/pdf/mechanisms-of-nucleation-and-growth-of-nanoparticles-in-50tbw7lwvb.pdf

Mechanisms of Nucleation and Growth of Nanoparticles in Solution

Key limitations of the colloidal semiconductor nanorods that have been reported so far are a significant distribution of lengths and diameters as well as the presence of irregular shapes produced by the current synthetic routes and, finally, the poor ability to fabricate large areas of oriented nanorod arrays. Here, we report a seeded-growth approach to the synthesis of asymmetric core−shell CdSe/CdS nanorods with regular shapes and narrow distributions of rod diameters and lengths, the latter being easily tunable up to 150 nm. These rods are highly fluorescent and show linearly polarized emission, whereby the emission energy depends mainly on the core diameter. We demonstrate their lateral alignment as well as their vertical self-alignment on substrates up to areas of several square micrometers.

Synthesis and Micrometer-Scale Assembly of Colloidal CdSe/CdS Nanorods Prepared by a Seeded Growth Approach

We report on the second family of layered perovskite white-light emitters with improved photoluminescence quantum efficiencies (PLQEs). Upon near-ultraviolet excitation, two new Pb–Cl and Pb–Br perovskites emit broadband “cold” and “warm” white light, respectively, with high color rendition. Emission from large, single crystals indicates an origin from the bulk material and not surface defect sites. The Pb–Br perovskite has a PLQE of 9%, which is undiminished after 3 months of continuous irradiation. Our mechanistic studies indicate that the emission has contributions from strong electron–phonon coupling in a deformable lattice and from a distribution of intrinsic trap states. These hybrids provide a tunable platform for combining the facile processability of organic materials with the structural definition of crystalline, inorganic solids.

/pdf/intrinsic-white-light-emission-from-layered-hybrid-2stgofakrl.pdf

Intrinsic white-light emission from layered hybrid perovskites.

We use organic cations to template the solution-state assembly of corrugated lead halide layers in bulk crystalline materials. These layered hybrids emit radiation across the entire visible spectrum upon ultraviolet excitation. They are promising as single-source white-light phosphors for use with ultraviolet light-emitting diodes in solid-state lighting devices. The broadband emission provides high color rendition and the chromaticity coordinates of the emission can be tuned through halide substitution. We have isolated materials that emit the "warm" white light sought for many indoor lighting applications as well as "cold" white light that approximates the visible region of the solar spectrum. Material syntheses are inexpensive and scalable and binding agents are not required for film deposition, eliminating problems of binder photodegradation. These well-defined and tunable structures provide a flexible platform for studying the rare phenomenon of intrinsic broadband emission from bulk materials.

/pdf/self-assembly-of-broadband-white-light-emitters-32y2hwzxoq.pdf

Self-assembly of broadband white-light emitters.

ConspectusWith nearly 20% of global electricity consumed by lighting, more efficient illumination sources can enable massive energy savings. However, effectively creating the high-quality white light required for indoor illumination remains a challenge. To accurately represent color, the illumination source must provide photons with all the energies visible to our eye. Such a broad emission is difficult to achieve from a single material. In commercial white-light sources, one or more light-emitting diodes, coated by one or more phosphors, yield a combined emission that appears white. However, combining emitters leads to changes in the emission color over time due to the unequal degradation rates of the emitters and efficiency losses due to overlapping absorption and emission energies of the different components. A single material that emits broadband white light (a continuous emission spanning 400–700 nm) would obviate these problems.In 2014, we described broadband white-light emission upon near-UV excita...

White-Light Emission from Layered Halide Perovskites.

Magic-sized cadmium selenide (CdSe) nanocrystals have been pyrolytically synthesized. These ultra-small nanocrystals exhibit broadband emission (420−710 nm) that covers most of the visible spectrum while not suffering from self absorption. This behavior is a direct result of the extremely narrow size distribution and unusually large Stokes shift (40−50 nm). The intrinsic properties of these ultra-small nanocrystals make them an ideal material for applications in solid state lighting and also the perfect platform to study the molecule-to-nanocrystal transition.

White-light emission from magic-sized cadmium selenide nanocrystals.

White-Light Emission from Magic-Sized Cadmium Selenide Nanocrystals

Alloy nanocrystals provide an additional degree of freedom in selecting desirable properties for nanoscale engineering because their physical and optical properties depend on both size and composition. We report the pyrolytic synthesis of homogeneously alloyed CdSxSe1-x nanocrystals in all proportions. The nanocrystals are characterized using UV−visible absorption spectroscopy, transmission electron microscopy, X-ray diffractrometry, and Rutherford backscattering spectrometry to determine precisely structure, size, and composition. The dependence of band gap on nanocrystal size and composition is elucidated, yielding a bowing constant of 0.29, in agreement with bulk values. In addition, the morphology of the resultant nanocrystals can be altered by changing the reaction conditions, generating structures ranging from homogeneous, spherical nanocrystals to one-dimensional gradient nanorods.

Homogeneously Alloyed CdSxSe1-x Nanocrystals: Synthesis, Characterization, and Composition/Size-Dependent Band Gap

In one aspect, the invention relates to an inorganic nanoparticle or nanocrystal, also referred to as a quantum dot, capable of emitting white light. In a further aspect, the invention relates to an inorganic nanoparticle capable of absorbing energy from a first electromagnetic region and capable of emitting light in a second electromagnetic region, wherein the second electromagnetic region comprises an at least about 50 nm wide band of wavelengths and to methods for the preparation thereof. Li further aspects, the invention relates to a frequency converter, a light emitting diode device, a modified fluorescent light source, an electroluminescent device, and an energy cascade system comprising the nanoparticle of the invention. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.

Broad-emission nanocrystals and methods of making and using same

The exciton dynamics of CdSe nanocrystals are intimately linked to the surface morphology. Photo-oxidation of the selenium surfaces of the nanocrystal leads to an increase in radiative decay efficiency from both the band edge and deep trap emission states. The addition of the primary amine hexadecylamine curtails nonradiative excitonic decay attributed to the dangling surface selenium orbitals by passivation of those trap sites by the methylene protons on the amine, leading to enhanced band edge emission and the absence of deep trap emission. Furthermore, CdSeZnSe core/shell nanocrystals are not immune from contributions from surface states because of the alignment of the band structures of the core and shell materials.

Michael J. Bowers

Papers

White-light emission from magic-sized cadmium selenide nanocrystals.

White-Light Emission from Magic-Sized Cadmium Selenide Nanocrystals

Homogeneously Alloyed CdSxSe1-x Nanocrystals: Synthesis, Characterization, and Composition/Size-Dependent Band Gap

Broad-emission nanocrystals and methods of making and using same

Effects of surface passivation on the exciton dynamics of CdSe nanocrystals as observed by ultrafast fluorescence upconversion spectroscopy