Direct and stepwise energy transfer from excitons to plasmons in close-packed metal and semiconductor nanoparticle monolayer films

We studied the dynamics of photoluminescence (PL) and energy transfer in close-packed monolayer films of CdSe and Au nanoparticles (NPs) assembled using the Langmuir-Blodgett technique. The PL intensity and dynamics depended on the ratio of CdSe to Au NPs in the mixed films. The PL quenching of CdSe NPs occurs through rapid energy transfer from excitons in CdSe NPs to plasmons in Au NPs. The PL decay curves of the mixed NPs monolayers are determined by three decay rates: the direct energy transfer between the nearest-neighbor CdSe and Au NPs (CdSe-->Au), the stepwise energy transfer from CdSe to CdSe to Au NPs (CdSe-->CdSe-->Au), and the radiative recombination in CdSe NPs.     

Peptide‐Targeted Gold Nanoparticles for Photodynamic Therapy of Brain Cancer

Targeted drug delivery using epidermal growth factor peptide‐targeted gold nanoparticles (EGF_pep‐Au NPs) is investigated as a novel approach for delivery of photodynamic therapy (PDT) agents, specifically Pc 4, to cancer. In vitro studies of PDT show that EGF_pep‐Au NP‐Pc 4 is twofold better at killing tumor cells than free Pc 4 after increasing localization in early endosomes. In vivo studies show that targeting with EGF_pep‐Au NP‐Pc 4 improves accumulation of fluorescence of Pc 4 in subcutaneous tumors by greater than threefold compared with untargeted Au NPs. Targeted drug delivery and treatment success can be imaged via the intrinsic fluorescence of the PDT drug Pc 4. Using Pc 4 fluorescence, it is demonstrated in vivo that EGF_pep‐Au NP‐Pc 4 impacts biodistribution of the NPs by decreasing the initial uptake by the reticuloendothelial system (RES) and by increasing the amount of Au NPs circulating in the blood 4 h after IV injection. Interestingly, in vivo PDT with EGF_pep‐Au NP‐Pc 4 results in interrupted tumor growth when compared with EGF_pep‐Au NP control mice when selectively activated with light. These data demonstrate that EGF_pep‐Au NP‐Pc 4 utilizes cancer‐specific biomarkers to improve drug delivery and therapeutic efficacy over untargeted drug delivery.     

Charge-transfer at silver/phthalocyanines interfaces

Valence band photoemission spectroscopy (VB-PES) and inverse photoemission spectroscopy (IPES) were employed to determine the occupied and unoccupied density of states upon silver deposition onto layers of two phthalocyanines (H₂Pc and CuPc). The two different Pc molecules give rise to very distinct behaviour already during the initial stage of silver deposition. While in the CuPc case no shift occurs in the energy levels, the H₂Pc highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are shifting simultaneously by 0.3 eV, i.e., the HOMO shifts away from the Fermi level while LUMO shifts towards the Fermi level. As the silver quantity increases the HOMO levels of both Pcs are shifting towards the Fermi level. When the Fermi level is resolved in the VB spectra, the characteristic features of H₂Pc and CuPc are smeared out to some extent. Shifts in HOMO and LUMO energy positions as well as changes in line shapes are discussed in terms of charge-transfer and chemical reactions at the interfaces.     

Steady State and Time Resolved Spectroscopic Study of CdSe and CdSe/ZnS QDs:FRET Approach

This article highlights some physical studies on the relaxation dynamics and Förster resonance energy transfer (FRET) of semiconductor quantum dots (QDs) to proximal dye molecule and the way these phenomena change with core to core-shell QD is discussed. Efforts to understand the optical and carrier relaxation dynamics of CdSe and CdSe/ZnS QDs are made by using absorption, steady-state fluorescence and time-resolved fluorescence (TCSPC) techniques. Steady-state as well as time-resolved fluorescence measurements were employed to evaluate the QD PL quenching induced by the proximal Rhodamine 101 dye molecule and to examine the influence of deep trap states on energy transfer efficiency. The FRET parameters such as spectral overlap, Förster distance, intermolecular distance for each donor-acceptor pair are determined and variation of these parameters from core to core-shell QD is discussed.     

