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      Implementation of high-quality warm-white light-emitting diodes by a model-experimental feedback approach using quantum dot-salt mixed crystals

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      Author
      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.
      Date
      2015
      Source Title
      ACS Applied Materials and Interfaces
      Print ISSN
      1944-8244
      Publisher
      American Chemical Society
      Volume
      7
      Issue
      41
      Pages
      23364 - 23371
      Language
      English
      Type
      Article
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      Abstract
      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.
      Keywords
      Colloidal nanocrystals
      Color conversion
      Composites
      Mixed crystals
      Quantum dots
      White LEDs
      Borate minerals
      Color
      Composite materials
      Diodes
      Ionic strength
      Lighting
      Nanocrystals
      Optical properties
      Semiconductor quantum dots
      Sodium borate
      Chemical and physical properties
      Colloidal nanocrystals
      Color conversions
      Correlated color temperature
      High color rendering index
      Mixed crystals
      White LED
      White light emitting diodes
      Light emitting diodes
      Permalink
      http://hdl.handle.net/11693/26685
      Published Version (Please cite this version)
      http://dx.doi.org/10.1021/acsami.5b08377
      Collections
      • Department of Electrical and Electronics Engineering 3337
      • Department of Physics 2149
      • Institute of Materials Science and Nanotechnology 1580

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