Browsing by Subject "White light emitting diodes"

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    A bright cadmium-free, hybrid organic/quantum dot white light-emitting diode
    (American Institute of Physics, 2012-12-06) Yang, X.; Divayana, Y.; Zhao, D.; Swee Leck, K.; Lu, F.; Tiam Tan, S.; Putu Abiyasa, A.; Zhao Y.; Demir, Hilmi Volkan; Wei Sun, X.
    We report a bright cadmium-free, InP-based quantum dot light-emitting diode (QD-LED) with efficient green emission. A maximum brightness close to 700 cd/m2 together with a relatively low turn-on voltage of 4.5 V has been achieved. With the design of a loosely packed QD layer resulting in the direct contact of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl) benzidine] (poly-TPD) and 2,2′,2″-(1,3,5-benzinetriyl)-tris(1- phenyl-1-H-benzimidazole) (TPBi) in the device, a ternary complementary white QD-LED consisting of blue component (poly-TPD), green component (QDs), and red component (exciplex formed at the interface between poly-TPD and TPBi) has been demonstrated. The resulting white QD-LED shows an excellent color rendering index of 95.
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    Construction of multi-layered white emitting organic nanoparticles by clicking polymers
    (Royal Society of Chemistry, 2015) Keita, H.; Güzeltürk, B.; Pennakalathil, J.; Erdem, T.; Demir, Hilmi Volkan; Tuncel, D.
    A series of blue, green and red emitting polymers that are appropriately functionalized with alkyne and azide functional groups have been prepared and clicked together to construct bi-layered and tri-layered white emitting core-shell type nanoparticles. Here the use of these organic hetero-nanoparticles as colour converters to realize a white light-emitting diode platform acquiring a colour quality comparable to the existing phosphor-based ones was also demonstrated. © The Royal Society of Chemistry.
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    ItemOpen Access
    Implementation of high-quality warm-white light-emitting diodes by a model-experimental feedback approach using quantum dot-salt mixed crystals
    (American Chemical Society, 2015) Adam, M.; Erdem, T.; Stachowski, G.M.; Soran-Erdem Z.; Lox, J. F. L.; Bauer, C.; Poppe, J.; Demir, Hilmi Volkan; Gaponik N.; Eychmüller A.
    In this work, a model-experimental feedback approach is developed and applied to fabricate high-quality, warm-white light-emitting diodes based on quantum dots (QDs) as color-conversion materials. Owing to their unique chemical and physical properties, QDs offer huge potential for lighting applications. Nevertheless, both emission stability and processability of the QDs are limited upon usage from solution. Incorporating them into a solid ionic matrix overcomes both of these drawbacks, while preserving the initial optical properties. Here borax (Na2B4O7·10H2O) is used as a host matrix because of its lower solubility and thereby reduced ionic strength in water in comparison with NaCl. This guarantees the stability of high-quality CdSe/ZnS QDs in the aqueous phase during crystallization and results in a 3.4 times higher loading amount of QDs within the borax crystals compared to NaCl. All steps from the synthesis via mixed crystal preparation to the warm-white LED preparation are verified by applying the model-experimental feedback, in which experimental data and numerical results provide feedback to each other recursively. These measures are taken to ensure a high luminous efficacy of optical radiation (LER) and a high color rendering index (CRI) of the final device as well as a correlated color temperature (CCT) comparable to an incandescent bulb. By doing so, a warm-white LED with a LER of 341 lm/Wopt, a CCT of 2720 K and a CRI of 91.1 is produced. Finally, we show that the emission stability of the QDs within the borax crystals on LEDs driven at high currents is significantly improved. These findings indicate that the proposed warm-white light-emitting diodes based on QDs-in-borax hold great promise for quality lighting. © 2015 American Chemical Society.
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    Warm-white light-emitting diodes integrated with colloidal quantum dots for high luminous efficacy and color rendering
    (2010) Nizamoglu, S.; Erdem, T.; Sun X.W.; Demir, Hilmi Volkan
    Warm-white LEDs (WLEDs) with high spectral quality and efficiency are required for lighting applications, but current experimental performances are limited. We report on nanocrystal quantum dot (NQD) hybridized WLEDs with high performance that exhibit a high luminous efficacy of optical radiation exceeding 350 lm/Wopt and a high color rendering index close to 90 at a low correlated color temperature <3000 K. These spectrally engineered WLEDs are obtained using a combination of CdSe/ZnS core/shell NQD nanophosphors integrated on blue InGaN/GaN LEDs. © 2010 Optical Society of America.