Stimulated emissions in aligned CdS nanowires at room temperature

Aligned CdS nanowires (NWs) were obtained through a simple thermal evaporation process with highly active CdS nanoparticles as the evaporation source. These NWs show prominent optical waveguides behavior under a continuous-wave (CW) laser excitation. Excitation intensity-dependent photoluminescence (PL) measurements show that these NWs exhibited both broad and supernarrow stimulated emission (lasing) under intense pulse optical excitation at room temperature. Raman scattering and time-resolved PL measurements were used to investigate the optical properties. The results indicated that the stimulated emission in these NWs involves the electron-hole plasma (EHP) and Farby-Perot (F-P) optical resonant processes at room temperature.     

Tuning Optical Properties of Si Quantum Dots by π‐Conjugated Capping Molecules

The absorption and photoluminescence (PL) properties of silicon quantum dots (QDs) are greatly influenced by their size and surface chemistry. Herein, we examined the optical properties of three Si QDs with increasing σ–π conjugation length: octyl‐, (trimethylsilyl)vinyl‐, and 2‐phenylvinyl‐capped Si QDs. The PL photon energy obtained from as‐prepared samples decreased by 0.1–0.3 eV, while the PL excitation (PLE) extended from 360 nm (octyl‐capped Si QDs) to 400 nm (2‐phenylvinyl‐capped Si QDs). A vibrational PL feature was observed in all samples with an energy separation of about 0.192±0.013 eV, which was explained based on electron–phonon coupling. After soft oxidization through drying, all samples showed blue PL with maxima at approximately 410 nm. A similar high‐energy peak was observed with the bare Si QD sample. The changes in the optical properties of Si QDs were mainly explained by the formation of additional states arising from the strong σ–π conjugation and QD oxidation.     

水相中CdTe纳米晶的制备及其光学性质

用不同稳定剂(巯基乙酸(TGA)、巯基丙酸(MPA)、L-半胱氨酸(L-Cys)、3-巯基-1,2-丙二醇(TG))在水相中制备了CdTe纳米晶, 并用透射电子显微镜(TEM)、X射线光电子能谱(XPS)和X射线粉末衍射(XRD)等技术对其进行了表征. 研究了不同水相合成条件对CdTe纳米晶光学性质的影响, 结果表明, n(Cd):n(Te)、溶液pH值、回流时间以及稳定剂的性质, 对纳米晶的光学性质具有显著影响. 制得的CdTe纳米晶发射峰窄且对称(半高全宽达38 nm), 用不同稳定剂制备的纳米晶发光量子效率有所不同, 用不同的激发波长对纳米晶进行激发时, 发射峰并未表现出明显的移动.     

Water soluble carbon nanoparticles: hydrothermal synthesis and excellent photoluminescence properties

Water-soluble carbon nanoparticles (CNPs) were fabricated by a facile, one step hydrothermal synthetic route using acid/alkali as additives. These CNPs emit bright photoluminescence (PL) covering the entire visible-near infrared (NIR) spectral range. PL measurements confirmed that the CNPs have up-conversion of PL properties, and that the NIR PL of the CNPs can also be observed by NIR excitation. Control experiments indicated that different additives can strongly affect the PL properties of the CNPs. With a combination of free dispersion in water and attractive PL properties, these CNPs hold promise for applications in nanotechnology.     

Revealing the Role of Tin(IV) Halides in the Anisotropic Growth of CsPbX3 Perovskite Nanoplates

CsPbX₃ perovskite nanoplates (PNPLs) were formed in a synthesis driven by SnX₄ (X=Cl, Br, I) salts. The role played by these hard Lewis acids in directing PNPL formation is addressed. Sn⁴⁺ disturbs the acid–base equilibrium of the system, increasing the protonation rate of oleylamine and inducing anisotropic growth of nanocrystals. Sn⁴⁺ cations influence the reaction dynamics owing to complexation with oleylamine molecules. By monitoring the photoluminescence excitation and photoluminescence (PL) spectra of the PNPLs grown at different temperatures, the influence of the thickness on their optical properties is mapped. Time‐resolved and spectrally resolved PL for colloidal dispersions with different optical densities reveals that the dependence of the overall PL lifetime on the emission wavelength do not originate from energy transfer between PNPLs but from the contribution of PNPLs with distinct thickness, indicating that thicker PNPLs exhibit longer PL lifetimes.     

