Ultralow threshold on-chip microcavity nanocrystal quantum dot lasers

Chemically synthesized nanocrystal, CdSe/ZnS (core/shell), quantum dots are coated on the surface of an ultrahigh-Q toroidal microcavity and the lasing is observed at room and liquid nitrogen temperature by pulsed excitation of quantum dots, either through tapered fiber or free space. Use of a tapered fiber coupling substantially lowered the threshold energy when compared with the case of free space excitation. The reason for the threshold reduction is attributed to the efficient delivery of pump pulses to the active gain region of the toroidal microcavity. Further threshold reduction was possible by quantum dot surface-coverage control. By decreasing the quantum dot numbers on the surface of the cavity, the threshold energy is further decreased down to 9.9 fJ

Facile fabrication of two-dimensional inorganic nanostructures and their conjugation to nanocrystals

Nanocomposites of two-dimensional (2D) inorganic nanosheets and inorganic nanocrystals are fabricated. Freestanding atomically flat gamma-AlOOH nanosheets (thickness <1 nm) are synthesized from a one-pot hydrothermal reaction. The freestanding and binder-free film composed of the gamma-AlOOH nanosheets is fabricated by sedimentation. Because they have positive zeta potentials in the pH range below ca. 9.3, the gamma-AlOOH nanosheets can function as positively charged 2D inorganic matrices in a broad pH range. By solution phase (pH 7.0) mixing of the gamma-AlOOH nanosheets (zeta potential: 30.7 +/- 0.8 mV) and inorganic nanocrystals with negative surface charge, including Au nanoparticles, Au nanorods, CdSe quantum dots, CdSe/CdS/ZnS quantum dots and CdSe nanorods, the nanocomposites are self-assembled via electrostatic interactions. Negatively charged inorganic nanostructures with a wide range of chemical compositions, shapes, sizes, surface ligands and adsorbates can be used as building blocks for gamma-AlOOH nanocomposites. Adsorption densities of inorganic nanocrystals on the nanocomposites can be controlled by varying concentrations of nanocrystal solutions. Nanocomposite films containing alternating layers of gamma-AlOOH and nanocrystals are obtained by a simple drop casting method.close3

Moxifloxacin: Clinically compatible contrast agent for multiphoton imaging

Multiphoton microscopy (MPM) is a nonlinear fluorescence microscopic technique widely used for cellular imaging of thick tissues and live animals in biological studies. However, MPM application to human tissues is limited by weak endogenous fluorescence in tissue and cytotoxicity of exogenous probes. Herein, we describe the applications of moxifloxacin, an FDA-approved antibiotic, as a cell-labeling agent for MPM. Moxifloxacin has bright intrinsic multiphoton fluorescence, good tissue penetration and high intracellular concentration. MPM with moxifloxacin was demonstrated in various cell lines, and animal tissues of cornea, skin, small intestine and bladder. Clinical application is promising since imaging based on moxifloxacin labeling could be 10 times faster than imaging based on endogenous fluorescence.1152sciescopu

Chip-scale photonics with plasmonic components

In this talk we will describe recent opportunities presented by plasmonics for chip-scale integration of photonic and electronic devices, including i)design of metal-insulator-metal plasmon waveguides that optimize the trade-off between mode localization and propagation loss in the visible and near-infrared ii) on-chip Si CMOS compatible light near-infrared light sources for coupling into plasmonic networks iii) plasmon-enhanced emission from quantum dots, and iv) opportunities for active plasmonic devices based on electro-optic and all-optical modulation of plasmon propagation

Ultralow threshold on-chip toroidal microcavity nanocrystal quantum dot lasers

We demonstrate an on-chip toroidal microcavity nanocrystal quantum dot laser with a threshold energy below 10 femto-Joules at room temperature, a factor of 1 million lower than previously reported for strongly-confined, nanocrystal quantum dot lasers

Moxifloxacin: Clinically compatible contrast agent for multiphoton imaging

Multiphoton microscopy (MPM) is a nonlinear fluorescence microscopic technique widely used for cellular imaging of thick tissues and live animals in biological studies. However, MPM application to human tissues is limited by weak endogenous fluorescence in tissue and cytotoxicity of exogenous probes. Herein, we describe the applications of moxifloxacin, an FDA-approved antibiotic, as a cell-labeling agent for MPM. Moxifloxacin has bright intrinsic multiphoton fluorescence, good tissue penetration and high intracellular concentration. MPM with moxifloxacin was demonstrated in various cell lines, and animal tissues of cornea, skin, small intestine and bladder. Clinical application is promising since imaging based on moxifloxacin labeling could be 10 times faster than imaging based on endogenous fluorescence.David H. Koch Institute for Integrative Cancer Research at MIT (Bridge Initiative

Novel type-II nanocrystal quantum dots and versatile oligomeric phosphine ligands

