Sanjun Zhang

Facile Large-Scale Synthesis of Monodisperse Mesoporous Silica Nanospheres with Tunable Pore Structure

Mesoporous silica nanoparticles (MSNs) are experiencing rapid development in the biomedical field for imaging and for use in heterogeneous catalysis. Although the synthesis of MSNs with various morphologies and particle sizes has been reported, synthesis of a pore network with monodispersion control below 200 nm is still challenging. We achieved this goal using mild conditions. The reaction occurred at atmospheric pressure with a templating sol-gel technique using cetyltrimethylammonium (CTA(+)) as the templating surfactant and small organic amines (SOAs) as the mineralizing agent. Production of small pore sizes was performed for the first time, using pure and redispersible monodispersed porous nanophases with either stellate (ST) or raspberry-like (RB) channel morphologies. Tosylate (Tos(-)) counterions favored ST and bromide (Br(-)) RB morphologies at ultralow SOA concentrations. Both anions yielded a worm-like (WO) morphology at high SOA concentrations. A three-step formation mechanism based on self-assembly and ion competition at the electrical palisade of micelles is proposed. Facile recovery and redispersion using specific SOAs allowed a high yield production at the kilogram scale. This novel technique has practical applications in industry.

Photoemission Mechanism of Water-Soluble Silver Nanoclusters: Ligand-to-Metal–Metal Charge Transfer vs Strong Coupling between Surface Plasmon and Emitters

Using carboxylate-protected silver nanoclusters (Ag-carboxylate NCs) as a model, we separately investigated the contribution of the ligand shell and the metal core to understand the nature of photoluminescence of Ag NCs. A new Ag(0)NCs@Ag(I)-carboxylate complex core-shell structural model has been proposed. The emission from the Ag-carboxylate NCs could be attributed to ligand-to-metal-metal charge transfer from Ag(I)-carboxylate complexes (the oxygen atom in the carboxylate ligands to the Ag(I) ions) to the Ag atoms and subsequent radiative relaxation. Additionally, we found that the emission wavelength of the Ag NCs depends on the excitation wavelength implying a strong coupling between surface plasmon and emitter in Ag NCs. The strong coupling between the surface plasmon and the emitter determines the quantum yield and lifetime. The emission mechanism of Ag NCs and its relation to the organic templates and metal cores were clearly clarified. The results should stimulate additional experimental and theoretical research on the molecular-level design of luminescent metal probes for optoelectronics and other applications.

Optical spectroscopy of two-dimensional layered (C6H5C2H4-NH3)2-PbI4 perovskite

We report on optical spectroscopy (photoluminescence and photoluminescence excitation) on two-dimensional self-organized layers of (C(6)H(5)C(2)H(4)-NH(3))(2)-PbI(4) perovskite. Temperature and excitation power dependance of the optical spectra gives a new insight into the excitonic and the phononic properties of this hybrid organic/inorganic semiconductor. In particular, exciton-phonon interaction is found to be more than one order of magnitude higher than in GaAs QWs. As a result, photoluminescence emission lines have to be interpreted in the framework of a polaron model.

Preparations and Characterizations of Luminescent Two Dimensional Organic-inorganic Perovskite Semiconductors

This article reviews the synthesis, structural and optical characterizations of some novel luminescent two dimensional organic-inorganic perovskite (2DOIP) semiconductors. These 2DOIP semiconductors show a self-assembled nano-layered structure, having the electronic structure of multi-quantum wells. 2DOIP thin layers and nanoparticles have been prepared through different methods. The structures of the 2DOIP semiconductors are characterized by atomic force microscopy and X-ray diffraction. The optical properties of the 2DOIP semiconductors are characterized from absorption and photoluminescence spectra measured at room and low temperatures. Influences of different components, in particular the organic parts, on the structural and optical properties of the 2DOIP semiconductors are discussed.

Passive mode locking in a diode-pumped Nd:GdVO/sub 4/ laser with a semiconductor saturable absorber mirror

We demonstrate Q-switched and CW passive mode locking in a laser-diode-pumped Nd:GdVO/sub 4/ laser with a semiconductor saturable absorber mirror. The repetition rate of the Q-switched envelope increased from 23.1 to 260 kHz as the pump power increased from 1.75 to 13.0 W. At a pump power of 13.7 W, the Q-switched mode locking changed to CW mode locking. The maximum average output power of 4.9 W with a 140-MHz repetition rate was obtained at a pump power of 17.9 W and the single mode-locked pulse energy was 0.035 /spl mu/J. The CW mode-locked pulse duration was measured to be /spl sim/11.5 ps.

