Browsing by Author "Shabani, Farzan"

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Open Access
All-colloidal parity–time-symmetric microfiber lasers balanced between the gain of colloidal quantum wells and the loss of colloidal metal nanoparticles
(Royal Society of Chemistry, 2022-08-23) Foroutan-Barenji, Sina; Shabani, Farzan; Işık, Ahmet Tarik; Dikmen, Zeynep; Demir, Hilmi Volkan
Lasers based on semiconductor colloidal quantum wells (CQWs) have attracted wide attention, thanks to their facile solution-processability, low threshold and wide range spectral tunability. Colloidal microlasers based on whispering-gallery-mode (WGM) resonators have already been widely demonstrated. However, due to their microscale size typically supporting multiple modes, they suffer from multimode competition and higher threshold. The ability to control the multiplicity of modes oscillating within colloidal laser resonators and achieving single-mode lasers is of fundamental importance in many photonic applications. Here we show that as a unique, simple and versatile architecture of all-colloidal lasers intrinsically enabled by balanced gain/loss segments, the lasing threshold reduction and spectral purification can be readily achieved in a system of a WGM-supported microfiber cavity by harnessing the notions of parity–time symmetry (PT). In particular, we demonstrate a proof-of-concept PT-symmetric microfiber laser employing CQWs as the colloidal gain medium along with a carefully tuned nanocomposite of Ag nanoparticles (Ag NPs) incorporated into a PMMA matrix altogether and conveniently coated around a coreless microfiber as a rigorously tailored colloidal loss medium to balance the gain. The realization of gain/loss segments in our PT-symmetric all-colloidal arrangement is independent of selected pumping, reducing the complexity of the system and making compact device applications feasible, where control over the pumping is not possible. We observed a reduction in the number of modes, resulting in a reduced threshold and enhanced output power of the PT-symmetric laser. The PT-symmetric CQW-WGM microcavity architecture offers new opportunities towards simple implementation of high-performance optical resonators for colloidal lasers.
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 synthetic pathways of atomically-flat complex nanocrystal heterostructures
(2024-01) Shabani, Farzan
Colloidal semiconductor nanocrystals (NCs) constitute one of the most important branches of nanoscience, with an increasingly high research interest, culminating with a Nobel Prize most recently. The nanometric size of these NCs allows for size-dependent optical properties, which provides an extra tool besides the composition to fine-tune these properties. Recent advancements in NC synthesis have been enabling important developments in the design and engineering of different shapes, compositions, and heterostructures of NCs. Accompanied by a deeper physical understanding and more sophisticated fabrication techniques, the NCs are now being integrated into many of the optoelectronic devices and are of prime importance for the next-generation optoelectronics. Despite all the progress, however, the full potential and synthesis dynamics of the NCs still need further investigation. Here, we addressed specifically four key aspects of the semiconductor NCs: shape engineering, electronic heterostructures, doping, and surface modification. In this thesis research, the synthesis dynamics, especially nucleation, growth and diffusion, were investigated in depth for different synthetic routes and conditions, and some of the important challenges were resolved. With the scarce number of proper emitters at longer wavelengths, in this thesis, a complex and thick heterostructure based on group II-VI nanoplatelets (NPLs) with relaxed quantum confinement was developed. The multi-shell design of the proposed NPLs helps overcome the unfavorable growth in the thickness direction, which, together with the cation dissolution/recrystallization and cation reorganization at high temperatures, relaxes the strain between the domains. The final NPLs, emitting in the deep-red region close to the bulk bandgap of CdSe, were used as an active layer in a light-emitting diode (LED) device and exhibited an exceptionally high external quantum efficiency (EQE) of 6.8% at electroluminescence peak wavelength of 701 nm, one of the best reported for colloids in this spectral range in the literature. Additionally, a novel heterostructure of multi-crown