Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Probing Excitons in Ultrathin PbS Nanoplatelets with Enhanced
  Near-Infrared Emission   Strongly quantum-confined 2D colloidal PbS nanoplatelets (NPLs) are highly
interesting materials for near-infrared optoelectronic applications. Here, we
use ultrafast transient optical absorption spectroscopy to study the
characteristics and dynamics of photoexcited excitons in ultrathin PbS NPLs
with a cubic (rock-salt) structure. The NPLs are synthesized at near room
temperature from lead oleate and thiourea precursors and show an optical
absorption onset at 680 nm (1.8 eV) as well as photoluminescence at 720 nm (1.7
eV). By treating PbS NPLs with CdCl2 in a post-synthetic step, their
photoluminescence quantum yield is strongly enhanced from 1.4 % to 19.4 %. The
surface treatment leads to an increased lead to sulfur ratio in the structures
and associated reduced non-radiative recombination. Exciton-phonon interactions
in pristine and CdCl2 treated PbS NPLs at frequencies of 1.8 and 2.2 THz are
apparent from coherent oscillations in the measured transient absorption
spectra. This study is an important step forward in unraveling and controlling
the optical properties of IV-VI semiconductor NPLs.

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The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
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The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
6
The categories of this paper are: astro-ph
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The categories of this paper are: q-alg
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The categories of this paper are: cmp-lg
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The categories of this paper are: alg-geom
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The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: supr-con
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The categories of this paper are: ao-sci
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The categories of this paper are: eess