High Luminescence Quantum Yield Research Articles

A strategy to increase phosphor brightness: Application with Ce3+-doped Gd3Sc2Al3O12

Y3Al5O12 (YAG) doped with Ce3+ ions is widely used as a phosphor for the generation of white light in LEDs. However, the material presents intrinsic drawbacks: (1) a yellow emission band lacking a red component, leading to a “cold” white light and (2) limited cerium incorporation (~ 3mol%), resulting in poor absorption and thus limiting the external quantum efficiency (EQE) of the LED device. In order to increase phosphor absorption and thus phosphor brightness, we propose here an original strategy based on the increase of Ce content in a phosphor compound, while preserving a high internal luminescence quantum yield. For this purpose, we introduce Ce3+-doped Gd3Sc2Al3O12 (GSAG: Ce). Gd3(1-x)Ce3xSc2Al3O12 polycrystalline samples were prepared through a solid-state microwave-assisted reaction, with x varying from 0 to 0.5; Ce3+ ions can be incorporated into the GSAG matrix with a concentration up to approximately x=0.18 (i.e. 18mol%) without the formation of a parasitic phase. The maximum emission wavelength is located at 573nm for a doping concentration of x=0.1, giving an orange feature to the emission. The internal luminescence quantum yield (Φ) is 52% for Ce concentration up to x=0.03. The EQE, which is proportional to the product of Φ by the Ce concentration when considering a thin transparent phosphor layer is predicted to be about 30% stronger when using GSAG doped with 10mol% Ce (x=0.1), with respect to YAG doped with 2mol% Ce (x=0.02).

Furan-based diketopyrrolopyrrole chromophores: Tuning the spectroscopic, electrochemical and aggregation-induced fluorescent properties with various intramolecular donor-acceptor spacers

A family of furan-based diketopyrrolopyrrole chromophores, which comprise different donor or acceptor spacers, was synthesized by classic Suzuki-Miyaura reactions between dibrominated diketopyrrolopyrrole intermediate and five substituted aromatic boronic acids. They have the same π-extended unit and different pyridyl, thienyl and triarylamino tails with various intramolecular donor-acceptor spacers. Furthermore, absorption and emission spectral studies reveal that all dyes show extraordinarily large molar absorption coefficients (εmax = 22 400–120 000 L mol−1 cm−1) and high luminescence quantum yields (Φs = 27–88%). Moreover, the TGA studies indicate that the triarylamino-extended compounds have excellent thermal stabilities. A systematical investigation has been carried out, including energy gap correlation among optical, electrochemical and computational data. All the targeted chromophores exhibit potential applications in luminescent materials and optoelectronic devices.

Yb3+-Activated Phosphate Glass

Phosphate glass with different Yb3+ concentrations was synthesized and studied. The composition of the glass made it possible to obtain optically uniform glass in small-volume crucibles. The basic spectral characteristics of the obtained glasses were determined and it was shown that the proposed matrix gives a high quantum yield of luminescence in a wide range of Yb3+ concentrations. The influence of the content of OH groups on the decay time of the Yb3+ luminescence was investigated. In view of its good cooking and casting properties this glass holds promise for use in the active media for near-IR solid-state and fiber lasers.

Silver Zeolite Composites‐Based LEDs: A Novel Solid‐State Lighting Approach

Silver clusters incorporated in a zeolite matrix represent a promising alternative for rare earth phosphors, organic dyes, and quantum dots as emitters in organic and hybrid organic/inorganic light‐emitting diodes (OLEDs). Compared to other existing types of emitters, they combine an excellent stability to oxygen and humidity with a high luminescence quantum yield and color tunability. This study reports on the first use of these silver exchanged zeolites embedded in polyvinyl carbazole (PVK), which is expected to act as a conducting matrix, as emitters in a single‐layer OLED. It is demonstrated that the introduction of these Ag zeolites leads to electroluminescence bands that clearly differ from pristine PVK OLEDs as well as from the photoluminescence spectra of the Ag zeolites. The current density and the spectral properties observed in these devices are strongly influenced by the zeolite silver loading, paving the way for a new type of easily tunable hybrid and cost‐effective OLEDs.

