Browsing by Subject "Macrocrystals"

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Open Access
Novel light-emitting devices of semiconductor quantum dots and conjugated polymer nanoparticles
(2016-08) Erdem, Talha
Starting with the modern times, lighting has become an essential part of our lives. Today, its share of the total energy consumption reaching 15% should not surprise us. This share further increases when the energy demand for display backlighting is taken into account. Therefore, increasing the effciency of the lighting sources is of significant importance for decreasing the carbon footprint for a sustainable environment. At this point, light-emitting diodes (LEDs) step forward as the most important candidate for revolutionizing the existing lighting systems; however, the current conventional technologies, which typically employ rare-earth ion based broad-band emitters, are plagued with low photometric effciency, lack of light quality, and incapability of the spectrum design for application-specific performance. As a remedy to these problems, in this thesis we study light-emitting diodes of quantum dots that are effcient narrow-band emitters as opposed to phosphors. These colloidal quantum dots allow for the achievement of the light source performance specific to each application. By employing this strength, we first present our design of quantum dot integrated LED display backlight for reducing the adverse effects of the displays on the human biological rhythm while maximizing the color definition. Here we also addressed the need for light sources exhibiting polarization anisotropy for display backlights by hybridizing self-assembled magnetic nanowires and quantum dots. To solve the emission stability problem of the quantum dots in solid-films, we demonstrated the incorporation of the quantum dots within crystalline matrices that act as a barrier against oxygen and humidity and substantially increase their emission stability. Another important strength of this technique has been the preservation of the dispersion quantum effciencies of the quantum dots in powder form and in solid-films. By employing these material systems, we designed and successfully demonstrated a warm white LED exhibiting successful color rendition capability and large spectral overlap with the human eye sensitivity function. We also showed that embedding quantum dots into crystalline matrices offers a robust platform to study the excitonic and plasmonic interactions, both of which we utilized for increasing the effciencies of the quantum dots in crystalline matrices. To meet the need for non-toxic color converter enabling color tuning, we also employed conjugated polymer nanoparticles and studied their near-field interaction with epitaxially grown quantum well nanopillars to boost their emission intensity. We believe that the materials and light sources that we presented in this thesis will enable to reach the targets for realizing high-effciency but also high-quality light sources for general lighting and displays.
Open Access
Sweet plasmonics: sucrose macrocrystals of metal nanoparticles
(Tsinghua University Press, 2015-03) Erdem, T.; Soran - Erdem, Z.; Hernandez - Martinez, P. L.; Sharma, V. K.; Akçalı, H.; Akçalı, I.; Gaponik N.; Eychmuller, A.; Demir, Hilmi Volkan
The realization of plasmonic structures generally necessitates expensive fabrication techniques, such as electron beam and focused ion beam lithography, allowing for the top-down fabrication of low-dimensional structures. Another approach to make plasmonic structures in a bottom-up fashion is colloidal synthesis, which is convenient for liquid-state applications or very thin solid films where aggregation problems are an important challenge. The architectures prepared using these methods are typically not robust enough for easy handling and convenient integration. Therefore, developing a new plasmonic robust platform having large-scale dimensions without adversely affecting the plasmonic features is in high demand. As a solution, here we present a new plasmonic composite structure consisting of gold nanoparticles (Au NPs) incorporated into sucrose macrocrystals on a large scale, while preserving the plasmonic nature of the Au NPs and providing robustness in handling at the same time. As a proof of concept demonstration, we present the fluorescence enhancement of green CdTe quantum dots (QDs) via plasmonic coupling with these Au NPs in the sucrose crystals. The obtained composite material exhibits centimeter scale dimensions and the resulting quantum efficiency (QE) is enhanced via the interplay between the Au NPs and CdTe QDs by 58% (from 24% to 38%). Moreover, a shortening in the photoluminescence lifetime from 11.0 to 7.40 ns, which corresponds to a field enhancement factor of 2.4, is observed upon the introduction of Au NPs into the QD incorporated macrocrystals. These results suggest that such "sweet" plasmonic crystals are promising for large-scale robust platforms to embed plasmonic nanoparticles.