title: Implementation of High-Quality Warm-White Light-Emitting Diodes by a Model-Experimental Feedback Approach Using Quantum Dot-Salt Mixed Crystals.
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.
authors.affiliation: Physical Chemistry, TU Dresden , Bergstr. 66b, 01062 Dresden, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Adam
authors.affiliation: Department of Electrical and Electronics Engineering, Department of Physics, and UNAM-Institute of Materials Science and Nanotechnology, Bilkent University , TR-06800 Ankara, Turkey.
authors.forename: Talha
authors.initials: T
authors.lastname: Erdem
authors.affiliation: Physical Chemistry, TU Dresden , Bergstr. 66b, 01062 Dresden, Germany.
authors.forename: Gordon M
authors.initials: GM
authors.lastname: Stachowski
authors.affiliation: Department of Electrical and Electronics Engineering, Department of Physics, and UNAM-Institute of Materials Science and Nanotechnology, Bilkent University , TR-06800 Ankara, Turkey.
authors.forename: Zeliha
authors.initials: Z
authors.lastname: Soran-Erdem
authors.affiliation: Physical Chemistry, TU Dresden , Bergstr. 66b, 01062 Dresden, Germany.
authors.forename: Josephine F L
authors.initials: JF
authors.lastname: Lox
authors.affiliation: Physical Chemistry, TU Dresden , Bergstr. 66b, 01062 Dresden, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Bauer
authors.affiliation: Physical Chemistry, TU Dresden , Bergstr. 66b, 01062 Dresden, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Poppe
authors.affiliation: Department of Electrical and Electronics Engineering, Department of Physics, and UNAM-Institute of Materials Science and Nanotechnology, Bilkent University , TR-06800 Ankara, Turkey.|LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering and School of Physical and Mathematical Sciences, Nanyang Technological University , Singapore 639798, Singapore.
authors.forename: Hilmi Volkan
authors.initials: HV
authors.lastname: Demir
authors.affiliation: Physical Chemistry, TU Dresden , Bergstr. 66b, 01062 Dresden, Germany.
authors.forename: Nikolai
authors.initials: N
authors.lastname: Gaponik
authors.affiliation: Physical Chemistry, TU Dresden , Bergstr. 66b, 01062 Dresden, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Eychmüller
keywords: colloidal nanocrystals; color conversion; composites; mixed crystals; quantum dots; white LEDs