36 research outputs found
Spectral diffusion of single semiconductor nanocrystals: the influence of the dielectric environment
We have explored the influence of different matrices on the emission line
shape of individual homogeneously coated CdSe/CdS/ZnS nanocrystals. The results
obtained corroborate previous observations of a correlation between blinking
events and spectral diffusion but in addition we have found that the extent of
spectral diffusion is almost independent of the dielectric environment of the
NC. Additionally, we report the observation of a correlation between the line
width and emission energy which is not expected to occur in the spherical -
symmetric NCs employed in this work. The implications of these results are
discussed.Comment: 3 pages, 3 figure
Oxygen-deficient photostable Cu2O for enhanced visible light photocatalytic activity
Oxygen vacancies in inorganic semiconductors play an important role in reducing electron-hole recombination, which may have important implications in photocatalysis. Cuprous oxide (Cu2O), a visible light active p-type semiconductor, is a promising photocatalyst. However, the synthesis of photostable Cu2O enriched with oxygen defects remains a challenge. We report a simple method for the gram-scale synthesis of highly photostable Cu2O nanoparticles by the hydrolysis of a Cu(i)-triethylamine [Cu(i)-TEA] complex at low temperature. The oxygen vacancies in these Cu2O nanoparticles led to a significant increase in the lifetimes of photogenerated charge carriers upon excitation with visible light. This, in combination with a suitable energy band structure, allowed Cu2O nanoparticles to exhibit outstanding photoactivity in visible light through the generation of electron-mediated hydroxyl (OH) radicals. This study highlights the significance of oxygen defects in enhancing the photocatalytic performance of promising semiconductor photocatalysts.V. B. thanks the Australian Research Council (ARC) for a
Future Fellowship (FT140101285) and funding support
through an ARC Discovery (DP170103477). ARC is also
acknowledged for DECRA Fellowships to E. D. G.
(DE170100164) and J. v. E. (DE150100427) and a Future
Fellowship to N. C. (FT1401000834). M. S. acknowledges RMIT
University for an Australian Postgraduate Award (APA). A. E. K.,
E. D. G., P. R. and R. R. acknowledge RMIT University for Vice
Chancellor Fellowships. V. B. recognizes the generous support
of the Ian Potter Foundation toward establishing an Ian Potter
NanoBioSensing Facility at RMIT University. The authors
acknowledge the support from the RMIT Microscopy and
Microanalysis Facility (RMMF) for technical assistance and
providing access to characterization facilities. This work was
also supported by the ARC Centre of Excellence for Nanoscale
BioPhotonics (CE140100003)
Synthesis and optical properties of CdSe core and core/shell nanocrystals
Deposited with permission of the author. © 2008 Joel Leonard van EmbdenThe synthesis of nanocrystals is unique compared to the formation of larger micron-sizesspecies as the final crystal sizes are not much larger than the primary nuclei. As a consequencethe final outcome of a nanocrystal synthesis i.e mean crystal size, concentrationand standard deviation is almost solely determined by the end of the nucleation phase. Directingthe growth of crystals beginning from aggregates of only tens of atoms into maturemonodisperse nanocrystals requires that the governing kinetics are strictly controlled at everymoment of the reaction. To effect this task various different ligands need to be employed,each performing a particular function during both nucleation and growth. (For complete abstract open document
Nucleation and growth of CdSe nanocrystals in a binary ligand system
The competing effects of two ligands, oleic acid (OA) and bis-(2,2,4-trimethylpentyl) phosphinic acid (TMPPA), on the nucleation rate and growth of CdSe nanocrystals in octadecene are reported. It is found that TMPPA acts as a high boiling point "nonsolvent" or "nucleating agent". Addition of TMPPA leads to higher initial particle yields and smaller particle diameters. Conversely, oleic acid inhibits nucleation and results in a drastic increase in "early time ripening" (ETR), a phenomenon that causes a rapid reduction in the number of particles within the first minutes of reaction. By controlling the number of nuclei formed with TMPPA and tuning the rate of ETR with oleic acid, high yields of particles can be obtained with sizes between 3 and 7 nm. Furthermore, in the absence of OA, the preparation of very small nanocrystals with diameters ~2 nm is facilitated
Review of the synthetic chemistry involved in the production of core/shell semiconductor nanocrystals
Passivation of CdSe semiconductor nanocrystals can be achieved by overcoating the particles with a homogeneous shell of a second semiconductor. Shell layers are grown in monolayer steps to ensure homogeneous growth of the shell. The relative band edges of the two materials determine the photoreactiveity of the resultant core-shell nanocrystals. The critical role of ligands in minimizing nucleation of the shell material during the growth of the passivating layer is emphasized. The delocalization of charge carriers into the shell layers can be followed spectroscopically during the growth processes. The relative spectral shifts are directly correlated to the relative energies of the band edges
Fluorine-Doped Tin Oxide Colloidal Nanocrystals
Fluorine-doped tin oxide (FTO) is one of the most studied and established materials for transparent electrode applications. However, the syntheses for FTO nanocrystals are currently very limited, especially for stable and well-dispersed colloids. Here, we present the synthesis and detailed characterization of FTO nanocrystals using a colloidal heat-up reaction. High-quality SnO2 quantum dots are synthesized with a tuneable fluorine amount up to ~10% atomic, and their structural, morphological and optical properties are fully characterized. These colloids show composition-dependent optical properties, including the rise of a dopant-induced surface plasmon resonance in the near infrared
Nanometre localisation of quantum dots using their blinking statistics in conjunction with single molecule detection algorithms
A method is presented for optically imaging the spatial distribution of semiconductor nanocrystals with nanometre spatial resolution. The semiconductor nanocrystals were first localised using various filtering and edge detection methods. Using their determined collective positions, a rendered superresolved image may be obtained
Cover picture: photosensitive nanocomposites: highly non-linear quantum dot doped nanocomposites for functional three-dimensional structures generated by two-photon polymerization
Baohua Jia, Min Gu, and co-workers report on p. 2463 (see http://hdl.handle.net/1959.3/88464) on novel quantum dot functionalized photosensitive nanocomposites showing ultrahigh third-order nonlinearity. The cover image shows functional three-dimensional micronano photonic structures, for example, photonic crystals can be fabricated in such active nanocomposites using the versatile two-photon poly-merisation method, opening various possibilities in active micro/nano devices, such as ultrafast switching, signal regeneration, and high speed demultiplexing systems
Quantum dot modified multiwall carbon nanotubes
A novel strategy for the fabrication of multiwall carbon nanotube - nanocrystal heterostructures is shown. Different quantum dots (QDs) with narrow size distributions were covalently coupled to carbon nanotubes (CNTs) and silica coated CNTs in a simple, uniform, and controllable manner. The structural and optical properties of CNT/QD heterostructures are characterized by electron microscopy and photoluminescence spectroscopy. Complete quenching of the PL bands in both QD core and core/shell heterostructures was observed after adsorption to the CNTs, presumably through either carrier ionization or energy transfer. The deposition of a silica shell around the CNTs, preserves the fluorescence properties by insulating the QD from the surface of the CNT