Browsing by Subject "Colloidal quantum dots"

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Open Access
Blue-and red-shifting amplified spontaneous emission of CdSe/CdS core/shell colloidal quantum dots
(IEEE, 2013) Kelestemur, Yusuf; Cihan, Ahmet Fatih; Güzeltürk, Burak; Yerli, Ozan; Kurum, U.; Yaglioglu H.G.; Elmali, A.; Demir, Hilmi Volkan
We report blue- and red-shifting amplified spontaneous emission of CdSe/CdS quantum dots, controlled by varying core/shell dimensions and modifying exciton-exciton interactions, with low optical gain threshold of two-photon absorption pumping. © 2013 The Optical Society.
Open Access
Cd-free Cu-doped ZnInS/ZnS Core/Shell nanocrystals: Controlled synthesis and photophysical properties
(SpringerOpen, 2018) Kaur, Manpreet; Sharma, Ashma; Olutaş, Murat; Erdem, Onur; Kumar, A.; Sharma, Manoj; Demir, Hilmi Volkan
Here, we report efficient composition-tunable Cu-doped ZnInS/ZnS (core and core/shell) colloidal nanocrystals (CNCs) synthesized by using a colloidal non-injection method. The initial precursors for the synthesis were used in oleate form rather than in powder form, resulting in a nearly defect-free photoluminescence (PL) emission. The change in Zn/In ratio tunes the percentage incorporation of Cu in CNCs. These highly monodisperse Cu-doped ZnInS CNCs having variable Zn/In ratios possess peak emission wavelength tunable from 550 to 650 nm in the visible spectrum. The quantum yield (QY) of these synthesized Cd-free CNCs increases from 6.0 to 65.0% after coating with a ZnS shell. The CNCs possessing emission from a mixed contribution of deep trap and dopant states to only dominant dopant-related Stokes-shifted emission are realized by a careful control of stoichiometric ratio of different reactant precursors during synthesis. The origin of this shift in emission was understood by using steady state and time-resolved fluorescence (TRF) spectroscopy studies. As a proof-of-concept demonstration, these blue excitable Cu-doped ZnInS/ZnS CNCs have been integrated with commercial blue LEDs to generate white-light emission (WLE). The suitable combination of these highly efficient doped CNCs results led to a Commission Internationale de l’Enclairage (CIE) color coordinates of (0.33, 0.31) at a color coordinate temperature (CCT) of 3694 K, with a luminous efficacy of optical radiation (LER) of 170 lm/Wopt and a color rendering index (CRI) of 88.
Open Access
Colloidal quantum dot light-emitting diodes employing phosphorescent small organic molecules as efficient exciton harvesters
(American Chemical Society, 2014) Mutlugun, E.; Guzelturk, B.; Abiyasa, A. P.; Gao, Y.; Sun X. W.; Demir, Hilmi Volkan
Nonradiative energy transfer (NRET) is an alternative excitation mechanism in colloidal quantum dot (QD) based electroluminescent devices (QLEDs). Here, we develop hybrid highly spectrally pure QLEDs that facilitate energy transfer pumping via NRET from a phosphorescent small organic molecule-codoped charge transport layer to the adjacent QDs. A partially codoped exciton funnelling electron transport layer is proposed and optimized for enhanced QLED performance while exhibiting very high color purity of 99%. These energy transfer pumped hybrid QLEDs demonstrate a 6-fold enhancement factor in the external quantum efficiency over the conventional QLED structure, in which energy transfer pumping is intrinsically weak.
Open Access
Colloidal synthesis and doping of semiconductor nanocrystals
(2015-07) Akgül, Mehmet Zafer
Colloidal semiconductor nanocrystals have drawn great interest for application areas in photonics and optoelectronics thanks to their superior optical properties including strong bandgap emission and tunability. Also, their suitability for solution-based processing has made them highly attractive for low-cost production of light-emitting diodes and lasers. Our objective in this thesis is to show the potential and versatility of semiconductor nanocrystals via colloidal synthesis and post-processing methods. The thesis work includes the synthesis of colloidal quantum dot and well structures and their post-doping and investigates their exciton decay dynamics. In this thesis a novel colloidal approach for the doping of zinc blende colloidal quantum wells was proposed and demonstrated for the first time. This new doping method uniquely relies on atomic layer deposition (ALD) process. Here we achieved the worlds first manganese-doped CdSe@CdS core@shell nanoplatelets using our technique of ALD-assisted doping. Also, we studied silver-doped CdTe quantum dots under different conditions. Our experimental work proved that the quantum yield enhancement of silver-doped CdTe quantum dots is a strong function of the nanocrystal size and doping concentration. Tuning the nanocrystal size and doping level, our aqueous core-only CdTe nanocrystals reached a record high photoluminescence quantum efficiency of 68%. For these quantum dots, various decay kinetics were proposed and the enhancement in the quantum yield was attributed to the trap state annihilation. The methods and results provided in this thesis contribute to the fundamental understanding of semiconductornanocrystals and pave the way for high-performance colloidal platforms and devices.
