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1.
Phys Rev Lett ; 124(15): 157402, 2020 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-32357015

RESUMO

Macroscopic coherence of Bose condensates is a fundamental and practical phenomenon in many-body systems, such as the long-range correlation of exciton-polariton condensates with a dipole density typically below the exciton Mott-transition limit. Here we extend the macroscopic coherence of electron-hole-photon interacting systems to a new region in the phase diagram-the high-density plasma region, where long-range correlation is generally assumed to be broken due to the rapid dephasing. Nonetheless, a cooperative state of electron-hole plasma does emerge through the sharing of the superfluorescence field in an optical microcavity. In addition to the in situ coherence of e-h plasma, a long-range correlation is formed between two 8-µm-spaced plasma ensembles even at room temperature. Quantized and self-modulated correlation modes are generated for e-h ensembles in the plasma region. By controlling the distance between the two ensembles, multiple coupling regimes are revealed, from strong correlation to perturbative phase correlation and finally to an incoherent classical case, which has potential implications for tunable and high-temperature-compatible quantum devices.

2.
Opt Express ; 24(11): 11654-67, 2016 May 30.
Artigo em Inglês | MEDLINE | ID: mdl-27410091

RESUMO

Tryptophan is a fluorescent amino acid common in proteins. Its absorption is largest for wavelengths λ ≲ 290 nm and its fluorescence emissions peak around 300-350 nm, depending upon the local environment. Here we report the observation of red fluorescence near 600 nm emerging from 488-nm continuous-wave (CW) laser photoexcitation of dry tryptophan (Trp) particles. With an excitation intensity below 0.5 kW/cm2, dry Trp particles yield distinctive Raman scattering peaks in the presence of relatively weak and spectrally broad emissions with λ ∼500-700 nm, allowing estimation of particle temperature at low excitation intensities. When the photoexcitation intensity is increased to 1 kW/cm2 or more for a few minutes, fluorescence intensity dramatically increases by more than two orders of magnitude. The fluorescence continues to increase in intensity and gradually shift to the red when photoexcitation intensity and the duration of exposure are increased. The resulting products absorb at visible wavelengths and generate red fluorescence with λ ∼ 650-800 nm with 633-nm CW laser excitation. We attribute the emergence of orange and red fluorescence in the Trp products to a photochemical transformation that is instigated by weak optical transitions to triplet states in Trp with 488-nm excitation and which may be expedited by a photothermal effect.


Assuntos
Espectrometria de Fluorescência , Análise Espectral Raman , Triptofano/química , Temperatura
3.
Nano Lett ; 13(5): 1920-7, 2013 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-23574534

RESUMO

Via the integration of nanocomposites comprising I-III-VI semiconductor quantum dots (QDs) decorated onto a single SnO2 nanowire (NW), we successfully fabricate an ultrahigh-sensitivity and wide spectral-response photodetector. Under the illumination of He-Cd laser (325 nm) with the photon energy larger than the band gap of SnO2 nanowire, remarkably, an ultrahigh photocurrent gain up to 2.5 × 10(5) has been achieved, and an enhancement factor can reach up to 700% (cf. bare SnO2 NW) as light illumination onto the wire with an excitation intensity of 15 W/m(2). Also, a high gain value up to 1.3 × 10(5) is attained with the excited photon energy (488 nm) smaller than the band gap of SnO2 nanowire. Several key factors contribute to ultrahigh photocurrent gain and wide spectral response. First, the decorated quantum dot processes an inherent nature of a large absorption coefficient above its band gap. Furthermore, the single SnO2 nanowire provides an excellent conduction path for the photogenerated carriers as well as bears a large surface-to-volume ratio so that the coupling strength with quantum dots can be greatly enhanced. Most importantly, the spatial separation of photogenerated electrons and holes can be easily achieved due to the charge transfer arising from a type II band alignment between QDs and SnO2 NW. This work thus demonstrates a new approach in which by selectively decorating suitable QDs the photocurrent gain of SnO2 NWs can be greatly enhanced and extended to a wide spectral range of photoresponse previously inaccessible, providing a very useful guideline to create cheap, nontoxic, and highly efficient photodetectors.

4.
Heliyon ; 10(6): e27752, 2024 Mar 30.
Artigo em Inglês | MEDLINE | ID: mdl-38560675

RESUMO

This study worked with Chunghwa Telecom to collect data from 17 rooftop solar photovoltaic plants installed on top of office buildings, warehouses, and computer rooms in northern, central and southern Taiwan from January 2021 to June 2023. A data pre-processing method combining linear regression and K Nearest Neighbor (k-NN) was proposed to estimate missing values for weather and power generation data. Outliers were processed using historical data and parameters highly correlated with power generation volumes were used to train an artificial intelligence (AI) model. To verify the reliability of this data pre-processing method, this study developed multilayer perceptron (MLP) and long short-term memory (LSTM) models to make short-term and medium-term power generation forecasts for the 17 solar photovoltaic plants. Study results showed that the proposed data pre-processing method reduced normalized root mean square error (nRMSE) for short- and medium-term forecasts in the MLP model by 17.47% and 11.06%, respectively, and also reduced the nRMSE for short- and medium-term forecasts in the LSTM model by 20.20% and 8.03%, respectively.