NPLs was designed and demonstrated, where several direct and indirect recombination pathways give rise to photoluminescence with both type-I and type-II characteristics. The design of these NPLs, especially the size of the domains, was shown to significantly impact the final optical properties that can activate/deactivate the recombination channels alongside the temperature. These multi-crown type-II NPLs exhibit an extremely high two-photon absorption cross-section with the highest value of 12.9 × 106 GM and low dark-bright exciton splitting energy critical for optoelectronic applications, including photodetectors, bioimaging and quantum devices. Next, we showed silver doping dynamics of core/shell NPLs, which previously proved challenging due to the self-purification after the shell growth. Here, the composition of the shell was shown to be an important factor in the destruction mechanism of the NPLs in the irreversible doping regime at high doping temperatures. The Ag:CdSe/CdZnS core/shell NPLs exhibit only dopant emission with superior paramagnetic properties compared to CdS-shelled NPLs thanks to better lattice preservation and higher dopant content. At last, a surface modification method was suggested and demonstrated for group I-III-VI NCs to enhance their electronic properties. Replacing the long-chain organic ligands with a S2- layer, injection of a negative charge and passivation of donor sites changed the behavior of the field-effect transistors (FETs) based on these NCs from p-type to n-type with more than a 105-fold enhancement in the carrier mobility. This method allowed fine-tuning of the optical properties of the NCs by the diffusion of the cations and shell formation. The findings of this thesis shine light on some of the important challenges in the field of semiconductor NCs while drawing a guideline for future research on the synthetic routes and optoelectronic properties. The thesis paves the way for future device integration of the developed NCs to fully realize their potential, while the demonstration of the more elaborated properties, including nonlinear absorption, paramagnetism and dark-bright exciton splitting, encourages further fundamental studies focusing on the physics of the semiconductor NCs.
Open Access
Color enrichment solids of spectrally pure colloidal quantum wells for wide color Span in displays
(Wiley-VCH Verlag GmbH & Co. KGaA, 2022-07-18) Erdem, T.; Soran Erdem, Z.; Işık, Furkan; Shabani, Farzan; Yazici, A. F.; Mutlugün, E.; Gaponik, N.; Demir, H. V.
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 ≈20% and ≈55%, respectively, while emission linewidths and peak wavelengths remain almost unaltered. Furthermore, sucrose matrix preserves ≈70% and ≈45% of the initial emission intensity of the green- and red-emitting CQWs after >60 h, respectively, which is ≈4× and ≈2× 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−1elect, respectively. With the liquid crystal display filters, this becomes 39 and 86 lm W−1elect, 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.
Open Access
Core-crown quantum nanoplatelets with favorable type-II heterojunctions boost charge separation and photocatalytic NO oxidation on TiO2
(Wiley, 2020-09) Ebrahimi, Elnaz; İrfan, Muhammad; Shabani, Farzan; Koçak, Yusuf; Karakurt, Bartu; Erdem, E.; Demir, Hilmi Volkan; Özensoy, Emrah
Functionalization of TiO2 (P25) with oleic acid‐capped CdSe(core)/CdSeTe(crown) quantum‐well nanoplatelets (NPL) yielded remarkable activity and selectivity toward nitrate formation in photocatalytic NOx oxidation and storage (PHONOS) under both ultraviolet (UV‐A) and visible (VIS) light irradiation. In the NPL/P25 photocatalytic system, photocatalytic active sites responsible for the NO(g) photo‐oxidation and NO2 formation reside mostly on titania, while the main function of the NPL is associated with the photocatalytic conversion of the generated NO2 into the adsorbed NO3− species, significantly boosting selectivity toward NOx storage. Photocatalytic improvement in NOx oxidation and storage upon NPL functionalization of titania can also be associated with enhanced electron‐hole separation due to a favorable Type‐II heterojunction formation and photo‐induced electron transfer from the CdSeTe crown to the CdSe core of the quantum well system, where the trapped electrons in the CdSe core can later be transferred to titania. Re‐usability of NPL/P25 system was also demonstrated upon prolonged use of the photocatalyst, where NPL/P25 catalyst surpassed P25 benchmark in all tests.
