Growth And Properties Of Lithium Tantalum Doped With Fe

Lithium tantalate (LiTaO₃) is an excellent synthetic crystal, which has many important properties, such as electro-optic, acousto-optic, piezoelectric, thermal-optic and photorefractive effects, etc. It is widely used in the optical fields, such as optical modulation, optical recording and frequency conversion. It is an ideal material to make the broadband, high-stability oscillator and high-sensitivity detectors. However, with the rapid development of the computers, information networks and multimedia technology, the appetite for more information storage capacity as the more and more demand of society, existing storage capacity and transfer rate can not meet requirements of the development. In the applications of high-density and high-capacity holographic information storage, the photorefractive property is the most important technical indicator.In the sensitive photorefractive impurity ions,Fe²⁺/Fe³⁺ are the most studied, widely used and the best doped ions, so I chose Fe²⁺/Fe³⁺ as the impurity ions of enhanced LiTaO₃ photorefractive effect.In this dissertation,selecting suitable temperature gradient, pulling speed and rotating speed, Fe:LiTaO₃ crystals were grown by the Czochraski method with intermediate frequency heating.There were no macroscopic defects and good optical homogeneity in the as-grown boules.X-ray powder diffraction experiment showed that lattice structure of the Fe:LiTaO₃ crystal was similar to that of the congruent sample.In Fe:LiTaO₃ crystals, results of unit cell parameters indicated that the lattice constant increased with the Fe2O₃ concentration increasing.The change mechanism of the UV-Vis absorption edge and the IR absorption peak was also discussed in the Fe:LiTaO₃ single crystals.Analysis results show that Fe ions took placing Li to be Fe 2L+i, it also excluded H+ as the same as Ta 4L+i. Absorption edge of Fe:LiTaO₃ shifts to the longer wavelength with the increase in iron content and there is a absorption peak in 520nm that is produced by Fe2+.The photorefractive properties of the Fe:LiTaO₃ crystals, including exponential gain coefficient were obtained by two-beam coupling experiments and the effective carriers densities were computed.The result indicates that exponential gain coefficient and the effective carriers densities are increased.