WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
Browse
22 results
Search Results
Article Citation - WoS: 4Citation - Scopus: 4Transparent Films Made of Highly Scattering Particles(Amer Chemical Soc, 2020-01-13) Erdem, Talha; Yang, Lan; Xu, Peicheng; Altintas, Yemliha; O'Neil, Thomas; Caciagli, Alessio; Eiser, ErikaToday, colloids are widely employed in various products from creams and coatings to electronics. The ability to control their chemical, optical, or electronic features by controlling their size and shape explains why these materials are so widely preferred. Nevertheless, altering some of these properties may also lead to some undesired side effects, one of which is an increase in optical scattering upon concentration. Here, we address this strong scattering issue in films made of binary colloidal suspensions. In particular, we focus on raspberry-type polymeric particles made of a spherical polystyrene core decorated by small hemispherical domains of acrylate with an overall positive charge, which display an unusual stability against aggregation in aqueous solutions. Their solid films display a brilliant red color due to Bragg scattering but appear completely white on account of strong scattering otherwise. To suppress the scattering and induce transparency, we prepared films by hybridizing them with oppositely charged PS particles with a size similar to that of the bumps on the raspberries. We report that the smaller PS particles prevent raspberry particle aggregation in solid films and suppress scattering by decreasing the spatial variation of the refractive index inside the film. We believe that the results presented here provide a simple strategy to suppress strong scattering of larger particles to be used in optical coatings.Article Citation - WoS: 12Citation - Scopus: 11Trans-Cis Isomerization Assisted Synthesis of Solution-Processable Yellow Fluorescent Maleic Anhydrides for White-Light Generation(Elsevier Science SA, 2015-12) Ozdemir, Mehmet; Genc, Sinan; Ozdemir, Resul; Altintas, Yemliha; Citir, Murat; Sen, Unal; Usta, HakanHeterocyclic maleic anhydride derivatives have been extensively studied in natural products chemistry over the past few decades. However, their incorporation into optoelectronic devices has lagged behind that of other pi-conjugated systems, and they have never been studied in white light emitting diodes (WLEDs). The development of emissive pi-conjugated materials for (WLEDs) has been an emerging scientific and technological research area to replace phosphors used in LED-based solid-state lighting. Here, we demonstrate the design, synthesis and characterization of two new highly emissive alkyl-substituted bis(thienyl)maleic anhydrides (C6-Th2MA and C12-Th2MA) with favorable photophysical properties. The new core is synthesized via a novel trans-to-cis isomerization-assisted one-pot reaction, which is demonstrated for the first time in the literature for the synthesis of a bis(heteroaryl)maleic anhydride. Due to its favorable absorption and fluorescence properties in the blue and yellow region of the visible spectrum, respectively, C12-Th2MA is studied as a potential wavelength-upconverting material. A WLED fabricated by drop-casting a polymeric solution of C12-Th2MA on a blue LED (InGaN, 455 nm) yields promising CIE coordinates and color-rendering index (CRI) values of (0.24, 0.20) and 65.0, respectively. Considering the simplicity of the current molecular structure and facile synthesis, alkyl-substituted bis(thienyl)maleic anhydrides stand as ideal phosphor alternatives. Therefore, the current findings may open new perspectives for the development of maleic anhydride-based small molecules for low-cost, energy-efficient, and solution-processed lighting technologies. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 4Citation - Scopus: 4Thermal Conductivity and Interfacial Energy of Solid Bi in the Bi-Ag Eutectic System(Springer, 2015-05-15) Altintas, Yemliha; Ozturk, Esra; Aksoz, Sezen; Keslioglu, Kazim; Marasli, Necmettin; Maraşlı, Necmettin; Keşlioğlu, Kâzım; Altıntas, YemlihaThe equilibrated grain boundary groove shapes for solid Bi (Bi-2.87 at.%Ag) in equilibrium with Bi-Ag eutectic liquid have been observed from quenched sample with a radial heat flow apparatus. The Gibbs-Thomson coefficient, solid-liquid interfacial energy and grain boundary energy of solid Bi have been determined from the observed grain boundary groove shapes. The variation of thermal conductivity with temperature for eutectic solid phase (Bi-4.7 at.