In this work the present state of art about the rare earth and transit
ion metal ion centers phenomenon in LiNbO3 has been analyzed. Particul
ar emphasis has been given to lanthanide trivalent rare earth ions (Pr
3+, Nd3+, Eu3+ Dy3+, Ho3+, Er3+, Tm3+ and Yb3+) and to the Cr3+ ion, w
here most of information has been reported. The structure of these cen
ters is consistent with different off-centered positions of the optica
lly active ions inside the Li+ octahedral site. Stoichiometry and codo
ping effects on the center distribution are discussed. Finally, possib
le models to explain the origin of the different centers are discussed
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