79,540 research outputs found
Hybrid remote quantum dot/powder phosphor designs for display backlights
Quantum dots are ideally suited for color conversion in light emitting diodes owing to their spectral tunability, high conversion efficiency and narrow emission bands. These properties are particularly important for display backlights; the highly saturated colors generated by quantum dots justify their higher production cost. Here, we demonstrate the benefits of a hybrid remote phosphor approach that combines a green-emitting europium-doped phosphor with red-emitting CdSe/CdS core/shell quantum dots. Different stacking geometries, including mixed and separate layers of both materials, are studied at the macroscopic and microscopic levels to identify the configuration that achieves maximum device efficiency while minimizing material usage. The influence of reabsorption, optical outcoupling and refractive index-matching between the layers is evaluated in detail with respect to device efficiency and cost. From the findings of this study, general guidelines are derived to optimize both the cost and efficiency of CdSe/CdS and other (potentially cadmium-free) quantum dot systems. When reabsorption of the green and/or red emission is significant compared to the absorption strength for the blue emission of the pumping light emitting diode, the hybrid remote phosphor approach becomes beneficial
A widely tunable few electron droplet
Quasi-static transport measurements are employed to characterize a few
electron quantum dot electrostatically defined in a GaAs/AlGaAs
heterostructure. The gate geometry allows observations on one and the same
electron droplet within a wide range of coupling strengths to the leads. The
weak coupling regime is described by discrete quantum states. At strong
interaction with the leads Kondo phenomena are observed as a function of a
magnetic field. By varying gate voltages the electron droplet can, in addition,
be distorted into a double quantum dot with a strong interdot tunnel coupling
while keeping track of the number of trapped electrons.Comment: 11 pages, 5 figure
Control of valley dynamics in silicon quantum dots in the presence of an interface step
Recent experiments on silicon nanostructures have seen breakthroughs toward
scalable, long-lived quantum information processing. The valley degree of
freedom plays a fundamental role in these devices, and the two lowest-energy
electronic states of a silicon quantum dot can form a valley qubit. In this
work, we show that a single-atom high step at the silicon/barrier interface
induces a strong interaction of the qubit and in-plane electric fields, and
analyze the consequences of this enhanced interaction on the dynamics of the
qubit. The charge densities of the qubit states are deformed differently by the
interface step, allowing non-demolition qubit readout via valley-to-charge
conversion. A gate-induced in-plane electric field together with the interface
step enables fast control of the valley qubit via electrically driven valley
resonance. We calculate single- and two-qubit gate times, as well as relaxation
and dephasing times, and present predictions for the parameter range where the
gate times can be much shorter than the relaxation time and dephasing is
reduced.Comment: 12 pages, 6 figure
A study to explore the use of orbital remote sensing to determine native arid plant distribution
The author has identified the following significant results. It is possible to determine, from ERTS imagery, native arid plant distribution. Using techniques of multispectral masking and extensive fieldwork, three native vegetation communities were defined and mapped in the Avra Valley study area. A map was made of the Yuma area with the aid of ground truth correlations between areas of desert pavement visible on ERTS images and unique vegetation types. With the exception of the Yuma soil-vegetation correlation phenomena, only very gross differentiations of desert vegetation communities can be made from ERTS data. Vegetation communities with obvious vegetation density differences such as saguaro-paloverde, creosote bush, and riparian vegetation can be separated on the Avra Valley imagery while more similar communities such as creosote bush and saltbush could not be differentiated. It is suggested that large differences in vegetation density are needed before the signatures of two different vegetation types can be differentiated on ERTS imagery. This is due to the relatively insignificant contribution of vegetation to the total radiometric signature of a given desert scene. Where more detailed information concerning the vegetation of arid regions is required, large scale imagery is appropriate
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