A simple 2,6-diphenylpyridine-based fluorescence “turn-on” chemosensor for Ag+ with a high luminescence quantum yield

A sensitive and simple 2,6-diphenylpyridine-based receptor servered as a “turn-on” fluorescent chemosensor was designed and synthesized for selectively sensing Ag+ ions in aqueous media with an anomalously quantum yield. The probe exhibits high selectivity toward Ag+ over other common metal ions, displaying a significant fluorescent turn on nature in the presence of Ag+. The fluorescence response is explained by X-ray diffraction analysis, mass spectrometry, and theoretical calculations. The unprecedentedly high luminescence quantum yield can be attributed to intraligand charge transfer (ILCT) transitions with mixed some Ag(I) 5p orbitals perturbation characters. Finally, the results of cell experiments show that the probe can be used to selectively detect Ag+ in mammalian cells.

Silver(I) Complexes of Diphenylpyridines: Crystal Structures, Luminescence Studies, Theoretical Insights, and Biological Activities.

A series of simple two-coordinated cationic silver(I) complexes, namely, [Ag{4-(4-R1 -phenyl)-2,6-diphenylpyridine}2 ]X (X=ClO4 - , BF4 - , or SO3 CF3 - ), with different electron-donating or -withdrawing groups (e.g., R1 =N(Me)2 , Me, H, Cl, and Br) on the phenyl ring, were successfully prepared. Extensive characterization of these complexes by various NMR spectroscopy techniques and mass spectrometry was further corroborated by single-crystal XRD analyses. Detailed photophysical investigations of [Ag{4-(4-N,N-dimethylaminophenyl)-2,6-diphenylpyridine}2 ]ClO4 (C1) displayed a strong room-temperature fluorescence in solution with an anomalously high luminescence quantum yield of 0.83. The effects of distinct substituent groups (C2-C5), π-conjugated aromatic rings (C6 and C7), and anions (C8 and C9) on the photoluminescence properties were evaluated. Furthermore, DFT and time-dependent DFT calculations were performed to discern the composition of the excited state, as well as to confirm the obtained relative emission energies upon substitution with electronically different ligands. These results indicated that the strong electron-donating substituent of N,N-dimethylamine played an important role in the unprecedented high luminescence quantum yield of C1. In addition, preliminary antimicrobial studies and confocal microscopy fluorescent imaging of HeLa cells labeled with these complexes reveal their potential applications in biological activities.

Colloidal quantum-dots surface and device structure engineering for high-performance light-emitting diodes

Abstract The application of colloidal quantum dots for light-emitting devices has attracted considerable attention in recent years, due to their unique optical properties such as size-dependent emission wavelength, sharp emission peak and high luminescent quantum yield. Tremendous efforts have been made to explore quantum dots for light-emission applications such as light-emitting diodes (LEDs) and light converters. The performance of quantum-dots-based light-emitting diodes (QD-LEDs) has been increasing rapidly in recent decades as the development of quantum-dots synthesis, surface-ligand engineering and device-architecture optimization. Recently, the external quantum efficiencies of red quantum-dots LEDs have exceeded 20.5% with good stability and narrow emission peak. In this review, we summarize the recent advances in QD-LEDs, focusing on quantum-dot surface engineering and device-architecture optimization.

Near-infrared emitting CdTeSe alloyed quantum dots: Raman scattering, photoluminescence and single-emitter optical properties

The synthesis of ternary core/shell zinc-blende CdTeSe/ZnSe quantum dots with optimal synthesis parameters is analyzed.

Manganese-doped near-infrared emitting nanocrystals for in vivo biomedical imaging.

Nanoprobes with multiple imaging modality have attracted a great deal of attention due to the capability of offering complementary information from each individual component. This work presents a hybrid approach to synthesize manganese doped near infrared (NIR) emitting quantum dots. The Mn-doping process was accomplished in aqueous phase followed by a phase transfer to organic phase for ZnS coating. This bimodal nanoprobe displayed high NIR luminescence quantum yield (~14%) and capability of magnetic resonance imaging (MRI) (1.44 mM-1 s-1). The RGD-targeted nanoprobes have been exploited for in vitro cell labelling, in vivo tumor targeting and lymph node mapping. In addition, no adverse toxic effects were observed, demonstrating the high biocompatibility of this nanoprobe.

