Browsing by Subject "Amplified spontaneous emission"

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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
Lateral size-dependent spontaneous and stimulated emission properties in colloidal CdSe nanoplatelets
(American Chemical Society, 2015) Olutaş, M.; Güzeltürk, B.; Keleştemur, Y.; Yeltik A.; Delikanlı, S.; Demir, Hilmi Volkan
Here, we systematically investigated the spontaneous and stimulated emission performances of solution-processed atomically flat quasi-2D nanoplatelets (NPLs) as a function of their lateral size using colloidal CdSe core NPLs. We found that the photoluminescence quantum efficiency of these NPLs decreases with increasing lateral size while their photoluminescence decay rate accelerates. This strongly suggests that nonradiative channels prevail in the NPL ensembles having extended lateral size, which is well-explained by the increasing number of the defected NPL subpopulation. In the case of stimulated emission the role of lateral size in NPLs influentially emerges both in the single- and two-photon absorption (1PA and 2PA) pumping. In the amplified spontaneous emission measurements, we uncovered that the stimulated emission thresholds of 1PA and 2PA exhibit completely opposite behavior with increasing lateral size. The NPLs with larger lateral sizes exhibited higher stimulated emission thresholds under 1PA pumping due to the dominating defected subpopulation in larger NPLs. On the other hand, surprisingly, larger NPLs remarkably revealed lower 2PA-pumped amplified spontaneous emission thresholds. This is attributed to the observation of a "giant" 2PA cross-section overwhelmingly growing with increasing lateral size and reaching record levels higher than 10(6) GM, at least an order of magnitude stronger than colloidal quantum dots and rods. These findings suggest that the lateral size control in the NPLs, which is commonly neglected, is essential to high-performance colloidal NPL optoelectronic devices in addition to the vertical monolayer control.
Open Access
Low-threshold lasing from copper-doped CdSe colloidal quantum wells
(Wiley, 2021-05-04) Yu, J.; Sharma, M.; Li, M.; Delikanlı, Savaş; Sharma, A.; Taimoor, M.; Altintas, Y.; McBride, J. R.; Kusserow, T.; Sum, T.; Demir, Hilmi Volkan
Transition metal doped colloidal nanomaterials (TMDCNMs) have recently attracted attention as promising nano-emitters due to dopant-induced properties. However, despite ample investigations on the steady-state and dynamic spectroscopy of TMDCNMs, experimental understandings of their performance in stimulated emission regimes are still elusive. Here, the optical gain properties of copper-doped CdSe colloidal quantum wells (CQWs) are systemically studied with a wide range of dopant concentration for the first time. This work demonstrates that the amplified spontaneous emission (ASE) threshold in copper-doped CQWs is a competing result between the biexciton formation, which is preferred to achieve population inversion, and the hole trapping which stymies the population inversion. An optimum amount of copper dopants enables the lowest ASE threshold of ≈7 µJ cm−2, about 8-fold reduction from that in undoped CQWs (≈58 µJ cm−2) under sub-nanosecond pulse excitation. Finally, a copper-doped CQW film embedded in a vertical cavity surface-emitting laser (VCSEL) structure yields an ultralow lasing threshold of 4.1 µJ cm−2. Exploiting optical gain from TMDCNMs may help to further boost the performance of colloidal-based lasers.
Open Access
Stable and low ‐ threshold optical gain in CdSe/CdS quantum dots: an all ‐ colloidal frequency up ‐ converted laser
(Wiley-VCH Verlag, 2015) Güzeltürk, B.; Keleşemur, Y.; Güngor, K.; Yeltik, A.; Akgül, M. Z.; Wang, Y.; Chen R.; Dang, C.; Sun, H.; Demir, Hilmi Volkan
An all-solution processed and all-colloidal laser is demonstrated using tailored CdSe/CdS core/shell quantum dots, which exhibit highly stable and low-threshold optical gain owing to substantially suppressed non-radiative Auger recombination.
Open Access
Thickness-tunable self-assembled colloidal nanoplatelet films enable ultrathin optical gain media
(American Chemical Society, 2020) Erdem, Onur; Foroutan, Sina; Gheshlaghi, Negar; Güzeltürk, B.; Altıntaş, Yemliha; Demir, Hilmi Volkan
We propose and demonstrate construction of highly uniform, multilayered superstructures of CdSe/CdZnS core/shell colloidal nanoplatelets (NPLs) using liquid interface self-assembly. These NPLs are sequentially deposited onto a solid substrate into slabs having monolayer-precise thickness across tens of cm2 areas. Because of near-unity surface coverage and excellent uniformity, amplified spontaneous emission (ASE) is observed from an uncharacteristically thin film having 6 NPL layers, corresponding to a mere 42 nm thickness. Furthermore, systematic studies on optical gain of these NPL superstructures having thicknesses ranging from 6 to 15 layers revealed the gradual reduction in gain threshold with increasing number of layers, along with a continuous spectral shift of the ASE peak (∼18 nm). These observations can be explained by the change in the optical mode confinement factor with the NPL waveguide thickness and propagation wavelength. This bottom-up construction technique for thickness-tunable, three-dimensional NPL superstructures can be used for large-area device fabrication.
Open Access
Ultralow threshold optical gain enabled by quantum rings of inverted type-I CdS/CdSe core/crown nanoplatelets in the blue
(Wiley-VCH Verlag GmbH & Co. KGaA, 2021-04-20) Delikanlı, Savaş; Işık, Furkan; Shabani, Farzan; Baruj, Hamed Dehghanpour; Taghipour, Nima; Demir, Hilmi Volkan
Achieving low-threshold optical gain for solution-processed materials is crucial for their real-life applications and deployment as gain media. However, the realization of low gain threshold in the blue region has shown to be technically an extremely challenging task using colloidal nanocrystals as a result of fast nonradiative Auger rates in smaller nanocrystals. Here, ultralow-threshold blue amplified spontaneous emission (ASE) (≈2.7 µJ cm−2) accompanied with a large net modal gain coefficient of 360 cm−1 in the blue enabled by blue-emitting (≈455–465 nm) colloidal quantum rings (QRs) of inverted type-I CdS/CdSe core/crown nanoplatelets (NPLs) is proposed and demonstrated. The synthesized QRs with controlled crown size outperform the best reported ASE thresholds and net modal gain coefficients from the solution-processed materials by ≈2.5- and ≈4-fold, respectively, in the similar blue spectral window. Utilizing this QR architecture, it is also shown that the ASE peak can be spectrally tuned by controlling the lateral size of the crown and hence quantum confinement in the lateral direction. These outstanding results support the prospects of these solution-processed QRs made of 2D hetero-NPLs in the challenging blue region as colloidal gain.