Raman study on vapor-phase equilibrated Er:LiNbO3 and Er:Ti:LiNbO3 crystals

Abstract

Raman spectra of Er:LiNbO3 crystal and Ti-diffusedEr:LiNbO3 strip waveguide, in which the Li/Nb ratio was altered using a vapor-phase equilibration (VPE) technique, were measured at room temperature in the wave-number range 50–3500 cm-1. Both 488 and 514.5 nm radiations were used to excite Raman scattering, A1(TO) and E(TO) modes were recorded at backward scattering geometry. The results indicated that the lattice vibrational spectra of the as-grown Er:LiNbO3 are almost the same as those of pure LiNbO3 except for the little shift of the peak position and the change of relative intensity of some peaks. In comparison with the spectra of as-grown Er:LiNbO3 crystal the vapor-phase equilibrated Er:LiNbO3 and Er:Ti:LiNbO3 crystals in the lattice vibrational region exhibit the following features: firstly, Raman peaks become narrow, indicating that the VPE process has brought Er:LiNbO3 and Er:Ti:LiNbO3 crystals closer to a stoichiometric composition; secondly, relative intensity of some peaks varies with the VPE time; and finally, slight blue shifting in peak position was observed. Some of these features were correlated with the NbO6 octahedra and with the site distribution of the doped Er ions. In addition, green fluorescence peaks and/or bands associated with the electron transitions 2H11/2?4I15/2 and 4S3/2?4I15/2 of the doped Er3+ were also observed. For 488 nm excitation they appear in the wavenumber range of 1200–3000 cm-1 and are well separated from lattice vibrational region; for 514.5 nm excitation, however, these fluorescence peaks shift towards the low wavenumber region and overlap partially with the lattice vibrational spectra.