Energy transfer between excitons and plasmons in semiconductor-metal hybrid nanostructures

We summarized our recent optical studies on semiconductor nanoparticle (NP) based hybrid nanostructures: isolated CdSe NPs on Au substrates, close-packed CdSe NP monolayers on Au substrates, and close-packed monolayers of mixed CdSe/Au NPs. Luminescence properties of semiconductor-metal hybrid nanostructures were studied by space-resolved optical imaging spectroscopy and time-resolved luminescence spectroscopy. The luminescence spectra and dynamics of isolated and assembled NPs depend on the local environments. We discuss exciton-plasmon interactions in semiconductor-metal hybrid nanostructures.     

Organic heterojunctions of layered perylene and phthalocyanine dyes: characterization with UV-photoelectron spectroscopy and luminescence quenching

We present here the characterization of organic/organic′ heterojunctions created from either of two perylene dyes, perylenetetracarboxylicdianhydride (PTCDA) or the bisimide derivative perylenetetracarboxylicdianhydride-N,N′-bis (butyl)imide (C4-PTCDI), and two chloro-metallated donor phthalocyanines (ClAlPc or ClInPc). The perylene dyes were selected to create thin films with the core of the perylene dye parallel to the substrate plane (PTCDA) or nearly vertical to the substrate plane, with layer planes defined by the butyl substituents (C4-PTCDI). We compare the frontier orbital offsets revealed by UV-photoelectron spectroscopy, and quenching of luminescence of the perylene dyes, as a function of Pc coverage. The ionization potentials (IPs) of the Pc layers, the degree to which interface dipoles are formed at the Pc/perylene dye interface, and the degree of quenching of the perylene luminescence are affected by the structure of the Pc/perylene interface. Pc/PTCDA heterojunctions show significant interface dipoles and higher IPs for the first-deposited Pc layers compared to Pc/C4-PTCDI heterojunctions, which show negligible interface dipoles and lower overall IP values for initial Pc layers. Luminescence of the selectively excited perylene layers is quenched by the addition of even submonolayer coverages of Pc. This quenching process occurs as a result of both energy transfer (perylene to Pc) and charge transfer (Pc to perylene). Luminescence from monomeric and aggregated ClAlPc and ClInPc monolayers is seen on C4-PTCDI films, whereas only luminescence from the aggregated forms of these Pcs is seen on PTCDA films. These studies reveal aspects of organic heterojunction energetics which may have important implications for organic solar cell design.     

Enhancement of ultrasonically induced cell damage by phthalocyanines in vitro

In this work, erythrocytes from carp were used as a nucleated cell model to test the hypothesis that the phthalocyanines (zinc - ZnPc and chloroaluminium -AlClPc) enhance ultrasonically induced damage in vitro. In order to confirm and complete our earlier investigation, the influence of ultrasound (US) and phthalocyanines (Pcs) on unresearched cellular components, was studied. Red blood cells were exposed to 1 MHz continuous ultrasound wave (0.61 and/or 2.44 W/cm²) in the presence or absence of phthalocyanines (3 μM). To identify target cell damage, we studied hemolysis, membrane fluidity and morphology of erythrocytes. To demonstrate the changes in the fluidity of plasma membrane we used the spectrofluorimetric methods using two fluorescence probes: 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5,-hexatriene (TMA-DPH) and 1,6-diphenyl-1,3,5-hexatriene (DPH). The effect of US and Pcs on nucleated erythrocytes morphology was estimated on the basis of microscopic observation.The enhancement of ultrasonically induced membrane damage by both phthalocyanines was observed in case of hemolysis, and membrane surface fluidity, in comparison to ultrasound. The authors also observed changes in the morphology of erythrocytes. The obtained results support the hypothesis that the Pcs enhance ultrasonically induced cell damage in vitro.Furthermore, the influence of ultrasound on phthalocyanines (Pcs) in medium and in cells was tested. The authors observed changes in the phthalocyanines absorption spectra in the medium and the increase in the intensity of phthalocyanines fluorescence in the cells. These data can suggest changes in the structure of phthalocyanines after ultrasound action.     

