Large Luminescence Enhancement Research Articles

Chemical unit co-substitution for a new far-red-emitting phosphor Ca3-6y(NaLu)3yLiSbO6:Mn4+ to achieve high quantum efficiency and superb thermal stability

The discovery of Mn4+-doped red phosphors with a high quantum efficiency (QE) and good thermal stability is of great interest for plant cultivation lighting. Here, for the first time, a new highly efficient and thermally stable far-red-emitting phosphor Ca3-6y(NaLu)3yLiSbO6:Mn4+ (CNULS:Mn4+) is reported. When a far-red-emitting phosphor Ca3LiSbO6:Mn4+ (CLS:Mn4+) was prepared via the solid-state reaction method, its maximum internal and external QEs are only 39.5% and 23.1%, respectively. Through the chemical unit co-substitution of [Na+−Lu3+] for [Ca2+−Ca2+] in CLS:Mn4+, its luminescence properties can be improved tremendously and the internal and external QEs for the substitution amount of y = 3% are as high as 80.1% and 47.4%, respectively. The large luminescence enhancement is attributed to the increase of structural rigidity induced by lattice contraction. The CNULS:Mn4+ phosphor exhibits excellent thermal stability with the emission intensity at 423 K remaining 87% of the value at 298 K. The LED device fabricated with the CNULS:Mn4+ (y = 3%) phosphor can produce bright and stable far-red emission, which matches well with the absorption spectrum of phytochrome PFR. These results suggest that the CNULS:Mn4+ phosphor could be a promising far-red-emitting converter for plant growth as well as solid-state lighting.

Origin of Intense Luminescence from Supramolecular 2D Molecular Crystals.

Luminescence enhancement in 2D molecular crystals (2D crystals) is promising for a variety of optical applications, yet the availability is limited because of unclear mechanism and inefficient design strategy of luminescence control. Herein, the room temperature phosphorescence from micron long molecular thin free-standing 2D crystals of a mono-cyclometalated Ir(III) complex designed at the water surface is reported. A large luminescence enhancement is observed from the 2D crystals at 300 K, which is comparable with the rigidified solution at 77 K suggesting room temperature phosphorescence origin of the luminescence. In situ synchrotron grazing incidence X-ray diffraction measurements determine the constituent centered rectangular unit cells with precise molecular conformation that promotes the formation of 2D crystals. The molecular crystal design leads to a reduced singlet-triplet energy gap (ΔEST ) and mixing of singlet-triplet states by spin-orbit coupling (SOC) for efficient intersystem crossing, which explains the phosphorescence origin at room temperature and luminescence enhancement. The supramolecular assembly process provides an elegant design strategy to realize room temperature phosphorescence from 2D crystals by rigid intermolecular interactions.

Aggregation induction of tetraphenylethylene AIEgen and its supramolecular aggregates toward light-emitting diodes

Aggregation behavior of luminophores is a subject of great interest over more than half a century. Aggregation generally causes quenching of luminescence of luminophores, which is detrimental for the solid state electroluminescence device fabrication. In oppose to the aggregation caused quenching, aggregation-induced emission phenomenon leads to highly luminescence state of luminophores upon aggregate formation. However, aggregation-induced emission behavior of the luminophores is commonly observed in irregular bulk solids, by adding antisolvents into a solution or in the biological cells, where the state of aggregation remains uncontrolled. Here we report on the synthesis of a new tailor made luminogen, 4′,4‴-(2,2-bis(4-methoxyphenyl)ethene-1,1-diyl)bis([1,1′-biphenyl]-4-carbaldehyde) (TPE 2) using Suzuki coupling reaction with high yield. We form the well-controlled supramolecular aggregates of TPE 2 ​at the air−water interface of a Langmuir trough. As a consequence, the mono- and multilayer Langmuir−Blodgett films of TPE 2 show a large enhancement of luminescence in comparison to the solution phase owing to the aggregation-induced emission phenomenon. We reveal inherent interaction of TPE 2 complexes within the supramolecular aggregates using density functional theory. This unique feature of luminescence enhancement is utilized for the fabrication of light-emitting diodes with low threshold voltage using TPE 2 as active layer. This study opens up the advantage of ordered supramolecular assembly to achieve optimal luminescence performances.

Supramolecular Aggregates of Tetraphenylethene-Cored AIEgen toward Mechanoluminescent and Electroluminescent Devices.

