Platelet-in-Box Colloidal Quantum Wells: CdSe/CdS@CdS Core/Crown@Shell Heteronanoplatelets Yusuf Kelestemur1, Burak Guzelturk1, Onur Erdem1, Murat Olutas1,2, Kivanc Gungor1 and Hilmi Volkan Demir1,3 1UNAM--Institute of Materials Science and Nanotechnology, Department of Electrical and Electronics Engineering, Department of Physics, Bilkent University, Ankara, 06800, Turkey 2Department of Physics, Abant Izzet Baysal University, Bolu, Turkey 3Microelectronics Division, School of Electrical and Electronics Engineering, and Physics and Applied Physics Division, School of Physical and Mathematical Sciences, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore Introduction CdSe/CdS@CdS Core/Crown@Shell NPLs In the last step, CdSe/CdS@CdS core/crown@shell NPLs have been synthesized having a novel 3D architecture resembling a platelet-in-box structure. Colloidal nanoplatelets (NPLs), which are also known as colloidal quantum wells, have recently emerged as a new class of semiconductor nanocrystals. While their lateral dimensions are on the order of tens of nanometer, they exhibit ‘magic-sized’ vertical thickness. Core/Crown@Shell NPLs exhibit higher PL-QY when compared to Core@Shell NPLs regardless of CdSe-core size, CdS-crown size and CdS-shell thickness 5 ML thick CdSe NPLs 4 ML thick CdSe NPLs 3 ML thick CdSe NPLs thickness-dependent optical properties -- narrow emission spectrum (<10 nm) synthesis of NPLs with atomically-flat surfaces -- suppressed inhomogeneous broadening giant oscillator strength -- ultrafast fluorescence lifetime suppression of Auger recombination -- quantum well-like electronic structure Different Architectures of Colloidal Quantum Wells strongly red-shifted emission with broad emission line width (~80 meV) Thanks to colloidal chemistry, assorted structures of colloidal quantum wells having vertically grown shell region and/or laterally grown crown region can be synthesized with a precise control of the shell thickness and the crown width. enhanced absorption cross-section with the coformation of CdS-crown and CdS-shell region , With the synthesis of different architectures of NPLs, optical and electronic properties of NPLs can be engineered to achieve, core NPLs increased fluorescence lifetimes (up to 13 ns) which is characteristics of quasi Type-II band alignment enhancement in the absorption cross-section suppression of Auger recombination higher quantum yield increase in the stability core/crown NPLs (laterally grown shell) core@shell NPLs (vertically grown shell) Optical Gain Performances of Colloidal Quantum Wells In this study, we have also studied systematically optical gain performances of CdSe/CdS@CdS core/crown@shell NPLs along with the CdSe core-only, CdSe/CdS core/crown and CdSe@CdS core@shell NPLs. Core/Crown@Shell NPLs exhibit the lowest gain threshold (~ 20µJ/cm2) thanks to suppressed Auger recombination and enhanced absorption cross-section CdSe Core NPLs First, CdSe NPLs having 4 ML thickness are synthesized and used as a seed for the synthesis of core/crown, core@shell and core/crown@shell architectures. narrower emission bandwidts (< 8 nm) quantum yield in the range of 30-50% in solution excellent self assembly on the TEM grid 100 nm a red-shifted amplified spontaneous emission with narrower emission line width (< 10 nm) CdSe/CdS Core/Crown NPLs In the second step, CdSe/CdS core/crown NPLs have been synthesized, where CdS-crown layer is grown only in the lateral direction. highly stable optical gain performance (~ 6 h) complete passivation of core with crown and shell layers CONCLUSION & FUTURE WORKS These findings indicate that carefully hetero-structured NPLs will play a critical role in building high-performance colloidal optoelectronic devices, which may even possibly challenge their traditional epitaxially grown thin-film based counterparts. References a higher level of photoluminescence quantum yield (up to 90%) is observed with the passivation of the periphery of the CdSe core NPLs [1] Ithurria, S. et al., J. Am. Chem. Soc. 2008, 130, 16504–16505. [2] Ithurria, S. et al., Nat. Mater. 2011, 10, 936–941. [3] Guzelturk, B., Kelestemur Y., et al., ACS Nano 2014, 8, 6599−6605. [4] Kelestemur Y. et al., Adv. Funct. Mater. 2016 (doi:10.1002/adfm.201600588). [5] Kelestemur Y. et al., J. Phys Chem. C 2015, 119, 2177-2185. Supports