Browsing by Author "Hernández-Martínez, P. L."

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Open Access
On the rational design of core/(multi)-Crown Type-II Heteronanoplatelets
(American Chemical Society, 2023-05-09) Demir, Hilmi Volkan; Delikanlı, Savaş; Canımkurbey, Betül; Hernández-Martínez, P. L.; Shabani, Farzan; Işık, Ahmet Tarık; Özkan, İlayda; Bozkaya, İklim; Bozkaya, Taylan; Işık, Furkan; Durmuşoglu, E. G.; İzmir, M.; Hakan, Akgün
Solution-processed two-dimensional nanoplatelets (NPLs) allowing lateral growth of a shell (crown) by not affecting the pure confinement in the vertical direction provide unprecedented opportunities for designing heterostructures for light-emitting and -harvesting applications. Here, we present a pathway for designing and synthesizing colloidal type-II core/(multi-)crown hetero-NPLs and investigate their optical properties. Stoke's shifted broad photoluminescence (PL) emission and long PL lifetime (∼few 100 ns) together with our wavefunction calculations confirm the type-II electronic structure in the synthesized CdS/CdSe1-xTexcore/crown hetero-NPLs. In addition, we experimentally obtained the band-offsets between CdS, CdTe, and CdSe in these NPLs. These results helped us designing hetero-NPLs with near-unity PL quantum yield in the CdSe/CdSe1-xTex/CdSe/CdS core/multicrown architecture. These core/multicrown hetero-NPLs have two type-II interfaces unlike traditional type-II NPLs having only one and possess a CdS ending layer for passivation and efficient suppression of stacking required for optoelectronic applications. The light-emitting diode (LED) obtained using multicrown hetero-NPLs exhibits a maximum luminance of 36,612 cd/m2and external quantum efficiency of 9.3%, which outcompetes the previous best results from type-II NPL-based LEDs. These findings may enable designs of future advanced heterostructures of NPLs which are anticipated to show desirable results, especially for LED and lasing platforms. © 2023 American Chemical Society. All rights reserved.
Open Access
Spectrally wide-range-tunable, efficient, and bright colloidal light-emitting diodes of quasi-2D nanoplatelets enabled by engineered alloyed heterostructures
(American Chemical Society, 2020) Altıntaş, Yemliha; Liu, B.; Hernández-Martínez, P. L.; Gheshlaghi, Negar; Shabani, Farzan; Sharma, Manoj; Wang, L.; Sun, H.; Mutlugün, Evren; Demir, Hilmi Volkan
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.
Open Access
Trion-mediated förster resonance energy transfer and optical gating effect in WS2/hBN/MoSe2 heterojunction
(American Chemical Society, 2020) Hu, Z.; Hernández-Martínez, P. L.; Liu, X.; Amara, M. R.; Zhao, W.; Watanabe, K.; Taniguchi, T.; Demir, Hilmi Volkan
van der Waals two-dimensional layered heterostructures have recently emerged as a platform, where the interlayer couplings give rise to interesting physics and multifunctionalities in optoelectronics. Such couplings can be rationally controlled by dielectric, separation, and stacking angles, which affect the overall charge or energy-transfer processes, and emergent potential landscape for twistronics. Herein, we report the efficient Förster resonance energy transfer (FRET) in WS2/ hBN/MoSe2 heterostructure, probed by both steady-state and timeresolved optical spectroscopy. We clarified the evolution behavior of the electron−hole pairs and free electrons from the trions, that is, ∼59.9% of the electron−hole pairs could transfer into MoSe2 by FRET channels (∼38 ps) while the free electrons accumulate at the WS2/hBN interface to photogate MoSe2. This study presents a clear picture of the FRET process in two-dimensional transition-metal dichalcogenides’ heterojunctions, which establishes the scientific foundation for developing the related heterojunction optoelectronic devices.