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We report the results of our investigation of agarose gel electrophoresis and hybridization of mercaptopropionic-acid-capped quantum dots (MPA-capped QDs) conjugated with short single-stranded DNA, as part of a study of closely spaced linear QD chains. The electrophoresis results suggest that migration speed and separation resolution depend on the amount of MPA on the QD surface. The QDs separated by electrophoresis according to DNA valence, i.e., the amount of DNA per particle, were used as building blocks for the synthesis of linear QD oligomers.

We report our recent trials examining the single-molecule three-dimensional (3D) detection of protein conformational dynamics at room temperature. Using molecular chaperones as model proteins and cadmium selenide (CdSe) semiconductor quantum dots (QDs) as nanometer-scale probes, we monitored the temporal evolution of ATP-induced conformation changes with a total internal reflection fluorescence (TIRF) microscopy imaging technique in buffer solutions. The two-dimensional (2D) degenerate nature of the emission dipoles of the QDs, due to the uniaxial wurtzite crystal structure, made it possible to capture the 3D orientation using a polarization modulation technique in real time. The temporal resolution was half the period of analyzer rotation. Although still insufficient, the obtained signals suggest possible 3D detection of specific motions, which supports the two-step conformational changes triggered by ATP attachment., 18th International Conference on Dynamical Processes in Excited States of Solids (DPC2013), August 4-9，2013, Fuzhou, China

In this paper, we describe the synthesis and characterization of quantum dot (QD) chains. We used small QD-DNA conjugates, i.e., short-ligand-capped QDs conjugated with short (15-mers) single-stranded DNA, as the building blocks. The small conjugates were separated based on the valence of the DNA, i.e., the amount of DNA per particle, using agarose gel electrophoresis. The conjugates formed self-assemblies composed of closely spaced (inter-particle spacing of 0.6–2 nm) QDs. We report the results of our investigation of the electrophoresis and hybridization of the conjugation.

The results of room-temperature fluorescence lifetime measurements are reported for the excitation of J aggregates (Js) of pseudoisocyanine chloride (PIC-Cl) prepared in potassium polyvinyl sulfate (PVS) polymer thin films, their aqueous solutions, and NaCl aqueous solutions. Variations of the microscopic morphologies of the aggregates were investigated. The results show that fluorescence decay features correlated to the morphology change. The observed fluorescence lifetime and quantum efficiency of PIC J aggregates (PIC-Js) in a NaCl aqueous solution were 310 ps and 28%, respectively. The lifetime of the fibril-shaped macroaggregates prepared in PVS thin films was below the instrumental time resolution of 5 ps, and the efficiency decreased to below 3%. The results indicate that PIC-Js prepared with PVS polymers have an increased nonradiative contribution to the excitation deactivation process. In particular, macro-Js with isolated fibril-shaped structures revealed nonradiative pathway(s) that are closely associated to the specific packaging morphology of the constituent meso-Js. The possibility of a destructive effect on the formation of cavity-polaritons is also discussed.

Versatile novel implementations in microspectroscopy are developed, which can provide angle-resolved optical spectroscopy at local sample areas almost in diffraction limit. By selecting focus position of light flux incident within the back focal plane of the objective lens radially from the position of the optical axis of the microscope with employing off-centered pinhole, we can obtain parallel beam with oblique incidence and its angle tuning at the sample surface. In this paper, we describe our specific optical setup and its practical working principle in detail. We report, as a demonstration of its performance, our latest studies on optical properties of cavity polariton states in the so-called quantum microcavity structures, which contain molecular J-aggregates of pseudoisocyanine (PIC) dye as active working materials. By using the microscope technique, we obtain a fair amount of improvement in the linewidth observation of cavity polariton spectra.

We report single molecule spectroscopic evidence of FRET in CdSe quantum dot (QD) conjugated with Cy5-labeled molecular chaperone systems in buffer solutions. Donor QDs are core-shell type nanocrystals covered with organic surfactants on their outermost surfaces, i.e. CdSe/ZnS/TOPO’s. As prototype molecular chaperones, we adopt prefoldins (PFDs), on which Cy5’s are labeled as acceptors. Donor QDs possess two-fold degenerate emission dipoles perpendicular to the c-axis, due to their Wurtzite crystal structures, while acceptor Cy5’s possess linear absorption and emission dipoles. Thus, their combination provides novel features to those in conventional FRET systems. PFDs are jellyfish-shaped hexameric co-chaperones of group II chaperonins, which recognize hydrophobic portions of denatured proteins and encapsulate them within their central cavities. Hence, PFDs will also capture the CdSe/ZnS/TOPO QDs due to its surface similarity to the denatured proteins. By introducing simple microscope setup for single QD-PFD-Cy5 spectroscopy, we have successfully captured the emission spectra in FRET regime. We also have observed peculiar features in time evolution profiles of single QD emissions conjugated with Cy5-labeled PFDs under polarization modulation measurements. Notable point of our hybrid conjugates is that they are biochemically in living action. We describe our present results in relation to possible protein reactions.

