1. 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 , Singapore
Introduction
NPLs
In the last step, 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.
NPLs exhibit higher PL-QY when compared to 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)
NPLs
(vertically grown shell)
Optical Gain Performances of Colloidal Quantum Wells
In this study, we have also studied systematically optical gain performances of NPLs along with the CdSe core-only, CdSe/CdS core/crown and NPLs.
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, and 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 (doi: /adfm ).
[5] Kelestemur Y. et al., J. Phys Chem. C 2015, 119,
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