Embargo
Colloidal synthesis and optical properties of heterostructured quantum wells
(2024-08) Işık, Furkan
Colloidal quantum wells (CQWs) have emerged as auspicious gain materials for next-generation colloidal nanolasers owing to their exceptional optoelectronic properties including intrinsically suppressed Auger recombination, large absorption cross-section, low cost of production, and the ability to precisely tailor their attributes. However, the realization of their photonic devices faces fundamental challenges inherent to semiconductor nanocrystals in general, which can be tackled via the design and engineering of their advanced heterostructures. In this thesis, we proposed multiple design strategies to address scientific obstacles associated with using such CQWs as gain materials and developed a variety of their rational heterostructure designs by implementing advanced synthesis techniques, allowing us to systematically study the structure-property relationship. We investigated the optical gain performance of these CQW heterostructures through spectral and temporal spectroscopy techniques to elucidate the underlying mechanisms, which guided us to improve the associated structural aspects of CQWs. This approach culminated in the development of superior CQW heterostructures possessing low optical gain thresholds, giant material gain coefficients, and long gain lifetimes, addressing all main specifications quantifying the quality of a gain material. We also presented proof-of-concept device demonstrations showcasing the advancement in the gain aspect of these CQW heterostructures, such as high-performance amplified spontaneous emission in solution and whispering gallery mode lasing with ultra-low thresholds. The findings of this thesis indicate highly engineered CQW heterostructures offer excellent gain media.
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
Electrically control amplified spontaneous emission in colloidal quantum dots
(American Association for the Advancement of Science, 2019) Yu, J.; Shendre, S.; Koh, W.; Liu, B.; Li, M.; Hou, S.; Hettiarachchi, C.; Delikanlı, S.; Hernandez-Martinez, P.; Birowosuto, M. D.; Wang, H.; Sum, T.; Demir, Hilmi Volkan; Dang, C.
Colloidal quantum dots (CQDs) are highly promising materials for light amplification thanks to their efficient photoluminescence, tunable emission wavelength and low-cost synthesis. Unfortunately, CQDs are suffering from band-edge state degeneracy which demands multiple excitons to achieve population inversion. As a result, non-radiative Auger recombination increases the lasing threshold and limits the gain lifetime. Here, benefiting from the negative charging, we demonstrate that the amplified spontaneous emission (ASE) threshold is controllable in a device where CQD film is exposed to an external electric field. Specifically, singly charged CQDs lower the threshold due to the preexisting electron in the conduction band, while strongly enhanced Auger recombination in doubly charged CQDs stymies the ASE. Experimental results and kinetic equation model show that ASE threshold reduces 10% even if our device only charges ~17% of the CQD population. Our results open new possibilities for controlling exciton recombination dynamics and achieving electrically pumped CQD lasers.
Open Access
Electroluminescence efficiency enhancement in quantum dot light-emitting diodes by embedding a silver nanoisland layer
(Wiley-VCH Verlag, 2015) Yang, X.; Hernandez-Martinez, P. L.; Dang C.; Mutlugün, E.; Zhang, K.; Demir, Hilmi Volkan; Sun X. W.
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 nano-islands, 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. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Emerging fields of colloidal nanophotonics for quality lighting to versatile lasing
(Springer Verlag, 2018) Demir, Hilmi Volkan
Solution-processed semiconductor nanocrystals have attracted increasingly greater interest in optoelectronics including color conversion and enrichment in quality lighting and display backlighting. Optical properties of these colloidal nanocrystals can be conveniently controlled by tailoring their shape, composition, and size in an effort to realize high-performance light generation and lasing. We now witness the expanding deployment of semiconductor nanocrystals in consumer products being adapted by giant electronics companies. Based on the rational design and control of excitonic processes in these nanocrystals, it is possible to achieve highly efficient light-emitting diodes and optically pumped lasers. In this chapter, we introduce an emerging field of nanocrystal optoelectronics with applications from quality lighting to versatile lasing. We look into the performance limits of color conversion using colloidal nanocrystals. Here we introduce a new concept of all-colloidal lasers developed by incorporating nanocrystal emitters as the optical gain media intimately into fully colloidal cavities. As an extreme case of solution-processed tightly-confined quasi-2D colloids, we also show that the atomically flat nanoplatelets uniquely offer record high optical gain coefficients and ultralow threshold stimulated emission. Given the recent accelerating progress in colloidal nanophotonics, solution-processed quantum materials now hold great promise to challenge their conventional epitaxial counterparts in the near future.