擬イソシアニン(PIC)分子による J 会合体を分散させたポリマー薄膜を活性層とする平行平板型微小共振器を作製し，J 会合体の励起子と共振器光子の強結合状態としての「共振器ポラリトン」を形成した．独自に工夫した光学系を用いて反射および発光スペクトルの角度依存性を計測し，偏光依存性，共振器ミラー依存性，活性層の J 会合体濃度依存性などとあわせ，室温でも安定で明瞭なポラリトン状態の生成を確認し，その特徴を精査した．加えて，顕微計測を応用した局所角度分解分光法を考案し，その動作を確認するとともに，J 会合体の高濃度極限の一形態とも考えられる「フィブリル構造」J 会合体のポラリトン状態の検証に向けて，その手法の適用を開始した．室温で安定な共振器ポラリトンの形成は，無機半導体の量子微小共振器では十分に達成し得ていない優れた特徴であり，J 会合体の有機半導体光ナノ材料としての優位性を示す好例である．無機半導体 QW による共振器ポラリトンとの比較の上で，その実体と将来性についても議論する．

We have investigated reflection properties of light-matter strong coupling in a planar metal-mirror microcavity with highly concentrated PIC J-aggregates. Large vacuum Rabi-splitting ranging from 100 to 250 meV is obtained depending on the concentration of the J-aggregates. The factors for providing these large Rabi-splitting will be discussed based on its concentration dependence. We also present our recent study focused on microscopic reflection properties of the microcavity. We have improved microscope optics which enables us to measure local reflection spectra within 0.3- μ m-diameter area. Observation of incident-light-angle dependence becomes possible. We found existence of micrometer-scale inhomogeneity in the Rabi-splitting (e.g. ± 10 % in a 17 μ m × 17 μ m region), which will be interpreted mainly by the spatial distribution of J’s in the active layer.

