OPTICAL-DETECTION OF EU3+ SITES IN LINBO3EU3+ AND LINBO3MGOEU3+

The fluorescence of Eu3+ in LiNbO3 has been investigated using laser-excited site-selection spectroscopy. Four different crystal-field sites, denoted as Eu(1), Eu(2), Eu(3), and Eu(4), have been detected and optically characterized through their corresponding 5D0 --> F-7(1) magnetic-dipole emission transitions. The local symmetry of the Eu3+ ions in these sites deviates slightly from the C3 main symmetry as a consequence of distortions perpendicular to the c ferroelectric axis. The relative concentrations of these sites have been studied as a function of the [Li]/[Nb] concentration ratio. It is suggested that the formation of Eu3+(Nb5+)-Eu3+(Li+) pairs is responsible for the major Eu(3) and Eu(4) sites, while the Eu(1) and Eu(2) sites correspond to Eu3+ ions in Nb5+ lattice positions but perturbed by different charge compensating defects. The effect of codoping with Mg2+ ions has also been investigated; the same Eu3+ sites as in the singly doped system are present, although the Eu(1) site is strongly enhanced in relation to the others.