Browsing by Author "Mutlugun, Evren"

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Arrays of multi-color emitting cesium lead halide perovskite nanocrystals and efficient white light generation by tailored anion exchange reactions and electrohydrodynamic jet printing
(Optica Publishing Group (formerly OSA), 2018) Altintas, Yemliha; Torun, Ilker; Yazici, Ahmet Faruk; Beskazak, Emre; Onses, M. Serdar; Mutlugun, Evren; 0000-0003-2747-7856; 0000-0003-3715-5594; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Altintas, Yemliha; Yazici, Ahmet Faruk; Beskazak, Emre; Mutlugun, Evren
We employ highly efficient and narrow band emitter Cesium-lead-halide perovskite nanocrystals, optimized by the anion exchange method, for efficient white light generation by patterning multiple lines of different colors via proposed electrohydrodynamic jet printing.
Cd-free quantum dot pellets for efficient white light generation
(OPTICAL SOC AMER, 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA, 2017) Altintas, Yemliha; Talpur, Mohammad Younis; Mutlugun, Evren; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü;
Semiconductor quantum dots have been on demand for niche optoelectronic applications providing color tenability and possessing high quantum yield and high extinction coefficient. Although the investigation of II-VI have attained a mature level of understanding of the photo physical properties, suppression of the nonradiative decay channels and enhancing the optical properties for III-V material systems still remain a challenge. In this study, we have developed and demonstrated a simple, very fast, and efficient strategy to synthesize the highly luminescent III-V group based In(Zn)P quantum dots (QDs) utilized by the effect of core growth temperature, revealing their emission kinetics and their outstanding application for white light generation. Varying the core growth temperature from 240 degrees C to 90 degrees C, limiting the extent of the precursors involved in the synthesis, and a substantial enhancement of the photoluminescence quantum yield up to 75% is demonstrated. Further modification of the synthesis procedure with optimizing the In:P precursor ratio for the first time up to 88.5 +/- 5.5% quantum yield of alloyed core/shell In(Zn)P/ZnS QDs is achieved, in which the whole synthesis process takes only around one hour. In addition, as a demonstration of Cd-free pellets, versatile pellets of green and orange emitting QDs within KCl macrocrystals are prepared. Hybridizing with blue LED, a white light with correlated color temperature of 4597K along with an unprecedentedly high color rendering index of 90 is presented. (C) 2017 Optical Society of America
CdSe/ZnS quantum dot films for high performance flexible lighting and display applications
(IOP PUBLISHING LTDTEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND, 2016) Altintas, Yemliha; Genc, Sinan; Talpur, Mohammad Younis; Mutlugun, Evren; 0000-0002-6909-723X; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Mutlugun, Evren; Altintas, Yemliha; Genc, Sinan; Talpur, Mohammad Younis
Colloidal quantum dots have attracted significant interest in recent years for lighting and display applications and have recently appeared in high-end market products. The integration of quantum dots with light emitting diodes has made them promising candidates for superior lighting applications with tunable optical characteristics. In this work we propose and demonstrate high quality colloidal quantum dots in their novel free-standing film forms to allow high quality white light generation to address flexible lighting and display applications. High quality quantum dots have been characterized using transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, steady state and time resolved photoluminescence and dynamic light scattering methods. The engineering of colloidal quantum dot composition and its optical properties in stand-alone film form has led to the experimentally high NTSC color gamut of 122.5 (CIE-1931) for display applications, color rendering index of 88.6, luminous efficacy of optical radiation value of 290 lm/W-opt and color temperature of 2763 K for lighting applications.