Eu3+ concentration dependent optical properties and energy transfer from host Gd3+ to Eu3+ in GdF3 nanocrystals

By using a hydrothermal method, a series of Eu³⁺ concentration dependent GdF₃ nanocrystals have been synthesized. The crystalline structures of samples are characterized by XRD patterns, the morphology and size of the samples are illustrated by FE-SEM images, and the optical properties of the samples are presented by PL excitation and emission spectra. The energy transfer from host Gd³⁺ to Eu³⁺ is observed in the Eu³⁺ doped GdF₃ nanocrystals. The optical properties of Eu³⁺ and the energy transfer efficiency from host Gd³⁺ to Eu³⁺ are discussed on the basis of the Eu³⁺ concentration dependent integrated PL excitation and emission spectra of Gd³⁺ and Eu³⁺. The discussion on optical properties of Eu³⁺ and the energy transfer from Gd³⁺ to Eu³⁺ is meaningful to design and synthesize Gd³⁺ based compounds.     

A class of nonplanar conjugated compounds with aggregation-induced emission: structural and optical properties of 2,5-diphenyl-1,4-distyrylbenzene derivatives with all cis double bonds

We have studied the structural and optical properties of four 2,5-diphenyl-1,4-distyrylbenzene derivatives with all cis double bonds. These compounds belong to a class of nonplanar conjugated compounds possessing a typical Aggregation-Induced Emission (AIE) property that has no emission in solution but intense emission in crystal. The four molecules are packed in different stacking modes with different intermolecular interactions, resulting in different crystalline state photoluminescence (PL) efficiency. The torsional molecular configuration increases the intermolecular distances effectively in the crystalline state, which decreases the difference of the optical properties from the frozen isolated molecules to the crystalline state. The Stokes shifts of these compounds are very large and the PL spectra have only one broad emission band with poor structure, due to the relatively large configuration difference between the ground state and the first singlet excited state, and the abundant vibration energy levels of the torsional molecule with changeable conformation.     

1,3-二苯基-2-吡唑啉纳米带的制备及其光波导性质

以1,3-二苯基-2-吡唑啉(DP)为目标化合物, 利用再沉淀方法, 以混合溶剂作为不良溶剂, 制备了形貌均一、宽度约2 μm、厚度200 nm和长度数十微米的一维纳米带状结构. 选区电子衍射结果证实, DP分子在纳米带中因为强的分子间π-π相互作用而沿着晶体[100]方向优势生长. 稳态光谱结果表明, DP纳米带具有不同于分子和体相材料的介观特性. 由于J-聚体在DP纳米带中优势形成, 其480 nm的发射峰与分子和体相材料相比分别红移了30和20 nm. 利用扫描近场光学显微镜进一步发现, 一维DP纳米带类似于天然的亚波长尺度谐振腔, 紫外激发DP分子发射的荧光被限域在DP纳米带中, 沿一维方向传导并在两端耦合输出.     

酸根离子掺杂对多孔阳极氧化铝光致发光特性的影响

采用电化学二次阳极氧化法分别在纯硫酸、纯草酸及硫酸-草酸混合电解液中制备了3个系列的多孔阳极氧化铝(AAO)样品, 考察了它们在250 nm光激发下的光致发光(PL)特性. 研究结果表明, 各系列AAO样品在350～450 nm波段范围内的PL谱形均完全相似, 具有相同的发光中心, 即氧空位缺陷态; 掺杂进入AAO样品的SO₄^2-和C₂O₄^2-分解形成的发光中心对应的光发射分别在288和328 nm附近; 对于硫酸-草酸混合电解液中生长的AAO样品, 其在328 nm附近的发光峰随着硫酸-草酸体积比的增大呈先增大后减少的变化, 而288 nm附近的发光峰却由基本消失到逐渐显现. 初步分析了该现象的成因.     