High-resolution surface-plasmon imaging in air and in water: V(z) curve and operating conditions

We present what are believed to be the first images obtained with a far-field high-resolution scanning surface-plasmon microscope in an aqueous medium. Measurements of V(z), the output response of the microscope, versus defocus z give a signature of the surface-plasmon propagation. V(z) is strongly conditioned by the laser beam diameter and the objectives numerical aperture, and we show how the operating mode (in air and in water) must be chosen to maximize the surface-plasmon field and to minimize diffraction (edge) effects.

Synthesis and optical properties of novel organic–inorganic hybrid UV (R–NH3)2PbCl4 semiconductors

We report on the synthesis and the optical properties of several novel ultraviolet (UV) semiconductors (R–NH3)2PbCl4. These semiconductors are two dimensional organic–inorganic perovskite (2DOIP) materials and have multiple quantum-well energy level structures. We systematically varied the organic components (R–NH3+), and discussed their influence on the self-organization ability, excitonic optical features, and long-term photo-stabilities of the 2DOIPs. The trends of selecting the organic groups to tailor the optical features and to improve the self-organization and long-term photo-stabilities of 2DOIPs are obtained by analyzing the experimental results. Self-organization abilities are found to be highly dependent on the interactions among the organic components. The excitonic optical properties of 2DOIPs are found to depend more on the steric structures, and less on the electronic structures and chemical properties of the organic groups (R–NH2) as long as the organic groups are optically inert. However, the long-term photo-stabilities of the (R–NH3)2PbCl4 semiconductors are highly dependent on the thermal and photo stabilities of organic components. We find a new UV semiconductor, (C6H11CH2NH3)2PbCl4 (CMPC), which has better photo-stability than the usually used (C6H5C2H4NH3)2PbCl4 (PEPC).

Instrument Response Standard in Time-Resolved Fluorescence Spectroscopy at Visible Wavelength: Quenched Fluorescein Sodium

Time-resolved fluorescence properties of quenched fluorescein sodium, including self-quenching and collisional quenching by iodide, have been studied by using a picosecond time-correlated single-photon counting (TCSPC) apparatus, together with an upconversion spectrophotofluorometer with a time resolution better than 300 fs. The steady-state fluorescence intensity of fluorescein sodium reached the maximum when its concentration was 510 μM with pH > 9. Both the fluorescence intensity and lifetime decreased with increasing concentrations of NaI quencher. When the NaI concentration was 12.2 M, a monoexponential decay with a lifetime as short as 17 ps was exactly determined for the first time using the femtosecond-resolved upconversion system. Picosecond time-resolved fluorescence measurements of circular permuted green and yellow fluorescent proteins (cpGFP and cpYFP) were reported, demonstrating that the fluorescence decay of quenched fluorescein sodium is a better approximation of the instrument response function (IRF) needed for the accurate deconvolution of fluorescence lifetime data, particularly for detectors used in the visible spectral region. We believe that this picosecond lifetime standard will find wide applications in fluorescence lifetime imaging microscopy (FLIM).

A Facile Strategy to Prepare Dendrimer-stabilized Gold Nanorods with Sub-10-nm Size for Efficient Photothermal Cancer Therapy

Gold (Au) nanoparticles are promising photothermal agents with the potential of clinical translation. However, the safety concerns of Au photothermal agents including the potential toxic compositions such as silver and copper elements in their structures and the relative large size-caused retention and accumulation in the body post-treatment are still questionable. In this article, we successfully synthesized dendrimer-stabilized Au nanorods (DSAuNRs) with pure Au composition and a sub-10-nm size in length, which represented much higher photothermal effect compared with dendrimer-encapsulated Au nanoparticles due to their significantly enhanced absorption in the near-infrared region. Furthermore, glycidol-modified DSAuNRs exhibited the excellent biocompatibility and further showed the high photothermal efficiency of killing cancer cells in vitro and retarding tumor growth in vivo. The investigation depicted an optimal photothermal agent with the desirable size and safe composition.

Sensitive Detection of Polycyclic Aromatic Molecules: Surface Enhanced Raman Scattering via π-π Stacking.

We report silver nanoparticles (Ag NPs) with high stability, sensitivity, and no surface enhanced Raman scattering (SERS) background. The Ag NPs were synthesized via a one-step process with polysodium styrenesulfonate (PSSS) templates, and they could efficiently adsorb polycyclic aromatic molecules via π-π stacking. The adsorption mechanisms and applicability were systematically studied by experimental measurements and theoretical simulations. When the polycyclic aromatic analytes were adsorbed on the PSSS-templated Ag NPs, the vibrations of π-π stacking-bound moieties were attenuated, yet those of the other unbound aromatic moieties increased. Most importantly, when the analytes had more than two π-π stacking binding sites, the PSSS-templated Ag NPs could trap the analytes by focusing through the optical force induced or via the simultaneously formed analyte-Ag NPs aggregates. This afforded high SERS intensity and very low detection limits.