Aggregation-induced emission

Luminogenic materials with aggregation-induced emission (AIE) attributes have attracted much interest since the debut of the AIE concept in 2001. In this critical review, recent progress in the area of AIE research is summarized. Typical examples of AIE systems are discussed, from which their structure-property relationships are derived. Through mechanistic decipherment of the photophysical processes, structural design strategies for generating new AIE luminogens are developed. Technological, especially optoelectronic and biological, applications of the AIE systems are exemplified to illustrate how the novel AIE effect can be utilized for high-tech innovations (183 references).     

Field emission spectroscopy

The first experimental evidence of the existence of electron states localised on a clean metal surface was available to us since 1967 in the form of the well known Swanson-Crouser hump in the energy distribution of electrons field-emitted from the W(100) plane, although it took some time before its interpretation as such, in 1976, was established beyond any doubt. Subsequently, angle-resolved photoemission proved to be a more competitive method for the investigation of surface states of metals and semiconductors. However, field emission remains a useful tool in surface physics research.

After a brief introduction to field emission spectroscopy, we review recent work which shows the potentiality of this technique in the investigation of the surface properties of semiconductors, ferromagnetic metals, thermal superconductors, and of the electronic structure of supported clusters.     

Photofield emission spectroscopy

A brief review of the investigations of optical excitations in the bulk and on the surfaces of metals by the photofield emission method is presented. The selected results show that the method is very useful for detailed penetration of band structure near the Fermi level. Examples for bulk band structures and surface density of states of tungsten, tantalum and titanium are presented and compared with theoretical results. The residual gas effect on surface states is described and discussed. Taking into consideration the thermocurrent produced by light radiation, a new and more detailed presentation of surface states observed for titanium (0001) face is shown as the density of states. The method of energy distribution of photofield emitted electrons is briefly mentioned. The inverse and two-photon photoemission methods are mentioned.     

Evolution of emission manners of organic light-emitting diodes: From emission of singlet exciton to emission of doublet exciton

The emission manners of organic light-emitting diodes(OLEDs) have experienced almost three-decade evolution.In this review,we briefly summarized the emission manners of OLEDs including:(ⅰ) emission from singlet exciton;(ⅱ) emission from triplet exciton;(ⅲ) emission from singlet exciton converted from triplet exciton.Then we introduced a new type of OLEDs with the emission from doublet exciton,wherein organic neutral radicals are used as emitters.Due to the spin-allowed transition of doublet excitons,using neutral radicals as emitters is believed to be a new way to break the 25%upper limit of internal quantum efficiency of OLEDs.The progress of emissive stable neutral radicals is also shortly reviewed.     

Metal-enhanced fluorescence exciplex emission

In this letter, we report the first observation of metal-enhanced exciplex fluorescence, observed from anthracene in the presence of diethylaniline. Anthracene in the presence of diethylaniline in close proximity to Silver Island Films (SIFs) shows enhanced monomer and exciplex emission as compared to a non-silvered control sample containing no silver nanoparticles. Our findings suggest two complementary methods for the enhancement: (i) surface plasmons can radiate coupled monomer and exciplex fluorescence efficiently, and (ii) enhanced absorption (enhanced electric near-field) further facilitates enhanced emission. Our exciplex studies help us to further understand the complex photophysics of the metal-enhanced fluorescence technology.     

Thermionic emission from fullerenes

We investigate the time dependence of carbon cluster ions, formed via thermionic emission from photoexcited fullerenes (C₆₀ and C₇₀). By pulsing the extraction field, we are able to observe delayed ions formed as late as 100 µs after excitation at 532 nm, 355 nm, or 266 nm. All even-sized clusters in the range 36 n 70 undergo thermionic emission.     

压致变色聚集诱导发光材料

聚集诱导发光化合物分子具有特殊的螺旋桨形扭曲构象结构, 导致其很难在结晶状态下进行紧密堆砌, 使得其结晶结构容易在外力的作用发生改变, 致使其分子能级水平和发光光谱发生变化, 产生压致发光变色现象. 因此, 聚集诱导发光化合物是压致发光变色材料的一个重要来源. 压致变色聚集诱导发光材料是一类重要的压致发光变色材料, 其既具有压致发光变色的性能, 又具有聚集诱导发光的性能. 它是一类智能材料, 在应力传感、商标防伪和发光器件等领域具有重要的潜在应用, 近年来受到人们极大的关注. 本文分类介绍了近年来压致变色聚集诱导发光材料的研究进展.     

Electron spin emission phenomena

A brief review of a method that has been used to observe transient ESR signals from short-lived radicals generated photolytically is presented. At short intervals emission spectra are observed, which in the cases studied (aromatic carbonyls in paraffins) show virtually no multiplet effect. One application of this observation is to the direct determination of electron spinlattice relaxation times in liquids. Some of the theoretical problems connected with the polarisation process are described, with particular reference to the role of radical re-encounters. Some simple analytical expressions for the polarisation are presented.     

Aggregation-induced emission of siloles

Aggregation-induced emission (AIE) is a unique and significant photophysical phenomenon that differs greatly from the commonly acknowledged aggregation-caused emission quenching observed for many π-conjugated planar chromophores. The mechanistic decipherment of the AIE phenomenon is of high importance for the advance of new AIE systems and exploitation of their potential applications. Propeller-like 2,3,4,5-tetraphenylsiloles are archetypal AIE-active luminogens, and have been adopted as a core part in the design of numerous luminescent materials with diverse functionalities. In this review article, we elucidate the impacts of substituents on the AIE activity and shed light on the structure–property relationship of siloles, with the aim of promoting the judicious design of AIE-active functional materials in the future. Recent representative advances of new silole-based functional materials and their potential applications are reviewed as well.     