Open Access
Energy-saving quality road lighting with colloidal quantum dot nanophosphors
(Walter de Gruyter GmbH, 2014) Erdem, T.; Kelestemur, Y.; Soran-Erdem, Z.; Ji, Y.; Demir, Hilmi Volkan
Here the first photometric study of road-lighting white light-emitting diodes (WLEDs) integrated with semiconductor colloidal quantum dots (QDs) is reported enabling higher luminance than conventional light sources, specifically in mesopic vision regimes essential to street lighting. Investigating over 100 million designs uncovers that quality road-lighting QD-WLEDs, with a color quality scale and color rendering index ≥85, enables 13-35% higher mesopic luminance than the sources commonly used in street lighting. Furthermore, these QD-WLEDs were shown to be electrically more efficient than conventional sources with power conversion efficiencies ≥16-29%. Considering this fact, an experimental proof-of-concept QD-WLED was demonstrated, which is the first account of QD based color conversion custom designed for street lighting applications. The obtained white LED achieved the targeted mesopic luminance levels in accordance with the road lighting standards of the USA and the UK. These results indicate that road-lighting QD-WLEDs are strongly promising for energy-saving quality road lighting. © 2014 Science Wise Publishing & De Gruyter 2014.
Open Access
Exciton dynamics in colloidal quantum-dot LEDs under active device operations
(American Chemical Society, 2018) Shendre, S.; Sharma, V. K.; Dang C.; Demir, Hilmi Volkan
Colloidal quantum-dot light-emitting diodes (QLEDs) are lucrative options for color-pure lighting sources. To achieve high-performance QLEDs, besides developing high-efficiency quantum dots (QDs), it is essential to understand their device physics. However, little understanding of the QD emission behavior in active QLEDs is one of the main factors hindering the improvement of device efficiency. In this work, we systematically studied the exciton dynamics of gradient composition CdSe@ZnS QDs during electroluminescence in a working QLED. With time-resolved photoluminescence analyses using fluorescence lifetime imaging microscopy we analyzed a large population of QDs spatially spreading over an extended area inside and outside the device. This allows us to reveal the statistically significant changes in the behavior of QD emission in the device at different levels of applied voltages and injection currents. We find that the QD emission efficiency first drops in device fabrication with Al electrode deposition and that the QD exciton lifetime is then statistically reduced further under the QLED's working conditions. This implies the nonradiative Auger recombination process is active in charged QDs as a result of imbalanced charge injection in a working QLED. Our results help to understand the exciton behavior during the operation of a QLED and demonstrate a new approach to explore the exciton dynamics statistically with a large QD population.
Open Access
Excitonically driven quantum dot light-emitting diodes: exLEDs
(Optical Society of America, 2013) Güzeltürk, Burak; Hernandez-Martinez, Pedro Ludwig; Sharma, Vijay Kumar; Coşkun, Yasemin; Ibrahimova, Vusala; Sun, X.W.; Tuncel, Donus; Demir, Hilmi Volkan
A hybrid platform of colloidal quantum dots integrated into conjugated polymers is eported for excitonically driven light-emitting diodes having pure quantum dot emission in the electroluminescence spectrum with substantially enhanced efficiency.
Open Access
Förster-type nonradiative energy transfer directed from colloidal quantum dots to epitaxial quantum wells for light harvesting applications
(Optical Society of America, 2011) Nizamoğlu, Sedat; Sarı, Emre; Baek J.-H.; Lee I.-H.; Demir, Hilmi Volkan
We report on Frster-type nonradiative energy transfer directed from CdSe/ZnS core/shell quantum dots to InGaN/GaN quantum wells with 69.6% efficiency at 1.527 ns-1 rate at room temperature for potential light harvesting and solar cells applications. © 2011 OSA.
