Browsing by Author "Soheyli, Ehsan"

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Enhanced photoluminescence emission intensity and stability of deep blue-emissive (Et3NH)PbBr3 perovskite nanocrystals by using metal-organic frameworks
(ELSEVIER, 2024) Hemmati, Tayebeh; Naghipour, Ali; Sahraei, Reza; Soheyli, Ehsan; 0000-0002-1403-7934; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Soheyli, Ehsan
The primary obstacle faced by researchers in the field of luminescent metal-halide perovskites is their inherent instability, prompting a shift in focus towards enhancing the stability of perovskite nanocrystals (PNCs). One of the promising approaches to address this challenge involves the utilization of metal-organic frameworks (MOFs) to fabricate PNCs@MOF composites. The present study reports a facile and low-cost colloidal strategy to prepare (Et3NH)PbBr3 PNCs followed by their encapsulation within UiO-67 to enhance their photoluminescence (PL) emission stability. The PNCs and modified UiO-67 were prepared separately via simple and efficient ligand-assisted reprecipitation (LARP) and hydrothermal methods, respectively. After modification of the UiO-67, the pore sizes experienced a substantial increase from 1.90 to 28.84 nm which significantly facilitated the localization of PNCs within the porous matrix. Under a full survey of experimental conditions, the resulting (Et3NH)PbBr3@UiO-67 composite exhibited a bright deep-blue emission at around 410 nm with an emission quantum yield of 52 %. The emission durability of the fabricated PNCs@MOF composites was assessed against temperature and long-time of storage, confirming the superior advantages of MOF even at elevated temperatures of up to 100 °C. The stable and luminous deep-blue emission displayed by the PNCs@MOF composites in this investigation, offers a promising advancement in materials development for optoelectronic applications.
Excitation-independent deep-blue emitting carbon dots with 62% emission quantum efficiency and monoexponential decay profile for high-resolution fingerprint identification
(IOP Publishing, 2022) Savaedi, Soheyla; Zheng, Guangsong; Lou, Qing; Sahraei, Reza; Shan, Chongxin; Soheyli, Ehsan; 0000-0002-1403-7934; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Soheyli, Ehsan
Reaching emissive nanomaterials at short wavelengths with a high quantum efficiency (QE) is an attractive task for researchers. This is more demanding in carbon dots (CDs) with diverse applications that usually emit photons at wavelengths around 450–620 nm. In this study, deep blue-emissive doped-CDs (d-CDs) with high photoluminescence (PL) QE up to 62% and excitation-independent properties were prepared via a short-time microwave irradiation method. The prepared CDs showed simultaneous amorphous and crystalline features, with average sizes of 4.75 nm and bright emission color located at 422 nm. It was found that the presence of sulfur-related dopant levels plays a key role in emission properties in such a way that the PL signal drops significantly in the absence of N-acetyl-l-cysteine (NAC) as a dopant source. On the other hand, the trisodium citrate dihydrate (TSC) was selected as a carbon source to form the main carbon skeleton without it no emission was recorded. Monoexponential-fitted recombination trend with an average lifetime of about 10 ns also confirmed excellent PL emission properties with uniform energy levels and minimized defect-contributing recombinations. The practical use of the as-prepared N, S-doped CDs was assessed in fingerprint detection indicating a bright and clear scheme for both core and termination regions of the fingerprint. Simplicity, cost-effectiveness, high-product yield, low toxicity, along with high/stable PL quantum efficiency in deep-blue wavelengths, and demonstrated ability for fingerprint purposes, support the prospective application of these dual doped-CDs for sensing and bioimaging applications.
