have
shown that the introduction of chromium oxide to the glasses results
in a reduction of the ESR signals intensity with increasing
the Cr2O3 content up to 0.3 mol%. For higher concentration, however,
an enhancement of the ESR signal was reported. This was reasoned
to the deep transformation of Cr3+ ions into the Cr6+ ions,
which reduces the spin density [10,11,22,23].