Open Access
Green stimulated emission boosted by nonradiative resonant energy transfer from blue quantum dots
(American Chemical Society, 2016) Gao, Y.; Yu, G.; Wang Y.; Dang C.; Sum, T. C.; Sun, H.; Demir, Hilmi Volkan
Thanks to their tunability and versatility, the colloidal quantum dots (CQDs) made of II-VI semiconductor compound offer the potential to bridge the "green gap" in conventional semiconductors. However, when the CQDs are pumped to much higher initial excitonic states compared to their bandgap, multiexciton interaction is enhanced, leading to a much higher stimulated emission threshold. Here, to circumvent this drawback, for the first time, we show a fully colloidal gain in green enabled by a partially indirect pumping approach assisted by Förster resonance energy transfer process. By introducing the blue CQDs as exciton donors, the lasing threshold of the green CQDs, is reduced dramatically. The blue CQDs thus serve as an energy-transferring buffer medium to reduce excitation energy from pumping photons in a controlled way by injecting photoinduced excitons into green CQDs. Our newly developed colloidal pumping scheme could enable efficient CQD lasers of full visible colors by a single pump source and cascaded exciton transfer. This would potentially pave the way for an efficient multicolor laser for lighting and display applications.
Open Access
High performance infrared photodetectors up to 2.8 μm wavelength based on lead selenide colloidal quantum dots
(OSA - The Optical Society, 2017) Thambidurai, M.; Jang, Y.; Shapiro, A.; Yuan, G.; Xiaonan, H.; Xuechao, Y.; Wang, Q. J.; Lifshitz, E.; Demir, Hilmi Volkan; Dang C.
The strong quantum confinement effect in lead selenide (PbSe) colloidal quantum dots (CQDs) allows to tune the bandgap of the material, covering a large spectral range from mid- to near infrared (NIR). Together with the advantages of low-cost solution processability, flexibility and easy scale-up production in comparison to conventional semiconductors especially in the mid- to near infrared range, PbSe CQDs have been a promising material for infrared optoelectronic applications. In this study, we synthesized monodisperse and high purity PbSe CQDs and then demonstrated the photodetectors working at different wavelengths up to 2.8 μm. Our high quality PbSe CQDs show clear multiple excitonic absorption peaks. PbSe CQD films of different thicknesses were deposited on interdigitated platinum electrodes by a simple drop casting technique to make the infrared photodetectors. At room temperature, the high performances of our PbSe CQD photodetectors were achieved with maximum responsivity, detectivity and external quantum efficiency of 0.96 A/W, 8.13 × 109 Jones and 78% at 5V bias. Furthermore, a series of infrared LEDs with a broad wavelength range from 1.5 μm to 3.4 μm was utilized to demonstrate the performance of our fabricated photodetectors with various PbSe CQD film thicknesses.
Open Access
Nonradiative energy transfer in colloidal CdSe nanoplatelet films
(Royal Society of Chemistry, 2015) Güzeltürk, B.; Olutas M.; Delikanlı, S.; Keleştemur, Y.; Erdem, O.; Demir, Hilmi Volkan
Nonradiative energy transfer (NRET) has been extensively studied in colloidal nanocrystal (quantum dots) and nanorod (quantum wires) assemblies. In this work, we present the first account of spectroscopic evidence of NRET in solid thin films of CdSe based colloidal nanoplatelets (NPLs), also known as colloidal quantum wells. The NRET was investigated as a function of the concentration of two NPL populations with different vertical thicknesses via steady state and time resolved spectroscopy. NRET takes place from the NPLs with smaller vertical thickness (i.e., larger band gap) to the ones with a larger vertical thickness (i.e., smaller band gap) with efficiency up to ∼60%. Here, we reveal that the NRET efficiency is limited in these NPL solid film assemblies due to the self-stacking of NPLs within their own population causing an increased distance between the donor-acceptor pairs, which is significantly different to previously studied colloidal quantum dot based architectures for nonradiative energy transfer. © The Royal Society of Chemistry 2015.
Open Access
pH tunable patterning of quantum dots
(Wiley-VCH Verlag GmbH & Co. KGaA, 2023-09-01) Torun, I.; Huang, C.; Kalay, M.; Shim, M.; Önses, M. Serdar
Patterning of quantum dots (QDs) is essential for many, especially high-tech, applications. Here, pH tunable assembly of QDs over functional patterns prepared by electrohydrodynamic jet printing of poly(2-vinylpyridine) is presented. The selective adsorption of QDs from water dispersions is mediated by the electrostatic interaction between the ligand composed of 3-mercaptopropionic acid and patterned poly(2-vinylpyridine). The pH of the dispersion provides tunability at two levels. First, the adsorption density of QDs and fluorescence from the patterns can be modulated for pH > approximate to 4. Second, patterned features show unique type of disintegration resulting in randomly positioned features within areas defined by the printing for pH <= approximate to 4. The first capability is useful for deterministic patterning of QDs, whereas the second one enables hierarchically structured encoding of information by generating stochastic features of QDs within areas defined by the printing. This second capability is exploited for generating addressable security labels based on unclonable features. Through image analysis and feature matching algorithms, it is demonstrated that such patterns are unclonable in nature and provide a suitable platform for anti-counterfeiting applications. Collectively, the presented approach not only enables effective patterning of QDs, but also establishes key guidelines for addressable assembly of colloidal nanomaterials.
