Emission properties of manganese-doped ZnS nanocrystals

We have performed steady-state and time-resolved fluorescence studies on undoped and Mn-doped ZnS nanocrystals with approximately 16 A diameter. While there is no band-edge emission, the intensity of the steady-state blue fluorescence from ZnS surface states decreases upon Mn incorporation, which gives rise to an orange emission. These results show that Mn incorporation competes very effectively with the donor-acceptor surface states for the energy transfer from the electron-hole pair excited across the band gap. In both undoped and doped samples, the time-resolved fluorescence studies establish the presence of a distribution of decay lifetimes possibly due to a number of emission centers in the nanocrystals. A faster short-time decay of the blue emission in the Mn-doped samples compared to that in the undoped sample suggests an additional decay channel for the surface states via an energy transfer from these states to the dopant levels.     

195Pt NMR of heteropolymetallic complexes containing secondary dithiooxamides as binucleating ligands

Monometallic [Pt{S-S2C2(NR)2H}2] (S-S2C2(NR)2H = kappa2-S,S-S2C2(NR)2H = bis-dialkyl-dithioxamidate, R = methyl, isoamyl, benzyl) and binuclear and trinuclear heterobimetallic complexes [Pt{S-S2C2(NR)2H}{mu-S2C2(NR)2}MLn] (mu-S2C2(NR)2 = kappa2-S,S(Pt)-kappa2-N,N(M)-S2C2(NR)2) and [Pt{{mu-S2C2(NR)2}MLn}2] (MLn+ = [(eta3-allyl)palladium]+, [bis-(2-phenylpyridine)rhodium]+, [(eta6-p-cymene)(chloro)ruthenium]+, [(1,4-cyclooctadiene)rhodium]+, [(pentamethylcyclopentadienyl)(chloro)rhodium]+) have been prepared and characterized. The progressive substitution of the residual amidic hydrogen in the [Pt{S-S2C2(NR)2H}2] complexes with a MLn+ metal fragment results in the deshielding of platinum nuclei, a red shift of the MLCT absorption maximum, and a decrease in the oxidation potential. Such behavior has been interpreted as a progressive electron shift from platinum to the binucleating ligands, the extent of which depends on the nature of MLn+ metal fragment.     

Emission properties of dihydropterins in aqueous solutions

Pterins belong to a class of heterocyclic compounds present in a wide range of living systems and accumulate in the skin of patients affected by vitiligo, a depigmentation disorder. The study of the emission of 7,8-dihydropterins is difficult because these compounds are more or less unstable in the presence of O(2) and their solutions are contaminated with oxidized pterins which have much higher fluorescence quantum yields (Φ(F)). In this work, the emission properties of six compounds of the dihydropterin family (6-formyl-7,8-dihydropterin (H(2)Fop), sepiapterin (Sep), 7,8-dihydrobiopterin (H(2)Bip), 7,8-dihydroneopterin (H(2)Nep), 6-hydroxymethyl-7,8-dihydropterin (H(2)Hmp), and 6-methyl-7,8-dihydropterin (H(2)Mep)) have been studied in aqueous solution. The fluorescence characteristics (spectra, Φ(F), lifetimes (τ(F))) of the neutral form of these compounds have been investigated using the single-photon-counting technique. Φ(F) and τ(F) values obtained lie in the ranges 3-9 × 10(-3) and 0.18-0.34 ns, respectively. The results are compared to those previously reported for oxidized pterins.     

Emission properties and applications of nanostructured luminescent oxide nanoparticles

Rare earth doped oxide materials are well known for their numerous applications in light emitting devices. An interesting issue is to study the emission properties of nanoparticles, with the aim to understand the influence of small size and surface effects on the emission processes. These particles could furthermore be used in new applications such as the elaboration of transparent emitting devices or new biological labels. The work presented here concerns highly luminescent rare earth doped yttrium vanadates (YVO₄:Eu) and lanthanum phosphate LaPO₄:Ce,Tb·xH₂O nanoparticles. Simple aqueous colloidal syntheses are used for the elaboration of concentrated colloids based on the progressive decomposition of polymeric precursors at moderate temperature (60–90 °C). Both types of particles exhibit strong emission (quantum yields of 25% and 45% for vanadates and phosphates, respectively), but significantly lower than that for the equivalent bulk materials. The alteration of the emission processes is discussed in terms of surface quenching effects. Improvements are obtained through the elaboration of core/shell nanostructures. Surface derivatization has been achieved through the controlled growth of an organically modified silica shell using a functionalized silane precursor. Two examples are given concerning the applications of those particles. The first one is the elaboration of transparent and highly luminescent thin films, obtained by the dispersion of the functionalized particles in a sol–gel silica matrix. The other one is the use of guanidine functionalized particles as biological labels for the single particle detection of sodium channels in cardiac cells.     

