Selective rearrangement of Nd3+ centers in LiNbO3 under ferroelectric domain inversion by electron beam writing

Abstract

Different values of the electronic charge provided by a direct electron beam writing system have been used to produce polarization inverted domain regions in the micrometer range on Nd3+ optically activated LiNbO3. The effect of the electronic charge on the Nd3+ center structure has been studied by means of low-temperature luminescence from Nd3+ ions. The axial crystal field acting on the Nd3+ centers has been analyzed through the F4 3/2 energy-level splitting of the Nd3+ ions. From there we have determined the position of Nd3+ ions into the Li+ octahedra for the different unequivalent centers in domains reversed with different electronic doses. The results show that the axial crystal field acting on the unequivalent Nd3+ centers can be selectively modified by means of the different doses applied to produce the inversion of the polarization. Moreover, a control of the discrete shifts suffered by the Nd3+ ions into the Li+ octahedra after the inversion process can be carried out in the range 0-0.02Å by selecting the type of Nd center to be shifted by means of the different electronic charge. The behavior of each Nd3+ center after the polarization inversion under different doses can be discriminated and the different nature, as well as the polar character of the Nd3+ centers, is clearly manifested