Resonant energy transfer in hybrid CdSe quantum dot (QD) conjugated with Cy5-labelled molecular chaperone systems is observed with single molecule imaging technique. Photonic QDs are the core-shell type nanocrystals covered with organic surfactants on the outermost surfaces, i.e. CdSe/ZnS/TOPO's, and prefoldin (PFD) is used as prototype molecular chaperons. PFD is a jellyfish-shaped hexameric co-chaperone of group II chaperonins, which recognize hydrophobic portion of denatured proteins and encapsulate them within its central cavity. So the CdSe/ZnS/TOPO QDs can also be captured be cause of its surface similarity to the denatured proteins. We have found one possible reaction pathway to get such artificial complex in aqueous solutions with keeping bioactivities of the proteins. Performance of the complex is evaluated by TIRF imaging microscopy. As the proteins are transparent in visible wavelength region, labeling dyes, Cy5, which also work as acceptors, are connected to detect their behaviors microscopically. Forster type energy transfer is observed from the QD donors to Cy5-labeled PFD acceptors in single molecule level, which can be a distinct evidence for the complex formation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present a study of strong exciton-photon coupling and its dependence on incident light polarization in a metal-metal mirror microcavity containing PIC J-aggregates. Rabi-splitting energies between upper and lower polariton branches are estimated as 94 meV and 69 meV for s- and p-polarized incident light, respectively. These large values are due to large oscillator strength of Frenkel excitons in the PIC J-aggregates and strong confinement of light attributed to the metallic microcavity as well. As for the effective thickness of the active layer for s-polarized light, a good agreement is obtained between Lfiteff = 201 nm deduced from the experimental data and Lcalceff = 207 nm calculated from the summation of the measured thickness of active layer with the estimated penetration depths into silver mirrors. We also discuss the difference in the polarization dependences of Rabi-splitting energy, quantitatively. It is concluded that the polarization dependence is mainly due to an alignment of the J-aggregates in the active layer and is not affected so much by anisotropy of the penetration depths into the silver mirrors. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We describe our improved synthesis and optical properties of high quality type II CdTe/CdSe nanocrystals (NCs). Specifically, clear shell-thickness dependences have been observed in the absorption and photoluminescence (PL) spectra and PL decay profiles as well. The magnitude of the lowest absorption band decreases drastically with large redshift as the shell thickness increases. The origin will be discussed on the bases of the model where the spatial configuration of the lowest electron-hole pair in the NCs changes from that of type I to type II as the shell thickness increases. As for the PL lifetime of the lowest electron-hole excitations, substantial increase is observed with increasing shell thickness. This can also be understood by considering the spatial configuration; spatial overlap between electron and hole wavefunctions decreases with increasing shell thickness, thus the lifetime increases. As for the NCs with extremely thin shell (∼1 ML; 1 ML = 0.35 nm), the PL lifetime seems much longer than expected. This suggests that the thin shells seem imperfect and work rather a kind of trap sites than layers. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present our recent study of microscopic single-molecule imaging on the artificial complex of tetramethylrhodamine linked with a propyl chain onto silica glass surface, i.e. an asymmetric fluorescence resonance energy transfer (FRET) structure with non-radiative acceptor. In the synthesis of the complex, we used a mixture of two kinds of isomers to introduce rather small photodynamic difference among them. This isomeric structure change will provide more or less a distinctive photophysical change in e.g. non-radiative relaxation rate. Our recent observation at room temperatures, so far, shows that such contributions can be discriminated in the histograms of the fluorescent spot intensities; broad but distinctive multi-components appear. To identify the isomeric difference as a cause of structures, some configurational assumptions are necessary. One such basic prerequisite is that the transition dipoles of the chromophores should be oriented almost parallel to the glass surface. In order to make clear the modeling, we also provide preliminary experiments on the polarization dependence of the imaging under rotating polarization in epi-illumination.

We report here the distinctive modifications of photoluminescence (PL) behaviors in single CdSe/ZnS/TOPO nanocrystals depending on their environments. Long-time traces of PL intensity from single nanocrystals have been obtained in both vacuum and a wet nitrogen atmosphere. While all of the nanocrystals in both environments exhibit PL blinking behaviors, i.e. on–off intermittency of PL intensity, as usual, some of the nanocrystals in the wet nitrogen atmosphere show significant increase in duration time of on-events. As for the duration time of blinking off-events, it is for the moment associated with the occasional events of carrier capturing at trap sites on or near the nanocrystal surfaces. We propose a model in which adsorbed water molecules at the trap sites on the nanocrystal surfaces transform them under light irradiation, which eventually decreases the occurrence of the trapping events due to their inactivation. It in turn increases the PL on-times. In addition to the drastic modification of the blinking profile, we also found that in the PL time traces some kinds of undulated behaviors, i.e. continuous and rather low frequency fluctuation of PL intensity, appear during each on-event in vacuum while they disappear totally in the wet nitrogen atmosphere. These results are also described on the basis of the inactivation model of the trap sites introduced above.

Feasibilities to stabilize CdSe/ZnS/trioctylphosphineoxide (TOPO) nanocrystals (quantum dots, QDs) in aqueous solutions with prefoldin macromolecules in their bioactive states are reported. Prefoldin is a jellyfish-shaped hexameric co-chaperone of the group II chaperonins. As a protein folding intermediate is captured within its central cavity, so CdSe/ZnS/TOPO QDs would also be included within this cavity. It is also found the QDs can be much more dispersed in aqueous solutions and suspended for certain period of time by adding trace amount of t-butanol in the buffer prior to the mixing of the QDs mother solution. While biochemical procedures are evaluated with ordinary fluorescence measurements, possible complex formations are also evaluated with TIRFM single-molecule detection techniques.