Exploring CsPbX3 (X = Cl, Br, I) Perovskite Nanocrystals in Amorphous Oxide Glasses: Innovations in Fabrication and Applications
(WILEY Online Library, 2024) Samiei, Sadaf; Soheyli, Ehsan; Vighnesh, Kunnathodi; Nabiyouni, Gholamreza; Rogach, Andrey L.; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Soheyli, Ehsan
Metal halide perovskites with excellent optical and electronic properties have become a trending material in the current research. However, their limited stability under ambient conditions degrades quality and threatens their potential commercialization as optoelectronic devices. Various approaches are adopted to improve the stability of perovskite nanocrystals (PeNC) while maintaining their advantageous optical properties, particularly strong luminescence. Among different possible improvement strategies, encapsulation of PeNCs within the amorphous glass matrices of inorganic oxides has drawn widespread attention because it ensures high resistance against chemical corrosion and high temperature, thus enhancing their chemical, thermal, and mechanical stability with improved light-emission characteristics. In this article, two types of materials, namely all-inorganic metal halide PeNCs and amorphous oxide glasses are briefly introduced, and then the methods are reviewed to fabricate and improve the quality of PeNC@glass composites. These methods are classified into three universal categories: compositional modification, structural modification, and dual encapsulation. In the final part of this review paper, examples of applications of PeNCs@glass composites in light-emitting devices and displays, data storage and anti-counterfeiting, lasing, photodetectors and X-ray detectors, photocatalysis, optical filters, solar concentrators, and batteries are provided.
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.
Impact of red emissive ZnCdTeS quantum dots on the electro-optic switching, dielectric and electrochemical features of nematic liquid crystal: Towards tunable optoelectronic systems
(ELSEVIER, 2023) Seidalilir, Zahra; Shishehbor, Sepideh; Soheyli, Ehsan; Sabaeian, Mohammad; 0000-0002-1403-7934; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Soheyli, Ehsan
In the present study, the concentration-dependent dielectric, electro-optical, and electrochemical properties of ZnCdTeS quantum dots (QDs) doped E7 nematic liquid crystal (NLC) mixtures were investigated. The dielectric permittivity components (epsilon(parallel to) and epsilon(perpendicular to)) and dielectric anisotropy (Delta epsilon -epsilon(parallel to) - epsilon perpendicular to.) of NLC samples containing varied concentrations of ZnCdTeS QDs (i. e. 0.10, 0.25, 0.50, 0.75, and 1 wt%) were measured at various temperatures. In the nematic phase, the results demonstrated that e. increases much more than epsilon(perpendicular to) upon an increase in the concentration of ZnCdTeS QDs. Delta epsilon enhanced as the concentration of QDs increased, reaching a maximum at 0.50 wt%, then decreased with further addition. Dielectric measurements revealed the formation of self-aligned QD arrays along the nematic director, which act similarly to multiple parallel capacitors in the NLC system. Moreover, electro-optical studies illustrated the significant effect of QDs doping on lowering the threshold voltage and response time. Interestingly, the optical switching-off time of NLC containing 0.50 wt% of the QDs decreased by similar to 50% compared to that of the pure E7 sample. The reduced screening effect resulting from the QDs ioncapturing mechanism, enhanced effective intermolecular interactions, and increased dielectric anisotropy in the NLC system are the major factors responsible for the improved electro-optical characteristics. The impedance behavior of NLC cells was studied in the frequency range of 0.1 Hz-100 kHz. It indicated that the addition of ZnCdTeS QDs results in a remarkable increase of 96% in the electrical conductivity of the NLC system. Furthermore, the QDs doping significantly improved the NLC device's charge capacitance. Such studies would undoubtedly be beneficial for designing next-generation tunable optoelectronic systems since QDs can be utilized for tuning the dielectric anisotropy, electro-optical characteristics, charge capacitance, and conductivity of NLCs.
Long-time stable colloidal Zn-Ag-In-S quantum dots with tunable midgap-involved emission
(AMER INST PHYSICS1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501, 2021) Sabzevari, Zahra; Sahraei, Reza; Jawhar, Nawzad Nadhim; Yazici, Ahmet Faruk; Mutlugun, Evren; Soheyli, Ehsan; 0000-0003-2747-7856; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Yazici, Ahmet Faruk; Mutlugun, Evren
Quaternary 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.