5.
Opt Express ; 21(15): 18538-52, 2013 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-23938726

RESUMO

The broadband parametric fluorescence from a nonlinear crystal can be used as a compact primary source instead of a blackbody for absolute measurements of instrument spectral efficiency. We describe such a setup for measuring the instrument spectral response function in the wavelength range from 450 to 1000 nm. We perform angle-resolved imaging spectroscopy of conical parametric fluorescence in a beta-barium borate crystal pumped by a 405-nm diode laser. The experimental angle-resolved spectra and the generation efficiency of parametric down-conversion agree with a plane-wave theoretical analysis.


Assuntos
Algoritmos , Iluminação/instrumentação , Iluminação/métodos , Espectrometria de Fluorescência/instrumentação , Espectrometria de Fluorescência/métodos , Desenho de Equipamento , Análise de Falha de Equipamento
6.
Small ; 4(2): 218-24, 2008 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-18196505

RESUMO

Highly uniform Fe3O4/SiO2 core/shell nanoparticles functionalized by phosphorescent iridium complexes (Ir) have been strategically designed and synthesized. The Fe3O4/SiO2(Ir) nanocomposite demonstrates its versatility in various applications: the magnetic core provides the capability for magnetic resonance imaging and the great enhancement of the spin-orbit coupling in the iridium complex makes it well suited for phosphorescent labeling and simultaneous singlet oxygen generation to induce apoptosis.


Assuntos
Nanopartículas Metálicas/química , Apoptose/efeitos dos fármacos , Fenômenos Químicos , Físico-Química , Meios de Contraste , Óxido Ferroso-Férrico , Células HeLa , Humanos , Irídio , Luminescência , Imageamento por Ressonância Magnética , Nanopartículas Metálicas/administração & dosagem , Microscopia Confocal , Microscopia Eletrônica de Transmissão , Nanotecnologia , Fotoquímica , Fotoquimioterapia , Fármacos Fotossensibilizantes , Dióxido de Silício , Oxigênio Singlete , Espectrofotometria
8.
Small ; 2(11): 1308-13, 2006 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-17192978

RESUMO

The tuning of CdSe quantum dot (QDs) sizes, and consequently their corresponding two-photon absorption (TPA) cross section, has been systematically investigated. As the size (diameter) of the quantum dots increases, the TPA cross section is found to be empirically related via a power-law proportionality of 3.5+/-0.5 and 5.6+/-0.7 to the diameters of CdSe and CdTe QDs, respectively. The results are tentatively rationalized via a theoretical model of two-photon excitation properties in a system incorporating excitons and defects.


Assuntos
Compostos de Cádmio/química , Nanotecnologia/métodos , Compostos de Selênio/química , Telúrio/química , Absorção , Luz , Nanopartículas Metálicas/química , Microscopia de Fluorescência , Modelos Estatísticos , Fotoquímica , Fótons , Pontos Quânticos
9.
Chem Commun (Camb) ; (3): 263-5, 2006 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-16391728

RESUMO

Based on 15-crown-5 functionalized CdSe/ZnS quantum dots (QDs), we report a novel fluorogenic sensor to probe K+ ions in H2O; recognition of K+ can be achieved via the Förster type of energy transfer between two different color QDs, so that [K+] of the order of 10(-6) M can be promptly detected.

11.
Small ; 1(12): 1215-20, 2005 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-17193422

RESUMO

The rational design and synthesis of CdSe/CdTe/ZnTe (core-shell-shell) type-II quantum dots are reported. Their photophysical properties are investigated via the interband CdSe-->ZnTe emission and its associated relaxation dynamics. In comparison to the strong CdSe (core only) emission (lambda(max) approximately 550 nm, Phi(f) approximately 0.28), a moderate CdSe-->CdTe emission (lambda(max) approximately 1026 nm, Phi(f) approximately 1.2 x 10(-3)) and rather weak CdSe-->ZnTe interband emission (lambda(max) approximately 1415 nm, Phi(f) approximately 1.1 x 10(-5)) are resolved for the CdSe/CdTe/ZnTe structure (3.4/1.8/1.3 nm). Capping CdSe/CdTe with ZnTe results in a distant electron-hole separation between CdSe (electron) and ZnTe (hole) via an intermediate CdTe layer. In the case of the CdSe/CdTe/ZnTe structure, a lifetime as long as 150 ns is observed for the CdSe-->ZnTe (1415 nm) emission. This result further indicates an enormously long radiative lifetime of approximately 10 ms. Upon excitation of the CdSe/CdTe/ZnTe structure, the long-lived charge separation may further serve as an excellent hole carrier for catalyzing the redox oxidation reaction.


