Growth and Defects of Lithium Terbium Fluoride Crystals

doi:10.16553/j.cnki.issn1000-985x.2025.0097

Abstract

Abstract: Lithium terbium fluoride （LTF） crystal is an ideal magneto-optical material for magneto-optic devices in high-power laser systems due to its excellent magneto-optical properties. However， its incongruent melting behavior and peritectic reaction during crystallization make crystal growth challenging. Particularly， the formation of terbium oxyfluoride （TbO_xF_3-2x） ‘floaters’ during the growth process severely hinders the preparation of large size， high-quality crystals. In this study， high-purity TbF₃ and LiF were used as starting materials. Under a protective atmosphere of Ar and CF₄ mixed gas， a complete， large size， pure-phase LTF crystal boule with a diameter of nearly 2 inch （1 inch=2.54 cm） was successfully grown using the resistance-heated Czochralski method. A detailed study of the scattering defects within the crystal boule was conducted， along with an analysis of their underlying causes. The research identified that the scattering defects inside the LTF crystal are granular and needle-like in nature. The formation of these defects is significantly attributed to the weak impurity exclusion capability during the crystallization process and localized deviations in composition. By refining the growth process， large size LTF crystals with exceptional optical quality were ultimately attained. The measured weak absorption coefficient of these crystals is 17.0 ppm/cm， notably lower than that of commercially available TGG crystals.

Key words: lithium terbium fluoride; magneto-optical crystal; large size; scattering defect; CZ method; peritectic reaction

CLC Number:

O782

DONG Chang, LI Xingwang, YIN Jiayi, WANG Yongguo. Growth and Defects of Lithium Terbium Fluoride Crystals[J]. Journal of Synthetic Crystals, 2025, 54(11): 1893-1898.

Figures/Tables 6

Fig.1 Photograph of LTF crystal boule

Fig.2 XRD pattern of LTF crystal powder

Fig.3 Photographs of scattering defects inside LTF crystal

Fig.4 Photograph of LTF crystal boule grown after improvement

Fig.5 Internal micrograph （a）， He-Ne parallel light projection image （b）， interference fringe pattern （c）， and orthogonally polarized light projection image （d） of the LTF crystal boule before improvement； internal micrograph （e）， He-Ne parallel light projection image （f）， interference fringe pattern （g）， and orthogonally polarized light projection image （h） of the LTF crystal boule after improvement

Fig.6 Weak absorption curves of TGG （a） and LTF （b） crystals at 1 064 nm wavelength

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