Browsing by Author "Yazici, Ahmet F."

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    Article
    Osmotic-Pressure-Induced Nematic Ordering in Suspensions of Laponite and Carboxy Methyl Cellulose
    (AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2020) Xu, Peicheng; Yazici, Ahmet F.; Erdem, Talha; Lekkerkerker, Henk N. W.; Mutlugun, Evren; Eiser, Erika; 0000-0003-2747-7856; 0000-0003-3905-376X; 0000-0003-2881-8157; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü
    Laponite is a synthetic clay that is known to form gels in aqueous suspensions at low concentrations (0.01 g/cm(3)) Although it is expected to form lyotropic liquid crystals, such phases usually do not form, as a consequence of laponite's tendency to form gels at concentrations below the threshold for liquid crystal formation. Here we show that macroscopic, birefringent phases of laponite can be prepared through osmotic compression of a laponite solution by an aqueous solution of carboxy methyl cellulose (CMC). We present polarization imaging studies showing how the initially dilute, isotropic laponite phase shrinks while developing typical birefringence colors between crossed polarizers. Using the MichelLevy interference charts, we were able to extract the refractive index and orientation of the laponite nanodisks in the compressed region. Our observations allow us to propose a tentative state diagram, indicating the concentration regions for which we obtain optically anisotropic gels.
  • Thumbnail Image
    Article
    Tailoring Quantum Dot Shell Thickness and Polyethylenimine Interlayers for Optimization of Inverted Quantum Dot Light-Emitting Diodes
    (MDPI, 2024) Yazici, Ahmet F.; Ocal, Sema Karabel; Bicer, Aysenur; Serin, Ramis B.; Kacar, Rifat; Ucar, Esin; Ulku, Alper; Erdem, Talha; Mutlugun, Evren; 0000-0003-3905-376X; 0000-0003-3715-5594; 0000-0003-2747-7856; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Yazici, Ahmet F.; Ocal, Sema Karabel; Bicer, Aysenur; Erdem, Talha; Mutlugun, Evren
    Quantum dot light-emitting diodes (QLEDs) hold great promise for next-generation display applications owing to their exceptional optical properties and versatile tunability. In this study, we investigate the effects of quantum dot (QD) shell thickness, polyethylenimine (PEI) concentration, and PEI layer position on the performance of inverted QLED devices. Two types of alloyed-core/shell QDs with varying shell thicknesses were synthesized using a one-pot method with mean particle sizes of 8.0 ± 0.9 nm and 10.3 ± 1.3 nm for thin- and thick-shelled QDs, respectively. Thick-shelled QDs exhibited a higher photoluminescence quantum yield (PLQY) and a narrower emission linewidth compared to their thin-shelled counterparts. Next, QLEDs employing these QDs were fabricated. The incorporation of PEI layers on either side of the QD emissive layer significantly enhanced device performance. Using PEI on the hole transport side resulted in greater improvement than on the electron injection side. Sandwiching the QD layer between two PEI layers led to the best performance, with a maximum external quantum efficiency (EQE) of 17% and a peak luminance of 91,174 cd/m2 achieved using an optimized PEI concentration of 0.025 wt% on both electron injection and hole injection sides. This study highlights the critical role of QD shell engineering and interfacial modification in achieving high-performance QLEDs for display applications.