Browsing by Author "Hernandez-Martinez, Pedro Ludwig"

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Efficient generation of emissive many-body correlations in copper-doped colloidal quantum wells
(Elsevier, 2022) Yu, Junhong; Sharma, Manoj; Li, Mingjie; Liu, Baiquan; Hernandez-Martinez, Pedro Ludwig; Delikanli, Savas; Sharma, Ashma; Altintas, Yemliha; Hettiarachchi, Chathuranga; Sum, Tze Chien; Demir, Hilmi Volkan; Dang, Cuong; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Altintas, Yemliha
Colloidal quantum wells (CQWs) provide an appealing platform to achieve emissive many-body correlations for novel optoelectronic devices, given that they act as hosts for strong carrier Coulomb interactions and present suppressed Auger recombination. However, the demonstrated high-order excitonic emission in CQWs requires ultrafast pumping with high excitation levels and can only be spec-trally resolved at the single-particle level under cryogenic condi-tions. Here, through systematic investigation using static power -dependent emission spectroscopy and transient carrier dynamics, we show that Cu-doped CdSe CQWs exhibit continuous-wave -pumped high-order excitonic emission at room temperature with a large binding energy of X64 meV. We attribute this unique behavior to dopant excitons in which the ultralong lifetime and the highly localized wavefunction facilitate the formation of many-body corre-lations. The spectrally resolved high-order excitonic emission gener-ated at power levels compatible with solar irradiation and electrical injection might pave the way for novel solution-processed solid-state devices.
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.
Near-Field Energy Transfer into Silicon Inversely Proportional to Distance Using Quasi-2D Colloidal Quantum Well Donors
(WILEY-V C H VERLAG GMBHPOSTFACH 101161, 69451 WEINHEIM, GERMANY, 2021) Humayun, Muhammad Hamza; Hernandez-Martinez, Pedro Ludwig; Gheshlaghi, Negar; Erdem, Onur; Altintas, Yemliha; Shabani, Farzan; Demir, Hilmi Volkan; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Altintas, Yemliha
Silicon is the most prevalent material system for light-harvesting applications; however, its inherent indirect bandgap and consequent weak absorption limits its potential in optoelectronics. This paper proposes to address this limitation by combining the sensitization of silicon with extraordinarily large absorption cross sections of quasi-2D colloidal quantum well nanoplatelets (NPLs) and to demonstrate excitation transfer from these NPLs to bulk silicon. Here, the distance dependency, d, of the resulting Forster resonant energy transfer from the NPL monolayer into a silicon substrate is systematically studied by tuning the thickness of a spacer layer (of Al2O3) in between them (varied from 1 to 50 nm in thickness). A slowly varying distance dependence of d(-1) with 25% efficiency at a donor-acceptor distance of 20 nm is observed. These results are corroborated with full electromagnetic solutions, which show that the inverse distance relationship emanates from the delocalized electric field intensity across both the NPL layer and the silicon because of the excitation of strong in-plane dipoles in the NPL monolayer. These findings pave the way for using colloidal NPLs as strong light-harvesting donors in combination with crystalline silicon as an acceptor medium for application in photovoltaic devices and other optoelectronic platforms.
Spectrally Wide-Range-Tunable, Efficient, and Bright Colloidal Light-Emitting Diodes of Quasi-2D Nanoplatelets Enabled by Engineered Alloyed Heterostructures
(AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2020) Altintas, Yemliha; Liu, Baiquan; Hernandez-Martinez, Pedro Ludwig; Gheshlaghi, Negar; Shabani, Farzan; Sharma, Manoj; Wang, Lin; Sun, Handong; Mutlugun, Evren; Demir, Hilmi Volkan; 0000-0003-1793-112X; 0000-0002-2261-7103; 0000-0001-9375-7683; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Recently, there has been tremendous interest in the synthesis and optoelectronic applications of quasi-two-dimensional colloidal nanoplatelets (NPLs). Thanks to the ultranarrow emission linewidth, high-extinction coefficient, and high photostability, NPLs offer an exciting opportunity for high-performance optoelectronics. However, until now, the applications of these NPLs are limited to available discrete emission ranges, limiting the full potential of these exotic materials as efficient light emitters. Here, we introduce a detailed systematic study on the synthesis of NPLs based on the alloying mechanisms in core/shell, core/alloyed shell, alloyed core/shell, and alloyed core/alloyed shell heterostructures. Through the engineering of the band gap supported by the theoretical calculations, we carefully designed and successfully synthesized the NPL emitters with continuously tunable emission. Unlike conventional NPLs showing discrete emission, here, we present highly efficient core/shell NPLs with fine spectral tunability from green to deep-red spectra. As an important demonstration of these efficient emitters, the first-time implementation of yellow NPL light-emitting diodes (LEDs) has been reported with record device performance, including the current efficiency surpassing 18.2 cd A(-1), power efficiency reaching 14.8 lm W-1, and record luminance exceeding 46 900 cd m(-2). This fine and wide-range color tunability in the visible range from stable and efficient core/shell NPLs is expected to be extremely important for the optoelectronic applications of the family of colloidal NPL emitters.
Tailored Synthesis of Iron Oxide Nanocrystals for Formation of Cuboid Mesocrystals
(AMER CHEMICAL SOC1155 16TH ST, NW, WASHINGTON, DC 20036, 2021) Soran-Erdem, Zeliha; Sharma, Vijay Kumar; Hernandez-Martinez, Pedro Ludwig; Demir, Hilmi Volkan; AGÜ, Mühendislik Fakültesi, Mühendislik Bilimleri Bölümü; Soran-Erdem, Zeliha
In this work, we systematically studied the shape- and size-controlled monodisperse synthesis of iron oxide nanocrystals (IONCs) for their use as building blocks in the formation of mesocrystals. For this aim, on understanding the influence of the oleic acid concentration, iron-oleate concentration, and heating rate on the synthesis of robust and reproducible IONCs with desired sizes and shapes, we synthesized highly monodisperse similar to 11 nm sized nanocubes and nanospheres. Magnetic measurements of both cubic and spherical IONCs revealed the presence of mixed paramagnetic and superparamagnetic phases in these nanocrystals. Moreover, we observed that the magnetic moments of the nanocubes are more substantial compared to their spherical counterparts. We then demonstrated a simple magnetic-field-assisted assembly of nanocubes into three-dimensional (3D) cuboid mesocrystals while nanospheres did not form any mesocrystals. These findings indicate that small cubic nanocrystals hold great promise as potential building blocks of 3D magnetic hierarchical structures with their superior magnetic properties and mesocrystal assembly capability, which may have high relevance in various fields ranging from high-density data storage to biomedical applications.