390 research outputs found
Error Comes With Imagination: A Probabilistic Theory of Mental Content
Thesis (PhD) - Indiana University, Philosophy, 2006In this dissertation, I develop a probabilistic theory of mental content that accounts for fundamental properties of mental representation. The theory that I develop falls under the category of causal/informational approaches. In contemporary philosophy, causal/informational approaches for explaining mental representation have been around since the 1950s. The main success of these approaches is to explain the link between the external world and mental entities. On the other hand, it turns out that accounting for misrepresentation cases presents an insurmountable problem for these approaches. The probabilistic theory that I develop keeps the positive features of causal/informational approaches and provides grounds for solving the problem of misrepresentation. The theory that I offer heavily draws from Dretske's 1981 framework. His framework borrows some notions such as entropy from Shannon & Weaver's Mathematical Theory of Communication which is a very successful formalism for engineering purposes. Dretske tries to explain mental representation, belief and knowledge by using the notion of informational content. Despite all of its appeals, however, the problem of misrepresentation also afflicts his framework. In this dissertation, I identify the reasons that cause problems in Dretske's framework. Identifying these reasons provides enough grounds for solving the problem of misrepresentation in the theory that I construct. I claim that the theory that I offer not only solves the problem of misrepresentation but also provides a research program for Cognitive Science and Neuroscience
Temperature-dependent Optoelectronic Properties of Quasi-2D Colloidal Cadmium Selenide Nanoplatelets
Colloidal Cadmium Selenide (CdSe) nanoplatelets (NPLs) are a recently
developed class of efficient luminescent nanomaterial suitable for
optoelectronic device applications. A change in temperature greatly affects
their electronic bandstructure and luminescence properties. It is important to
understand how-and-why the characteristics of NPLs are influenced, particularly
at elevated temperature, where both reversible and irreversible quenching
processes come into picture. Here we present a study on the effect of elevated
temperature on the characteristics of colloidal CdSe NPLs. We used an
effective-mass envelope function theory based 8-band kp model and
density-matrix theory considering exciton-phonon interaction. We observed the
photoluminescence (PL) spectra at various temperatures for their photon
emission energy, PL linewidth and intensity by considering the exciton-phonon
interaction with both acoustic and optical phonons using Bose-Einstein
statistical factors. With rise in temperature we observed a fall in the
transition energy (emission redshift), matrix element, Fermi factor and quasi
Fermi separation, with reduction in intraband state gaps and increased
interband coupling. Also, there was a fall in the PL intensity, along with
spectral broadening due to an intraband scattering effect. The predicted
transition energy values and simulated PL spectra at varying temperatures
exhibit appreciable consistency with experimental results. Our findings have
important implications for application of NPLs in optoelectronic devices, such
as NPL lasers and LEDs, operating much above room temperature.Comment: Published in Royal Society of Chemistry, Nanoscale (12 pages, 9
figures
Anomalous Spectral Characteristics of Ultrathin sub-nm Colloidal CdSe Nanoplatelets
We demonstrate high quantum yield broad photoluminescence emission of
ultrathin sub-nanometer CdSe nanoplatelets (two-monolayer). They also exhibit
polarization-characterized lateral size dependent anomalous heavy hole and
light/split-off hole absorption intensities.Comment: Published in Conference on Lasers and Electro-Optics (CLEO): Science
and Innovations 2017, San Jose, CA, USA, 14-19 May 2017 (2 pages, 3 figures
Exciton Dynamics of Colloidal Semiconductor Quantum Well Stacks
Colloidal semiconductor nanoplatelets (NPLs) have recently emerged as a new class of colloidal nanocrystals. NPLs are quasi two-dimensional nanocrystals having atomically flat surfaces and have unique properties such as narrow photoluminescence (PL) emission (similar to 10 nm) and giant oscillator strength. NPLs can be self-assembled into stacks. These are one-dimensional superstructures that can contain tens or hundreds of NPLs in one chain
Energy-saving quality road lighting with colloidal quantum dot nanophosphors
Here the first photometric study of road-lighting white light-emitting diodes (WLEDs) integrated with semiconductor colloidal quantum dots (QDs) is reported enabling higher luminance than conventional light sources, specifically in mesopic vision regimes essential to street lighting. Investigating over 100 million designs uncovers that quality road-lighting QD-WLEDs, with a color quality scale and color rendering index >= 85, enables 13-35% higher mesopic luminance than the sources commonly used in street lighting. Furthermore, these QD-WLEDs were shown to be electrically more efficient than conventional sources with power conversion efficiencies >= 16-29%. Considering this fact, an experimental proof-of-concept QD-WLED was demonstrated, which is the first account of QD based color conversion custom designed for street lighting applications. The obtained white LED achieved the targeted mesopic luminance levels in accordance with the road lighting standards of the USA and the UK. These results indicate that road-lighting QD-WLEDs are strongly promising for energy-saving quality road lighting
SILICA NANOPARTICLE FORMATION BY USING DROPLET-BASED MICROREACTOR
This paper describes a method for the synthesis of silica nanoparticles that can be later used for coating of quantum dots inside a microfluidic reactor. Here, a droplet-based system is used where two reagents were mixed inside the droplets to obtain silica. Particles in the size range of 25 +/- 2.7 nm were obtained with comparable size distribution to controlled batch wise synthesis methods. This method is suitable to be used later to coat CdSe nanoparticles inside the microreactor
Excitonic improvement of colloidal nanocrystals in salt powder matrix for quality lighting and color enrichment
Here we report excitonic improvement in color-converting colloidal nanocrystal powders enabled by co-integrating nonpolar green-and red-emitting nanocrystal energy transfer pairs into a single LiCl salt matrix. This leads to nonradiative energy transfer (NRET) between the cointegrated nanocrystals in the host matrix. Here we systematically studied the resulting NRET process by varying donor and acceptor concentrations in the powders. We observed that NRET is a strong function of both of the nanocrystal concentrations and that NRET efficiency increases with increasing acceptor concentration. Nevertheless, with increasing donor concentration in the powders, NRET efficiency was found to first increase ( up to a maximum level of 53.9%) but then to decrease. As a device demonstrator, we employed these NRET-improved nanocrystal powders as color-converters on blue light-emitting diodes ( LEDs), with the resulting hybrid LED exhibiting a luminous efficiency > 70 lm/Welect. The proposed excitonic nanocrystal powders potentially hold great promise for quality lighting and color enrichment applications. (C) 2015 Optical Society of Americ
Ultralow Threshold One-Photon- and Two-Photon-Pumped Optical Gain Media of Blue-Emitting Colloidal Quantum Dot Films
Colloidal quantum dots (QDs) offer advantageous properties as an optical gain media for lasers. Optical gain in the QDs has been shown in the whole visible spectrum, yet it has been intrinsically challenging to realize efficient amplified spontaneous emission (ASE) and lasing in the blue region of the visible spectrum. Here, we synthesize large-sized core/gradient shell CdZnS/ZnS QDs as an efficient optical gain media in the blue spectral range. In this Letter, we demonstrate for the first time that two-photon-absorption-pumped ASE from the blue-emitting QD is achievable with a threshold as low as 6 mJ/cm(2). Utilizing these QDs, we also report one-photon-absorption-pumped ASE at an ultralow threshold of similar to 60 mu J/cm(2), which is comparable to the state-of-the-art red-emitting QD-based gain media. This one-photon-pumped ASE threshold is an order of magnitude better than that of the previously reported best blue-emitting QD-based gain media
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