Terahertz Conductivity within Colloidal CsPbBr3 Perovskite Nanocrystals: Remarkably High Carrier Mobilities and Large Diffusion Lengths

Colloidal CsPbBr3 perovskite nanocrystals (NCs) have emerged as an excellent light emitting material in last one year. Using time domain and time-resolved THz spectroscopy and density functional theory based calculations, we establish 3-fold free carrier recombination mechanism, namely, nonradiative Auger, bimolecular electron-hole recombination, and inefficient trap-assisted recombination in 11 nm sized colloidal CsPbBr3 NCs. Our results confirm a negligible influence of surface defects in trapping charge carriers, which in turn results into desirable intrinsic transport properties, from the perspective of device applications, such as remarkably high carrier mobility (∼4500 cm(2) V(-1) s(-1)), large diffusion length (>9.2 μm), and high luminescence quantum yield (80%). Despite being solution processed and possessing a large surface to volume ratio, this combination of high carrier mobility and diffusion length, along with nearly ideal photoluminescence quantum yield, is unique compared to any other colloidal quantum dot system.

Recent Progress in Quantum Dot Based White Light-Emitting Devices

Colloidal semiconductor quantum dots (QDs) have been widely employed as components of white light-emitting diodes (WLEDs) due to their excellent optical properties (highly saturated emission color, high luminescence quantum yield) as well as thermal and chemical stability. Much effort has been devoted to realize efficient QD-based WLEDs, including the synthesis of superior luminescent nanomaterials with excellent stabilities, and the design of advanced devices structures. In this paper, after introducing photometric parameters of the contemporary QD-based WLEDs, we highlight the recent progress in these devices grouped according to three main mechanisms for white light generation: optical excitation, direct charge carrier injection, and Förster resonance energy transfer. The methods to generate white light, the design of QD emitters and QD-based devices, as well as their fabrication techniques are considered, and the key scientific and technological challenges in the QD-based WLEDs are highlighted. Novel light-emitting materials for WLEDs such as carbon-based nanoparticles are also considered.

Absorption and luminescence spectra of 5-aryl-3-methyl-1,2,4-oxadiazoles and their chelate complexes with Zinc(II) and copper(II)

5-(2-Hydroxyphenyl)-3-methyl-1,2,4-oxadiazole and its O-methyl and O-acyl derivatives, as well as zinc(II) and copper(II) chelates, were synthesized. All these compounds showed luminescence with the emission maxima ranging from λ = 332 to 490 nm, but only 5-(2-methoxyphenyl)- and 5-(2-acetoxyphenyl)-3-methyl-1,2,4-oxadiazoles and zinc(II) complex of 5-(2-hydroxyphenyl)-3-methyl-1,2,4-oxadiazole were characterized by high luminescence quantum yield (φ = 0.308–0.452, 0.089–0.153, and 0.115–0.334, respectively). Stable conformers of 5-(2-hydroxyphenyl)-3-methyl-1,2,4-oxadiazole with different structures of the coordination entity were identified by DFT quantum chemical calculations.

Near‐IR Emitting Iridium(III) Complexes with Heteroaromatic β‐Diketonate Ancillary Ligands for Efficient Solution‐Processed OLEDs: Structure–Property Correlations

AbstractThree NIR‐emitting neutral IrIII complexes [Ir(iqbt)2(dpm)] (1), [Ir(iqbt)2(tta)] (2), and [Ir(iqbt)2(dtdk)] (3) based on the 1‐(benzo[b]thiophen‐2‐yl)‐isoquinolinate (iqtb) were synthesized and characterized (dpm=2,2,6,6‐tetramethyl‐3,5‐heptanedionate; tta=2‐thienoyltrifluoroacetonate; dtdk=1,3‐di(thiophen‐2‐yl)propane‐1,3‐dionate). The compounds emit between λ=680 and 850 nm with high luminescence quantum yields (up to 16 %). By combining electrochemistry, photophysical measurements, and computational modelling, the relationship between the structure, energy levels, and properties were investigated. NIR‐emitting, solution‐processed phosphorescent organic light‐emitting devices (PHOLEDs) were fabricated using the complexes. The devices show remarkable external quantum efficiencies (above 3 % with 1) with negligible efficiency roll‐off values, exceeding the highest reported values for solution‐processible NIR emitters.