We have investigated photobrightening effects of photoluminescence (PL) from CdSe/ZnS/TOPO nanocrystals (NCs) in ambient nitrogen gas saturated with water molecules (H 2 O/N 2 ). The PL intensities from NC ensemble samples increase more than twice after 1200-s irradiation of cw light. These increases mostly recover to their previous values under continuous light irradiation when we evacuate the H 2 O/N 2 atmosphere. These results indicate that the adsorption of H 2 O molecules onto NC surfaces provides some functions as to restore almost reversibly the PL-quenching defects or trap sites on or near the NC surfaces. To elucidate the mechanism of this restoring function microscopically, we have also measured time evolution of PL intensity profiles from single NCs both in H 2 O/N 2 and in vacuum. While blinking behaviors of the PL intensity being observed in both environments, we have found significant increase of PL on-times in case of single NC observations in the H 2 O/N 2 compared with those in vacuum. As for the blinking off-times, it is for the moment associated with the occasional events of carrier captures at the trap sites on or near the NC surfaces. Thus, we propose the photo-adsorption of H 2 O molecules inactivates these trap sites and decreases the occurrence of the capturing events, which in turn increase PL on-times and eventually provide the photobrightenings.

We present our recent study of single fluorescent molecules with specific structure, i.e. tetramethylrhodamine derivative linked with a propyl chain onto silica glass surface. For fluorescent reagent in its synthesis, we used a mixture of two kinds of isomers, which provides a sample with single molecules photophysically different each other even if chemically the same. The isomeric structural difference so introduced in the molecules will provide rather small but probably distinctive photophysical difference, for example, in non-radiative relaxation rates, which we try to detect out with our improved single-molecule microscope imaging technique. To make clear the detectability of such weak inter- or intra-molecular interactions microscopically is significant for versatile applications of single-molecule detections in life science. Our present observation at room temperatures shows so far that such decoupled contributions can be discriminated in the histograms of the intensities of the observed fluorescent spots as broader but separated multi-component structures in the distribution under specific experimental configurations. We will discuss some of the prerequisite for such detections; suitable spatio-temporal resolutions with sufficient S/N ratio, algorithms for data analysis, etc. but also precise sample operations are inevitable.

We have investigated photoluminescence (PL) properties of CdSe/ZnS/TOPO nanocrystals (NCs) in various kinds of gases at one atmospheric pressure. Increase of PL intensity with spectral shift is observed under 488 nm cw light irradiation in all cases. Especially, the PL intensity increases more than twice after 1200 s irradiation in nitrogen gases saturated with vapor of polar molecules, such as H2O and NH3. The increased PL intensity with the spectral shift mostly recovers to its previous values when the sample is evacuated under continuous light irradiation. These results indicate that photo-adsorption of the polar molecules onto NC surfaces provides some reversible restoring functions to the PL quenching defects or trap sites on or near the surfaces. The existence of the trap sites on NC surfaces is already widely introduced for describing e.g., blinking phenomena. Assuming part of these traps being charged, we propose the photo-induced effects can be understood as charge-compensated inactivation of the trap sites due to the adsorption of the polar molecules consistently.

Results on microscopic fluorescence imaging and spectroscopy of fibril-shaped J-aggregates of pseudoisocyanine dyes prepared in thin film matrices of polyvinyl sulfate (PVS) are reported compared with simultaneous observation of the reflection micro-spectroscopy. While the shape of the local reflectance spectra show huge broadening and sometimes dip structures at higher local reflectance levels, we have found that local fluorescence spectra are rather simple and narrow single peak appears at 572 nm or bit longer which is almost coincide with that of ordinary J-band. The result is not inconsistent with the exciton–polariton onset scheme, based on which initial reflectance properties are interpreted. Anomalous local polarization dependences are also observed in fluorescent transition dipoles as in the local reflectance observation, indicating the anomaly is inherent to the fibril formation.

To optimize far-field detection optics as well as to extend fundamental skills related to molecular manipulation, samples for single molecule fluorescence detection are fabricated by chemically immobilizing rhodamine-6G derivative molecules on a silica glass surface. While the dye molecules are bleached out within several 10s to 100s of seconds in air as usual, the sample as well as far-field detection system works efficiently. The histogram of the integrated counts of the individual fluorescent spots in the observed images indicates that most of the spots observed involve single chromophores for each spot. The histogram also indicates that there exist two kinds of distinctive molecular sites in the immobilized samples, whereas only single site is detected in the rhodamine-6G spin-coated samples. We consider so far that the existence of the two sites may correspond to the local molecular configurations caused by the mixture of two types of isomers in the cross-linked chromophores. Observation of blinking profiles is also described.