Cesium-lead based inorganic perovskite quantum-dots as interfacial layer for highly stable perovskite solar cells with exceeding 21% efficiency
(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2019) Akin, Seckin; Altintas, Yemliha; Mutlugun, Evren; Sonmezoglu, Savas; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Despite the excellent photovoltaic performances of perovskite solar cells (PSCs), the instability of PSCs under severe environment (e.g. humidity, light-induced, etc.) limits further commercialization of such devices. Therefore, in recent years, research on the long-term stability improvement of PSCs has been actively carried out in perovskite field. To address these issues, we demonstrated the incorporation of ultra-thin interfacial layer of inorganic CsPbBr1.85I1.15 perovskite quantum-dots (PQDs) that can effectively passivate defects at or near to the perovskite/hole transport material (HTM) interface, significantly suppressing interfacial recombination. This passivation layer increased the open circuit voltage (V-oc) of triple-cation perovskite cells by as much as 50 mV, with champion cells achieving V-oc similar to 1.14 V. As a result, we obtained hysteresis-free cells with the efficiency beyond 21%. More importantly, devices based on such architecture are capable of resisting humidity and light-induced. Remarkably, the device employing CsPbBr1.85I1.15 demonstrated a superb shelf-stability aganist to humidity under ambient conditions (R.H. >= 40%), retaining nearly 91% of initial efficiency after 30 days, while the efficiency of control device rapidly dropped to 45% from its initial value under the same conditions. Besides benefiting from the high moisture resistivity as well as supressed ion migration, PSC5 based on PQDs showed better operational stability (retaining 94% of their initial performance) than that of the PQDs-free one under continuous light irradiation over 400 h. In addition, a faster PL decay time of 4.66 ns was attained for perovskite/PQDs structure (5.77 ns for only PQDs structure) due to the favorable energy transfer at the interface, indicating a Forster resonance energy transfer (FRET) mechanism. This work indicates that inorganic PQDs are important materials as interlayer in PSC5 to supremely enhance the device stability and efficiency.
Colloidal Quantum Dot Light-Emitting Diodes Employing Phosphorescent Small Organic Molecules as Efficient Exciton Harvesters
(AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2014) Mutlugun, Evren; Guzelturk, Burak; Abiyasa, Agus Putu; Gao, Yuan; Sun, Xiao Wei; Demir, Hilmi Volkan; AGÜ, Mühendislik Fakültesi, Elektrik & Elektronik Mühendisliği Bölümü;
Nonradiative energy transfer (NRET) is an alternative excitation mechanism in colloidal quantum dot (QD) based electroluminescent devices (QLEDs). Here, we develop hybrid highly spectrally pure QLEDs that facilitate energy transfer pumping via NRET from a phosphorescent small organic molecule-codoped charge transport layer to the adjacent QDs. A partially codoped exciton funnelling electron transport layer is proposed and optimized for enhanced QLED performance while exhibiting very high color purity of 99%. These energy transfer pumped hybrid QLEDs demonstrate a 6-fold enhancement factor in the external quantum efficiency over the conventional QLED structure, in which energy transfer pumping is intrinsically weak.
Color Enrichment Solids of Spectrally Pure Colloidal Quantum Wells for Wide Color Span in Displays
(WILEY-V C H VERLAG GMBH, 2022) Erdem, Talha; Soran-Erdem, Zeliha; Isik, Furkan; Shabani, Farzan; Yazici, Ahmet Faruk; Mutlugun, Evren; Gaponik, Nikolai; Demir, Hilmi Volkan; 0000-0001-7607-9286; 0000-0003-2747-7856; 0000-0003-3905-376X; 0000-0003-3715-5594; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Erdem, Talha; Soran-Erdem, Zeliha; Yazıcı, Ahmet Faruk; Mutlugün, Evren
Colloidal quantum wells (CQWs) are excellent candidates for lighting and display applications owing to their narrow emission linewidths (<30 nm). However, realizing their efficient and stable light-emitting solids remains a challenge. To address this problem, stable, efficient solids of CQWs incorporated into crystal matrices are shown. Green-emitting CdSe/CdS core/crown and red-emitting CdSe/CdS core/shell CQWs wrapped into these crystal solids are employed as proof-of-concept demonstrations of light-emitting diode (LED) integration targeting a wide color span in display backlighting. The quantum yield of the green- and red-emitting CQW-containing solids of sucrose reach approximate to 20% and approximate to 55%, respectively, while emission linewidths and peak wavelengths remain almost unaltered. Furthermore, sucrose matrix preserves approximate to 70% and approximate to 45% of the initial emission intensity of the green- and red-emitting CQWs after >60 h, respectively, which is approximate to 4x and approximate to 2x better than the drop-casted CQW films and reference (KCl) host. Color-converting LEDs of these green- and red-emitting CQWs in sucrose possess luminous efficiencies 122 and 189 lm W-elect(-1), respectively. With the liquid crystal display filters, this becomes 39 and 86 lm W-elect(-1), respectively, providing with a color gamut 25% broader than the National Television Standards Committee standard. These results prove that CQW solids enable efficient and stable color converters for display and lighting applications.
