Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Citation - WoS: 1Citation - Scopus: 1Tailoring Quantum Dot Shell Thickness and Polyethylenimine Interlayers for Optimization of Inverted Quantum Dot Light-Emitting Diodes(MDPI, 2024-07-11) Yazici, Ahmet F.; Ocal, Sema Karabel; Bicer, Aysenur; Serin, Ramis B.; Kacar, Rifat; Ucar, Esin; Mutlugun, EvrenQuantum 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.Article Citation - WoS: 3Citation - Scopus: 3Superior CdSe/ZnS@Fe2O3 Yolk-Shell Nanoparticles as Optically Active MRI Contrast Agents(Wiley-VCH Verlag GmbH, 2022-07) Ekici, Derya D.; Mutlugun, EvrenWe have developed a robust synthesis methodology for quantum dots (QDs) nanoparticles with magnetic properties designed for biomodal imaging. These nanocrsytlas consists of a semiconductor quantum dot core with engineered fluorescence, which is located in a paramagnetic iron oxide shell that acts as a magnetic resonance imaging (MRI) contrast agent. Yolk-shell CdSe/ZnS@Fe2O3 nanoparticles (NPs) are synthesized via sonochemical decomposition of iron pentacarbonyl (Fe(CO)(5)) using the oleylamine (OAm) as the ligand. The sonochemical synthesis method of magnetic fluorescent NPs that can be used as MRI contrast agents provided advantages such as improved quantum efficiency and homogeneous size distributions. It has been determined that the luminescence efficiency of quantum dots decreases in coatings that can be made at high temperatures by thermal decomposition. In order to eliminate the disadvantage of elevated temperatures, the sonochemical decomposition method, which allows coating at low temperatures, has been used. With this method, yolk-shell (CdSe/ZnS@Fe2O3) nanoparticles were produced with high photoluminescence quantum efficiency and homogeneous size distributions. The synthesis magnetic fluorescent NPs optimized was determined to have the injection temperature of Fe(CO)(5) at 60 degrees C, Fe(CO)(5)/CdSe@ZnS ratio 0.7, OAm/Fe(CO)(5) volume ratio 1.43 with an oxidation time 5 min. Under these conditions, the quantum efficiency was found to be 78 %, nanoparticle sizes between 11-14 nm and r(1) value was 0.199, r(2) value was 0.518 in MRI analysis. These optically active magnetic fluorescent nanoparticles as positive contrast agents (T1 weighted) are predicted to pave the way for the future of advanced bio-imaging systems.Article Citation - WoS: 1Citation - Scopus: 1Osmotic-Pressure Nematic Ordering in Suspensions of Laponite and Carboxy Methyl Cellulose(Amer Chemical Soc, 2020-10-12) Xu, Peicheng; Yazici, Ahmet F.; Erdem, Talha; Lekkerkerker, Henk N. W.; Mutlugun, Evren; Eiser, ErikaLaponite 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.Article Citation - WoS: 12Citation - Scopus: 11Long-Time Stable Colloidal Zn-Ag Quantum Dots With Tunable Midgap-Involved Emission(AIP Publishing, 2021-02-11) Sabzevari, Zahra; Sahraei, Reza; Jawhar, Nawzad Nadhim; Yazici, Ahmet Faruk; Mutlugun, Evren; Soheyli, EhsanQuaternary Zn-Ag-In-S (ZAIS) quantum dots (QDs) with efficient, tunable, and stable photoluminescence (PL) emission were prepared via a simple, effective, and low-cost reflux method. The structural analysis revealed the dominance of the quantum confinement effect. The calculated PL emission quantum yield was enhanced from 8.2% to 28.7% with experimental parameters indicating their marked influence on the PL emission properties of the final product. Particularly, it was found that by varying the precursors' feeding ratio, tunable emission from green to red was achieved. A set of direct and indirect pieces of evidence such as the broad-band emission spectrum (FWHM>100nm), large Stokes shift more than 120nm, and predominantly a biexponentially long-lived decay profile with an average lifetime of about 366ns were observed, showing the contribution of midgap localized energy levels in the recombination process. These data were obtained independently on the experimental condition used, which confirmed that this is mostly an intrinsic electronic property of quaternary In-based QDs. Finally, to ensure the stability of QDs in terms of colloidal and optical emission, their emission ability was evaluated after 26 months of storage. Colloidal QDs were still luminescent with strong yellowish-orange color with emission efficiency of similar to 20.3% after 26 months. The combination of synthesis simplicity, compositional non-toxicity, PL emission superiority (strong, tunable, stable, and long lifetime emission), and colloidal stabilities confirms that the present ZAIS QDs are promising candidates for a wide range of applications in biomedicine, anticounterfeiting, and optoelectronics.Article Citation - WoS: 21Citation - Scopus: 21Efficient Forster Resonance Energy Transfer Donors of In(Zn)P/ZnS Quantum Dots(Amer Chemical Soc, 2017-01-26) Altintas, Yemliha; Talpur, Mohammad Younis; Mutlugun, Evren; Altlntas, YemlihaWe demonstrate a detailed investigation of the effect of the type and concentration of zinc precursor on the optical properties of In(Zn)P/ZnS quantum dots. We achieved up to 87% quantum yield along with 54 nm emission bandwidth for the green emitters with changing the concentration of the Zn