Red,Green, and Blue Luminescence by Carbon Dots: Full‐Color Emission Tuning and Multicolor Cellular Imaging

A facile approach for preparation of photoluminescent (PL) carbon dots (CDs) is reported. The three resulting CDs emit bright and stable red, green and blue (RGB) colors of luminescence, under a single ultraviolet‐light excitation. Alterations of PL emission of these CDs are tentatively proposed to result from the difference in their particle size and nitrogen content. Interestingly, up‐conversion (UC)PL of these CDs is also observed. Moreover, flexible full‐color emissive PVA films can be achieved through mixing two or three CDs in the appropriate ratios. These CDs also show low cytotoxicity and excellent cellular imaging capability. The facile preparation and unique optical features make these CDs potentially useful in numerous applications such as light‐emitting diodes, full‐color displays, and multiplexed (UC)PL bioimaging.     

Oxygen and relative humidity monitoring with films tailored for enhanced photoluminescence

Approaches to generate porous or doped sensing films, which significantly enhance the photoluminescence (PL) of oxygen optical sensors, and thus improve the signal-to-noise (S/N) ratio, are presented. Tailored films, which enable monitoring the relative humidity (RH) as well, are also presented. Effective porous structures, in which the O₂-sensitive dye Pt octaethylporphyrin (PtOEP) or the Pd analog PdOEP was embedded, were realized by first generating blend films of polyethylene glycol (PEG) with polystyrene (PS) or with ethyl cellulose (EC), and then immersing the dried films in water to remove the water-soluble PEG. This approach creates pores (voids) in the sensing films. The dielectric contrast between the films’ constituents and the voids increases photon scattering, which in turn increases the optical path of the excitation light within the film, and hence light absorption by the dye, and its PL. Optimized sensing films with a PEG:PS ratio of 1:4 (PEG’s molecular weight M_w ∼8000) led to ∼4.4× enhancement in the PL (in comparison to PS films). Lower M_w ∼200 PEG with a PEG:EC ratio of 1:1 led to a PL enhancement of ∼4.7×. Film-dependent PL enhancements were observed at all oxygen concentrations. The strong PL enhancement enables (i) using lower dye (luminophore) concentrations, (ii) reducing power consumption and enhancing the sensor’s operational lifetime when using organic light emitting diodes (OLEDs) as excitation sources, (iii) improving performance when using compact photodetectors with no internal gain, and (iv) reliably extending the dynamic range.     

Photoluminescence from C60-coupled porous structures formed on Fe+-implanted silicon

111-oriented p-type Si wafer with a resistivity of 1-5 Omega cm was implanted with Fe+ and then annealed at 1100 degrees C in N2 for 60 min, followed by anodization in a solution of HF to form porous structure with beta-FeSi2 nanocrystallites. Photoluminescence (PL) spectral measurements show that a strong PL peak appears in the range of 610-670 nm. The position of the PL peak remains unchanged, but its intensity increases with the storage time in air until about three months and then saturates. C60 molecules were chemically coupled on the porous structure through a kind of silane coupling agent to form a nanocomposite. It is revealed that the stable PL peak monotonically shifts to a pinning wavelength at 570 nm. Experimental results from PL, PL excitation, Raman scattering, and x-ray diffraction measurements clearly show that the pinned PL originates from optical transition in C60-related defect states, whereas the photoexcited carriers occur in the beta-FeSi2 nanocrystallites formed during anodization. This work opens a new way to tailor nanometer environment for seeking optimal luminescent properties.     