Luminescent materials possessing both the mechanoluminescence (MCL) and electroluminescence (EL) properties are the quest for sensing and optoelectronic applications. We report on the synthesis of a new tailor-made luminogen, 1,2-bis(4-(1-([1,1'-biphenyl]-4-yl)-2,2-diphenylvinyl)phenyl)-1,2-diphenylethene (TPE 5), using Suzuki coupling reaction with high yield. An aggregation-induced emission (AIE) active complex TPE 5 forms supramolecular spherical aggregates at the air-water interface of a Langmuir trough. As a consequence, a large enhancement of luminescence is obtained from the mono- and multilayer Langmuir-Blodgett films of TPE 5 owing to the AIE effect. The luminogen TPE 5 exhibits a reversible MCL response, displaying photoluminescence switching due to change in the crystalline states under external stimuli. The unique feature of luminescence enhancement upon aggregate formation is utilized for the fabrication of light-emitting diodes with low threshold voltage using supramolecular aggregates as the active layer. This work demonstrates an efficient strategy for obtaining controlled supramolecular aggregates of AIEgen with a potential in the dual applications of MCL and EL.

Tunable, broadband and high-efficiency Si/Ge hot luminescence with plasmonic nanocavity array

In addition to the massive application in the electronics industry for decades, silicon has been considered as one of the best candidates for the photonics industry. However, a high-efficiency, broadband light source is still a challenge. In this paper, we theoretically propose a Si/Ge based platform consisting of plasmonic nanocavity array to realize the tunable, broadband, and high-efficiency Si/Ge hot luminescence from infrared to visible region with large luminescence enhancement (about 103). It is demonstrated that the large luminescence enhancement is due to the resonance between the intrinsic hot luminescence and the plasmonic nanocavity modes with ultra-small effective mode volumes. And, the size and Ge composition of Si1−xGex nanowire can be tuned to realize the tunable and broadband luminescence. This study gives rise to many applications in silicon photonics, like ultrafast optical communications, sensors, and on-chip spectral measurements.

Self-Assembly of an Europium-Containing Polyoxometalate and the Arginine/Lysine-Rich Peptides from Human Papillomavirus Capsid Protein L1 in Forming Luminescence-Enhanced Hybrid Nanoparticles

Through a self-assembly of arginine/lysine-rich peptide from human papillomavirus (HPV) capsid protein and an Eu-containing polyoxometalate (POM), Na9[EuW10O36]·32H2O (EuW10), the formation of well-defined hybrid nanospheres in aqueous solution is presented, showing large luminescence enhancement of POM and use as a potential “turn-on” fluorescence probe in biology. The binding mechanisms between them have been explored at the molecular level by using transmission electron microscopy (TEM), scanning electron microscopy (SEM), fluorescence spectra, isothermal titration calorimetry (ITC), ζ-potential, and nuclear magnetic resonance (1H NMR) titration spectra. ITC study confirmed the assembly was completely enthalpy driven, and ζ-potential proved that the driving force was governed mainly by the electrostatic interaction. 1H NMR spectroscopy indicated changes in hydrogen bond of EuW10 and the peptide segment, and the binding model was clarified. Our design constructed the self-assembly fabrication of well-de...

Enhanced luminescence of Tb3+/Eu3+ doped tellurium oxide glass containing silver nanostructures

We report on energy transfer studies in terbium (Tb3+)—europium (Eu3+) doped TeO2–ZnO–Na2O–PbO glass containing silver nanostructures. The samples excitation was made using ultraviolet radiation at 355 nm. Luminescence spectra were recorded from ≈480 to ≈700 nm. Enhanced Eu3+ luminescence at ≈590 nm (transition D50−F71) and ≈614 nm (transition D50−F72) are observed. The large luminescence enhancement was obtained due to the simultaneous contribution of the Tb3+–Eu3+ energy transfer and the contribution of the intensified local field on the Eu3+ ions located near silver nanostructures.

