Electron Magnetic Resonance Study of Cr³⁺ Paramagnetic Impurity Ions in an Alexandrite Single Crystal

The electron magnetic resonance (EMR) of the paramagnetic CrSUP3+/SUP ion in an alexandrite single crystal (BeAl₂O₄:CrSUP3+/SUP) has been investigated. The resonance fields of CrSUP3+/SUP impurity ion measured with a Q-band electron magnetic resonance spectrometer were obtained under angular variation along crystallographic ab-, bc-, and ca-planes. The spectroscopic splitting parameters gSUBij/SUB and the 2SUPnd/SUP order zero-field splitting parameters DSUBij/SUB of the CrSUP3+/SUP(II)-center at Al3+(II) site in an alexandrite single crystal with mirror symmetry are obtained by using the effective spin Hamiltonian. The EMR parameters and rotation patterns show that the actual local site symmetry of the CrSUP3+/SUP ion is monoclinic. The number of magnetic resonance signals and crystal structures were compared and analyzed in detail where impurity ions in a single crystal are replaced. It turns out that the CrSUP3+/SUP impurity ions in an alexandrite single crystal occupies the AlSUP3+/SUP(II) site without charge compensation instead of the BeSUP2+/SUP and AlSUP3+/SUP(I) sites.