Spectroscopic data were presented which clarified the nature of the Cr3+ centers and Cr3+-related defect in LiNbO3:Cr,Mg crystals containing an excess of Li+ ions. Apart from quite well known lines associated with the 4T2 → 4A2 and 2E → 4A2 transitions of the Cr3+ ions, the luminescence spectrum of this crystal revealed some additional relatively narrow lines at 750 to 860nm. High-pressure and magneto-optical measurements of crystallographically oriented samples of this crystal were carried out at 10K. The measured spectra, decay times, pressure coefficients, and the dependence of the luminescence on high magnetic field show that the luminescence lines observed in Li-rich LiNbO3:Cr,Mg originate from both Cr3+ ions and strongly antiferromagnetically coupled Cr3+-Cr3+ first nearest-neighbor pairs. The ground-state levels of the pairs could be described by the isotropic exchange interaction, JS1S2+j(S1·S2)2, where S1 and S2 were the total spins of each of the two Cr ions. The obtained results permitted the determination of the ground-state spin-spin exchange constants as well as the excited-state zero field splitting constant.

High-Pressure and Magneto-Optical Studies of Cr-Related Defects in the Lithium-Rich LiNbO3:Cr,Mg Crystal. A.Kamińska, A.Suchocki, S.Kobyakov, L.Arizmendi, M.Potemski, F.J.Teran: Physical Review B, 2007, 76[14], 144117 (10pp)