Browsing by Author "Durmuşoğlu, E. G."

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Open Access
Blue-emitting CdSe nanoplatelets enabled by sulfur-alloyed heterostructures for light-emitting diodes with low turn-on voltage
(American Chemical Society, 2021-12-28) İzmir, M.; Sharma, A.; Shendre, S.; Durmuşoğlu, E. G.; Sharma, V. K.; Shabani, Farzan; Baruj, Hamed Dehghanpour; Delikanlı, Savaş; Sharma, M.; Demir, Hilmi Volkan
Colloidal nanoplatelets (NPLs) have emerged as the last class of semiconductor nanocrystals for their potential optoelectronic applications. The heterostructures of these nanocrystals can achieve high photoluminescence quantum yield and enhanced photostability, along with color purity. Such advantages make them a promising candidate for solution-processable light-emitting diodes (LEDs). However, to date, blue-emitting CdSe nanoplatelets (NPLs) exhibit poor photoluminescence quantum yield and also typically suffer from a rolled-up morphology. To mitigate these problems in this work, we propose and demonstrate efficient alloyed 4 ML CdSe1–xSx nanoplatelets having a CdS crown with enhanced photoluminescence quantum yields (up to 60%) in the blue region (462–487 nm). We successfully used these NPLs as an electrically driven active emitter in the blue-emitting NPL-LEDs with a low turn-on voltage of ∼4 V. The Commission Internationale de L’Eclairage (CIE) coordinates of (0.23, 0.14) were obtained for these blue-emitting NPL-LEDs. These emitters could potentially open up the opportunity for full-color displays using these NPL-based blue LEDs in conjunction with the red and green ones.
Open Access
Colloidal semiconductor quantum well supraparticles as low-threshold and photostable microlasers
(Wiley-VCH Verlag GmbH & Co. KGaA, 2025-01-08) Alves, P. U.; Quinn, G.; Strain, M. J.; Durmuşoğlu, E. G.; Sharma, M.; Demir, Hilmi Volkan; Edwards, P. R.; Martin, R. W.; Dawson, M. D.; Laurand, N.
This study introduces and compares the lasing performance of micron-sized and sphere-shaped supraparticle (SP) lasers fabricated through bottom-upassembly of II-VI semiconductor colloidal quantum wells (CQWs) with their counterparts made of quantum dots (CQDs). CQWs consist of a 4-monolayers thick CdSe core and an 8-monolayers thick $Cd_xZn_{1-x}S$ shell with a nominal size of 14 × 15 × 4.2 nm, and CQDs of $CdS_xSe_{1-x}/ZnS$with 6 nm diameter. SPs areoptically characterized with a 0.76 ns pulse laser (spot size: 2.88 × 10$^{−7}$ cm$^2$ )at 532 nm, and emit in the 620–670 nm spectral range. Results show thatCQW SPs have lasing thresholds twice as low (0.1–0.3 nJ) as CQD SPs(0.3–0.6 nJ), and stress tests using a constant 0.6 nJ optical pump energy demonstrate that CQW SPs withstand lasing emission for longer than CQDSPs. Lasing emission in CQW and CQD SPs under continuous operation yields half-lives of $𝝉_{CQW SP}$ ≈150 min and $𝝉_{CQD SP}$ ≈22 min, respectively. The half-life of CQW SPs is further extended to $𝝉_{QW}$ ≈385 min when optically pumped at 0.5 nJ. Such results compare favorably to those in the literature and highlight the performance of CdSe-based CQW SPs for laser applications.
Open Access
Gradient Type-II CdSe/CdSeTe/CdTe Core/Crown/Crown heteronanoplatelets with asymmetric shape and disproportional excitonic properties
(Wiley-VCH Verlag GmbH & Co. KGaA, 2023-01-17) Shabani, Farzan; Hernandez Martinez, P. L.; Shermet, Nina; Korkut, Hilal; Sarpkaya, İbrahim; Baruj, Hamed Dehghanpour; Delikanlı, Savaş; Işık, Furkan; Durmuşoğlu, E. G.; Demir, Hilmi Volkan
Characterized by their strong 1D confinement and long-lifetime red-shifted emission spectra, colloidal nanoplatelets (NPLs) with type-II electronic structure provide an exciting ground to design complex heterostructures with remarkable properties. This work demonstrates the synthesis and optical characterization of CdSe/CdSeTe/CdTe core/crown/crown NPLs having a step-wise gradient electronic structure and disproportional wavefunction distribution, in which the excitonic properties of the electron and hole can be finely tuned through adjusting the geometry of the intermediate crown. The first crown with staggered configuration gives rise to a series of direct and indirect transition channels that activation/deactivation of each channel is possible through wavefunction engineering. Moreover, these NPLs allow for switching between active channels with temperature, where lattice contraction directly affects the electron–hole (e–h) overlap. Dominated by the indirect transition channels over direct transitions, the lifetime of the NPLs starts to increase at 9 K, indicative of low dark-bright exciton splitting energy. The charge transfer states from the two type-II interfaces promote a large number of indirect transitions, which effectively increase the absorption of low-energy photons critical for nonlinear properties. As a result, these NPLs demonstrate exceptionally high two-photon absorption cross-sections with the highest value of 12.9 × 10$^{6}$ GM and superlinear behavior.
Open Access
High external quantum efficiency light-emitting diodes enabled by advanced heterostructures of Type-II nanoplatelets
(American Chemical Society, 2023-04-25) Durmuşoğlu, E. G.; Hu, S.; Hernandez-Martinez, P. L.; İzmir, M.; Shabani, Farzan; Guo, M.; Gao, H.; Işık, Furkan; Delikanlı, Savaş; Sharma, V. K.; Liu, B.; Demir, Hilmi Volkan
Colloidal quantum wells (CQWs), also known as nanoplatelets (NPLs), are exciting material systems for numerous photonic applications, including lasers and light-emitting diodes (LEDs). Although many successful type-I NPL-LEDs with high device performance have been demonstrated, type-II NPLs are not fully exploited for LED applications, even with alloyed type-II NPLs with enhanced optical properties. Here, we present the development of CdSe/CdTe/CdSe core/crown/crown (multi-crowned) type-II NPLs and systematic investigation of their optical properties, including their comparison with the traditional core/crown counterparts. Unlike traditional type-II NPLs such as CdSe/CdTe, CdTe/CdSe, and CdSe/CdSexTe1–x core/crown heterostructures, here the proposed advanced heterostructure reaps the benefits of having two type-II transition channels, resulting in a high quantum yield (QY) of 83% and a long fluorescence lifetime of 73.3 ns. These type-II transitions were confirmed experimentally by optical measurements and theoretically using electron and hole wave function modeling. Computational study shows that the multi-crowned NPLs provide a better-distributed hole wave function along the CdTe crown, while the electron wave function is delocalized in the CdSe core and CdSe crown layers. As a proof-of-concept demonstration, NPL-LEDs based on these multi-crowned NPLs were designed and fabricated with a record high external quantum efficiency (EQE) of 7.83% among type-II NPL-LEDs. These findings are expected to induce advanced designs of NPL heterostructures to reach a fascinating level of performance, especially in LEDs and lasers.
Open Access
Measuring the ultrafast spectral diffusion and vibronic coupling dynamics in CdSe colloidal quantum wells using two-dimensional electronic spectroscopy
(American Chemical Society, 2023-02-14) Nguyen, H. L.; Do, T. N.; Durmuşoğlu, E. G.; İzmir, M.; Sarkar, R.; Pal, S.; Prezhdo, O. V.; Demir, Hilmi Volkan; Tan, H.-S.
We measure the ultrafast spectral diffusion, vibronic dynamics, and energy relaxation of a CdSe colloidal quantum wells (CQWs) system at room temperature using two-dimensional electronic spectroscopy (2DES). The energy relaxation of light-hole (LH) excitons and hot carriers to heavy-hole (HH) excitons is resolved with a time scale of ∼210 fs. We observe the equilibration dynamics between the spectroscopically accessible HH excitonic state and a dark state with a time scale of ∼160 fs. We use the center line slope analysis to quantify the spectral diffusion dynamics in HH excitons, which contains an apparent sub-200 fs decay together with oscillatory features resolved at 4 and 25 meV. These observations can be explained by the coupling to various lattice phonon modes. We further perform quantum calculations that can replicate and explain the observed dynamics. The 4 meV mode is observed to be in the near-critically damped regime and may be mediating the transition between the bright and dark HH excitons. These findings show that 2DES can provide a comprehensive and detailed characterization of the ultrafast spectral properties in CQWs and similar nanomaterials.
Open Access
Near-unity emitting, widely tailorable, and stable exciton concentrators built from doubly gradient 2D semiconductor nanoplatelets
(American Chemical Society, 2023-10-24) Liang, X.; Durmuşoğlu, E. G.; Lunina, M.; Hernandez-Martinez, P. L.; Valuckas, V.; Yan, F.; Lekina, Y.; Sharma, V. K.; Yin, T.; Ha, S. T.; Shen, Z. X.; Sun, H.; Kuznetsov, A.; Demir, Hilmi Volkan
The strength of electrostatic interactions (EIs) between electrons and holes within semiconductor nanocrystals profoundly affects the performance of their optoelectronic systems, and different optoelectronic devices demand distinct EI strength of the active medium. However, achieving a broad range and fine-tuning of the EI strength for specific optoelectronic applications is a daunting challenge, especially in quasi two-dimensional core–shell semiconductor nanoplatelets (NPLs), as the epitaxial growth of the inorganic shell along the direction of the thickness that solely contributes to the quantum confined effect significantly undermines the strength of the EI. Herein we propose and demonstrate a doubly gradient (DG) core–shell architecture of semiconductor NPLs for on-demand tailoring of the EI strength by controlling the localized exciton concentration via in-plane architectural modulation, demonstrated by a wide tuning of radiative recombination rate and exciton binding energy. Moreover, these exciton-concentration-engineered DG NPLs also exhibit a near-unity quantum yield, high photo- and thermal stability, and considerably suppressed self-absorption. As proof-of-concept demonstrations, highly efficient color converters and high-performance light-emitting diodes (external quantum efficiency: 16.9%, maximum luminance: 43,000 cd/m2) have been achieved based on the DG NPLs. This work thus provides insights into the development of high-performance colloidal optoelectronic device applications.
Open Access
Room-temperature lasing in colloidal nanoplatelets via mie-resonant bound states in the continuum
(American Chemical Society, 2020) Wu, M.; Ha, S. T.; Shendre, S.; Durmuşoğlu, E. G.; Koh, W.-K.; Abujetas, D. R.; Sanchez-Gil, J. A.; Paniagua-Domínguez, R.; Demir, Hilmi Volkan; Kuznetsov, A. I.
Solid-state room-temperature lasing with tunability in a wide range of wavelengths is desirable for many applications. To achieve this, besides an efficient gain material with a tunable emission wavelength, a high quality-factor optical cavity is essential. Here, we combine a film of colloidal CdSe/CdZnS core–shell nanoplatelets with square arrays of nanocylinders made of titanium dioxide to achieve optically pumped lasing at visible wavelengths and room temperature. The all-dielectric arrays support bound states in the continuum (BICs), which result from lattice-mediated Mie resonances and boast infinite quality factors in theory. In particular, we demonstrate lasing from a BIC that originates from out-of-plane magnetic dipoles oscillating in phase. By adjusting the diameter of the cylinders, we tune the lasing wavelength across the gain bandwidth of the nanoplatelets. The spectral tunability of both the cavity resonance and nanoplatelet gain, together with efficient light confinement in BICs, promises low-threshold lasing with wide selectivity in wavelengths.
Open Access
Ultrahigh green and red optical gain cross sections from solutions of colloidal quantum well heterostructures
(American Chemical Society, 2021-03-11) Delikanli, Savaş; Erdem, Onur; Işık, Furkan; Dehghanpour Baruj, Hamed; Shabani, Farzan; Yağcı, Hüseyin Bilge; Durmuşoğlu, E. G.; Demir, Hilmi Volkan
We demonstrate amplified spontaneous emission (ASE) in solution with ultralow thresholds of 30 μJ/cm2 in red and of 44 μJ/cm2 in green from engineered colloidal quantum well (CQW) heterostructures. For this purpose, CdSe/CdS core/crown CQWs, designed to hit the green region, and CdSe/CdS@CdxZn1–xS core/crown@gradient-alloyed shell CQWs, further tuned to reach the red region by shell alloying, were employed to achieve high-performance ASE in the visible range. The net modal gain of these CQWs reaches 530 cm–1 for the green and 201 cm–1 for the red, 2–3 orders of magnitude larger than those of colloidal quantum dots (QDs) in solution. To explain the root cause for ultrahigh gain coefficient in solution, we show for the first time that the gain cross sections of these CQWs is ≥3.3 × 10–14 cm2 in the green and ≥1.3 × 10–14 cm2 in the red, which are two orders of magnitude larger compared to those of CQDs.