precursors. Employing efficient green emitters as the donor species, we demonstrated an efficient Forster resonance energy transfer (FRET) couple of green and red emitting InP-based quantum dots. With a FRET efficiency level of 70.3% achieved (analyzed from the donor lifetime with and without an acceptor), we further demonstrated the enhancement of the acceptor emission nearly twofold due to the energy transfer. Our results provide new insights toward the understanding of the excitonic interactions among donor and acceptor quantum dots of the III-V family for light harvesting applications.Article Citation - WoS: 15Citation - Scopus: 14Effects of Silver Nanowires and Their Surface Modification on Electromagnetic Interference, Transport and Mechanical Properties of an Aerospace Grade Epoxy(Sage Publications Ltd, 2024-03-03) Ozkutlu Demirel, Merve; Ozturkmen, Mahide B.; Savas, Muzeyyen; Mutlugun, Evren; Erdem, Talha; Oz, YahyaThe aerospace industry has progressively grown its use of composites. Electrically conductive nanocomposites are among important modern materials for this sector. We report on a bulk composite containing silver nanowires (AgNW) and an aerospace grade epoxy for use in carbon fiber reinforced polymers (CFRPs). AgNWs' surfaces were also modified to enhance their ability to be dispersed in epoxy. Composites were obtained by use of three-roll milling which is of major interest for industrial applications, especially for the aerospace sector, since the process is scalable and works for aerospace grade resins with high curing temperatures. Our main objective is to improve the electromagnetic interference (EMI) shielding performance of CFRPs via improving the properties of the resin material. The addition of AgNWs did not considerably alter the flexural strength of the epoxy, however the composite with surface-modified AgNWs has a 46 % higher flexural strength. Adding AgNWs over a low threshold concentration of 0.05 wt% significantly enhanced the electrical conductivity. Conductivities above the percolation threshold lie around 102 S/m. At a concentration of 5 wt% AgNW, the EMI shielding efficiency (SE) of epoxy increased from 3.49 to 12.31 dB. Moreover, the thermal stability of the epoxy was unaffected by AgNWs. As a result, it was discovered that (surface modified) AgNWs improved the (multifunctional) capabilities of the aerospace grade epoxy resin which might be used in CFRPs to further enhance properties of composites parts, demonstrating suitability of AgNWs' as a reinforcement material in aerospace applications.Article Citation - WoS: 3Citation - Scopus: 3Designed Optimization of Photoluminescence Emission for Carbon Dots With Bright Blue Emission at 416 NM and Mono-Exponential Decay Lifetime(Elsevier, 2025-09) Ruwaih, Mohammed Abbas; Soheyli, Ehsan; Naji, Jalil; Mutlugun, Evren; Kikhavani, Tavan; Sahraei, Reza; Abbas Ruwaih, MohammedThe presented study introduces optimized blue-emissive carbon dots (CDs) with high photoluminescence efficiency up to 65 % at 416 nm, large Stokes shift (69 nm), and full-width at half maximum (FWHM) of 73 nm. Xray photoelectron spectroscopy confirmed the formation of carbon-based bonds as the main component of CDs, with reliable amounts of O, S, and N as dopant components. These features, along with single-exponential time-decay profile at long average lifetime of 10.05 ns, supported the significant role of uniformly distributed mid-gap energy levels in the recombination process. The simplicity, low-cost, non-toxicity, and short reaction time of CDs, along with their excellent emission properties in the deep-blue region, make them suitable for use in environmental monitoring and high-contrast bioimaging.Article Citation - WoS: 44Citation - Scopus: 46Highly Efficient Cd-Free Alloyed Core/Shell Quantum Dots With Optimized Precursor Concentrations(Amer Chemical Soc, 2016) Altintas, Yemliha; Talpur, Mohammad Younis; Unlu, Miray; Mutlugun, EvrenThe chemical composition, the emission spectral bandwidth, and photoluminescence quantum yield of a semiconductor quantum dot (QD) play an important role in the assessment of the performance of the applications related to the quantum dots. Quantum dots based on environmentally friendly compositions with high optical performance have been in demand for high-end technological applications. In this work, we propose and demonstrate a detailed synthesis approach for environmentally friendly and highly efficient InPZnS alloy/ZnS shell quantum dots. Following a systematic study of the ratio and type of the precursors involved, we achieved alloyed core shell InPZnS/ZnS QDs with tunable emission across the visible spectrum, having a record quantum efficiency up to 78% along with a full width at half-maximum as narrow as 45 nm. The effect of the systematic shell growth has been further investigated using time-resolved photoluminescence characterizations along with the observation of the suppression of the nonradiative decay channels, with the photoluminescence lifetime prolonged from 20.3 to 50.4 ns. The development of highly efficient and environmentally friendly QDs will pave the way for robust, sustainable optoelectronic applications.