Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coupling of excitons and defect states in boron-nitride nanostructures   The signature of defects in the optical spectra of hexagonal boron nitride
(BN) is investigated using many body perturbation theory. A single BN-sheet
serves as a model for different layered BN- nanostructures and crystals. In the
sheet we embed prototypical defects such as a substitutional impurity, isolated
Boron and Nitrogen vacancies, and the di-vacancy. Transitions between the deep
defect levels and extended states produce characteristic excitation bands that
should be responsible for the emission band around 4 eV, observed in
luminescence experiments. In addition, defect bound excitons occur that are
consistently treated in our ab initio approach along with the "free" exciton.
For defects in strong concentration, the co-existence of both bound and free
excitons adds sub-structure to the main exciton peak and provides an
explanation for the corresponding feature in cathodo and photo-luminescence
spectra.

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The categories of this paper are: q-bio
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The categories of this paper are: quant-ph
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The categories of this paper are: math-ph
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The categories of this paper are: econ
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The categories of this paper are: cmp-lg
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The categories of this paper are: solv-int
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The categories of this paper are: chem-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-ex
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The categories of this paper are: acc-phys
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The categories of this paper are: atom-ph
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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom