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We demonstrated that radiative recombination rate of CdSe/ZnS nanocrystal quantum dots is enhanced by local surface plasmon of an adjacent Au layer as a consequence of the Purcell effect. I...

A green emitting Ba1.98SiO4−δN2/3δ:Eu0.02 phosphor with an appreciable intensity was synthesized using the gas-reduction–nitridation (GRN) method. SEM revealed agglomerated Ba1.98SiO4−δN2/3δ:Eu0.02 particles with irregular morphologies and a primary particle size of 1–2.5 μm. The phosphor showed emission lines of Eu2+ corresponding to the 4f65d1 → 4f7 transition under 370 nm excitation. As the GRN process was conducted to incorporate N3− into the lattice, both the excitation and emission intensity of Ba1.98SiO4−δN2/3δ:Eu0.02 were enhanced greatly compared to Ba1.98SiO4:Eu0.02. The decay time of Ba1.98SiO4−δN2/3δ:Eu0.02 showed that N entered the Ba1.98SiO4:Eu0.02 lattices to replace O to form a NO point defect. The electroluminescence intensity of Ba1.98SiO4−δN2/3δ:Eu0.02 at 503 nm increased with increasing forward bias current. Intense green LEDs were fabricated by coating the synthesized phosphors on the cap of the near-ultraviolet InGaN LEDs (λem = 375 nm). Overall, this phosphor appears to be a promising candidate for solid-state lighting applications.

We demonstrate that the Stimulated Emission Depletion (STED) concept, which is usually invoked for fluorescence, can be extended to photoacoustic effects. When two-nanosecond pulses of exciting and stimulating light are synchronized, 80% of the acoustic signal generated through excited state absorption (ESA) can be quenched. Regarding the cross-sections for stimulated emission and ESA, a model gives a good order of magnitude in the depletion efficiency. The transient molecular orientation, usually measured via the fluorescence anisotropy, can be accessed in photoacoustic when STED is implemented.

We report all-optical polarization switching based on resonant excitation of spin-polarized e-h pairs in CdSe nanocrystal quantum dots at room temperature. Pump-probe experiments have been performed using the same and the opposite configurations of circular polarizations. Comparing the co- and the cross-circular polarization cases, it is quite evident that selectively-excited spins are flipped to a balanced state within 1 ps and that during this time, the two spin states are equally populated. The all-optical switching results are found to be in close agreement with pump-probe experimental results. The optical switching technique proposed in the present investigation should be extremely useful for future ultrafast terabit communication systems.

The optical modal gain spectrum for a ZnO thin film was measured by using a variable stripe length method. Using the dierential equation for amplified spontaneous emission in a stripe geometry, we obtained stripe-length-dependent gain spectra, which enabled us to investigate the gain saturation in long stripe lengths. When the stripe was shorter than the saturation length, our analysis was in a good agreement with the gain obtained by commonly-used analysis [1]. For intermediate density ( nMott). Both gains saturate with increasing stripe length, but the electron-hole plasma becomes relatively dominant for long stripe lengths ( 1000 µm) while the exciton-exciton scattering is relatively suppressed. This result suggests that exciton-exciton scattering gain saturation is more vulnerable to increase in the stripe length increase since the excitonic stimulated emission occurs on a coherence scale of the localized area.

Optical gain measurements with femtosecond excitation were performed in CdSe colloidal quantum dots (QDs) dissolved in toluene using the variable stripe length method. Instead of ZnS-shell overcoating, we found that the spectral narrowing and intensity enhancement of the fluorescence can be achieved alternatively by excluding octadecene (ODE) at the preparation of QDs. The maximum gain (∼1.5 mm−1) in the ODE-excluded CdSe QDs is comparable to that of CdSe/ZnS core–shell structures. Despite the uniform size distribution ( σ = 0.25 nm ), a broad gain spectrum appears in both cases due to the recombination of many excited levels between biexciton and exciton states. The remaining surface states in the ODE-excluded CdSe QDs also contribute to gain (1.0 mm−1), which is involved with a three-level process.

International audience; We report a novel optical resolution photoacoustic microscopy concept to obtain an axial resolution only by optical methods. The photoacoustic signal is generated through a non-radiative relaxation from a level that is populated by excited state absorption. This two-step excitation process of a single laser enables to achieve an optical sectioning without any acoustic selectivity, whereby a full optical resolution photoacoustic microscopy is obtained. We bring a proof of this concept using Rhodamine and Zinc Tetraphenylporphyrin dyes known for their efficient excited state absorption process.In vivo sub-femtoliter resolution photoacoustic microscopy with higher frame rates," Sci. Rep. 5, 15421 (2015). 13. Y. Yamaoka, M. Nambu, and T. Takamatsu, "Fine depth resolution of two-photon absorption-induced photoacoustic microscopy using low-frequency bandpass filtering," Opt.

A single In 0.49 Ga 0.51 P quantum well sandwiched by In 0.49 Ga 0.51 P/In 0.49 (Ga 0.6 Al 0.4 ) 0.51 P digital alloy structures was investigated in terms of optical modal gain, where gain saturation effects were also considered for both changes in wavelength and stripe length by using a modal gain contour map analysis. We found the gain threshold density is considerably lower by an order of magnitude when compared to the Mott density (∼2 × 10 12 cm −2 ), which can be attributed to a carrier-harvesting effect through the mini-band of the digital alloy.