Color Simulation and Demonstration of Perovskite Nanocrystal Filters for Wide Color Gamut Displays
(Institute of Electrical and Electronics Engineers Inc., 2018) Genc, Sinan; Yazici, Ahmet Faruk; Beskazak, Emre; Uran, Can; Mutlugun, Evren; 0000-0002-6909-723X; 0000-0003-2747-7856; 0000-0003-3715-5594; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Genc, Sinan; Yazici, Ahmet Faruk; Beskazak, Emre; Mutlugun, Evren
In this study, we define spectral parameters of perovskite nanocrystals to improve LCD color gamut, replacing color filters (CFs) with perovskite based subpixels. The optimization of the CFs has been enhanced 15.8% (98.43% of Rec.2020) in simulation and 13.8% experimentally, with 97.37% color gamut coverage.
The effect of fourth color component on enhancement of color gamut
(IEEE345 E 47TH ST, NEW YORK, NY 10017 USA, 2017) Genc, Sinan; Uguz, Mustafa; Mutlugun, Evren; 0000-0002-6909-723X; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü
In this work, we simulate and analyse the peak emission wavelength and full-width-at-half-maximum (FWHM) parameters of nano emitters using four-color mixing approach to provide a tetragonal area as large as possible in CIE-1931, reaching over 160% NTSC area using emitters having 30nm FWHM.
The effect of ligand chain length on the optical properties of alloyed core-shell InPZnS/ZnS quantum dots
(ELSEVIER SCIENCE SAPO BOX 564, 1001 LAUSANNE, SWITZERLAND, 2017) Altintas, Yemliha; Talpur, Mohammad Younis; Mutlugun, Evren; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü
In 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.
Efficient Forster Resonance Energy Transfer Donors of In(Zn)P/ZnS Quantum Dots
(AMER CHEMICAL SOC1155 16TH ST, NW, WASHINGTON, DC 20036, 2017) Altintas, Yemliha; Talpur, Mohammad Younis; Mutlugun, Evren; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü
We 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.
Electrochemical and Optical Multi-Detection of Escherichia coli Through Magneto-Optic Nanoparticles: A Pencil-on-Paper Biosensor
(MDPI, 2024) Soysaldi, Furkan; Ekici, Derya Dincyurek; Soylu, Mehmet cagri; Mutlugun, Evren; 0000-0003-1120-5557; 0000-0001-5807-9944; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Ekici, Derya Dincyurek; Mutlugun, Evren
Escherichia coli (E. coli) detection suffers from slow analysis time and high costs, along with the need for specificity. While state-of-the-art electrochemical biosensors are cost-efficient and easy to implement, their sensitivity and analysis time still require improvement. In this work, we present a paper-based electrochemical biosensor utilizing magnetic core-shell Fe2O3@CdSe/ZnS quantum dots (MQDs) to achieve fast detection, low cost, and high sensitivity. Using electrochemical impedance spectroscopy (EIS) as the detection technique, the biosensor achieved a limit of detection of 2.7 x 10(2) CFU/mL for E. coli bacteria across a concentration range of 10(2)-10(8) CFU/mL, with a relative standard deviation (RSD) of 3.5781%. From an optical perspective, as E. coli concentration increased steadily from 10(4) to 10(7) CFU/mL, quantum dot fluorescence showed over 60% lifetime quenching. This hybrid biosensor thus provides rapid, highly sensitive E. coli detection with a fast analysis time of 30 min. This study, which combines the detection advantages of electrochemical and optical biosensor systems in a graphite-based paper sensor for the first time, has the potential to meet the needs of point-of-care applications. It is thought that future studies that will aim to examine the performance of the production-optimized, portable, graphite-based sensor system on real food samples, environmental samples, and especially medical clinical samples will be promising.