Vibrational study of the secondary thioamide function,the intramolecular resonance assisted and intermolecular hydrogen bonding in NN'-hydroxyalkyl dithiooxamides

The article describes the vibrational characterization of the secondary thioamide formation and especially a spectroscopical interesting study of different types of hydrogen bonding in NN'-dihydroxyalkyldithiooxamides.     

Emission energies and photophysical properties of ladder oligo(p-aniline)s

Emission properties and the photophysics of three ladder oligo(p-aniline)s; namely 5,11-diethyl-6,12-dimethylindolo[3,2-b]carbazole (DIMER 2P), 14-ethyl-5,8-dihydro-diindolo[3,2-b:2′,3′-h]carbazole (TRIMER 2P), and 5,8,14-triethyl-diindolo[3,2-b:2′,3′-h]carbazole (TRIMER 3P) are presented. The optimization (relaxation) of the first singlet excited electronic state (S₁) has been done using the restricted configuration interaction (singles) (RCIS/6-31G*) approach. The excitation to the S₁ state does not cause important changes in the geometrical parameters of the compounds, as is experimentally corroborated by the small Stokes shifts. Emission energies from the relaxed excited states have been obtained from TDDFT calculations performed on the S₁ optimized geometries and have been correlated with the corresponding fluorescence spectra of the derivatives dissolved in dichloromethane. A good agreement has been found between TDDFT emission energies and the (0,0) fluorescence bands. As predicted from theoretical calculations, all compounds exhibit small Stokes shift, which testify the rigidity of these ladder compounds. Moreover, this theoretical approach provides a good evaluation of the bathochromic shifts caused by the increase in the conjugation length or by the presence of alkyl chains on the nitrogen atoms. Finally, the fluorescence quantum yield and lifetime of the compounds in dichloromethane have been obtained. From these data, the radiative and nonradiative rate constants of the deactivation of the S₁ state have been determined.     

聚集诱导发光

聚集诱导发光(AIE)是唐本忠院士于2001年提出的一个科学概念,是指一类在溶液中不发光或者发光微弱的分子聚集后发光显著增强的现象。高效固态发光的AIE材料有望从根本上解决有机发光材料面临的聚集导致发光猝灭难题,具有重大的实际应用价值。从分子内旋转受限到分子内运动受限,从聚集诱导发光到聚集体科学,AIE领域已经取得了许多原创性的成果。在本综述中,我们从AIE材料的分类、机理、概念衍生、性能、应用和挑战等方面讨论了AIE领域最近取得的显著进展。希望本综述能激发更多关于分子聚集体的研究,并推动材料、化学和生物医学等学科的进一步交叉融合和更大发展。     

Emission band shape probes of the mixed-valence excited state properties of polypyridyl-bridged bis-ruthenium(II) complexes

The absorption spectra and emission spectral band shapes of several polypyridine-ligand (PP) bridged bis-ruthenium(II) complexes imply that the Ru(II)/Ru(III) electronic coupling is weak in their lowest energy metal to ligand charge transfer (MLCT) excited states. Many of these PP-bridging ligands contain pyrazine moieties and the weak electronic coupling of the excited states contrasts to the strong electronic coupling inferred for the correlated mixed-valence ground states. Although the bimetallic complexes emit at significantly lower energy than their monometallic analogs, the vibronic contributions to their 77 K emission spectra are much stronger than expected based on comparison to the monometallic analogs (around twofold in some complexes) and this feature is characteristic of bimetallic complexes in which the mixed-valence excited states are electronically localized. The weaker excited state than ground state donor/acceptor electronic coupling in this class of complexes is attributed to PP-mediated super-exchange coupling in which the mediating orbital of the bridging ligand (PP-LUMO) is partly occupied in the MLCT excited states, but is unoccupied in the ground states; therefore, the vertical Ru(III)-PP⁻ (MLCT) energy is larger and the mixing coefficient smaller in these excited states than is found for Ru(II)-PP in the corresponding ground states.     