Amplified spontaneous emission,optical waveguide and polarized emission based on 2,5-diaminoterephthalates

A series of 2,5-diaminoterephthalates with a simple structure were synthesized through one-step reaction, and their bar-shaped single crystals with a large size and a smooth surface have been obtained via the solvent-evaporation method. These crystals exhibit bright emission with fluorescence quantum yields higher than 0.2. They display the waveguide property, and low optical loss coefficients for waveguide have been determined for the crystal of one compound. In addition, the crystal can cause linear polarization of the light emitted from it, with a high polarization contrast of 0.70. Most importantly, these crystals can realize amplified spontaneous emission(ASE), including the red ASE, with appreciable energy thresholds of 72–198 k W/cm~2 and high gain coefficients, which suggests the potential of these crystals for the application in organic solid-state lasers.     

UV emission of I2 from the ion-pair state following amplified spontaneous emission

This paper reports the results of processes resulting in D0(u) (+)-X (1)Sigma(g) (+) emission when a single rovibrational level of the E0(g) (+) state is prepared. Our study reveals that two kinds of processes populate the D0(u) (+) state; which one occurs depends on the experimental conditions. One process involves amplified spontaneous emission from the E0(g) (+) state. The other is collision-induced energy transfer in self-quenching. We distinguish these two processes from the time profiles of fluorescence signals. These processes give completely different vibrational distributions in the D0(u) (+) state from a given rovibrational level of the E0(g) (+) state. The discrepancy between our results and previous results for the E0(g) (+)-->D0(u) (+) relaxation is briefly discussed.     

Wavelength table of chromium emission lines in argon glow discharge optical emission spectrometry

A wavelength table of chromium lines emitted from an argon glow discharge plasma, which comprises 2049 atomic and ionic emission lines in the wavelength range of 200–440 nm, is presented. The relative intensities are rather different from the data of published wavelength tables based on arc-excited and spark-excited spectra. Emission lines of Ar, Ti, V, Fe, Ni, and Cu in the neighborhood of the prominent Cr emission lines are also compiled as a table. These tables could be employed for the analytical applications in glow discharge optical emission spectrometry. All of the data are presented as Supplementary Electronic Material. Recieved: 22 December 1999 / Revised: 25 February 2000 / Accepted: 25 February 2000     

Wavelength table of chromium emission lines in argon glow discharge optical emission spectrometry

A wavelength table of chromium lines emitted from an argon glow discharge plasma, which comprises 2049 atomic and ionic emission lines in the wavelength range of 200–440 nm, is presented. The relative intensities are rather different from the data of published wavelength tables based on arc-excited and spark-excited spectra. Emission lines of Ar, Ti, V, Fe, Ni, and Cu in the neighborhood of the prominent Cr emission lines are also compiled as a table. These tables could be employed for the analytical applications in glow discharge optical emission spectrometry. All of the data are presented as Supplementary Electronic Material.     

Microsecond-pulse glow discharge atomic emission

A microsecond pulsed glow discharge was produced with high pulse magnitude and small duty cycle. Time resolved emission and absorption spectroscopy was applied to study the processes of atomization, excitation and ionization in the glow discharge. Experimental results show that, without overheating the sample, the emission peak intensity is several orders greater than that obtained in the conventional dc mode. This implies that a much more intense plasma is generated during pulsed on region.     

Surface-plasmon-coupled emission of quantum dots

We studied surface plasmon-coupled emission (SPCE) of semiconductor quantum dots (QDs). These QDs are water-soluble ZnS-capped CdSe nanoparticles stabilized using lysine cross-linked mercaptoundecanoic acid. The QDs were spin-coated from 0.75% PVA solution on a glass slide covered with 50 nm of silver and a 5-nm protective SiO(2) layer. Excited QDs induced surface plasmons in a thin silver layer. Surface plasmons emitted a hollow cone of radiation into an attached hemispherical glass prism at a narrow angle of 48.5 degrees. This directional radiation (SPCE) preserves the spectral properties of QD emission and is highly p-polarized irrespective of the excitation polarization. The SPCE spectrum depends on the observation angle because of the intrinsic dispersive properties of SPCE phenomenon. The remarkable photostability can make QDs superior to organic fluorophores when long exposure to the intense excitation is needed. The nanosize QDs also introduce a roughness near the metal layer, which results in a many-fold increase of the coupling of the incident light to the surface plasmons. This scattered incident illumination transformed into directional, polarized radiation can be used simultaneously with SPCE to develop devices based on both quantum dot emission and light scattered from surface plasmons on a rough surface.     

Ultraviolet emission of molecular chlorine

The UV emission of Cl₂ from a new valence-shell state having 0⁺_u symmetry (T_c ≈ 59774 cm^?1, r_c ≈ 3.0 Å) was observed by focusing ≈ 500 nm laser radiation to gaseous chlorine. Excitation was achieved by virtual two-photon absorption from the B ³Π_0⁺u state formed by single-photon absorption stepwisely. The emission spectra showed transitions to the ground state as well as to the repulsive grade estate dissociating to Cl²P) + Cl(²P) products.