Electroluminescence Efficiency Enhancement in Quantum Dot Light-Emitting Diodes by Embedding a Silver Nanoisland Layer
(WILEY-V C H VERLAG GMBH, POSTFACH 101161, 69451 WEINHEIM, GERMANY, 2015) Yang, Xuyong; Hernandez-Martinez, Pedro Ludwig; Dang, Cuong; Mutlugun, Evren; Zhang, Kang; Demir, Hilmi Volkan; Sun, Xiao Wei; AGÜ, Mühendislik Fakültesi, Elektrik & Elektronik Mühendisliği Bölümü;
A colloidal quantum dot light-emitting diode (QLED) is reported with substantially enhanced electroluminescence by embedding a thin layer of Ag nanoislands into hole transport layer. The maximum external quantum efficiency (EQE) of 7.1% achieved in the present work is the highest efficiency value reported for green-emitting QLEDs with a similar structure, which corresponds to 46% enhancement compared with the reference device. The relevant mechanisms enabling the EQE enhancement are associated with the near-field enhancement via an effective coupling between excitons of the quantum dot emitters and localized surface plasmons around Ag nanoislands, which are found to lead to good agreement between the simulation results and the experimental data, providing us with a useful insight important for plasmonic QLEDs.
Excitonic interaction amongst InP/ZnS salt pellets
(ROYAL SOC CHEMISTRYTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2017) Altintas, Yemliha; Yazici, Ahmet Faruk; Unlu, Miray; Dadi, Seyma; Genc, Sinan; Mutlugun, Evren; 0000-0002-6909-723X; 0000-0003-2747-7856; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü
Salt matrix has recently been introduced as a promising robust platform for embedding colloidal quantum dots to provide them with photo stability for versatile applications. This work demonstrates the excitonic interaction amongst high efficiency colloidal InP/ZnS quantum dots embedded in a KCl salt matrix. By varying the donor acceptor ratio within the solid platform, 65% Forster Resonance Energy Transfer (FRET) efficiency was attained. Optimizing the donor : acceptor ratio, we demonstrated the first FRET-enabled Cd-free pellets for white light generation possessing a color rendering index (CRI) of 84.7, correlated color temperature (CCT) of 5347.5 K, and a high luminous efficacy of optical radiation value (LER) of 324.3 lm/W-opt. Our study of excitonic interactions within quantum dot-loaded salt matrices will open new possibilities for future versatile optoelectronic applications.
FRET enabled light harvesting within quantum dot loaded nanofibers
(IOP PUBLISHING LTD, TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND, 2018) Altintas, Yemliha; Kiremitler, Nuri Burak; Genc, Sinan; Onses, M. Serdar; Mutlugun, Evren; 0000-0001-6898-7700; 0000-0002-6909-723X; 0000-0001-6065-4899; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The spatial control of the nano-emitters in novel light harvesting platforms offers great potential for the manipulation of the excitonic interaction amongst the donor-acceptor pairs of energy transferring agents. In this work, we report colloidal quantum dot loaded electrospun nanofibers as a light harvesting platform to study the excitonic interaction among them. The donor emission lifetime modified from 12.46 ns to 7.45 ns with the change in the ratio of green and red quantum dots in the nanofiber, as a result of confining acceptor quantum dots in close proximity. The spectrally narrow emitter luminescent nanofiber platforms have further been investigated for their potential of white light generation. The hybrid platform of blue LED integrated electrospun nanofibers has been shown to demonstrate a correlated color temperature of 3632.5 K, luminous efficacy of optical radiation value of 307.7 lm/W-opt along with color rendering index value of 60.