Open Access
Phonon-assisted nonradiative energy transfer from colloidal quantum dots to monocrystalline bulk silicon
(IEEE, 2012) Yeltik, Aydan; Güzeltürk, Burak; Hernandez-Martinez, Pedro L.; Demir, Volkan Demir
Silicon is one of the most dominant materials in photovoltaics. To increase optical absorption of silicon solar cells, colloidal quantum dots (QDs) have been proposed as a good sensitizer candidate owing to their favorably high absorption cross-section and tunable emission and absorption properties. To this end, QD sensitization of silicon has previously been studied by mostly facilitating radiative energy transfer (RET) [1,2]. Although RET based sensitization has achieved a considerable increase in conversion efficiencies in silicon photovoltaics, RET is fundamentally limited due to the effective coupling problem of emitted photons to silicon. Alternatively, nonradiative energy transfer (NRET), which relies on near field dipole-dipole coupling [3], has been shown to be feasible in sensitizer-silicon hybrid systems [4-8]. Although colloidal QDs as a sensitizer have been used to facilitate NRET into silicon, the detailed mechanisms of NRET to an indirect bandgap nonluminecent material, together with the role of phonon assistance and temperature activation, have not been fully understood to date. In this study, we propose a QD-silicon nanostructure hybrid platform to study the NRET dynamics as a function of temperature for distinct separation thicknesses between the donor QDs and the acceptor silicon plane. Here, we show NRET from colloidal QDs to bulk Si using phonon assisted absorption, developing its physical model to explain temperature-dependent lifetime dynamics of NRET in these QD-Si hybrids. © 2012 IEEE.
Open Access
Physics of nonradiative energy transfer in the complex media of 0D, 2D and 3D materials
(2016-07) Yeltik, Aydan
Quantum-confined colloidal nanostructures with strong excitonic properties have emerged as promising light harvesting components in photonics and optoelectronics over the past 20 years. With their favorable photophysical characteristics, three-dimensional-confined colloidal quantum dots and 2D-confined colloidal quantum wells have garnered great attention in the fields ranging from biology and chemistry to physics and engineering. It is technologically significant to utilize the key characteristics of these brightly luminescent nanomaterials through hybridizing and/or interfacing with various technological materials including 3D bulk silicon, graphene based 2D structures such as graphene oxide and reduced graphene oxide, and 2D layered transition metal dichalcogenides such as molybdenum disulphide. Compelling partnership of these appealing materials can be achieved through the nonradiative energy transfer (NRET), which is a phenomenon involving both the exciton and charge transfer mechanisms. Along with the hybrids of low dimensional particles with the conventional bulk materials, the closely interacting structures of these colloidal and layered nanomaterials have widespread interest at both the fundamental science and application levels. From these physical and technological points of view, in this thesis, we addressed important scientific problems and proposed innovative solutions including both the experimental and theoretical approaches in interfacing complex media of 0D, 2D and 3D materials and showing strong NRET interactions. Our key achievements include high excitonic enhancement in silicon and graphene based materials with the integration of nanoparticles, comprehensive photophysical investigation of the newly emerging nanomaterials and successful tailoring of the colloidal nanostructures to the next-generation optoelectronic applications.
Open Access
Singlet and Triplet Exciton Harvesting in the Thin Films of Colloidal Quantum Dots Interfacing Phosphorescent Small Organic Molecules
(American Chemical Society, 2014) Guzelturk, B.; Hernandez Martinez P.L.; Zhao, D.; Sun X.W.; Demir, Hilmi Volkan
Efficient nonradiative energy transfer is reported in an inorganic/organic thin film that consists of a CdSe/ZnS core/shell colloidal quantum dot (QD) layer interfaced with a phosphorescent small organic molecule (FIrpic) codoped fluorescent host (TCTA) layer. The nonradiative energy transfer in these thin films is revealed to have a cascaded energy transfer nature: first from the fluorescent host TCTA to phosphorescent FIrpic and then to QDs. The nonradiative energy transfer in these films enables very efficient singlet and triplet state harvesting by the QDs with a concomitant fluorescence enhancement factor up to 2.5-fold, while overall nonradiative energy transfer efficiency is as high as 95%. The experimental results are successfully supported by the theoretical energy transfer model developed here, which considers exciton diffusion assisted Förster-type near-field dipole-dipole coupling within the hybrid films. © 2014 American Chemical Society.