有機分子の配位結合によって結晶表面を封止したCdSeナノ結晶の合成法, および, ナノ結晶表面におけるZnS積層膜作製法の最適化を行い, 吸収・発光測定と高分解電子顕微鏡撮影 (HRTEM) より試料の評価を行った. その先鋭な吸収・発光バンドは, サイズ分散の狭さと結晶性の良さを示しており, HRTEM像からもこの事実が確認できる. また, 最適化により, 常に発光量子効率が室温で50%を超えるナノ結晶の作製が可能となった. この試料を用いて, 自作走査型レーザー顕微鏡で単一ナノ結晶の発光強度時間変化を観測したところ, 突然の激しい発光強度の乱高下や, 光照射に伴う発光明滅周期の増加などを示すこれまでの報告にないナノ結晶が多数観測された. その原因を究明するため, メゾスコッピックな系といえる1000個程度のナノ結晶の集団からの積分発光強度を測定し, その光照射効果を測定したところ, 通常のナノ結晶とは逆の光照射に伴う発光強度の増大が確認され, その増大はナノ結晶周辺の気体雰囲気の種類に依存することが明らかになった. 以上の単一とメゾスコピック系におけるナノ結晶の異常な発光の振舞いは, 気体分子の光吸着がナノ結晶表面の無輻射緩和中心に対して封止効果をもたらすことに起因すると考えられる.

Results on microscopic reflection imaging and spectroscopy of fibril-shaped J-aggregates of pseudoisocyanyne dyes prepared in thin film matrices of polyvinyle alcohol (PVA) are reported. We have found that formation of fibril-shaped structures with sub-micron widths is also possible in PVA. Despite the aggregation mechanism should be different from those in polyvinyl sulfate, reflection images and local spectroscopy show that the exciton–polariton characters are basically similar in the two matrices. Anomalous polarization dependence is also observed in PVA and seems rather strengthened.

Results on microscopic reflection imaging and spectroscopy of J-aggregates of pseudoisocyanine dyes in thin film matrices of polyvinyl sulfate, polyvinyl alcohol and polystyrene are reported. Despite different aggregation mechanisms in the three polymers, reflection images show formation of similar, highly reflecting fiber-like nanostructures in all samples. Local reflectance spectra reveal large inhomogeneities of local optical properties that are determined by an onset of exciton–polariton character.

Recent results of two types of mesoscopic-structured excitonic systems are reported. First is the synthesis of CdSe and CdSe/ZnS nanocrystals by pyrolysis of organometallic reagents in coordinating solvents TOPO-TOP and/or TOPO-TOP-HDA mixtures and their optical properties are characterized. Microscopic passivation by ZnS overcoating provides enhancement of their radiative recombination process, i.e. maximum quantum efficiency reaches over 50% for the moment. To increase the range of the sizes of obtained nanocrystals, 2-step injection of Cd/Se precursors seems effective. The second is J-aggregates by PIC-Cl dye molecules prepared in thin PVA polymer films. In specific condition, also in PVA as in ionic PVS, coherent J-segments seem gathered together to form sub-micron width fibril-like structures. Microscopy and spectroscopy of individual fibril structures are described.

The synthesis of semiconductor nanocrystals (CdSe) by pyrolysis of organometallic reagents and their optical properties are reported. By controlling the relative amount of precursors to be injected into the coordinating solvent, e.g. TOPO, we have modified the sizes and quality of nanocrystals successfully, the spectrum of which shows fairly sharp excitonic spectral features even in a limited size range. Passivation with overcoating ZnS provides a large enhancement of the fluorescence intensity, i.e. quantum efficiency reaches over 50% at room temperature in the best case. To prepare nanocrystals larger than ∼4.0 nm, 2-step injection of CdSe precursors seems suitable, where some amount of TOPO is added separately to the reaction vessel prior to the secondary injection. With this additional process ZnS-overcoated CdSe nanocrystals of high quantum efficiency can be obtained with high reproducibility.

Controls of mesoscopic structure of organic dye molecules such as formation of the J-aggregates are important for the purpose of achieving highly efficient and ultrafast nonlinear-optical properties. Squarylium dyes with alkyl substituents form J-aggregates with highly ordered two-dimensional structure in their monomolecular layer on water surface (Langmuir film). By absorption saturation measurement using femtosecond pump-probe method, 30 times larger and 10 times faster optical responses than their solution in chloroform were observed for the J-aggregates. We also succeed in transferring the Langmuir film on a glass substrate for a LB-film using post surface coating by poly-purfluorocarbon. This LB-film, which preserves two-dimensional structure, also exhibited similar femtosecond responses to the Langmuir film.