Assuntos
Compostos de Cádmio/química , Pontos Quânticos , Compostos de Selênio/química , Semicondutores , Telúrio/química , Zinco/química , Absorção , Fenômenos Químicos , Físico-Química , Elétrons , Microscopia Eletrônica de Transmissão , Espectrofotometria , Temperatura
12.
Sci Rep ; 5: 17044, 2015 Nov 24.
Artigo em Inglês | MEDLINE | ID: mdl-26596907

RESUMO

We report ab initio calculations of the spin splitting of the uppermost valence band (UVB) and the lowermost conduction band (LCB) in bulk and atomically thin GaS, GaSe, GaTe, and InSe. These layered monochalcogenides appear in four major polytypes depending on the stacking order, except for the monoclinic GaTe. Bulk and few-layer ε-and γ -type, and odd-number ß-type GaS, GaSe, and InSe crystals are noncentrosymmetric. The spin splittings of the UVB and the LCB near the Γ-point in the Brillouin zone are finite, but still smaller than those in a zinc-blende semiconductor such as GaAs. On the other hand, the spin splitting is zero in centrosymmetric bulk and even-number few-layer ß-type GaS, GaSe, and InSe, owing to the constraint of spatial inversion symmetry. By contrast, GaTe exhibits zero spin splitting because it is centrosymmetric down to a single layer. In these monochalcogenide semiconductors, the separation of the non-degenerate conduction and valence bands from adjacent bands results in the suppression of Elliot-Yafet spin relaxation mechanism. Therefore, the electron- and hole-spin relaxation times in these systems with zero or minimal spin splittings are expected to exceed those in GaAs when the D'yakonov-Perel' spin relaxation mechanism is also suppressed.

13.
Sci Rep ; 5: 15347, 2015 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-26477277

RESUMO

We demonstrate sequential lasing at two well-separated energies in a highly photoexcited planar microcavity at room temperature. Two spatially overlapped lasing states with distinct polarization properties appear at energies more than 5 meV apart. Under a circularly polarized nonresonant 2 ps pulse excitation, a sub-10-ps transient circularly polarized high-energy (HE) state emerges within 10 ps after the pulse excitation. This HE state is followed by a pulsed state that lasts for 20-50 ps at a low energy (LE) state. The HE state is highly circularly polarized as a result of a spin-preserving stimulated process, while the LE state shows a significantly reduced circular polarization because of a diminishing spin imbalance.

15.
ACS Nano ; 5(5): 4177-87, 2011 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-21548648

RESUMO

Trifunctional uniform nanoparticles comprising a manganese nanocrystal core and a functionalized mesoporous silica shell (MnO@mSiO(2)(Ir)@PEG, where Ir is an emissive iridium complex and PEG is polyethylene glycol) have been strategically designed and synthesized. The T(1) signal can be optimized by forming hollow core (H-MnO@mSiO(2)(Ir)@PEG) via a novel and facile etching process, for which the mechanism has been discussed in detail. Systematic investigation on correlation for longitudinal relaxation (T(1)) versus core shapes and shell silica porosity of the nanocomposites (MnO, H-MnO, MnO@SiO(2), MnO@mSiO(2), H-MnO@mSiO(2)) has been carried out. The results show that the worm-like nanochannels in the mesoporous silica shell not only increase water permeability to the interior hollow manganese oxide core for T(1) signal but also enhance photodynamic therapy (PDT) efficacy by enabling the free diffusion of oxygen. Notably, the H-MnO@mSiO(2)(Ir)@PEG nanocomposite with promising r(1) relaxivity demonstrates its versatility, in which the magnetic core provides the capability for magnetic resonance imaging, while the simultaneous red phosphorescence and singlet oxygen generation from the Ir complex are capable of providing optical imaging and inducing apoptosis, respectively.


Assuntos
Cristalização/métodos , Compostos de Manganês/química , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Óxidos/química , Dióxido de Silício/química , Titânio/química , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Tamanho da Partícula , Porosidade , Propriedades de Superfície
16.
Adv Mater ; 23(45): 5451-5, 2011 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-22009656

RESUMO

A record high PCE of up to 3.2% demonstrates that the efficiency of hybrid solar cells (HSCs) can be boosted by utilizing a unique mono-aniline end group of PSBTBT-NH(2) as a strong anchor to attach to CdTe nanocrystal surfaces and by simultaneously exploiting benzene-1,3-dithiol solvent-vapor annealing to improve the charge separation at the donor/acceptor interface, which leads to efficient charge transportation in the HSCs.