We propose an amplified all-optical polarization phase modulator assisted by a local surface plasmon in Au-hybrid CdSe quantum dots. When the local surface plasmon of a spherical Au quantum dot is in resonance with the exciton energy level of a CdSe quantum dot, a significant enhancement of the linear and nonlinear refractive index is found in both the real and imaginary terms via the interaction with the dipole field of the local surface plasmon. Given a gating pulse intensity, an elliptical polarization induced by the phase retardation is described in terms of elliptical and rotational angles. In the case that a larger excitation than the bleaching intensity is applied, the signal light can be amplified due to the presence of gain in the CdSe quantum dot. This enables a longer propagation of the signal light relative to the metal loss, resulting in more feasible polarization modulation. (C) 2012 Optical Society of America

Semiconductor nanomaterials have attracted considerable attention in the design of high efficiency PL up-conversion in heterojunctions or nanostructures at extremely low continuous wave (cw)-excitation intensity. In this study, bioconjugated hybrids were constructed using CdTe and Au nanoparticles (NPs), where two-fold PL enhancement was observed in the solution state. These results are in accordance with theoretical predictions of the local-field effects associated with the combined influence of strong localization of the collective plasmon modes in metallic-semiconducting hybrids and multi-photon absorption into its localized plasmon modes. The feasibility of the nanohybrids as sensors was demonstrated by breaking the bioconjugation through thermal stress, which induced a rapid decrease in luminescence intensity. It is believed that the phenomena is applicable to high-compacted optoelectronic devices and sensing systems that take advantage of both quantum confinement effects and nonlinear optical properties.

We performed time-resolved luminescence and polarization-resolved pump-probe experiments in CdSe/ZnS nanocrystals (NCs) under low and high excitations at room temperatures. At high excitations, the PL spectra shows a red shift (0.54 meV) and two-step decay. In pump-probe experiments, we observed very fast spin-flip process (~1 ps) and population oscillation, which is attributed to the Rabi oscillation.

We have prepared a primary film battery which shows improved shelf life and long-term stabiltiy. We tried to optimize a multi-layered packaging film by considering gas permeability, chemical affinity, and film thickness. We also optimized conducting layer thickness, cathode/anode thickness and their compositions taking N/P rato into account. We introduced a variety of hydrogel polymers, newly developed electrolyte solutions, and novel separators to enhance the ionic conductivity value of gel-type polymer electrolyte/separator system for peak power and high power property.

Surface-plasmon-assisted modal gain enhancement was investigated in Au-hybrid CdSe/ZnS nanocrystal quantum dots. A fivefold enhancement of the modal gain was observed at room temperature in the presence of a Au film by using modal gain contour map analysis, and the photoluminescence intensity and size-selective photoluminescence excitation intensity increased significantly. The enhanced modal gain was attributed to the multiexciton states of neutral and charged biexciton and triexciton.

The polarization dependence of modal gain was examined in ZnO using a variable stripe length method, where the transverse electric (TE) mode gain was dominant over the transverse magnetic (TM) mode gain due to the polarization asymmetry of the wurtzite structure. Modal gain saturation was also investigated using a modal gain contour map for the wavelength and stripe length. The TE modal gain and degree of polarization increased with increasing stripe length up to a threshold length (∼100 μm). At longer stripe lengths, rapid reduction in the carrier density along the stripe resulted in gain saturation and a spectral redshift.

Deposition of high-crystal-quality ZnO nanocrystalline thin films (NCTFs) on a lattice-mismatched sapphire substrate was achieved using a pulsed laser deposition technique, and surface channel waveguides were fabricated by using a laser irradiation process. The optical structure defined on the film was characterized using a scanning electron microscope while the optical gain of unstructured and optically structured NCTFs was measured using the variable stripe length method (VSLM). We present a new analysis of a VSLM to study gain saturation for various stripe lengths, and its validity was confirmed by the consistent result obtained by using a widely used method for short stripe lengths. In the case of unstructured films, the inelastic exciton–exciton scattering dominates the stimulated emission (P-band) below Mott density while not only N-band due to the electron–hole plasma but also the exciton–exciton scattering contribute to the lasing beyond Mott density. These results suggest that the exciton–exciton scattering occurs in a localized space of a coherence scale, so the coexistence of the N-band and the P-band stimulated emission beyond the Mott density originates from the non-uniform spatial distribution. An induced cavity defined on a ZnO NCTF sample, showing constant periodic mode features, is confirmed which is attributed to local densification produced due to a refractive index change in a structured arc region.

Transient gain spectra were measured for an In0.02Ga0.98N / In0.16Ga0.84N multiple quantum well by using the variable-stripe-length method (VSLM) in combination with the ultrafast optical Kerr-gate (OKG) technique. Gain dynamics were measured for a range of excitation lengths from short (50 mu m) to long (350 mu m) stripes with the sample under femtosecond photoexcitation. Analysis of the temporal behaviour of gain and chemical potential suggests that stimulated emission originates from a photoexcited electron-hole plasma at early times; at later times, localized states dominate as the electron-hole plasma becomes exhausted. Gain reduction at early times is attributable to coupling of the electron-hole plasma with photons along the stripe, whilst localized states are less susceptible to gain saturation.