Journal
ACS NANO
Volume 9, Issue 5, Pages 5041-5050Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.5b01927
Keywords
semiconductor nanoplatelets; colloidal quantum wells; lateral size; photoluminescence quantum efficiency; amplified spontaneous emission; stimulated emission; giant two-photon absorption cross-section
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Funding
- Singapore National Research Foundation [NRF-RF-2009-09, NRF-CRP-6-2010-02]
- Science and Engineering Research Council, Agency for Science, Technology and Research (A*STAR) of Singapore [092 101 0057, 112 120 2009]
- ESF-EURYI
- TUBA-GEBIP
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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.
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