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

Raman spectra of Er:LiNbO3 crystal and Ti-diffused Er:LiNbO3 strip waveguid e, in which the Li/Nb ratio was altered using a vapor-phase equilibration ( VPE) technique, were measured at room temperature in the wavenumber range 5 0-3500 cm(-1). Both 488 and 514.5 nm radiations were used to excite Raman s cattering, A(1)(TO) and E(TO) modes were recorded at backward scattering ge ometry. The results indicated that the lattice vibrational spectra of the a s-grown Er:LiNbO3 are almost the same as those of purl LiNbO3 except for th e 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 t he vapor phase equilibrated Er:LiNbO3 and Er:Ti:LiNbO3 crystals in the latt ice vibrational region exhibit the following features: firstly, Raman peaks become narrow, indicating that the VPE process has brought Er:LiNbO3 and E r:Ti:LiNbO3 crystals closer to a stoichiometric composition; secondly, rela tive intensity of some peaks varies with the VPE time; and finally, slight blue shifting in peak position was observed. Some of these features were co rrelated with the NbO6 octahedra and with the site distribution of the dope d Er ions. In addition, green fluorescence peaks and/or bands associated wi th the electron transitions H-2(11/2) --> I-4(15/2) and S-4(3/2) --> I-4(15 /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 la ttice vibrational region; for 514.5 nm excitation, however, these fluoresce nce peaks shift towards the low wavenumber region and overlap partially wit h the lattice vibrational spectra.