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Abstract: We report the synthesis, characterization, and photoluminescence (PL) properties of colloidal I-III-VI2 CuInS2 and CuInS2/ZnS nanocrystals (NCs). Absorption shoulder and PL bands of the NCs are located at higher energy than those of band gap energy of bulk crystals due to a quantum-confinement effect. The PL band has a relatively large Stokes-shift, broad linewidth, and long decay-time, which suggests that the PL originates from a recombination of confined-excitions associated with donor(s) and/or acceptor(s). We found that quantum yield of the PL depends strongly on the photon-energy of excitation light and that it is up to 40-50% in resonant excitation at the energy positions corresponding to the absorption shoulder. Detailed properties and possible dynamics will be described. We also present preliminary results of PL properties focused on single NCs. There exist highluminescent NCs exhibiting so-called PL blinking as similar with II-VI NCs, while the others are dark NCs. 73.21.La, 78.47.jd, 78.67.Bf, 78.67.Hc [Copyright &y& Elsevier]

Planar microcavities containing pseudoisocyanine (PIC) J-aggregates dispersed in PVS polymer matrices are prepared and the formation of exciton-photon strong coupling states, so-called cavity-polaritons, are investigated by angle-resolved reflectivity and photoluminescence spectroscopy at room temperatures. The polarization of incident light, structure/materials of cavity mirrors and concentrations of J-aggregates are systematically changed and their optical properties are inspected in detail. Moreover, a custom-made microspectroscopy illumination system allowed us to obtain detailed angle resolved optical properties in local-area regime with diffraction-limited resolution. We confirmed the stable and well-defined formation of the polariton states even by Ag-Ag mirrors at room temperature, which is hard to achieve by present inorganic semiconductor nanostructures. Based on these findings, peculiarities of PIC-J aggregates as nano-scaled constitutions are described. We also describe briefly the optical properties of so-called fibril-shaped PIC-J aggregates associated with polariton formation as well as a possible high-density limiting case of J-aggregate-based opto-organic materials. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Photobrightening and photobluing effects of photoluminescence (PL) from CdSe/ZnS/TOPO nanocrystal ensembles, i.e. ca. 1000 nanocrystals, have been investigated in several environments. The PL intensity increases more than twice with blue shift under continuous light irradiation in a wet nitrogen (H2O/N2) atmosphere, while in a pure nitrogen atmosphere and vacuum their behaviors are nothing particular. In addition, increasing rates of both the brightening and bluing effects in the H2O/N2 atmosphere depend on irradiation intensities. These results suggest that both effects should be associated with photo-adsorption of water molecules onto nanocrystal surfaces. As for the brightening effect, we propose that the photo-adsorption of water molecules provides some restoring functions to PL-quenching defects or trap-sites on or near nanocrystal surfaces. On the other hand, the origin of the bluing effect is not clear from the results of the ensemble measurements. To get further insight into the bluing effect, PL spectra from single nanocrystals are measured under continuous light irradiation in cyclic environments in which the H2O/N2 atmosphere and vacuum are alternating. As a result, blue-shifted PL induced by the light irradiation in the H2O/N2 atmosphere recovers almost to its initial one reversibly under evacuation. The mechanism of the photobluing effect will be discussed also on the bases of the photobrightening model introduced above. [Copyright &y& Elsevier]

Abstract: We have investigated photobrightening effects of photoluminescence (PL) from CdSe/ZnS/TOPO nanocrystals (NCs) in ambient nitrogen gas saturated with water molecules (H2O/N2). 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 H2O/N2 atmosphere. These results indicate that the adsorption of H2O 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 H2O/N2 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 H2O/N2 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 H2O 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. [Copyright &y& Elsevier]

Abstract: 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 488nm cw light irradiation in all cases. Especially, the PL intensity increases more than twice after 1200s 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. [Copyright &y& Elsevier]

We describe the synthesis of capped-CdSe and capped-CdSe/ZnS nanocrystals and their characterization by micro-spectroscopy of their optical properties as well as high-resolution transmission electron microscope (HRTEM) observations. The narrow spectral bandwidth of absorption and photoluminescence (PL) indicates that the size distributions of the nanoparticles are satisfactorily narrow and that the nanoparticles are nanocrystals, which is confirmed by HRTEM observations. Passivation with overcoating ZnS provides a large enhancement of the photoluminescence intensity, i.e., quantum efficiency reached over 50%. PL observations emitted from the luminescent single nanocrystal are carried out using our custom-made laser scanning optical microscope. A large number of nanocrystals show anomalous on-and-off behavior of their PL. To investigate an origin of the anomalous behavior, we measured integrated PL intensity emitted from over 1000 nanocrystals. As a result, the enhancement of PL intensity is observed with increasing exposure time of excitation light depending on the kind of gases. These photo-induced phenomena are interpreted by the model that the nanocrystals are passivated by the polar molecules, especially water. [ABSTRACT FROM AUTHOR]