%Ag) has been measured. The ratio of thermal conductivity of equilibrated eutectic liquid phase to eutectic solid phase has also been measured with a Bridgman-type growth apparatus at the melting temperature. The Gibbs-Thomson coefficient, solid-liquid interfacial energy and grain boundary energy of solid Bi in equilibrium with Bi-Ag eutectic liquid were determined to be (9.2 +/- A 0.6) x 10(-8) K m, (52.7 +/- A 6.3) x 10(-3) J m(-2) and (102.4 +/- A 13.3) x 10(-3) J m(-2), respectively, from observed grain boundary groove shapes.Article Citation - WoS: 23Citation - Scopus: 21The Measurements of Electrical and Thermal Conductivity Variations With Temperature and Phonon Component of the Thermal Conductivity in Sn-Cd Sn-In Sn-Ag and Sn-Bi Alloys(Elsevier France-editions Scientifiques Medicales Elsevier, 2016-02) Altintas, Yemliha; Kaygisiz, Yusuf; Ozturk, Esra; Aksoz, Sezen; Keslioglu, Kazim; Marasli, Necmettin; Kayglslz, Yusuf; Altlntas, YemlihaThe electrical and thermal conductivity variations with temperature for lead-free ternary solders, namely Sn-41.39 at.% Cd-6.69 at.% Sb, Sn-49 at.% In-1 at.% Cu, Sn-50 at.% Ag-10 at.% Bi and Sn-32 at.% Bi-3 at.% Zn alloys, were measured by the d.c. four-point probe method and radial heat flow apparatus, respectively. The contributions of electrons and phonons to the thermal conductivity were separately determined by using the measured values of the thermal and electrical conductivities obtained by the Wiedemann-Franz law in the lead-free ternary solders. The percentages of the phonon component of thermal conductivity were found to be in the range of 46-55%, 46-50%, 38-47% and 69-73% for Sn-41.39 at.% Cd-6.69 at.% SU, Sn-49 at.% In-1 at.% Cu, Sn-50 at.% Ag-10 at.% Bi and Sn-32 at.% Bi-3 at.% Zn alloys at the ranges of 318-443 K temperature, respectively. The temperature coefficients (alpha) of electrical conductivity for the lead-free ternary solders were found to be 2.47 x 10(-3), 4.97 x 10(-3), 1.14 x 10(-3) and 1.00 x 10(-3) K-1, respectively. The thermal conductivities of the solid phases at their melting temperature and the thermal temperature coefficients for the lead-free ternary solders were also found to be 47.72 +/- 2.38, 68.57 +/- 3.42, 73.52 +/- 3.67, 37.53 +/- 1.87 W/Km and 1.47 x 10(-3), 1.48 x 10(-3), 1.85 x 10(-3) and 2.21 x 10(-3) K-1, respectively. (C) 2015 Elsevier Masson SAS. All rights reserved.Article Citation - WoS: 3Citation - Scopus: 4The Experimental Determination of Thermophysical Properties of Intermetallic CuAl2 Phase in Equilibrium With (Al Plus Cu Plus Si) Liquid(Academic Press Ltd- Elsevier Science Ltd, 2016-06) Altintas, Yemliha; Aksoz, Sezen; Keslioglu, Kazim; Marasli, Necmettin; Keşlioʇlu, KâzImThe equilibrated grain boundary groove shapes of solid CuAl2 in equilibrium with (Al + Cu + Si) eutectic liquid were observed from a quenched sample by using a radial heat flow apparatus. The Gibbs-Thomson coefficient, (solid + liquid) interfacial energy and grain boundary energy of the solid CuAl2 were determined from these observed shapes. The thermal conductivity of the eutectic solid and the thermal conductivity ratio of eutectic liquid to the eutectic solid in the (Al + 26.82 wt.% Cu + 5.27 wt.% Si) eutectic alloy at its eutectic melting temperature were also measured with a radial heat flow apparatus and a Bridgman-type growth apparatus, respectively. The three phases of (Al + Cu + Si) alloy have detected as Al solution, Si and theta (CuAl2) phases with EDX composition analysis and the microstructure of these phases were photographed by SEM. (C) 2016 Elsevier Ltd. All rights reserved.Article Citation - WoS: 1Citation - Scopus: 1The Experimental Determination of Interfacial Energies for Solid Zn in Equilibrium With Zn-Al Liquid(Springer, 2015-06-16) Altintas, Yemliha; Ozturk, Esra; Aksoz, Sezen; Keslioglu, Kazim; Marasli, NecmettinThe equilibrated grain boundary groove shapes of solid Zn in equilibrium with Zn-Al-Sb liquid were observed from a quenched sample using a radial heat flow apparatus. The Gibbs-Thomson coefficient, solid-liquid interfacial energy, and grain boundary energy of the solid Zn were determined from the observed grain boundary groove shapes. The thermal conductivity of the eutectic solid phase for Zn-0.4 at. pct Al-0.4 at. pct Sb alloy and the thermal conductivity ratio of the liquid phase to the solid phase for Zn-0.4 at. pct Al-0.4 at. pct Sb alloy at eutectic temperature were also measured with a radial heat flow apparatus and a Bridgman-type growth apparatus, respectively.Article Citation - WoS: 15Citation - Scopus: 14The Effect of Ligand Chain Length on the Optical Properties of Alloyed Core-Shell InPZnS/ZnS Quantum Dots(Elsevier Science SA, 2017-07) Altintas, Yemliha; Talpur, Mohammad Younis; Mutlugun, EvrenIn this work, we demonstrate the effect of organic ligands on the optical properties of alloyed core-shell InPZnS/ZnS quantum dots (QDs). We have systematically studied the synthesis and characterization of InPZnS/ZnS QDs using short and long chain length ligands i.e., butyric (C4), hexanoic (C6), octanoic (C8), dodecanoic (C12), myristic (C14), palmitic (C16) and stearic acids (C18), respectively. This study