Nanowire-Shaped MoS2@MoO3 Nanocomposites as a Hole Injection Layer for Quantum Dot Light-Emitting Diodes
(AMER CHEMICAL SOC, 2022) Bastami, Nasim; Soheyli, Ehsan; Arslan, Aysenur; Sahraei, Reza; Yazici, Ahmet Faruk; Mutlugun, Evren; 0000-0003-2747-7856; 0000-0002-1403-7934; 0000-0003-3715-5594; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Soheyli, Ehsan; Arslan, Ayşenur; Yazıcı, Ahmet Faruk; Mutlugün, Evren
Molybdenum disulfides and molybdenum trioxides are structures that possess the potential to work as efficient charge transport layers in optoelectronic devices. In the present study, as opposed to the existing Mo-based nanostructures in flake, sheet, or spherical forms, an extremely simple and low-cost hydrothermal method is used to prepare nanowires (NWs) of MoS2@MoO3 (MSO) composites. The synthesis method includes several advantages including easy handling and processing of inexpensive precursors to reach stable MSO NWs without the need for an oxygen-free medium, which would facilitate the possibility of mass production of these nanostructures. The structural analysis confirmed the formation of MSO nanocomposites with different Mo valence states, as well as NWs of average length and diameter of 70 nm and 5 nm, respectively. In order to demonstrate their potential for optoelectronic applications, MSO NWs were blended into hole injection layers (HILs) in quantum dot-based lightemitting diodes (QLEDs). Electroluminescence measurements show a substantial enhancement in both luminance (from 44,330 to 68,630 cd.m−2 ) and external quantum efficiency (from 1.6 to 2.3%), based on the increase in the ratio of MSO NWs from 3 to 10%. Interestingly, the addition of 10% volume of MSO NWs resulted in a remarkably smoother HIL with improved current efficiency and stability in green-emitting QLEDs. The simplicity and cost-effective features of the synthesis method along with outstanding favorable morphology demonstrated their ability to enhance the QLED performance and mark them as promising agents for optoelectronics.
Preparation of highly emissive and reproducible Cu-In-S/ZnS core/shell quantum dots with a mid-gap emission character
(Cu-In-S/ZnS; Quantum dots; Photoluminescence quantum yield; Donor-acceptor recombination, 2020) Jawhar, Nawzad Nadhim; Soheyli, Ehsan; Yazici, Ahmet Faruk; Mutlugun, Evren; Sahraei, Reza; 0000-0001-7104-2126; 0000-0003-2747-7856; 0000-0002-1403-7934; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü
Copper indium sulfide (CIS) quantum dots (QDs) are one of the newest types of luminescent semiconductors with low-toxicity and earth-abundant features. The present work reports the successful aqueous synthesis of CIS/ZnS core/shell QDs using dual-stabilizing agents of N-acetyl-L-cysteine and trisodium citrate. Off-stoichiometric QDs with In-rich compositions were found to be very small and highly emissive after coating by a shell of wide bandgap ZnS. The effect of various experimental parameters was evaluated to achieve highly reproducible QDs with bright reddish emission. Results showed a significant contribution of mid-gap defect states in the recombination processes (based on the gradual increase in absorbance recorded for samples, relatively high Urbach energy, large Stokes shift, large FWHM value in PL spectra, as well as the long-lived PL decay time). In addition, the chemical stability of samples was investigated using highly oxidant H2O2 agent and results demonstrate their superior stability. The combination of low-toxicity, intense and stable emission, along with synthetic advantages demonstrates that the present aqueous-soluble and emissive QDs can be considered as an excellent bio-photonic structure suitable for different fields of biological imaging and diagnostics. (C) 2020 Elsevier B.V. All rights reserved.
Rational design of chemical bath deposition technique for successful preparation of Mn-doped CdS nanostructured thin films with controlled optical properties
(ELSEVIER SCI LTDTHE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2021) Kharabaneh, Farzaneh Khani; Ghavidel, Elham; Soheyli, Ehsan; Yazici, Ahmet Faruk; Jawhar, Nawzad Nadhim; Mutlugun, Evren; Sahraei, Reza; 0000-0003-2747-7856; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Yazici, Ahmet Faruk; Mutlugun, Evren
The introduction of a rational design for depositing internally-doped nanostructured thin films is of great importance for optoelectronics. In this presented work, Mn-doped CdS thin films with high purity in composition were prepared through the chemical bath deposition technique using a nucleation-doping strategy. This work focuses on an improved chemical design to eliminate mostly ignored property of conventionally doped nanoscale thin films. The synthesis strategy was initiated by the initial formation of MnS nuclei in a colloidal depositing solution followed by injection of cadmium precursor to diffuse into the initial nuclei and play the role of host CdS matrix which was the beginning of the deposition process. Upon optimization of the PL-emission, it was revealed that relative intensity of Mn2+-related peak to the excitonic peak has significantly increased (similar to 100 times) in 80 degrees C, pH = 6, and precursor molar ratio of Cd:Mn:EDTA:S equal to 1:3:0.4:5, at deposition time of 300-min. The TRPL measurements further revealed the effective contribution of Mn-related midgap states with long-lived decay curve character, which confirms the success of the designed approach to reach internally doped thin films. It was found that the deposition temperature, amount of Cd/Mn/TA precursors, and deposition time are the most important experimental parameters in the proposed synthesis approach. Due to the versatility, generality, and colloidal advantages of this method, it can be extended to the other structures with various types of dopant agent.