Photoreactivity and emission properties of liquid-crystalline twin dimers containing cinnamic acid moieties at both ends of ethylene glycol spacers. II. Emission properties

Emission properties of liquid-crystalline twin dimers containing 4-methoxy-cinnamic acid moieties at both ends of various ethylene glycol derivatives (nEGMC), where n denotes the number of the ethylene glycol units in the spacers, have been explored by steady-state and time resolved fluorescence spectroscopy in relation to the morphology of the system. Characteristic emissions were observed in the twin dimers, particularly in 2EGMC and 5EGMC, which were ascribed to excimer emission, and the energy gap between the locally excited state (monomer emission) and the excimer state and could be correlated to the difference in the spatial orientation of the mesogenic 4-methoxycinnamate groups adopted in nEGMC in the ground state. The picosecond time resolved fluorescence spectroscopy revealed no observed rise in the excimer emission in any sample at any temperature, indicating that the excimer is most probably formed by direct excitation of the pair wise arrangement of the 4-methoxycinnamate moieties in the ground state; thus, the excimer formation behaviour reflects well the ground state morphology of the twin dimers.     

为什么有机分子在溶液中会因聚集而发光？

<正>自2001年,“聚集诱导发光”现象被唐本忠教授研究团队以专有名词形式提出来以后1,受到了人们的广泛关注,近年来相关的研究更是取得了长足的进展。在其众多的推测机理中,目前比较广为人知的是“限制分子运动”的机制2。这种解释非常生动直观,但是在原理上尚需深入研究。尽管限制分子运动对于有效避免快速非辐射弛豫过程至关重要,但其作用的结果并不能导致电子激发态的产生——其是诱导发光的关键。     

Aggregation-Induced Emission Leading to White Light Emission in Diphenylbenzofulvene Derivatives

The search for a unique molecular system able to efficiently emit in the total visible range of the electromagnetic spectra, i. e., white light emission (WLE), is a topic of intense research. We here show that aggregates formed by diphenylbenzofulvene ( DPBF ) derivatives are from two to four orders of magnitude more emissive than their monomers. From a simple strategy, involving structural modification of a DPBF propelled shape core, a close match with the pure white light emission coordinates is obtained with a combination of two derivatives in films, with featured solid-state emission, without involvement of D−A groups or energy transfer processes.     

Emission Characteristics of Jet Configurations for Jet-Boosted Glow Discharge Atomic Emission Spectrometry

Comparisons of emission characteristics and analytical performance have been made between three types of jet configuration. These include cone-jet configuration, six-jet configuration, and cylinder-jet configuration. The cone-jet configuration shows the highest emission intensity among all jet configurations. Regardless of the jet configuration, the Cu II 224.70 nm emission line was found to be the most dominant of all Cu emission lines. The intensity ratios of the resonance line Cu I 324.75 to a nonresonance line Cu I 282.44 nm was 1.3 for the six-jet configuration, 2.3 for the cylinder jet, and 2.8 for the cone jet. This may indicate that self-absorption was significant in six-jet configuration. The effects of main and auxiliary gas flow rates on the emission characteristics for the cone jet configuration were also investigated. The intensity of Cu I at 324.75 and 327.40 nm decreases about 30% when the gas flow rate increased from 0 to 150 ml/min, while the intensities of Cu II 224.70 nm and the UV–Visible Cu I 510.55-, 515.32-, and 521.82-nm lines increased by a factor of 2 to 3. The decrease in intensity of the resonance line relative to the Cu II and Cu I green lines may be caused by self-absorption. The cone-jet and six-jet configurations show comparable values of precision, linearity, and detection limits, while the cylinder-jet configuration provides the worst analytical performance among three types of jet configurations. The linearity of the calibration curve was the worst in the six-jet configuration due to self-absorption.     

原子发射光谱分析

本文是《分析试验室》期刊定期评述中“原子发射光谱分析”课题的第一篇评述文章。文中对1987～1990年期间我国原子发射光谱分析(AES)领域所取得的进展作了全面评述。内容包括概述、火焰发射光谱法、电弧发射光谱法、火花发射光谱法、电感耦合等离子体原子发射光谱法、直流等离子体原子发射光谱法、微波等离子体原子发射光谱法、亚稳态能量转移发射光谱法、激光显微发射光谱法、空心阴极灯和Grimm灯发射光谱法等方面。     

ZnO荧光粉中的紫外发射和绿色发射之间的关系

通过在低氧分压和真空中热处理ZnO粉末, 获得了ZnO荧光粉. ZnO荧光粉有两个发射谱带, 分别位于380 nm(紫外)和510 nm(绿色). 紫外谱带对应于ZnO中的激子发射, 是一个单中心发光过程；绿色谱带是一个复合发光过程, 与ZnO中的本征缺陷相关, 如氧空位、锌空位等. 实验表明, 高密度的激发条件有利于紫外发射, 而低氧分压下的热处理有利于提高绿色发射谱带的强度. 研究结果还表明, 与紫外发射相联系的激子可向与本征缺陷相联系的绿色发光中心传递能量, 这种传递可能是通过激子扩散实现的.