Giant Alloyed Hot Injection Shells Enable Ultralow Optical Gain Threshold in Colloidal Quantum Wells
(AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2019) Altintas, Yemliha; Gungor, Kivanc; Gao, Yuan; Sak, Mustafa; Quliyeva, Ulviyya; Bappi, Golam; Mutlugun, Evren; Sargent, Edward H.; Demir, Hilmi Volkan; 0000-0003-0396-6495; 0000-0003-1793-112X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
As an attractive materials system for high- Record-low optical gain threshold in giant-shell COWs performance optoelectronics, colloidal nanoplatelets (NPLs) benefit from atomic-level precision in thickness, minimizing emission inhomogeneous broadening. Much progress has been made to enhance their photoluminescence quantum yield (PLQY) and photostability. However, to date, layer-by-layer growth of shells at room temperature has resulted in defects that limit PLQY and thus curtail the 0.2 performance of NPLs as an optical gain medium. Here, we introduce a hot-injection method growing giant alloyed shells using an approach that reduces core/shell lattice mismatch and suppresses Auger recombination. Near-unity PLQY is achieved with a narrow full-width-at-half-maximum (20 nm), accompanied by emission tunability (from 610 to 650 nm). The biexciton lifetime exceeds 1 ns, an order of magnitude longer than in conventional colloidal quantum dots (CQDs). Reduced Auger recombination enables record-low amplified spontaneous emission threshold of 2.4 mu J cm(-2) under one-photon pumping. This is lower by a factor of 2.5 than the best previously reported value in nanocrystals (6 /kJ cm(-2) for CdSe/CdS NPLs). Here, we also report single-mode lasing operation with a 0.55 mu J cm(-2) threshold under two-photoexcitation, which is also the best among nanocrystals (compared to 0.76 mu J cm(-2) from CdSe/CdS CQDs in the Fabry-Perot cavity). These findings indicate that hot-injection growth of thick alloyed shells makes ultrahigh performance NPLs.
Hibrit Kuantum Noktacık-Nanofiber Esnek Elektrolüminesant Aygıtlar
(TUBİTAK, 2019) Mutlugün, Evren; Usta, Hakan; Önses, Serdar; 0000-0003-3715-5594; 0000-0002-0618-1979; 0000-0001-6898-7700; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Mutlugun, Evren; Usta, Hakan; ÖNSES, Mustafa Serdar
Yarı iletken kuantum noktacıklar üstün renk dönüşüm özellikleri, yüksek soğurma katsayıları ve kararlılıkları sebebiyle son yıllarda aydınlatma ve ekran teknolojileri için oldukça önemli malzemeler durumundadır. Genel itibariyle II-VI ve III-V malzemeler temelli kuantum noktacıklar, optik ya da elektriksel olarak uyarılma sayesinde yüksek verimlilikle ışık üretimi sağlamaktadırlar. Sahip oldukları spektral dar ışımaları sayesinde özellikle ekran teknolojileri için saf renk özelliklerini ön plana çıkaran kuantum noktacıklar, geleneksel olarak kullanılan fosfor katkılı ışıyıcıların yerini almaktadır. Renk saflığının oldukça ön planda olduğu ekran teknolojileri için de kuantum noktalar LCD arka plan aydınlatmada üstün nitelikli beyaz ışık üretimini sağlamak için kullanılmakta ve ticari açıdan da önem kazanmaktadır. Nanofiberler ise organik yarıiletken malzemelerin optoelektronik uygulamalarda 3 boyutlu alanlar için önerdiği yüksek verimlilik, hafiflik, geniş alanlara uygulanabilme özelliklerini fiziksel olarak 1 boyutta gerçekleştirebilen, desenlenebilir ve elektroeğirme yöntemi ile farklı yüzeylere uygulanabilir çözümler sunmaktadır. Gerçekleştirdiğimiz proje nano boyutlu fiber yapıları içerisinde kuantum noktaların