Spectrally Tunable White Light-Emitting Diodes Based on Carbon Quantum Dot-Doped Poly(N-vinylcarbazole) Composites
(AMER CHEMICAL SOC, 2024) Sahin Tiras, Kevser; Biçer, Aysenur; Soheyli, Ehsan; Mutlugun, Evren; 0000-0001-5523-4769; 0000-0003-3715-5594; 0000-0002-1403-7934; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Bicer, Aysenur; Soheyli, Ehsan; Mutlugun, Evren
Electroluminescent white light-emitting diodes (WLEDs) are always of great interest for emerging display applications. Carbon-based quantum dots (CQDs) are the newest emerging nanoscale materials that can be employed for this purpose, owing to their broad and bright light emission properties. In the present work, highly luminescent CQDs with an emission quantum yield of 60% were prepared via a colloidal solvothermal method and subsequent silica gel column chromatography. The photoluminescence (PL) peak was located at 550 nm possessing yellow emission, with a full width at halfmaximum of 98 nm and a relatively long lifetime of 10.23 ns through a single-exponential recombination pathway. CQDs were employed in an electroluminescent device architecture of an ITO/PEDOT:PSS/TFB/CQD:PVK/TPBi/LiF/Al structure and blended with poly(N-vinylcarbazole) (PVK) to evaluate their ability to reach white electroluminescent emission. Results confirmed a high external quantum efficiency (EQE) of 0.76% and a maximum luminescence of 774.3 cd·m−2 . Tuning the ratio between CQDs and PVK from 1:10.25 to 1:5.75 resulted in a systematic shift in CIE x−y coordinates from 0.23−0.26 to 0.21−0.24, located close to the cool white region. The results of the present study can be considered a step forward in fabricating efficient WLEDs based on low-cost CQDs.
Tuning the Shades of Red Emission in InP/ZnSe/ZnS Nanocrystals with Narrow Full Width for Fabrication of Light-Emitting Diodes
(AMER CHEMICAL SOC, 2023) Soheyli, Ehsan; Bicer, Aysenur; Ozel, Sultan Suleyman; Tiras, Kevser Sahin; Mutlugun, Evren; 0000-0002-1403-7934; 0000-0001-5523-4769; 0000-0003-3715-5594; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Soheyli, Ehsan; Bicer, Aysenur; Ozel, Sultan Suleyman; Mutlugun, Evren
While Cd-based luminescent nanocrystals (NCs) are the most mature NCs for fabricating efficient red light-emitting diodes (LEDs), their toxicity related limitation is inevitable, making it necessary to find a promising alternative. From this point of view, multishell-coated, red-emissive InP-based NCs are excellent luminescent nanomaterials for use as an emissive layer in electroluminescent (EL) devices. However, due to the presence of oxidation states, they suffer from a wide emission spectrum, which limits their performance. This study uses tris-(dimethyl-amino)-phosphine (3DMA-P) as a low-cost aminophosphine precursor and a double HF treatment to suggest an upscaled, cost-effective, and one-pot hot-injection synthesis of purely red-emissive InP-based NCs. The InP core structures were coated with thick layers of ZnSe and ZnS shells to prevent charge delocalization and to create a narrow size distribution. The purified NCs showed an intense emission signal as narrow as 43 nm across the entire red wavelength range (626-670 nm) with an emission quantum efficiency of 74% at 632 nm. The purified samples also showed an emission quantum efficiency of 60% for far-red wavelengths of 670 nm with a narrow full width of 50 nm. The samples showed a relatively long average emission lifetime of 50-70 ns with a biexponential decay profile. To demonstrate the practical ability of the prepared NCs in optoelectronics, we fabricated a red-emissive InP-based LEDs. The best-performing device showed an external quantum efficiency (EQE) of 1.16%, a luminance of 1039 cd m(-2), and a current efficiency of 0.88 cd A(-1).