COMPOSITIONAL EFFECT ON CR3-CR CONGRUENT AND STOICHIOMETRIC CRYSTALS(SITE DISTRIBUTION IN MGO OR ZNO CODOPED LINBO3)

In this letter optical and electron paramagnetic resonance (EPR) techn iques are used to investigate the effect of stoichiometry changes on t he site distribution of Cr3+ ions in LiNbO3:Cr crystals with (or witho ut) MgO or ZnO codoping. In congruent (Li0.95Nb1.01O3) crystals codope d with MgO (ZnO) the Cr3+ ions begin to enter into the Nb5+ site for c oncentrations higher than 4.5% (4.7%). Below this MgO (ZnO) threshold Cr3+ ions enter only into the Li+ sites. However, for nominally stoich iometric (LiNbO3) crystals, the threshold concentration is much lower (between O and 0.2% in our crystals). The use of Cr3+ ions as an optic al and paramagnetic probe to evaluate the grade of stoichiometry is co nsidered.