Experimental investigation of energy transfer between CdSe/ZnS quantum dots and different-sized gold nanoparticles

Hybrid nanostructures of quantum dots(QDs) and metallic nanostructure are attractive for future use in a variety of optoelectronic devices. For photodetection applications, it is important that the photoluminescence (PL) of QDs is quenched by the metallic nanostructures. Here, the quenching efficiency of CdSe/ZnS core-shell quantum dots (QDs) with different sized gold nanoparticles (NPs) films through energy transfer is investigated by measuring the PL intensity of the hybrid nanostructures. In our research, the gold NPs films are formed by the post-annealing of the deposited Au films on the quartz substrate. We find that the energy transfer from the QDs to the Au NPs strongly depends on the sizes of the Au NPs. For CdSe/ZnS QDs direct contact with the Au NPs films, the largest energy transfer efficiency are detected when the resonance absorption peak of the Au NPs is nearest to the emission peak of the CdSe/ZnS QDs. However, when there is a PMMA spacer between the QDs layer and the Au NPs films, firstly, we find that the energy transfer efficiency is weakened, and the largest energy transfer efficiency is obtained when the resonant absorption peak of the Au NPs is farthest to the emission peak wavelength of CdSe/ZnS QDs. These results will be useful for the potential design of the high efficiency QDs optoelectronic devices.     

硒化镉发光量子点的制备及其在有机发光器件中的应用

硒化镉量子点具有随粒径尺寸改变,而产生发光波长调变的特性,目前已被广泛研究。本研究是由化学溶胶法合成不同粒径尺寸的核壳型CdSe／ZnS硒化镉量子点,其表面包覆十六烷基胺,避免分子团聚现象。在由硒化镉成核温度的控制,成功地制备一系列具有各种尺寸粒径的核壳型硒化镉量子点(2—6nm)。本研究也合成了含有纳米金粒子于核壳型硒化镉量子点,实验结果发现：硒化镉发光效率明显的提高。在有机发光器件的应用方面,将发光波长为505nm核壳型CdSe／ZnS量子点掺入溶有发光波长为570nm铱化合物的氯仿溶液时,其溶液的光致发光光谱表明,原量子点的发光特性消失,只有铱化合物的发光依然存在,且其发光强度呈现明显增强趋势,我们推测此现象源自于量子点到铱化合物能量转移的机制。我们也以含有核壳型硒化镉量子点的铱化合物与PVK混合材料为发光层,成功的制作发光二极管器件,器件的发光效率因核壳型硒化镉的掺杂,明显提高2倍多。     

Application of metal nanoparticles/porous silicon diffraction grating in rhodamine 6 G fluorescence signal enhancement

We present a technique for fabricating a fluorescence enhancement device composed of metal nanoparticles(NPs) and porous silicon(PSi) diffraction grating.The fluorescence emission enhancement properties of the PSi and the fluorescence enhancement of the probe molecules are studied on PSi gratings.The fluorescence enhancement of the probe molecules on a fluorescence enhancement device is further improved through the deposition of metal NPs onto the PSi grating.In comparison to metal NP/PSi devices,metal NP periodic distributions can produce a stronger fluorescence enhancement that couples with the PSi grating fluorescence enhancement to achieve an overall three-fold enhancement of the fluorescence intensity.     

Mix-substituted phthalocyanines of a “push–pull”-type and their metal complexes as prospective nanostructured materials for optoelectronics

To study the influence of structural features of phthalocyanine (Pc) derivatives on their physico-chemical properties in bulk and thin films, 23 new phthalocyanines with different quantity and ratio of donor (alkyloxy-groups, in fragment “A”) and acceptor (Cl-, in fragment “B”) substituents in one molecule of the A₃B, ABAB and AABB types with varied length of alkyloxy-substituents and their metal complexes were designed and synthesized. A comparative analysis of spectral, mesomorphic and photoelectric properties of these mix-substituted phthalocyanines of a “push–pull” type was performed. It was shown that non-peripheral substitution by alkyloxy-fragments in hetero-substituted Pcs (similar to homo-substituted Pc) leads to red-shifting of the Q-band into near-IR region. The intensity of photoluminescence, position of peaks and their splitting are strongly connected with chemical structure of Pcs and the type of solvent. In contrast to non-mesogenic octyloxy-Pc (A4) having alkyloxy-substituents in non-peripheral positions, 22 of 23 synthesized compounds possess columnar mesomorphism. The change of donor–acceptor ratio can influence the type of mesophase. A new approach to the creation of materials for optoelectronics is proposed and implemented, which includes design of compounds possessing vitrification from mesophase with maintenance of a columnar order, absorption in the near IR-region of the spectrum and good performance electrophysical characteristics simultaneously.     