Open Access
Deep-red-emitting colloidal quantum well light-emitting diodes enabled through a complex design of core/crown/double shell heterostructure
(Wiley, 2022-02-24) Shabani, Farzan; Dehghanpour Baruj, Hamed; Yurdakul, Iklim; Delikanlı, Savaş; Gheshlaghi, Negar; Işık, Furkan; Liu, B.; Altıntaş, Yemliha; Canımkurbey, Betül; Demir, Hilmi Volkan
Extending the emission peak wavelength of quasi-2D colloidal quantum wells has been an important quest to fully exploit the potential of these materials, which has not been possible due to the complications arising from the partial dissolution and recrystallization during growth to date. Here, the synthetic pathway of (CdSe/CdS)@(1-4 CdS/CdZnS) (core/crown)@(colloidal atomic layer deposition shell/hot injection shell) hetero-nanoplatelets (NPLs) using multiple techniques, which together enable highly efficient emission beyond 700 nm in the deep-red region, is proposed and demonstrated. Given the challenges of using conventional hot injection procedure, a method that allows to obtain sufficiently thick and passivated NPLs as the seeds is developed. Consequently, through the final hot injection shell coating, thick NPLs with superior optical properties including a high photoluminescence quantum yield of 88% are achieved. These NPLs emitting at 701 nm exhibit a full-width-at-half-maximum of 26 nm, enabled by the successfully maintained quasi-2D shape and minimum defects of the resulting heterostructure. The deep-red light-emitting diode (LED) device fabricated with these NPLs has shown to yield a high external quantum efficiency of 6.8% at 701 nm, which is on par with other types of LEDs in this spectral range. © 2021 Wiley-VCH GmbH
Open Access
Direct laser writing of resonant periodic nanostructures in thin light-emitting films of CdSe/CdZnS core/shell nanoplatelets
(AIP Publishing LLC, 2022-11-28) Azizov, R.; Sinev, I.; Işık, Furkan; Shabani, Farzan; Pushkarev, A.; Yurdakul, İklim; Delikanli, Savaş; Demir, Hilmi Volkan; Makarov, S.
Core/shell CdSe/CdZnS nanoplatelets (NPLs) are a promising class of nanomaterials for lasing applications owing to their low thresholds and high stability of stimulated emission generation as compared with many other types of colloids. Moreover, they can be self-assembled into high-quality thin films by simple methods of deposition. However, the high throughput and reproducible methods for nanopatterning of such films for advanced light-emitting applications are still missing. In this work, we show direct laser writing on thin films assembled from CdSe/CdZnS NPLs using either spin-coating or the self-assembly method for the purpose of fabricating. Using theoretical calculations, we design the period of the structures to achieve high quality-factor optical modes in the emission band of NPLs. In these nanostructured NPL films, fabricated according to the design, we observe photoluminescence enhancement and directional outcoupling effects. The proposed approach holds great potential for LEDs with improved outcoupling and for distributed feedback lasers or lasers based on bound states in the continuum with directly written optical cavities.
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
High-performance deep red colloidal quantum well light-emitting diodes enabled by the understanding of charge dynamics
(American Chemical Society, 2022-07-11) Hu, S.; Shabani, Farzan; Liu, B.; Zhang, L.; Guo, M.; Lu, G; Zhou, Z.; Wang, J.; Huang, J.C.; Min, Y.; Xue, Q.; Demir, Hilmi Volkan; Liu, C.
Colloidal quantum wells (CQWs) have emerged as a promising family of two-dimensional (2D) optoelectronic materials with outstanding properties, including ultranarrow luminescence emission, nearly unity quantum yield, and large extinction coefficient. However, the performance of CQWs based light-emitting diodes (CQW-LEDs) is far from satisfactory, particularly for deep red emissions (≥660 nm). Herein, high efficiency, ultra-low-efficiency roll-off, high luminance, and extremely saturated deep red CQW-LEDs are reported. A key feature for the high performance is the understanding of charge dynamics achieved by introducing an efficient electron transport layer, ZnMgO, which enables balanced charge injection, reduced nonradiative channels, and smooth films. The CQW-LEDs based on (CdSe/CdS)@(CdS/CdZnS) ((core/crown)@(colloidal atomic layer deposition shell/hot injection shell)) show an external quantum efficiency of 9.89%, which is a record value for 2D nanocrystal LEDs with deep red emissions. The device also exhibits an ultra-low-efficiency roll-off and a high luminance of 3853 cd m−2. Additionally, an exceptional color purity with the CIE coordinates of (0.719, 0.278) is obtained, indicating that the color gamut covers 102% of the International Telecommunication Union Recommendation BT 2020 (Rec. 2020) standard in the CIE 1931 color space, which is the best for CQW-LEDs. Furthermore, an active-matrix CQW-LED pixel circuit is demonstrated. The findings imply that the understanding of charge dynamics not only enables high-performance CQW-LEDs and can be further applied to other kinds of nanocrystal LEDs but also is beneficial to the development of CQW-LEDs-based display technology and related integrated optoelectronics.