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2003.Vita.Includes bibliographical references.This thesis describes the syntheses, characterizations, and applications of novel type-II quantum dots and versatile oligomeric phosphine ligands. Type-II band engineered quantum dots (CdTe/CdSe(core/shell) and CdSe/ZnTe(core/shell) heterostructures) are synthesized by chemical means. The optical properties of these type-II quantum dots are studied in parallel with their type-I counterparts. The spatial distributions of carriers are controlled within the type-II quantum dots, which make their properties strongly governed by the band offset of the comprising materials. This allows access to optical transition energies that are not restricted to bandgap energies. The type-II quantum dots can emit at lower energies than the bandgaps of comprising materials. The type-II emission can be tailored by the shell thickness as well as the core size. The enhanced control over the carrier distributions afforded by these type-II materials is useful for many applications such as photovoltaics, and photoconduction devices. A new family of oligomeric alkyl phosphine ligands is synthesized for quantum dots. These oligomeric phosphines show effective binding affinity to quantum dot surfaces. They form thin and secure organic shells that stabilize quantum dots in diverse environments. They maintain high photoluminescence quantum yield of the quantum dots, and enable homogeneous incorporation into various matrices. They present a chemically flexible structure that can be used for further chemistry, such as crosslinking, co-polymerization, and conjugation to biomolecules. Selection of optimal quantum dot wavelengths for biomedical assays and imaging is studied by simple mathematical modeling.(cont.) Exploiting the design flexibilities of type-II quantum dots and the superior stabilities from oligomeric phosphine ligands, aqueous soluble near-infrared quantum dots for biomedical imaging are obtained. They are optimized for the emission wavelength, absorption cross-section, hydrodynamic size, and photoluminescence quantum yield. Using these quantum dots in small and large animal model systems, sentinel lymph node mapping, a major cancer staging procedure, is successfully performed in real-time using near-infrared light. Oliogomeric phosphine ligands with polymerizable moieties are used to incorporate quantum dots into polymer microspheres. The ligands enable co-polymerization of quantum dots with heterogeneous polymer matrices without phase separations or aggregations. Their potential applications for full color, particle-based displays, and information storage are demonstrated.by Sungjee Kim.Ph.D

Indium phosphide magic-sized clusters: chemistry and applications

This paper reviews developments in the synthesis of InP quantum dots (QDs) and research on InP magic-sized clusters (MSCs), which occur as intermediates during the growth of InP QDs. We classify research on InP MSCs into (1) synthesis and characterization and (2) applications. Several InP MSCs have been developed using low reaction temperatures or strong binding ligands. InP MSCs passivated by carboxylate, amine or phosphonate ligands and InP MSCs that incorporate heterogeneous atoms (Cl or Zn) have been synthesized. We also review tools to characterize MSCs and show the intermediate characteristics of InP MSCs. InP MSCs have been used as synthesis precursors for spherical InP QDs and nonspherical InP nanostructures, such as elongated, branched, and hyperbranched/dendrimer-like morphologies. We also present MSC-mediated growth mechanisms involving fragments, monomers or other nanoclusters. Research on the chemistry and applications of InP MSCs has uncovered the formation process of InP nanomaterials. Developments in the luminescent properties of InP MSCs, InP QDs and elongated InP nanostructures would be useful in displays. This review encompasses syntheses, characterizations, and applications of InP magic-sized clusters (MSCs) which are originally found as intermediates during the growth of InP quantum dots (QDs). Various tools to characterize MSCs and the intermediate characteristics of InP MSCs and InP MSCs having incorporated heterogeneous atoms such as chlorine or zinc are discussed. Developments in the syntheses of InP QDs and MSC-mediated growth mechanisms involving fragments, monomers or other nanoclusters are also addressed.11Nsciescopu

Tuning Both Bandedge Exciton Dynamics and Energy Transfer Dynamics in Mn-Doped QDs via Doping of Ag Co-Dopants

Doping in colloidal semiconductor nanocrystals (NCs) is an attractive approach for giving new functionalities which come from enhanced interactions between strongly quantum confined band-edge exciton wavefunction and dopant ions. However, fundamental analyses on doped NCs such as precise location and site(interstitial/substitutional) of dopants and correlations between co-dopants were rarely reported because of physical complexity of the system. Here we investigated role of Ag co- dopants in Mn-doped NCs through spectroscopic approaches. Through sophisticated and multi-step, cation exchange and shell overcoating processes, we successfully synthesized co-doped NCs with well-defined doping depth and dopant concentration. With different doping concentration of Ag ions, two completely different trends arise in intensity changes of both band-edge photoluminescence (PL) and Mn dopant sensitized phosphorescence. We also figured out that they are also affected by relative distribution between Mn and Ag ions which shows possibility of sensitive tuning of branching between band-edge dynamics and energy transfer dynamics.1