Near-IR Emitting Iridium(III) Complexes with Heteroaromatic β-Diketonate Ancillary Ligands for Efficient Solution-Processed OLEDs: Structure-Property Correlations.

Three NIR-emitting neutral Ir(III) complexes [Ir(iqbt)2 (dpm)] (1), [Ir(iqbt)2 (tta)] (2), and [Ir(iqbt)2 (dtdk)] (3) based on the 1-(benzo[b]thiophen-2-yl)-isoquinolinate (iqtb) were synthesized and characterized (dpm=2,2,6,6-tetramethyl-3,5-heptanedionate; tta=2-thienoyltrifluoroacetonate; dtdk=1,3-di(thiophen-2-yl)propane-1,3-dionate). The compounds emit between λ=680 and 850 nm with high luminescence quantum yields (up to 16 %). By combining electrochemistry, photophysical measurements, and computational modelling, the relationship between the structure, energy levels, and properties were investigated. NIR-emitting, solution-processed phosphorescent organic light-emitting devices (PHOLEDs) were fabricated using the complexes. The devices show remarkable external quantum efficiencies (above 3 % with 1) with negligible efficiency roll-off values, exceeding the highest reported values for solution-processible NIR emitters.

Visible light-induced lanthanide polymer nanocomposites based on clays for bioimaging applications

Lanthanide complexes have attracted increased attention in recent years for their unique photophysical properties such as large Stokes shifts, narrow bandwidth, long radiative lifetimes, and high luminescence quantum yield. However, low photochemical stability and poor mechanical properties limit the technological applicability of lanthanide complexes. Two natural clay minerals, fibrillar palygorskite (Pal) and tubular halloysite nanotubes (HNTs), are known for their extreme stabilities and high surface area and show promise as new carriers of luminescent lanthanide complexes for further applications. In this report, clay-based lanthanide polymer nanocomposites clay–polyethyleneimine (PEI)–MPTP–Eu(DBM)3 have been fabricated by attaching a lanthanide complex onto the surface of PEI-modified Pal or HNTs. The formed nanocomposites display visible light-excitable features with a wide excitation wavelength range from UV to visible light, a long luminescence lifetime, and improved photoluminescence stability. Their excellent luminescence, high suspension stability, and low cytotoxicity in cell studies result in the potential applications of the as-prepared nanocomposites for cell imaging in biological systems.

Optics of colloidal quantum-confined CdSe nanoscrolls

Nanostructures in the form of colloidal CdSe nanoplatelets rolled into scrolls are investigated. The morphology of these scrolls is analysed and their basic geometric parameters are determined (diameter , longitudinal size ) by TEM microscopy. Absorption and photoluminescence spectra of these objects are recorded, and the luminescence decay kinetics is studied. It is shown that the optical properties of CdSe nanoscrolls differ significantly from the properties of CdSe quantum dots and that these nanoscrolls are attractive for nanophotonic devices due to large oscillator strengths of the transition, small widths of excitonic peaks and short luminescence decay times. Nanoscrolls can be used to design hybrid organic – inorganic pure-color LEDs with a high luminescence quantum yield and low operating voltages.

Surface Complexation-Based Biocompatible Magnetofluorescent Nanoprobe for Targeted Cellular Imaging

We report the synthesis of a magnetofluorescent biocompatible nanoprobe-following room temperature complexation reaction between Fe3O4-ZnS nanocomposite and 8-hydroxyquinoline (HQ). The composite nanoprobe exhibited high luminescence quantum yield, low rate of photobleaching, reasonable excited-state lifetime, luminescence stability especially in human blood serum, superparamagnetism and no apparent cytotoxicity. Moreover, the nanoprobe could be used for spatio-controlled cell labeling in the presence of an external magnetic field. The ease of synthesis and cell labeling in vitro make it a suitable candidate for targeted bioimaging applications.