üstün renk dönüştürücü özelliklerini ön plana çıkarmış, farklı mimarilerde enerji transferinin de çalışıldığı fotolüminesans ve elektrolüminesans temelli aygıtlar gerçekleştirilmiştir. Bu projede %16’ya ulaşan dış kuantum verimliliğine (external quantum efficiency) sahip aygıt gösterimleri ve yüksek kaliteli beyaz ışık eldesi gerçekleştirilmiştir. Aynı zamanda esnek, ayarlanabilir renk özelliklerinde aygıt üretimi için gösterilen kuantum nokta aygıtlar saf ve spektral olarak simetrik ışımayı sağlama yetisinde, üstün renk özellikleri ile yüksek kaliteli esnek elektrolüminesant aygıt üretimini mümkün kılmaktadır. Önümüzdeki 10 yıl içerisinde küresel ekran teknolojileri pazarının 100 milyar dolarlar mertebesine ulaşacağı bilgisi doğrultusunda (Global Industry Analysts, Inc., raporu) en önemli aşamalardan biri de özellikle esnek mimarilerde üstün renk özelliklerine sahip malzemeleri gerçekleştirmek olacaktır. Yeni nesil esnek elektrolüminesant aygıtların aydınlatma ve ekran teknolojilerinde önemli bir paya sahip olacağı beklenmektedir. Bu tür yeni nesil yapıların gerçekleştirilmesi, fiziksel mekanizmaların araştırılması ve teknolojik problemlerine çözüm üretilme süreci büyük resimde çok kritik önemdedir. Teknolojiye yön verme doğrultusunda önerilen proje ekseninde yapılacak olan yatırımın ülkemiz için yüksek teknoloji üretme hamlesine büyük bir katkıda bulunacağı, yeni bilgi, ürün ve patent süreçlerini geliştireceği, ülkemizde bu alanda yetişmiş insan gücüne katkıda bulunup ülkemiz rekabet gücünü arttıracağı öngörülmektedir.
Highly Efficient Cd-Free Alloyed Core/Shell Quantum Dots with Optimized Precursor Concentrations
(AMER CHEMICAL SOC1155 16TH ST, NW, WASHINGTON, DC 20036, 2016) Altintas, Yemliha; Talpur, Mohammad Younis; Unlu, Miray; Mutlugun, Evren; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Mutlugun, Evren; Altintas, Yemliha; Talpur, Mohammad Younis; Unlu, Miray
The 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.
Highly flexible, electrically driven, top-emitting, quantum dot light-emitting stickers
(American Chemical Society, 2014) Yang, Xuyong; Mutlugun, Evren; Dang, Cuong; Dev, Kapil; Gao, Yuan; Tan, Swee Tiam; Sun, Xiao Wei; Demir, Hilmi Volkan; 0000-0003-3715-5594; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Mutlugun, Evren
Flexible information displays are key elements in future optoelectronic devices. Quantum dot light-emitting diodes (QLEDs) with advantages in color quality, stability, and cost-effectiveness are emerging as a candidate for single-material, full color light sources. Despite the recent advances in QLED technology, making high-performance flexible QLEDs still remains a big challenge due to limited choices of proper materials and device architectures as well as poor mechanical stability. Here, we show highly efficient, large-area QLED tapes emitting in red, green, and blue (RGB) colors with top-emitting design and polyimide tapes as flexible substrates. The brightness and quantum efficiency are 20 000 cd/m2 and 4.03%, respectively, the highest values reported for flexible QLEDs. Besides the excellent electroluminescence performance, these QLED films are highly flexible and mechanically robust to use as electrically driven light-emitting stickers by placing on or removing from any curved surface, facilitating versatile LED applications. Our QLED tapes present a step toward practical quantum dot based platforms for high-performance flexible displays and solid-state lighting.