Open Access
Highly directional highly efficient solution processed light emitting diodes of all face down
(Wiley-VCH Verlag GmbH & Co. KGaA, 2023-04-06) Baruj, Hamed Dehghanpour; Bozkaya, İklim; Canımkurbey, Betül; Işık, Ahmet Tarık; Shabani, Farzan; Delikanlı, Savaş; Shendre, S.; Erdem, Onur; Işık, Furkan; Demir, Hilmi Volkan
Semiconductor colloidal quantum wells (CQWs) provide anisotropic emission behavior originating from their anisotropic optical transition dipole moments (TDMs). Here, solution-processed colloidal quantum well light-emitting diodes (CQW-LEDs) of a single all-face-down oriented self-assembled monolayer (SAM) film of CQWs that collectively enable a supreme level of IP TDMs at 92% in the ensemble emission are shown. This significantly enhances the outcoupling efficiency from 22% (of standard randomly-oriented emitters) to 34% (of face-down oriented emitters) in the LED. As a result, the external quantum efficiency reaches a record high level of 18.1% for the solution-processed type of CQW-LEDs, putting their efficiency performance on par with the hybrid organic-inorganic evaporation-based CQW-LEDs and all other best solution-processed LEDs. This SAM-CQW-LED architecture allows for a high maximum brightness of 19,800 cd m$^{−2}$ with a long operational lifetime of 247 h at 100 cd m$^{−2}$ as well as a stable saturated deep-red emission (651 nm) with a low turn-on voltage of 1.7 eV at a current density of 1 mA cm$^{−2}$ and a high J$_{90}$ of 99.58 mA cm$^{−2}$. These findings indicate the effectiveness of oriented self-assembly of CQWs as an electrically-driven emissive layer in improving outcoupling and external quantum efficiencies in the CQW-LEDs.
Open Access
Near-field energy transfer into silicon inversely proportional to distance using quasi-2D colloidal quantum well donors
(Wiley-VCH Verlag GmbH & Co. KGaA, 2021-09-12) Humayun, Muhammad Hamza; Hernandez-Martinez, Pedro Ludwig; Gheshlaghi, Negar; Erdem, Onur; Altıntaş, Yemliha; Shabani, Farzan; Demir, Hilmi Volkan
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 Förster 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.