The Influence of Surface Trapping and Dark States on the Fluorescence Emission Efficiency and Lifetime of CdSe and CdSe/ZnS Quantum Dots

To investigate the influence of surface trapping and dark states on CdSe and CdSe/ZnS quantum dots (QDs), we studied the absorption, fluorescence intensity and lifetime by using one-and two-photon excitation, respectively. Experimental results show that both one- and two-photon fluorescence emission efficiencies of the QDs enhance greatly and the lifetime increase after capping CdSe with ZnS due to the effective surface passivation. The lifetime of one-photon fluorescence of CdSe and CdSe/ZnS QDs increase with increasing emission wavelength in a supralinear way, which is attributed to the energy transfer of dark excitons. On the contrary, the lifetime of two-photon fluorescence of bare and core-shell QDs decrease with increasing emission wavelength, and this indicates that the surface trapping is the dominant decay mechanism in this case.     

Tetraalkyl-substituted zinc phthalocyanines used as anode buffer layers for organic light-emitting diodes

Two soluble tetraalkyl-substituted zinc phthalocyanines(ZnPcs) for use as anode buffer layer materials in tris(8-hydroxyquinoline)aluminum(Al_(q3))-based organic light-emitting diodes(OLEDs) are presented in this work. The holeblocking properties of these Zn Pc layers slowed the hole injection process into the Al_(q3) emissive layer greatly and thus reduced the production of unstable cationic Al_(q3)(Alq_3~+) species. This led to the enhanced brightness and efficiency when compared with the corresponding properties of OLEDs based on the popular poly-(3, 4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT: PSS) buffer layer. Furthermore, because of the high thermal and chemical stabilities of these Zn Pcs, a nonaqueous film fabrication process was realized together with improved charge balance in the OLEDs and enhanced OLED lifetimes.     

Excitonic photoluminescence characteristics of amorphous silicon nanoparticles embedded in silicon nitride film

We have investigated the photoluminescence (PL) properties of amorphous silicon nanoparticles (a-Si NPs) embedded in silicon nitride film (Si-in-SiN_x) grown by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique. The PL spectrum of the film exhibits a broad band constituted of two Gaussian components. From photoluminescence excitation (PLE) measurements, it is elucidated that the two PL bands are associated with the a-Si NPs and the silicon nitride matrix surrounding a-Si NPs, respectively. The existence of Stokes shift between PL and absorption edge indicates that radiative recombination of carriers occurs in the states at the surface of the Si NPs, whereas their generation takes place in the a-Si NPs cores and the silicon nitride matrix, respectively. The visible PL of the film originates from the radiative recombination of excitons trapped in the surface states. At decreasing excitation energy (E_ex), the PL peak energy was found to be redshifted, accompanied by a narrowing of the bandwidth. These results are explained by surface exciton recombination model taking into account there existing a size distribution of a-Si NPs in the silicon nitride matrix.     

光诱导新型羧基芳基苄醚树枝配体周边取代酞菁锌(Ⅱ)配合物的分子内能量转移

通过紫外光谱法、稳态和时间分辨荧光光谱法比较,研究了光诱导新型1-2代羧基芳基苄醚树枝配体周边取代酞菁锌(Ⅱ)配合物的分子内能量转移。研究结果表明：1-2代羧基芳基苄醚树枝配体周边取代酞菁锌(Ⅱ)配合物主要以单体形式存在于二甲基亚砜中;在270 nm处树枝配体吸收峰强度随着树枝代数增加而增加,因此树枝配体的光捕获能力增强;树枝代数对酞菁核的荧光特性影响显著,随着树枝代数增加,荧光寿命和荧光量子产率降低;在270 nm激发,能量从外围树枝配体(给体)传递给酞菁核心(受体),这一过程中外围树枝充当能量肼的角色,随着树枝代数增加,分子内能量转移效率增大。因此,新型羧基为端基的芳基苄醚树枝酞菁锌配合物是一类新型光捕获天线结构的化合物。     

Coherent exciton-plasmon interaction in the hybrid semiconductor quantum dot and metal nanoparticle complex

We studied theoretically the exciton coherent dynamics in the hybrid complex composed of CdTe quantum dot (QDs) and rodlike Au nanoparticles (NPs) by the self-consistent approach. Through adjusting the aspect ratio of the rodlike Au NPs, the radiative rate of the exciton and the nonradiative energy transfer rate from the QD to the Au NP are tunable in the wide range 0.05-4 ns(-1) and 4.4 x 10(-4) to 2.6 ns(-1), respectively; consequently, the period of Rabi oscillations of exciton population is tunable in the range 0.6 pi-9 pi.     