We report our recent observations on anomalous reflection properties of organic microcavity containing PIC J-aggregates in fibril-shaped structures as one of their highest-density limiting case. Even in ordinary low density PIC-Js dispersed in polymer matrices, they easily go into the exciton-photon strong coupling regime and new quantum states, i.e. exciton-polaritons, are formed. Vacuum Rabi-splitting, an indicator of the coupling strength, can be controlled by the density of PIC-Js in the microcavities in low density regime. Fibril-shaped PIC-J aggregates are bundle-like, self-assembled higher-order structure of Js and are considered as a high-density limiting case. Angular dependence of the local reflection spectra are observed by our improved microscopy. While in the low density cases, clear anti-crossing behaviours of the two branches appear, which is the evidence of the polariton formations, the highest-density limiting cases show one or two anomalous reflection dip structures with almost no angular dependence. The result is inconsistent with neither ordinary polariton reflection property nor bare exciton nor cavity photon properties. We tentatively consider that the anomaly is inherent to the fibril formation and is caused by possible breakdown of polariton coherence due to the inter-fiber energy transfer. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

TOPO (trioctyl phosphine oxide) capped-CdSe nanocrystals were prepared chemically by injecting organometallic reagents into a hot coordinating solvent over a range of optical absorption peaks of 482 ~580 nm . For limited size range of nanocrystals, we have succeeded to synthesize high quality nanocrystals which show fairly sharp excitonic spectral features, by controlling the particle size with the concentration of precursors. Overcoating of ZnS following the synthesis of CdSe nanocrystals have lead to a large enhancement of the fluorescence intensity (quantumefficiency).

Highly reflecting nanostructures of pseudoisocyanine J aggregates in a thin polymer film are prepared. Simultaneous atomic force microscope and reflection microscopic studies show a high degree of correlation between structural and optical properties on submicrometer scales. As a result of strong coupling between light and the aggregate excitonic states, optical modes evolve in the polariton-like reflectance spectra of the aggregate nanostructures which function as self-assembled optical microcavities.

Modulation of the polarization state of incident light in reflection microspectroscopy is used to study locally the orientations of exciton transition dipole moments of fiberlike nanostructures of J-aggregates of pseudoisocyanine dyes. The lowest exciton state assumes a wide range of directions with respect to the long axis of the fibers, from parallel to perpendicular. This behavior is correlated with the onset of polariton-like character of the local reflectance spectra. The results imply that a new structural model has to be conceived to explain the observed phenomena.

Photoluminescence properties were measured for vacuum-deposited thin films of magnesium, chloroaluminum, bromoaluminum, and metal-free phthalocyanines (MgPc, AlClPc, AlBrPc, and H2Pc). For MgPc, Al...

We present results on reflection microscopy and local spectroscopy of J-aggregates of pseudoisocyanine dyes in a thin film polymer matrix. Local reflectance spectra reveal a wide distribution of optical properties within different locations of one sample. The spectral lineshapes and absolute reflectivities are suggested to originate from varying strength of exciton-photon interaction. Polarization dependence measurements of local reflectivities at different wavelengths provide orientations of the excitonic transition dipole moments with respect to the orientation of the aggregate fibers.

We report a recent study on photoluminescence (PL) properties of CdSe/ZnS/TOPO nanocrystals (NCs) in a planar full microcavity composed of top and bottom two metal (Ag) mirrors, and also in a similar structure but without top mirror, i.e. half-microcavity, respectively. Angular-dependencies of PL spectra and PL decay curves have been measured to investigate PL modifications due to light-matter coupling in the microcavities. Obtained results indicate that PL dynamics are drastically changed depending on the microcavity structures. In the full-microcavity, PL emission is directed at particular angles and its decay-time is shortened, both of which can be described in terms of so-called Purcell effect, i.e. the interaction between photon-modes and confined excitons in the NCs. As for the half-microcavity, anomalous PL band appears at low energy side of a main PL band associated with the confined excitons. The origin of the anomalous PL will be interpreted as due to the interaction between specific photon-modes in the half-microcavity structure and excitons associated with surface states. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report results on reflection microscopy and local spectroscopy of aggregates of pseudoisocyanine chloride prepared in thin film of polyvinylsulfate. The aggregates assemble into fiber-like structures of relatively high reflectivity of up to 20%. Locally, the fibers show a large variety of reflectance spectra from sharp peaks at the position of the absorption J-band to broad bands with further structures near their maxima. Polarization experiments confirm that transition dipoles responsible for the J-band are oriented along the fibers. A simple theoretical model taking into account polariton-like excitations and finite dimensions of the fibers is used to simulate the experimental results.

