Color science and technology of novel nanophosphors for high-efficiency high-quality LEDs
Demir, Hilmi Volkan
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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.
KeywordsWhite light emitting diodes (white LED)
TK7871.89.L53 E73 2011
Light emitting diodes.
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