Color science and technology of novel nanophosphors for high-efficiency high-quality LEDs
Author(s)
Advisor
Demir, Hilmi VolkanDate
2011Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
Today almost one-fifth of the world‟s electrical energy is consumed for artificial
lighting. To revolutionize general lighting to reduce its energy consumption,
high-efficiency, high-quality light-emitting diodes (LEDs) are necessary.
However, to achieve the targeted energy efficiency, present technologies have
important drawbacks. For example, phosphor-based LEDs suffer from the
emission tail of red phosphors towards longer wavelengths. This deep-red
emission decreases substantially the luminous efficiency of optical radiation.
Additionally, the emission spectrum of phosphor powders cannot be controlled
properly for high-quality lighting, as this requires careful spectral tuning. At this
point, new nanophosphors made of colloidal quantum dots and crosslinkable
conjugated polymer nanoparticles have risen among the most promising
alternative color convertors because they allow for an excellent capability of
spectral tuning. In this thesis, we propose and present high-efficiency, highquality
white LEDs using quantum dot nanophosphors that that exhibit luminous
efficacy of optical radiation ≥380 lm/Wopt, color rendering index ≥90 and
correlated color temperature ≤4000 K. We find that Stoke‟s shift causes a
fundamental loss >15%, which limits the maximum feasible luminous efficiency
to 326.6 lm/Welect. Considering a state-of-the-art blue LED (with 81.3% photon
conversion efficiency), this corresponds to 265.5 lm/Welect. To achieve 100 and 200 lm/Welect, the layered quantum dot films are required to have respective
quantum efficiencies of 39 and 79%. In addition, we report our numerical
modeling and experimental demonstrations of the quantum dot integrated LEDs
for the different vision regimes of human eye. Finally, we present LEDs based
on the color tuning capability of conjugated polymer nanoparticles for the first
time. Considering the outcomes of this thesis, we believe that our research
efforts will help the development and industrialization of white light emitting
diodes using nanophosphor components.
Keywords
White light emitting diodes (white LED)Color science
Photometry
Luminous efficacy
Color rendering
Color temperature
Color tuning
Spectral tuning
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