We report red PL and EL properties of a reduced porphyrin, tetraphenylchlorin (TPC). In monomer solution TPC emitted a red PL band at 655 nm. In solid mono-film TPC emitted a red PL band at 660 nm but it also emitted two far-red PL bands at 725 and 750 nm due to aggregated emission sites in the film. EL devices in which TPC were doped at concentrations of 1.6–3.7 wt.% within an Alq 3 host layer showed red EL color due to a 660-nm emission of TPC monomer with a width of 20 nm. The red-emitting devices using α-NPD as a hole-transport layer had maximum luminance higher than those using TPD did. Among the red devices, we obtained a maximum luminance of 520 cd/m 2 with chromaticity coordinates of x =0.620 and y =0.31.

Inner structure of isolated intact chloroplasts was observed for the first time by a method of laser scanning microscopy at the temperature of liquid nitrogen at 77 K. The microscope, based on gradient index optics, has a maximum resolution of 440 nm at the wavelength of 650 nm. Chloroplasts were excited into the Q-band of chlorophyll b by a krypton laser line at 647.6 nm and fluorescence was detected using two different interference filters. The 680 nm interference filter detects the regions where photosystem (PS) 2 mainly occurs, the 730 nm interference filter detects domains with predominant location of PS1. Since PS1 occurs mainly in stroma lamellae, whereas PS2 occurs mainly in grana regions we were able to view the structure of thylakoid membrane in isolated intact chloroplast that is the closest to in vivo state.

We report on a design of a laser scanning solid immersion microscope based on gradient index optics that is suitable for low-temperature excitation spectroscopy on the single molecule level. Further, we present a hole-burning study of a system consisting of molecular J-aggregates and associated trap states. These two studies are pre-requisites for microscopic high-resolution excitation spectroscopy performed on individual fibers of J-aggregates of pseudoisocyanine in a polymer film. Preliminary results of the microscopic study are further compared with microscopic reflection spectroscopy measured on identical systems at room temperature.

Fabrication and femtosecond nonlinear optical response of Langmuir−Blodgett (LB) films with two-dimensional J-aggregates are described. Single-layer LB-films were deposited on glass substrates from mono-molecular layers of squarylium dye J-aggregates at an air−water interface (Langmuir film). To obtain LB-films containing J-aggregates, deposition of the Langmuir film with compression slightly in excess of that required for monolayer occupation was necessary. Coating the surface of the LB-films with a glassy perfluorocarbon polymer soon after deposition was effective in enhancing the formation of J-aggregates and stabilizing their structures. The LB-films of squarylium dye J-aggregates exhibit a single J-band at 783 nm with an extremely large absorbance of 0.2/monolayer, which is comparable to that of the Langmuir films. The morphology of J-aggregates in the LB-films was characterized by transmission images obtained using a near-field scanning optical microscope (NSOM) at a resonant wavelength of 780 nm. T...

A scanning optical microscope for low temperature imaging and spectroscopy with a gradient index rod-shaped microlens as an objective lens is presented. The solid immersion effect enhances the resolution to 310 nm of the full-width at half-maximum at the wavelength of 545 nm. Laser scanning mechanism located outside an optical cryostat enables to achieve large scanning ranges independent of temperature. The performance is demonstrated at 1.6 K on single molecules of terrylene in a dodecane crystal and on molecular J aggregates in thin polymer films.

Fibril-shaped J-aggregates of pseudoisocyanine dyes are prepared in thin-film matrices of polyvinyl sulfate and their microscopic fluorescence and reflectance imaging are investigated at room temperatures. Improved experiment, both in sample preparations and in microscope optics, allows us to resolve the higher-energy bands in the spectrum and to determine the directions of local absorption and fluorescence transition dipoles more precisely. Based on the anisotropies of the local transition dipoles, we have assigned the 540 nm middle band to be the upper exciton, Davidov split, transition and the higher 495 nm to its vibronic sub-band, while the J-band at 572 nm to be the lower Frenkel exciton transition. Assuming linear chain directions of individual J's to be parallel in average to the long axis of the fibril, the result also implies that a zigzag-type molecular conformation is most suitable for the model of PIC-J aggregates.

