chiral ligand induction and alloying were employed to endow the racemic nanoclusters with chirality and photoelectrochemical reactivity. S-Au9Ag4 and R-Au9Ag4 exhibited chirality and bright-red emission (quantum yield = 4.2%) in the ground and excited states. The enantiomers showed mirror-imaged CPECL signals at 805 nm owing to their highly intense and stable ECL emission in the presence of tripropylamine as a co-reactant. The ECL dissymmetry factor of the enantiomers at 805 nm was calculated to be ±3 × 10-3, which is comparable with that obtained from their photoluminescence. The obtained nanocluster CPECL platform shows the discrimination of chiral 2-chloropropionic acid. The integration of optical activity and ECL in metal nanoclusters provides the opportunity to achieve enantiomer discrimination and local chirality detection with high sensitivity and contrast.