Red,Green, and Blue Luminescence by Carbon Dots: Full‐Color Emission Tuning and Multicolor Cellular Imaging

A facile approach for preparation of photoluminescent (PL) carbon dots (CDs) is reported. The three resulting CDs emit bright and stable red, green and blue (RGB) colors of luminescence, under a single ultraviolet‐light excitation. Alterations of PL emission of these CDs are tentatively proposed to result from the difference in their particle size and nitrogen content. Interestingly, up‐conversion (UC)PL of these CDs is also observed. Moreover, flexible full‐color emissive PVA films can be achieved through mixing two or three CDs in the appropriate ratios. These CDs also show low cytotoxicity and excellent cellular imaging capability. The facile preparation and unique optical features make these CDs potentially useful in numerous applications such as light‐emitting diodes, full‐color displays, and multiplexed (UC)PL bioimaging.     

Synthesis and characterization of polyketanils with 3,8-diamino-6-phenylphenanthridine moieties exhibiting light emitting properties molecular and supramolecular engineering concept

Relationship between structures and properties of new conjugated polyketanils (PKs) with special architectures, synthesized from three diketones, i.e. p-dibenzoylbenzene, dibenzyl, trans-1,2-dibenzoylethylene and 3,8-diamino-6-phenylphenanthridine, was investigated. The photoluminescence (PL) of green, yellow and red emitting light polymers and their blend was studied. These included the effects of excitation wavelength, concentration and film thickness on the PL. Photoluminescence properties of the PKs before and after protonation with 10-Camphorsulfonic acid (CSA) were tested. The structure formation of (PKs)(1)(CSA)(2) complexes are discussed on the basis of FTIR spectroscopy.     

CdS量子点的制备及细胞膜初步荧光标记

以巯基乙酸为稳定剂,通过控制反应温度、反应时间及pH值,在水相中合成了稳定的受激发出紫光、蓝光、绿光、黄光和红光的CdS量子点;通过紫外可见吸收光谱、荧光光谱和X射线衍射谱(XRD)对产物的光学性能和晶体结构进行了表征,结果表明所合成的CdS量子点分散性较好,量子产率为8%,为立方晶型,粒径约1 nm;利用荧光倒置显微镜观察了量子点在洋葱内表皮细胞膜上聚集及受激发射荧光行为,实现细胞膜初步标记.     

Semiempirical molecular orbital studies on p-quinodimethane. Electronic structure assignments based on total energies and comparisons with photoelectron and absorption spectra

The electronic structure of p-quinodimethane has been investigated using both CNDO/S and INDO molecular orbital approximations. It is found that the energetically favorable configuration is a “quinoid” construction leading to a spin-paired singlet ground state. Comparisons of the calculated excitation energies and orbital orderings with optical and photoemission measurements are consistent with this assignment. The “quinoid” configuration is found to be energetically unfavorable toward the formation of a low-lying triplet or “biradical”-like state. Charge density distributions, however, suggest a high ground state chemical reactivity.     

Interesting Magnetic and Optical Properties of ZnO Co-doped with Transition Metal and Carbon

Magnetic and optical properties of ZnO co-doped with transition metal and carbon have been investigated using density functional theory based on first-principles ultrasoft pseudopoten-tial method. Upon co-doping with transition metal (TM) and carbon, the calculated results show a shift in the Fermi level and a remarkable change in the covalency of ZnO. Such cases energetically favor ferromagnetic semiconductor with high Curie temperature due to p-d exchange interaction between TM ions and holes induced by C doping. The total en-ergy difference between the ferromagnetic and the antiferromagnetic configurations, spatial charge and spin density, which determine the magnetic ordering, were calculated in co-doped systems for further analysis of magnetic properties. It was also discovered that optical prop-erties in the higher energy region remain relatively unchanged while those at the low energyregion are changed after the co-doping. These changes of optical properties are qualitatively explained based on the calculated electronic structure. The validity of our calculation in comparison with other theoretical predictions will further motivate the experimental inves-tigation of (TM, C) co-doped ZnO diluted magnetic semiconductors.     

Singlet-singlet annihilation leading to a charge-transfer intermediate in chromophore-end-capped pentaphenylenes.

The excited-state properties of two peryleneimide chromophore end-capped pentaphenylene compounds were investigated in detail using femtosecond transient absorption and single-photon timing experiments. Singlet-singlet annihilation was found to promote one chromophore into a higher excited state and results in the formation of an ultra-short-living intermediate charge-transfer (CT) state in the S(n)-S(1) deactivation pathway. In low-polarity solvents, this CT state is found to be energetically higher than the first excited state and thus cannot be populated via one-photon excitation. The observed CT state decays with a time constant of about 1 ps to form the lowest singlet excited state. These results demonstrate the potential use of the singlet-singlet annihilation as a novel tool in studying reactions occurring in states that are energetically above the S(1).     

Semiconductor quantum dots and metal nanoparticles: syntheses,optical properties,and biological applications

We review the syntheses, optical properties, and biological applications of cadmium selenide (CdSe) and cadmium selenide–zinc sulfide (CdSe–ZnS) quantum dots (QDs) and gold (Au) and silver (Ag) nanoparticles (NPs). Specifically, we selected the syntheses of QDs and Au and Ag NPs in aqueous and organic phases, size- and shape-dependent photoluminescence (PL) of QDs and plasmon of metal NPs, and their bioimaging applications. The PL properties of QDs are discussed with reference to their band gap structure and various electronic transitions, relations of PL and photoactivated PL with surface defects, and blinking of single QDs. Optical properties of Ag and Au NPs are discussed with reference to their size- and shape-dependent surface plasmon bands, electron dynamics and relaxation, and surface-enhanced Raman scattering (SERS). The bioimaging applications are discussed with reference to in vitro and in vivo imaging of live cells, and in vivo imaging of cancers, tumor vasculature, and lymph nodes. Other aspects of the review are in vivo deep tissue imaging, multiphoton excitation, NIR fluorescence and SERS imaging, and toxic effects of NPs and their clearance from the body. Figure Semiconductor quantum dots and metal nanoparticles have extensive applications, e.g., in vitro and in vivo bioimaging Tamitake Itoh and Abdulaziz Anas contributed equally to this article.     

Optical properties of N-succinimidyl bithiophene and the effects of the binding to biomolecules: comparison between coupled-cluster and time-dependent density functional theory calculations and experiments

We report a joint theoretical-experimental study on the optical properties of 5-N-succinimidyl-2,2'-bithiophene (NS-2T), a prototype system for a new class of biomarkers. Time-dependent density functional theory (TD-DFT) and approximate coupled-cluster single and doubles (CC2) calculations are performed in the ground and excited states. Theoretical results are compared with absorption, photoluminescence (PL), time-resolved PL, and PL quantum efficiency measurements. The excited state of NS-2T has a larger dipole moment as compared to that of the ground state, explaining the experimental shift of the PL peak in solvents of different polarity, and a smaller intersystem crossing (ISC) rate as compared to that of isolated bithiophene (2T), explaining the increased PL quantum efficiency. We also studied two model systems to describe the effects of the covalent binding of NS-2T to biomolecules and proteins with the epsilon-NH(2) lysine groups. These model systems show optical properties closer to 2T, as the PL quantum efficiency is reduced due to the increased ISC rate. Theoretical calculations and experimental results show that covalent binding of NS-2T to a biomolecule will blue-shift the absorption but not the photoluminescence. CC2 and TD-DFT can very well describe the absorption and photoluminescence energies of all three systems, but the presence of several charge-transfer transitions in the TD-DFT spectrum of NS-2T required the use of a correlated method to validate the TD-DFT results.