Recombination dynamics of intense near-UV luminescence from In x Ga 1− x N ( x ⩽0.1) ternary alloy epitaxial layers, especially from Si-doped ternary alloy layers, has been studied by means of time-resolved spectroscopy. The intensity of the near-UV luminescence from Si-doped layers was approximately one order of magnitude stronger than that from undoped layers. Furthermore, an additional sharp luminescence line was observed under high-density excitation only from the Si-doped layers. The effects of Si-doping on the optical properties of In x Ga 1− x N layers are discussed.

By analyzing the mechanism of J-aggregate formation with a squarylium dye on the water surface, we succeeded to obtain a mono-molecular layer with an extremely large optical density (>0.3). Because of the homogeneous and fine structure of this film, an ultrafast nonlinear optical response exhibiting a two-dimensional mono-molecular layer nature was observed at room temperature.

A silicon phthalocyanine (Pc) compound PcSi[OSi(CH3)3]2 in solid phase emitted a relatively intense fluorescence as compared with other solid Pc compounds. At room temperature fluorescence spectrum of the solid SiPc had three major bands peaking at 715, 781 and 840 nm, and total fluorescence yield was estimated to be ∼10−2, which was about 1/20 of that of solution. Different time-resolved decay profiles of these bands proved that the fluorescence had at least two emission origins. With decreasing temperature fluorescence intensity and spectrum changed drastically. In particular, below 60 K the 715 nm band became quite sharp and intense. Total intensity at 5 K was about ten times as large as that at 300 K.

Low temperature excitation spectra of pseudoisocyanine J-aggregates in poly(vinyl sulfate) thin films on sub-micron scales are presented. Individual J-aggregates are located by scanning microscopy using a gradient index SELFOC lens. The excitation spectra show large inhomogeneous broadening with super-imposed statistical fine structure.

A broad fluorescence band red-shifted from the absorption line of J-aggregate of pseudoisocyanine chloride in thin films of poly(vinyl sulfate) has been investigated. The fluorescence originates from traps populated by energy transfer from the excitonic band of the J-aggregate. The shift of the fluorescence maxima and the decrease of its intensity with increasing temperature have been explained by interaction of the trap with a 39 cm-1 phonon mode. Spectral hole burning study shows that the traps are functionally associated with the whole J-aggregate fiber rather than with individual coherently coupled segments of the aggregate.

Two-photon absorption processes of biexcitons in ZnS-based quantum-well structures have been studied by means of photoluminescence excitation spectroscopy. The peak position of two-photon absorption of biexcitons was dependent on the detected energy position in the photoluminescence excitation measurement. The energy difference between the one-photon exciton resonance and the two-photon biexciton resonance increased as the detected energy position was moved towards the lower-energy side of the biexciton luminescence. This result indicated the biexciton localization and the resultant increase in the biexciton binding energy.

Luminescence dynamics of Si-doped In x Ga 1-x N epitaxial films has been studied by means of time-resolved luminescence spectroscopy at low temperature. Under the band-to-band excitation the recombination dynamics shows a typical model of exciton localization in ternary alloyed mixed crystals and/or donor-induced luminescence centers. With the increase of the excitation density the sharp luminescence band appears from the high-energy side of the luminescence peak. The sharp peak shifts to the low-energy side as time proceeds. The observed feature can neither be explained by the usual models of biexciton nor by a electron-hole plasma.

Excitonic structure of J-bands of pseudo-isocyanine bromide J-aggregates in WEG glasses at 4.7 K has been investigated by persistent spectral hole burning. Clear crossover of hole line shape was observed in the intensity dependence of pulse laser burning (7ns, 10-Hz repetition). With decreasing the intensity the line shape changes from non-resonant red-shifted (∼3 cm -1 from the laser frequency ω B ) broad hole to resonant sharp hole, which is similar to those obtained by cw-laser. With cw-laser light for burning, clear zero-phonon hole was formed with the width of 0.36 cm -1 . The hole profile seems strongly dominated by the peak intensity of the burning light. We proposed the existence of the crossover is due to switching from the |1-ex state resonance by one-photon absorption to the |2-ex state resonance by two-photon absorption using real dipole-allowed |1-ex state. The model provides the offset of the hole is equal to half of the difference of k = 2 and k = 1 exciton energy, from which we can deduce a coherence length N = 56 as typical order of magnitude. Further experiments are described, which basically support the interpretation.