A purple diamond has an absorption coefficient of the Ib type nitrogen at 500 nm, within the range of 0.2-2 cm, an absorption coefficient of the N-V center at an absorption peak of 570 nm, within the range of 0.3-10 cm, and absorption coefficients of the GR1 center, H2 center, H3 center, and H4 center which are less than
Diamond is a wide-band-gap material with large donor and acceptor
ionization energies. In principle, at room temperature and
below, the Fermi energy is pinned close to the donor or
acceptor level, depending on which is present in the higher
concentration. In semiconductors with shallow donors and
acceptors the equilibrium charge states of defects are
determined by the position of the Fermi level. However, in an
insulating material like diamond we show that the calculated
position of the Fermi level does not necessarily predict the
correct charge state of a defect, and propose instead that the
charge state is influenced by the proximity of the defect to a
donor (or acceptor). Qualitatively this accounts for the
dependence of the charge state on the concentration of isolated
substitutional nitrogen and also explains why many optical
centres can be present in two different charge states in the
same diamond.
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