Open Access
Near-infrared emission from CdSe-Based nanoplatelets induced by Ytterbium doping
(American Chemical Society, 2023-02-15) İzmir, Merve; Durmusoglu, Emek G.; Sharma, Manoj; Shabani, Farzan; Işık, Furkan; Delikanlı, Savaş; Sharma, Vijay Kumar; Demir, Hilmi Volkan
Cadmium selenide (CdSe) nanoplatelets (NPLs) have attracted significant attention thanks to their favorable optical properties, including narrow emission linewidths, reduced Auger recombination, and a high absorption cross section. However, the photoluminescence (PL) quantum yield (QY) in the near-infrared (NIR) region is poor as compared to that in the visible region. Doping of metal ions is proven to be a successful strategy for inducing Stokes-shifted NIR emission. Here, we report the first account of the successful doping of ytterbium (Yb) into CdSe NPLs by a modified seeded-growth method. The successful incorporation of divalent Yb ions into CdSe NPLs resulted in an additional NIR emission apart from their excitonic emission. By optimizing the dopant concentration, we observed an impressive PL QY of ∼55% for these Yb-doped NPLs. Detailed elemental and optical characterizations were conducted to understand the emerging photophysical properties of these Yb-doped NPLs. These NIR-emitting lanthanide-doped CdSe NPLs might have applications in the next-generation bioimaging, night vision, and photodetection. © 2023 The Authors. Published by American Chemical Society
Open Access
Observation of optical gain from aqueous quantum well heterostructures in water
(Royal Society of Chemistry, 2022-09-25) Delikanlı, Savaş; Durmuşoğlu, E.G.; Erdem, Onur; Shabani, Farzan; Kumar, Satish; Barujb, Hamed Dehghanpour; Demir, Hilmi Volkan; Işık, Furkan; Canımkurbey, Betül
Although achieving optical gain using aqueous solutions of colloidal nanocrystals as a gain medium is exceptionally beneficial for bio-optoelectronic applications, the realization of optical gain in an aqueous medium using solution-processed nanocrystals has been extremely challenging because of the need for surface modification to make nanocrystals water dispersible while still maintaining their gain. Here, we present the achievement of optical gain in an aqueous medium using an advanced architecture of CdSe/CdS@CdxZn1−xS core/crown@gradient-alloyed shell colloidal quantum wells (CQWs) with an ultralow threshold of ∼3.4 μJ cm−2 and an ultralong gain lifetime of ∼2.6 ns. This demonstration of optical gain in an aqueous medium is a result of the carefully heterostructured CQWs having large absorption cross-section and gain cross-section in addition to inherently slow Auger recombination in these CQWs. Furthermore, we show low-threshold in-water amplified spontaneous emission (ASE) from these aqueous CQWs with a threshold of 120 μJ cm−2. In addition, we demonstrate a whispering gallery mode laser with a low threshold of ∼30 μJ cm−2 obtained by incorporating films of CQWs by exploiting layer-by-layer approach on a fiber. The observation of low-threshold optical gain with ultralong gain lifetime presents a significant step toward the realization of advanced optofluidic colloidal lasers and their continuous-wave pumping.
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
Plasmon-enhanced photoresponse of single silver nanowires and their network devices
(Royal Society of Chemistry, 2022-02-11) Razeghi, Mohammadali; Üstünçelik, Merve; Shabani, Farzan; Demir, Hilmi Volkan; Kasırga, T. Serkan
The photo-bolometric effect is critically important in optoelectronic structures and devices employing metallic electrodes with nanoscale features due to heating caused by the plasmonic field enhancement. One peculiar case is individual silver nanowires (Ag NWs) and their networks. Ag NW-networks exhibit excellent thermal, electrical, and mechanical properties, providing a simple yet reliable alternative to common flexible transparent electrode materials used in optoelectronic devices. To date, there have been no reports on the photoresponse of Ag NWs. In this study, we show that single Ag NWs and networks of such Ag NWs possess a significant, intrinsic photoresponse, thanks to the photo-bolometric effect, as directly observed and measured using scanning photocurrent microscopy. Surface plasmon polaritons (SPPs) created at the contact metals or plasmons created at the nanowire-metal structures cause heating at the junctions where a plasmonic field enhancement is possible. The local heating of the Ag NWs results in negative photoconductance due to the bolometric effect. Here an open-circuit response due to the plasmon-enhanced Seebeck effect was recorded at the NW-metal contact junctions. The SPP-assisted bolometric effect is found to be further enhanced by decorating the Ag NWs with Ag nanoparticles. These observations are relevant to the use of metallic nanowires in plasmonic applications in particular and in optoelectronics in general. Our findings may pave the path for plasmonics-enabled sensing without spectroscopic detection.
