Abstract
The optical spectroscopy of Cr3+ ions doped into near-stoichiometric LiNbO3 crystals, pure and co-doped with MgO, has been investigated.
In the near-stoichiometric LiNbO3:Cr(0.2 mol%):Mg(2 mol%) crystal, the optical spectra resemble those previously observed for congruent LiNbO3:Cr:MgO samples when the total MgO content exceeds the 4.6 mol% threshold. The coexistence of two types of Cr3+ centre ([Cr]Li and [Cr]Nb) characterized the optical and luminescence spectra of this sample. The concentration equilibrium between the two types of centre is strongly displaced towards the [Cr3+ ] Nb centre, permitting us to obtain with accuracy the parameters of the broad bands. The R-line associated with the [Cr]Nb centre is only observable in the low-temperature emission spectrum. The Fano anti-resonance lines present have been observed to be more pronounced for the near-stoichiometric samples than for congruent ones.
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