Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photoluminescence of silicon-vacancy defects in nanodiamonds of
  different chondrites   Photoluminescence spectra show that silicon impurity is present in lattice of
some nanodiamond grains (ND) of various chondrites as a silicon-vacancy (SiV)
defect. The relative intensity of the SiV band in the diamond-rich separates
depends on chemical composition of meteorites and on size of ND grains. The
strongest signal is found for the size separates enriched in small grains; thus
confirming our earlier conclusion that the SiV defects preferentially reside in
the smallest (less than 2 nm) grains. The difference in relative intensities of
the SiV luminescence in the diamond-rich separates of individual meteorites are
due to variable conditions of thermal metamorphism of their parent bodies
and/or uneven sampling of nanodiamonds populations. Annealing of separates in
air eliminates surface sp2-carbon, consequently, the SiV luminescence is
enhanced. Strong and well-defined luminescence and absorption of the SiV defect
is a promising feature to locate cold (< 250 {\deg}C) nanodiamonds in space.

3
The categories of this paper are: physics
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
27
The categories of this paper are: comp-gas
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci