The effect of Mg doping on the Raman spectra of LiNbO₃ crystals

Abstract

LiNbO3:Mg crystals doped with 0-8 mol% Mg with stoichiometric, intermediate and congruent compositions were systematically investigated by Raman spectroscopy in backscattering y(zx)y and y(zz)y geometries. The halfwidths of E(TO3) -E(TO9) and A1(TO1) -A1(TO4) bands, which have a significant composition dependence for undoped LiNbO3 crystals, show only weak Mg-concentration dependence below the photorefractive threshold. This is a consequence of the counteracting effect of the decreasing amount of Nb ions at Li-ion sites (Nb Li ) and increasing amount of Mg ions at Li-ion sites (Mg Li ). The halfwidths of these bands, however, increase linearly with growing Mg content for samples above the threshold, irrespective of the Li/Nb ratio. The same effect was observed in the Mg dependence of the position and halfwidth of the two-phonon band at about 689 -705 cm −1 . The change in the Mg concentration dependence of these parameters at a given Li/Nb ratio determines the same threshold value as that concluded from IR and UV spectroscopic measurements.1 Introduction LiNbO 3 is a well-known non-linear optical material, but its application is often limited by the photorefractive effect. The resistance to optical damage induced by the photorefractive effect can be improved by doping the crystal with MgO above a threshold concentration [1]. Many physical properties depend on MgO addition and change at the threshold value, e.g. , UV absorption edge [3], Raman spectrum [4] etc. In previous Raman experiments the Mg incorporation was investigated only in congruent crystals [4,5]. In the present work 0-8 mol% Mg-doped LiNbO 3 crystals grown from congruent, stoichiometric and intermediate compositions were systematically studied by Raman spectroscopy. Our aim was to understand the incorporation mechanism of Mg ions into the lattice and to determine the composition of the crystal (including the Mg content) using a simple, non-destructive, spectroscopic method.

Growth, defect structure, and THz application of stoichiometric lithium niobate

“…67,83 However, our series of undoped and Mg-doped LiNbO 3 crystals with different Li/Nb ratios successfully used in other experiments for clarifying the incorporation mechanism of Mg ions led us to extend the investigations also to Raman spectroscopy. 74,84 The E(TO 3 )-E(TO 9 ) and A 1 (TO 1 )-A 1 (TO 4 ) phonon modes were investigated in y(zx)y and y(zz)y geometries, respectively. The normalized E(TO) spectra of undoped and heavily Mg-doped (7.8 mol.…”

“…The E(TO) band positions, except for the E(TO 7 ) mode, 74,84 are practically independent of the Mg doping and Li/Nb ratio as well (the frequency data are scattered in a range of about …”

μ-Raman spectroscopy characterization of LiNbO3 femtosecond laser written waveguides

“…The Nd:Mg:LiNbO 3 Raman spectrum was compared with pure LiNbO 3 in the following works. [39][40][41] In these works, the following information is reported: for the A 1 (TO) 2 and A 1 (TO) 3 modes, small energy displacements were detected between doped and undoped LiNbO 3 , while for the A 1 (TO) 1 and A 1 (TO) 4 modes, no energy shift between doped and undoped LiNbO 3 was detected.…”

Interface and thickness dependent domain switching and stability in Mg doped lithium niobate

“…Therefore, contributions to the measured internal electric fields by PE induced long-range distortions are also likely and will be further investigated in Section III C. ions into the crystal leads to changes in parameters (intensity, position, and width) of existing peaks especially if the sites of involved oscillations are occupied by the dopants. 39,44,46 Furthermore, bands that would usually not be permitted for symmetry reasons appear and are ascribed to photorefraction 44,47,48 and defect induced symmetry breaking, 49 which explains the A(TO 4 ) band visible around 625 cm…”