New spectroscopic investigation of Cr3+ centres in LiNbO3 crystals

We have studied Cr3+ emission in LiNbO3 crystals with compositions close to stoichiometry, which were not investigated up to now. The emission spectra recorded at low temperature exhibits new peaks at 13555 and 13415 cm(-1) The measurement of the fluorescence decays and the recording of the excitation spectra monitored at all the emission peaks were performed in order to determine the different Cr3+ centres in lithium niobate as well as their energy levels contributing to the emission experiments. Three Cr3+ centres permit to describe the various features of the emission spectra. The main centre corresponds to the weak crystal field scheme and yields the broad emission band as well as the new peaks which have a vibronic origin. The two other Cr3+ centres agree with the high crystal field scheme and display the sharp R-lines at 13685 and 13614 cm(-1). (C) 1999 Published by Elsevier Science B.V. All rights reserved.