Assuntos
Ar , Compostos de Cádmio/química , Fontes de Energia Elétrica , Nanocompostos/química , Nanotecnologia/métodos , Compostos de Organossilício/química , Polímeros/química , Luz Solar , Telúrio/química , Tiadiazóis/química , Modelos Moleculares , Conformação Molecular
17.
ACS Nano ; 2(4): 750-6, 2008 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-19206607

RESUMO

In the absence of an external direction-controlling process, exclusive self-bundled arrays of CdS nanorods are formed using a facile solution-based method involving trioctylphosphine (TOP) and tetradecylphosphonic acids (TDPA) as cosurfactants. CdS self-bundled arrays with an area of as large as 2.0 microm(2) could be obtained. A detailed mechanistic investigation leads us to conclude that the matching in nanorod concentration, intrinsic properties of CdS, and the hydrocarbon chains of the surfactants between adjacent CdS rods play key roles in the self-assembly. In sharp contrast to the defect dominant emission in solutions, the self-bundled CdS nanorods exhibit optical emission nearly free from the defect-states, demonstrating their potential for applications in luminescence and photovoltaic devices.


Assuntos
Compostos de Cádmio/química , Cristalização/métodos , Nanotecnologia/métodos , Nanotubos/química , Nanotubos/ultraestrutura , Compostos de Selênio/química , Substâncias Macromoleculares/química , Teste de Materiais , Microesferas , Conformação Molecular , Tamanho da Partícula , Propriedades de Superfície
18.
Nanotechnology ; 19(11): 115702, 2008 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-21730562

RESUMO

Recombination dynamics in CdTe/CdSe core-shell type-II quantum dots (QDs) has been investigated by time-resolved photoluminescence (PL) spectroscopy. A very long PL decay time of several hundred nanoseconds has been found at low temperature, which can be rationalized by the spatially separated electrons and holes occurring in a type-II heterostructure. For the temperature dependence of the radiative lifetime, the linewidth and the peak energy of PL spectra show that the recombination of carriers is dominated by delocalized excitons at temperatures below 150 K, while the mixture of delocalized excitons, electrons and holes overwhelms the process at higher temperature. The binding energy of delocalized excitons obtained from the temperature dependence of the non-radiative lifetime is consistent with the theoretical value. The energy dependence of lifetime measurements reveals a third power relationship between the radiative lifetime and the radius of QDs, the light of which can be shed by the quantum confinement effect. In addition, the radiative decay rate is found to be proportional to the square root of excitation power, arising from the change of wavefunction overlap of electrons and holes due to the band bending effect, which is an inherent character of a type-II band alignment.

19.
NMR Biomed ; 21(8): 820-9, 2008 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-18470957

RESUMO

Our goal was to analyze the changes in morphology and physiological function (phagocytosis, migratory capabilities, humoral and cellular response, and nitric oxide secretion) of murine macrophages after labeling with a clinically used superparamagnetic iron oxide (SPIO), ferucarbotran. In SPIO-treated macrophages, nanoparticles were taken up in the cytoplasm and accumulated in a membrane-bound organelle. Macrophage proliferation and viability were not modified after SPIO labeling. Phagocytic function decreased after labeling with only 10 microg Fe/mL SPIO, whereas other functions including migration and production of tumor necrosis factor-alpha and nitric oxide increased at the highest SPIO concentration (100 microg Fe/mL).


Assuntos
Compostos Férricos , Macrófagos/citologia , Macrófagos/fisiologia , Imageamento por Ressonância Magnética/métodos , Magnetismo , Fagocitose/fisiologia , Animais , Linhagem Celular , Proliferação de Células , Tamanho Celular , Sobrevivência Celular , Meios de Contraste , Camundongos , Coloração e Rotulagem/métodos
20.
Chemphyschem ; 7(1): 222-8, 2006 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-16404768

RESUMO

Syntheses of CdTe/CdSe type-II quantum dots (QDs) using CdO and CdCl2 as precursors for core and shell, respectively, are reported. Characterization was made via near-IR interband emission, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDX), and X-ray diffraction (XRD). Femtosecond fluorescence upconversion measurements on the relaxation dynamics of the CdTe core (in CdTe/CdSe) emission and CdTe/CdSe interband emission reveal that as the size of the core increases from 5.3, 6.1 to 6.9 nm, the rate of photoinduced electron separation decreases from 1.96, 1.44 to 1.07 x10(12) s(-1). The finite rates of the initial charge separation are tentatively rationalized by the small electron-phonon coupling, causing weak coupling between the initial and charge-separated states.

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