Three-photon-excited luminescence from unsymmetrical cyanostilbene aggregates: morphology tuning and targeted bioimaging.

We report an experimental observation of aggregation-induced enhanced luminescence upon three-photon excitation in aggregates formed from a class of unsymmetrical cyanostilbene derivatives. Changing side chains (-CH3, -C6H13, -C7H15O3, and folic acid) attached to the cyanostilbene core leads to instantaneous formation of aggregates with sizes ranging from micrometer to nanometer scale in aqueous conditions. The crystal structure of a derivative with a methyl side chain reveals the planarization in the unsymmetrical cyanostilbene core, causing luminescence from corresponding aggregates upon three-photon excitation. Furthermore, folic acid attached cyanostilbene forms well-dispersed spherical nanoaggregates that show a high three-photon cross-section of 6.0 × 10(-80) cm(6) s(2) photon(-2) and high luminescence quantum yield in water. In order to demonstrate the targeted bioimaging capability of the nanoaggregates, three cell lines (HEK293 healthy cell line, MCF7 cancerous cell line, and HeLa cancerous cell line) were employed for the investigations on the basis of their different folate receptor expression level. Two kinds of nanoaggregates with and without the folic acid targeting ligand were chosen for three-photon bioimaging studies. The cell viability of three types of cells incubated with high concentration of nanoaggregates still remained above 70% after 24 h. It was observed that the nanoaggregates without the folic acid unit could not undergo the endocytosis by both healthy and cancerous cell lines. No obvious endocytosis of folic acid attached nanoaggregates was observed from the HEK293 and MCF7 cell lines having a low expression of the folate receptor. Interestingly, a significant amount of endocytosis and internalization of folic acid attached nanoaggregates was observed from HeLa cells with a high expression of the folate receptor under three-photon excitation, indicating targeted bioimaging of folic acid attached nanoaggregates to the cancer cell line. This study presents a paradigm of using organic nanoaggregates for targeted three-photon bioimaging.

A family of extended heterocyclic oligomers with thienylene/thiazolylene vinylene cores and triphenylamino/carbazolyl terminals

A series of semiconducting thienylene/thiazolylene vinylene oligomers with triphenylamino/carbazolyl terminal groups have been designed and prepared successfully. Synthetic, structural, thermal, spectral and electrochemical comparisons have been carried out for related compounds. The photophysical results demonstrate that all the vinylene oligomers and their precursors show high luminescence quantum yields. In addition, X-ray single-crystal structure analysis of a typical thiophene based double-bond compound 7 indicates a molecular length of 2.72 nm with the E-configuration.

Graphene oxide-phosphor hybrid nanoscrolls with high luminescent quantum yield: synthesis, structural, and X-ray absorption studies.

Highly luminescent graphene oxide (GO)-phosphor hybrid thin films with a maximum quantum yield of 9.6% were synthesized via a simple chemical method. An intense luminescence emission peak at 537 nm and a broad emission peak at 400 nm were observed from the GO-phosphor hybrid films. The maximum quantum yield of the emissions from the hybrid films was found to be 9.6%, which is 48 times higher than that of pristine GO films. The GO-phosphor hybrids were prepared via spin-coating and subsequent postannealing of the films, resulting in scrolling of the GO sheets. The resulting GO nanoscrolls exhibited a length of ∼2 μm with nanoscale interior cavities. Transmission electron microscopy and selected-area electron diffraction analyses revealed that the lattice structure of the tubular scrolls is similar to that of carbon nanotubes. While pristine GO films are p-type, in the GO-phosphor hybrids, the Fermi level shifted upward and fell between the HOMO-LUMO gap due to phosphor attachment via C-N bonding. The highly luminescent GO-phosphor hybrids will find important applications in graphene-based optoelectronic devices.