Open Access
Self-resonant microlasers of colloidal quantum wells constructed by direct deep patterning
(American Chemical Society, 2021-06-09) Gheshlaghi, Negar; Foroutan-Barenji, Sina; Erdem, Onur; Altintas, Yemliha; Shabani, Farzan; Humayun, Muhammad Hamza; Demir, Hilmi Volkan
Here, the first account of self-resonant fully colloidal μ-lasers made from colloidal quantum well (CQW) solution is reported. A deep patterning technique is developed to fabricate well-defined high aspect-ratio on-chip CQW resonators made of grating waveguides and in-plane reflectors. The fabricated waveguide-coupled laser, enabling tight optical confinement, assures in-plane lasing. CQWs of the patterned layers are closed-packed with sharp edges and residual-free lifted-off surfaces. Additionally, the method is successfully applied to various nanoparticles including colloidal quantum dots and metal nanoparticles. It is observed that the patterning process does not affect the nanocrystals (NCs) immobilized in the attained patterns and the different physical and chemical properties of the NCs remain pristine. Thanks to the deep patterning capability of the proposed method, patterns of NCs with subwavelength lateral feature sizes and micron-scale heights can possibly be fabricated in high aspect ratios.
Open Access
Simultaneous dual-color amplified spontaneous emission and lasing from colloidal quantum well gain media in their own layered waveguide and cavity
(Wiley-VCH GmbH, 2023-03-26) Işık, Ahmet Tarık; Shabani, Farzan; Işık, Furkan; Kumar, Satish; Delikanli, Savaş; Demir, Hilmi Volkan
Micro/nanoscale semiconductor multicolor lasers offer great potential for enhanced-performance photonic circuits. Colloidal quantum wells (CQWs) are excellent candidates as active materials for these platforms owing to their superior properties including suppressed Auger recombination and large absorption cross-section. In this work, multicolor optical gain and lasing from the heterostructures of CQWs as the gain media in their own all-solution processed optical cavity are proposed and demonstrated for the first time. Here, using a simple waveguide slab consisting of the thin films of green-emitting CdSeS/Cd0.1Zn0.9S core/hot-injection-shell grown CQWs and red-emitting CdSe/CdS@CdZnS core/crown@shell CQWs, a transparent low refractive index colloidal spacing layer of silica nanoparticles (NPs) is devised that critically suppresses otherwise detrimental nonradiative energy transfer between the green and red-emitting CQWs. This multilayer configuration is key to enabling simultaneous amplified spontaneous emission behavior in two colors with low threshold levels. This layered architecture is further adapted to a whispering-gallery-mode cavity by fabricating a microdisk pattern directly out of these CQWs-NPs-CQWs colloids. The resulting device exhibits dual-color multimode lasing both at 569 and 648 nm at the same time. This unique multicolor lasing layered architecture holds great promise for on-chip photonic applications such as dual-color biological imaging.
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
Thermodynamic silver doping of core/shell colloidal quantum wells imparted with paramagnetic properties emitting at near-infrared
(American Chemical Society, 2023-05-29) Shabani, Farzan; Ahmad, Muhammad; Kumar, Satish; Delikanlı, Savaş; Işık, Furkan; Bhattacharya, A.; Petrou, A.; Demir, Hilmi Volkan
Two-dimensional (2D) core/shell nanoplatelets (NPLs) synthesized via the hot-injection method provide excellent thermal and chemical stability for high-temperature doping, where an expanded and flexible lattice is required. Here, a thermodynamic approach toward silver doping of these NPLs is proposed and demonstrated, which previously proved to be challenging due to the fast self-purification of the dopants with the introduction of the shell. Maintaining the doping procedure in the reversible regime ensured the integrity of the NPLs and allowed a high level of doping; however, the equilibrium condition is further complicated by environmental factors that affect the chemical activity of the cations and the surface composition of the NPLs. Two main deterioration mechanisms in the irreversible regime were observed: ZnS-shelled NPLs suffered preferential etching, while CdS-shelled NPLs underwent cleavage and fragmentation. Alloying of the shell minimized both mechanisms for CdZnS-shelled NPLs and preserved the metastable state of the NPLs, including their 2D shape and crystalline structure. Distribution of silver ions in the lattice of the NPLs directly affected the recombination dynamics and enabled fine-tuning of the near-infrared emission beside the exciton confinement. These silver-doped CdZnS-shelled NPLs are shown further to exhibit enhanced paramagnetic properties with Zeeman splitting and Brillouin-like bound-exciton polarization as a function of the magnetic field, critical for spintronic applications