Diamonds IV

Lattice Defects, Impurities and Color

As stated in references 17, 18 of my DIAMONDS II blog, impurity atoms and lattice vacancy defects are responsible for the coloration of diamonds [Ref 1].  A lattice vacancy (V) without a carbon atom in the diamond lattice which partners with one to four neighboring nitrogen atoms (N), in colored diamonds, as well as the space taken by an adjacent pair of them partnering with a nickel atom (Ni), are present in colored diamonds. These atom-vacancy structures are shown in Figures 1 to 6 of this Blog.  Boron atoms (B), substituting for carbon atoms in the crystal lattice, give rise to the blue color.  Hydrogen atoms, possibly associated with lattice vacancies, and nitrogen atoms may also be responsible for imparting color [Ref 2].

Figure 1.  The N3 -nitrogen Center [Ref 1].  The vacancy is the space at the tips of four unfilled carbon bonds.
Figure 2.  H3-nitrogen Center [Ref 2].  The vacancy is at the tips of the four unfilled nitrogen bonds.
Figure 3.  The NVO-nitrogen Center [Ref 3].
Figure 4.  The NV-1-nitrogen Center.  Only the carbon bond of one carbon atom is unfilled [Ref 4].
Figure 5.  Boron substituting for a carbon atom in diamond.  [Ref 5].
Figure 6.  Nickel atom occupying the space of a di-vacancy
[Ref 6].

References for the N3-nitrogen center, the H3-nitrogen center, the NVO-nitrogen center, the NV-1-nitrogen center, the boron atom substation for a carbon atom, and the Nickel Di-vacancy center are described respectively in Refs 3, 4.

The colors of diamonds associated with these lattice defects and impurities are referred to in my DIAMONDS II Blog and shown below in Table I.

TABLE I

DEFECT/IMPURITY                     DIAMOND COLOR
N3-nitrogen centerYellow
H3-nitrogen centerGreen
NVO-nitrogen centerPink
NV-1-nitrogen centerPink
Boron atom substation for carbonBlue
Nickel Di-vacancyGreen
Uncertain defect due to HydrogenGrey-brown, Yellow, Pink

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