Breaking the phonon bottleneck in semiconductor nanocrystals via multiphonon emission induced by intrinsic nonadiabatic interactions

We observe ultrafast 1P-to-1S intraband relaxation in PbSe and CdSe nanocrystals (NCs) that have distinct energy spectra. While ultrafast dynamics in CdSe NCs has typically been interpreted in terms of electron-hole energy transfer, this mechanism is not active in PbSe NCs because of sparse densities of states in the conduction and valence bands. Our observations of temperature activation and confinement-enhanced relaxation in PbSe NCs can be explained by efficient multiphonon emission triggered by nonadiabatic electron-phonon interactions and are indicative of large, size-dependent, intraband Huang-Rhys parameters.     

采用非绝热动力学模拟探究溶剂效应对桨-轮形状的给体-受体复合物的激发态弛豫动力学的影响

充分理解给体-受体复合物的激发态动力学在实验和理论上都具有非常重要的意义. 本文首次结合电子结构计算和非绝热动力学模拟,探索了最近合成的一个桨-轮形状的给体-受体复合物的光致动力学过程,该复合物由三个氟硼二吡咯基团和一个六氧杂并三苯构成. 根据计算结果,得出结论,桨-轮形状的给体-受体复合物共轭物在激发时将被提升到氟硼二吡咯片段的局部激发状态,然后发生超快局部激发电子态到电荷转移电子态的激子转移. 与先前实验工作中提出的光致电子转移机理不同,这种激子转移过程伴随着从氟硼二吡咯基团到六氧杂并三苯基团上的空穴. 此外,还发现溶剂效应在该体系的光致动力学中起着重要作用. 具体而言,强极性的乙腈溶剂加速了空穴转移动力学,这可以归因于溶剂对电荷转移状态的显著影响,即局部激发和电荷转移激子之间的能隙大大减小,而与此同时非绝热耦合增加,这两个因素都可以促进空穴转移过程. 目前的工作不仅为桨-轮形状的给体-受体复合物的潜在光诱导机制提供了有价值的见解,而且有助于未来设计具有更好光电性能的新型给体-受体复合物.     

新型可溶性酞菁的合成及谱学性质研究

近百年来,因为酞菁在信息等很多领域都有很广泛的应用,所以一直是科学家研究的热点课题。随着科技的不断发展,人类社会不断进步的需要,具有新功能的新式酞菁合成工作,依旧是酞菁科技工作者的目标。为此,改变合成路线,合成了新型的酞菁材料：4,8,15,22-四[3,3-4(羟苯基)-3H-异苯并呋喃酮]酞菁镍(铜),3-[3,3-二(4-羟苯基)-3H-异苯并呋喃酮]邻苯二腈分别与铜和镍盐反应,以正戊醇为溶剂,用1,8-二氮杂二环(5,4,0)十一碳-7-烯(DBU)为催化剂,在一定温度下合成4,8,15,22-四[3,3-二(4-羟苯基)-3H-异苯并呋喃酮]酞菁。通过对合成产物进行测定,证明合成物质是目标产物,并研究其相关紫外光谱, 荧光光谱和光致发光光谱的谱学性质。     

The Influence of Surface-Modification Technology on the Spectral Characteristics of Hydrophilic CdSe/ZnS Nanoparticles upon Interaction with Polyelectrolytes

The spectral and kinetic characteristics of CdSe/ZnS nanoparticles (NPs) surface-modified with cysteamine by two different methods are considered upon interaction with polyelectrolytes. With the use of steady-state and time-resolved fluorescence spectroscopies, it is shown that the fluorescence intensity and stability of NPs in the presence of polyelectrolytes depend on the surface-modification method. It is found that hydrophilic NPs obtained at the interface between two immiscible liquids (chloroform–water) are more resistant to aggregation.