Enhancement of luminescence efficiency of f–f transitions from Tb 3+ due to energy transfer from Ce 3+ in Al 2O 3 crystalline ceramic powders prepared by low temperature direct combustion synthesis

In this Letter, we report the structural and luminescent properties of Tb:Ce:Al 2O 3 crystalline ceramic powders prepared through combustion synthesis at low temperature (∼280 °C). The presence of Ce 3+ (1.0 mol%) in the sample resulted in an enhancement of Tb 3+ (1.0 mol%) overall emission intensity by a factor of ∼50. The analysis of the luminescence dynamics for the 5D 4 → 7F 6 transition (∼545 nm) of Tb 3+ demonstrated that the mechanism responsible for the large enhancement of luminescence observed is efficient energy transfer from Ce 3+ to Tb 3+.

New luminescent terbium complex for the determination of DNA

New terbium complexes of derivatives of 2-oxo-4-hydroxy-quinoline-3-carboxylic acid are reported, which are highly luminescent, water soluble and do not require luminescence enhancers. The triplet-state energy levels of the ligands, the relative quantum yields (QYs) and the excitation maxima of the respective terbium chelates were determined. The large luminescence enhancement of one of these complexes by nucleic acids was investigated and a mechanism of its interaction with DNA is proposed. The optimal conditions for determination of DNA are equal concentrations of Tb 3+ and ligand R 1 ( C=1×10 −6 M), pH 9.0. Under optimal conditions the luminescence intensity (RI) is proportional to the concentration of fish sperm DNA (fsDNA) or calf thymus DNA (ctDNA), respectively, within the range of 0.05–1.5 μg ml −1. The detection limits were 10 ng ml −1 for fsDNA and 12 ng ml −1 for ctDNA.

Synthesis and structural, electrochemical, and optical properties of Ru(II) complexes with azobis(2,2'-bipyridine)s.

Two new ditopic ligands, 5,5"-azobis(2,2'-bipyridine) (5,5"-azo) and 5,5"-azoxybis(2,2'-bipyridine) (5,5"-azoxy), were prepared by the reduction of nitro precursors. Mononuclear and dinuclear Ru(II) complexes having one of these bridging ligands and 2,2'-bipyridine terminal ligands were also prepared, and their properties were compared with previously reported Ru(II) complexes having 4,4"-azobis(2,2'-bipyridine) (4,4"-azo). The X-ray crystal structure showed that 5,5"-azo adopts the trans conformation and a planar rodlike shape. The X-ray crystal structure of [(bpy)(2)Ru(5,5"-azo)Ru(bpy)(2)](PF(6))(4) (Ru(5,5"-azo)Ru) showed that the bridging ligand is in the trans conformation and nearly planar also in the complex and the metal-to-metal distance is 10.0 A. The azo or azoxy ligand in these complexes exhibits reduction processes at less negative potentials than the terminal bpy's due to the low-lying pi level. The electronic absorption spectra for the complexes having 5,5"-azo or 5,5"-azoxy exhibit an extended low-energy metal-to-ligand charge-transfer absorption. The ligands, 5,5"-azo and 5,5"-azoxy, and the mononuclear complex, [(bpy)(2)Ru(5,5"-azo)](2+), isomerize reversibly upon light irradiation. The low-energy MLCT state sensitizes the isomerization of the azo moiety in this complex. While [(bpy)(2)Ru(4,4"-azo)Ru(bpy)(2)](PF(6))(4) exhibits light switch properties, namely, significant electrochromism and a large luminescence enhancement, upon reduction, Ru(5,5"-azo)Ru does not show these properties. The radical anion formation upon reduction of these complexes has been confirmed by ESR spectroscopy.

Luminescence enhancement of EuS nanoclusters in zeolite

Large luminescence enhancement was observed in EuS clusters formed in ultrastable zeolite-Y by solid-state diffusion in vacuum at 600 °C. The emission of EuS clusters shifts to higher energies relative to that of bulk EuS powder. The blueshift and the emission enhancement are attributed to quantum-size confinement and are discussed based on the magnetic exciton and the magnetic polaron models, respectively.

Studies of calcium influx into squid giant axons with aequorin.

AbstractCalcium‐influx associated with the action potential was studied in squid giant axons using an EDTA‐free preparation of aequorin as a probe. Associated with an individual action potential there was a transient increase in aequorin luminescence and the time course of this increase was examined on a kinetic basis. The luminescent response associated with a train of action potentials was compared with that expected on the basis of superposition of individual responses. The analyses of luminescence curves produced by long trains of action potentials were complicated by failure of superposition. A long pulse of inward current was found to produce a very large enhancement of luminescence.