Browsing by Subject "Leds"

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    Green/yellow solid state lighting via radiative and nonradiative energy transfer involving colloidal semiconductor nanocrystals
    (IEEE, 2009-08-05) Nizamoglu, S.; Sari, E.; Baek, J. H.; Lee, I. H; Demir, Hilmi Volkan
    LEDs made of In(x)Ga(1-x)N and (Al(x)Ga(1-x))(1-y)In(y)P suffer from significantly reduced quantum efficiency and luminous efficiency in the green/yellow spectral ranges. To address these problems, we present the design, growth, fabrication, hybridization, and characterization of proof-of-concept green/yellow hybrid LEDs that utilize radiative and nonradiative [Forster resonance energy transfer (FRET)] energy transfers in their colloidal semiconductor nanocrystals (NCs) integrated on near-UV LEDs. In our first NC-LED, we realize a color-converted LED that incorporate green-emitting CdSe/ZnS core/shell NCs (lambda(PL) = 548 nm) on near-UV InGaN/GaN LEDs (lambda(EL) = 379 nm). In our second NC-LED, we implement a color-converted FRET-enhanced LED. For that, we hybridize a custom-design assembly of cyan-and green-emitting CdSe/ZnS core/shell NCs (lambda(PL) = 490 and 548 nm) on near-UV LEDs. Using a proper mixture of differently sized NCs, we obtain a quantum efficiency enhancement of 9% by recycling trapped excitons via FRET. With FRET-NC-LEDs, we show that it is possible to obtain a luminous efficacy of 425 lm/W(opt) and a luminous efficiency of 94 lm/W, using near-UV LEDs with a 40% external quantum efficiency. Finally, we investigate FRET-converted light-emitting structures that use nonradiative energy transfer directly from epitaxial quantum wells to colloidal NCs. These proof-of-concept demonstrations show that FRET-based NC-LEDs hold promise for efficient solid-state lighting in green/yellow.
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    ItemOpen Access
    Spatially Selective Assembly of Quantum Dot Light Emitters in an LED Using Engineered Peptides
    (American Chemical Society, 2011-02-23) Demir, Hilmi Volkan; Seker, U. O. S.; Zengin, G.; Mutlugun, E.; Sari, E.; Tamerler, C.; Sarikaya, M.
    Semiconductor nanocrystal quantum dots are utilized in numerous applications in nano- and biotechnology. In device applications, where several different material components are involved, quantum dots typically need to be assembled at explicit locations for enhanced functionality. Conventional approaches cannot meet these requirements where assembly of nanocrystals is usually material-nonspecific, thereby limiting the control of their spatial distribution. Here we demonstrate directed self-assembly of quantum dot emitters at material-specific locations in a color-conversion LED containing several material components including a metal, a dielectric, and a semiconductor. We achieve a spatially selective immobilization of quantum dot emitters by using the unique material selectivity characteristics provided by the engineered solid-binding peptides as smart linkers. Peptide-decorated quantum dots exhibited several orders of magnitude higher photoluminescence compared to the control groups, thus, potentially opening up novel ways to advance these photonic platforms in applications ranging from chemical to biodetection.