Highly luminescent ZnCdTeS nanocrystals with wide spectral tunability for efficient color-conversion white-light-emitting-diodes
(IOP PUBLISHING LTDTEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND, 2021) Soheyli, Ehsan; Zargoush, Sirous; Yazici, Ahmet Faruk; Sahraei, Reza; Mutlugun, Evren; 0000-0003-2747-7856; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Yazici, Faruk Ahmet; Mutlugun, Evren
CdTe-based semiconductor nanocrystals (NCs) with size and composition-dependent efficient bandgap properties are historically mature nanomaterials for colloidal optoelectronic applications. In this work, we present the highly luminescent quaternary ZnCdTeS NCs with tunable emission across a wide visible spectrum from green to red spectral range. Prepared via a direct aqueous-based approach, a second capping agent of trisodium citrate (TSC) was used to enhance the photoluminescence (PL) emission efficiency, the chemical stability, and to spectrally widen the coverage of the emission spectra of ZnCdTeS NCs. Adding TCS created a remarkable blue shift from 572 nm in the absence of TSC, to 548 nm. On the other hand, upon optimization of experimental parameters, superior ZnCdTeS NCs with a narrow PL profile typically less than 50 nm, the high quantum efficiency of 76%, and tunable emission from 515-to-645 nm were synthesized in an aqueous solvent. The keynotes were the superior and reproducible luminescent properties for the core only NCs, without shell and using relatively low reaction temperatures. It was shown that in the suggested synthesis method, the high efficiency emitted color of ZnCdTeS NCs can be easily controlled from 515-to-650 nm with excellent stability against harsh conditions. The biexponential decay profiles of samples prepared at different reaction temperatures demonstrated that the average recombination lifetime is below 40 ns and increases with the growth of the ZnCdTeS NCs. Results reveal that the excitonic energy levels have the main role in the recombination process. Finally, to demonstrate the functional advantages of the prepared NCs in optoelectronics, the NCs were used to fabricate color-conversion white light-emitting diodes. The color coordinate of the device is recorded as (0.4951, 0.3647) with CRI of 91, CCT of 1954 K, and LER of 251 lm W-1 by employing only two distinct emitters for color conversion.
Highly Stable, Near-Unity Efficiency Atomically Flat Semiconductor Nanocrystals of CdSe/ZnS Hetero-Nanoplatelets Enabled by ZnS-Shell Hot-Injection Growth
(WILEY-V C H VERLAG GMBH, POSTFACH 101161, 69451 WEINHEIM, GERMANY, 2019) Altintas, Yemliha; Quliyeva, Ulviyya; Gungor, Kivanc; Erdem, Onur; Kelestemur, Yusuf; Mutlugun, Evren; Kovalenko, Maksym V.; Demir, Hilmi Volkan; 0000-0003-1793-112X; 0000-0003-1616-2728; 0000-0002-4628-0197; 0000-0003-2212-965X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Colloidal semiconductor nanoplatelets (NPLs) offer important benefits in nanocrystal optoelectronics with their unique excitonic properties. For NPLs, colloidal atomic layer deposition (c-ALD) provides the ability to produce their core/shell heterostructures. However, as c-ALD takes place at room temperature, this technique allows for only limited stability and low quantum yield. Here, highly stable, near-unity efficiency CdSe/ZnS NPLs are shown using hot-injection (HI) shell growth performed at 573 K, enabling routinely reproducible quantum yields up to 98%. These CdSe/ZnS HI-shell hetero-NPLs fully recover their initial photoluminescence (PL) intensity in solution after a heating cycle from 300 to 525 K under inert gas atmosphere, and their solid films exhibit 100% recovery of their initial PL intensity after a heating cycle up to 400 K under ambient atmosphere, by far outperforming the control group of c-ALD shell-coated CdSe/ZnS NPLs, which can sustain only 20% of their PL. In optical gain measurements, these core/HI-shell NPLs exhibit ultralow gain thresholds reaching approximate to 7 mu J cm(-2). Despite being annealed at 500 K, these ZnS-HI-shell NPLs possess low gain thresholds as small as 25 mu J cm(-2). These findings indicate that the proposed 573 K HI-shell-grown CdSe/ZnS NPLs hold great promise for extraordinarily high performance in nanocrystal optoelectronics.