achieved more than 85% quantum yield with 43 nm full-width-half maximum value, using dodecanoic acid as the capping ligand. The properties of the QDs with short and long chain length ligands have been analyzed using UV Vis absorption spectrophotometer, steady state and time resolved photoluminescence spectrometer, X-ray diffraction, Zeta sizer, transmission electron microscopy and energy dispersive X-ray spectroscopy. (C) 2017 Published by Elsevier B.V.Article Citation - WoS: 16Citation - Scopus: 17Solid-State Encapsulation and Color Tuning in Films of Cesium Lead Halide Perovskite Nanocrystals for White Light Generation(Amer Chemical Soc, 2019-01-30) Torun, Ilker; Altintas, Yemliha; Yazici, Ahmet Faruk; Mutlugun, Evren; Onses, M. SerdarPerovskite nanocrystals (PNCs) are highly demanding nanomaterials for solid-state lighting applications. A challenge for their exploitation in practical applications is the insufficient ambient and water stability associated with their ionic nature. Here we report a novel route for solid-state encapsulation of films of perovskite nanocrystals (PNCs) through vapor-phase deposition of a thin and hydrophobic layer of fluoroalkyltrichlorosilanes (FAS). High quality nanoscale crystals of CsPbBr3 were synthesized with well established colloidal methods and coated on solid substrates. The films of PNCs were then subjected to vapor of FAS for short durations of time (<60 s) in ambient atmosphere, resulting in deposition of a thin (<20 nm) hydrophobic layer. Besides providing a barrier for water and humidity, the vapor-phase deposition of FAS was accompanied by the blue shift of the emission wavelength of the PNCs. The color shift results from the partial exchange of Br with Cl anions, which emerge during the self-hydrolysis of the silane molecules. Throughout this process, we demonstrate the enhanced water stability of the films of PNCs and fine tunability of the wavelength in films from 516 nm to 488 nm. The fabrication of a white-light-emitting diode and tunability of the color coordinates with the duration of the FAS deposition were demonstrated. The rapid, scalable, and inexpensive solid-state encapsulation approach shows great promise for films of halide perovskites.Article Citation - WoS: 128Citation - Scopus: 136Record High External Quantum Efficiency of 19.2% Achieved in Light-Emitting Diodes of Colloidal Quantum Wells Enabled by Hot-Injection Shell Growth(Wiley-VCH Verlag GmbH, 2019-12-23) Liu, Baiquan; Altintas, Yemliha; Wang, Lin; Shendre, Sushant; Sharma, Manoj; Sun, Handong; Demir, Hilmi VolkanColloidal quantum wells (CQWs) are regarded as a highly promising class of optoelectronic materials, thanks to their unique excitonic characteristics of high extinction coefficients and ultranarrow emission bandwidths. Although the exploration of CQWs in light-emitting diodes (LEDs) is impressive, the performance of CQW-LEDs lags far behind other types of soft-material LEDs (e.g., organic LEDs, colloidal-quantum-dot LEDs, and perovskite LEDs). Herein, high-efficiency CQW-LEDs reaching close to the theoretical limit are reported. A key factor for this high performance is the exploitation of hot-injection shell (HIS) growth of CQWs, which enables a near-unity photoluminescence quantum yield (PLQY), reduces nonradiative channels, ensures smooth films, and enhances the stability. Remarkably, the PLQY remains 95% in solution and 87% in film despite rigorous cleaning. Through systematically understanding their shape-, composition-, and device-engineering, the CQW-LEDs using CdSe/Cd0.25Zn0.75S core/HIS CQWs exhibit a maximum external quantum efficiency of 19.2%. Additionally, a high luminance of 23 490 cd m(-2), extremely saturated red color with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.715, 0.283), and stable emission are obtained. The findings indicate that HIS-grown CQWs enable high-performance solution-processed LEDs, which may pave the path for future CQW-based display and lighting technologies.Article Citation - WoS: 6Citation - Scopus: 6Plasmon Enhanced Emission of Perovskite Quantum Dot Films(Cambridge Univ Press, 2018-01-09) Dadi, Seyma; Altintas, Yemliha; Beskazak, Emre; Mutlugun, Evren; Dadl, Seyma; Altlntas, YemlihaWe propose and demonstrate the photoluminescence enhancement of CsPbBr3 perovskite quantum dot films in the presence of Au nanoparticles. Embedded into a polymer matrix, Au nanoparticle-quantum dot film assemble prepared by an easy spin coating method enabled the photoluminescence enhancement of perovskite quantum dot films up to 78%. The properties of the synthesized perovskite QDs and gold nanoparticles have been analysed using high resolution transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, UV-Vis absorption spectrophotometer, steady state and time-resolved photoluminescence spectrometer.
- «
- 1 (current)
- 2
- 3
- »