Firstly, for the absorption due to chromium ions, it is clear that
the spectra show two prominent absorption bands peaking
620 nm (peak 1) and 440 nm (peak2). They correspond, respectively,
to the 4A2g?4T2g and 4A2g?4T1g transitions [5,6,11,26].
A third weak band at 389 nm (peak 3), which is usually related
to 4A2g?2A1g transition, is shown. Its low intensity indicates the
presence of Cr6+ ions traces [5,11]. The crystal field (Dq) and the
Racah (B) parameters were estimated from the spectral positions
of the absorption bands as