Browsing by Subject "Photoluminescence quantum yields"

Now showing 1 - 4 of 4

Open Access
Alloyed heterostructures of CdSexS1-x nanoplatelets with highly tunable optical gain performance
(American Chemical Society, 2017) Kelestemur Y.; Dede, D.; Gungor K.; Usanmaz, C. F.; Erdem, O.; Demir, Hilmi Volkan
Here, we designed and synthesized alloyed heterostructures of CdSexS1-x nanoplatelets (NPLs) using CdS coating in the lateral and vertical directions for the achievement of highly tunable optical gain performance. By using homogeneously alloyed CdSexS1-x core NPLs as a seed, we prepared CdSexS1-x/CdS core/crown NPLs, where CdS crown region is extended only in the lateral direction. With the sidewall passivation around inner CdSexS1-x cores, we achieved enhanced photoluminescence quantum yield (PL-QY) (reaching 60%), together with increased absorption cross-section and improved stability without changing the emission spectrum of CdSexS1-x alloyed core NPLs. In addition, we further extended the spectral tunability of these solution-processed NPLs with the synthesis of CdSexS1-x/CdS core/shell NPLs. Depending on the sulfur composition of the CdSexS1-x core and thickness of the CdS shell, CdSexS1-x/CdS core/shell NPLs possessed highly tunable emission characteristics within the spectral range of 560-650 nm. Finally, we studied the optical gain performances of different heterostructures of CdSexS1-x alloyed NPLs offering great advantages, including reduced reabsorption and spectrally tunable optical gain range. Despite their decreased PL-QY and reduced absorption cross-section upon increasing the sulfur composition, CdSexS1-x based NPLs exhibit highly tunable amplified spontaneous emission performance together with low gain thresholds down to ∼53 μJ/cm2.
Open Access
CdSe/CdSe1-xTex core/crown heteronanoplatelets: tuning the excitonic properties without changing the thickness
(American Chemical Society, 2017) Kelestemur Y.; Guzelturk, B.; Erdem, O.; Olutas M.; Erdem, T.; Usanmaz, C. F.; Gungor K.; Demir, Hilmi Volkan
Here we designed and synthesized CdSe/CdSe1-xTex core/crown nanoplatelets (NPLs) with controlled crown compositions by using the core-seeded-growth approach. We confirmed the uniform growth of the crown regions with well-defined shape and compositions by employing transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. By precisely tuning the composition of the CdSe1-xTex crown region from pure CdTe (x = 1.00) to almost pure CdSe doped with several Te atoms (x = 0.02), we achieved tunable excitonic properties without changing the thickness of the NPLs and demonstrated the evolution of type-II electronic structure. Upon increasing the Te concentration in the crown region, we obtained continuously tunable photoluminescence peaks within the range of ∼570 nm (for CdSe1-xTex crown with x = 0.02) and ∼660 nm (for CdSe1-xTex crown with x = 1.00). Furthermore, with the formation of the CdSe1-xTex crown region, we observed substantially improved photoluminescence quantum yields (up to ∼95%) owing to the suppression of nonradiative hole trap sites. Also, we found significantly increased fluorescence lifetimes from ∼49 up to ∼326 ns with increasing Te content in the crown, suggesting the transition from quasi-type-II to type-II electronic structure. With their tunable excitonic properties, this novel material presented here will find ubiquitous use in various efficient light-emitting and -harvesting applications.
Open Access
Mn2+-doped CdSe/CdS core/multishell colloidal quantum wells enabling tunable carrier-dopant exchange interactions
(American Chemical Society, 2015) Delikanlı, S.; Akgül, M. Z.; Murphy, J. R.; Barman, B.; Tsai, Y.; Scrace, T.; Zhang, P.; Bozok, B.; Hernández-Martínez, P.L.; Christodoulides, J.; Cartwright, A. N.; Petrou, A.; Demir, Hilmi Volkan
In this work, we report the manifestations of carrier-dopant exchange interactions in colloidal Mn2+-doped CdSe/CdS core/multishell quantum wells. The carrier-magnetic ion exchange interaction effects are tunable through wave function engineering. In our quantum well heterostructures, manganese was incorporated by growing a Cd0.985Mn0.015S monolayer shell on undoped CdSe nanoplatelets using the colloidal atomic layer deposition technique. Unlike previously synthesized Mn2+-doped colloidal nanostructures, the location of the Mn ions was controlled with atomic layer precision in our heterostructures. This is realized by controlling the spatial overlap between the carrier wave functions with the manganese ions by adjusting the location, composition, and number of the CdSe, Cd1-xMnxS, and CdS layers. The photoluminescence quantum yield of our magnetic heterostructures was found to be as high as 20% at room temperature with a narrow photoluminescence bandwidth of ∼22 nm. Our colloidal quantum wells, which exhibit magneto-optical properties analogous to those of epitaxially grown quantum wells, offer new opportunities for solution-processed spin-based semiconductor devices. © 2015 American Chemical Society.
Open Access
Unraveling the ultralow threshold stimulated emission from CdZnS/ZnS quantum dot and enabling high ‐ Q microlasers
(Wiley-VCH Verlag, 2015) Wang Y.; Fong, K. E.; Yang, S.; Ta, V.; Gao, Y.; Wang, Z.; Nalla, V.; Demir, Hilmi Volkan; Sun, H.
The newly engineered ternary CdZnS/ZnS colloidal quantum dots (CQDs) are found to exhibit remarkably high photoluminescence quantum yield and excellent optical gain properties. However, the underlying mechanisms, which could offer the guidelines for devising CQDs for optimized photonic devices, remain undisclosed. In this work, through comprehensive steady-state and time-resolved spectroscopy studies on a series of CdZnS-based CQDs, we unambiguously clarify that CdZnS-based CQDs are inherently superior optical gain media in the blue spectral range due to the slow Auger process and that the ultralow threshold stimulated emission is enabled by surface/interface engineering. Furthermore, external cavity-free high-Q quasitoroid microlasers were produced from self-assembly of CdZnS/ZnS CQDs by facile inkjet printing technique. Detailed spectroscopy analysis confirms the whispering gallery mode lasing mechanism of the quasitoroid microlasers. This tempting microlaser fabrication method should be applicable to other solution-processed gain materials, which could trigger broad research interests. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA.