Effect of necking on Czochralski-grown LiF crystals and its influence on crystalline perfection and the correlated physical properties

A bulk single crystal of lithium fluoride (LiF) was grown using an in-house-developed Czochralski crystal puller. The effect of necking on crystalline perfection, which in turn was found to influence the optical and dielectric properties, was studied. The crystalline perfection of the grown crystal was assessed along the length of the boule using high-resolution X-ray diffraction (HRXRD), and it was found that the grain boundaries that were present in the seed crystal were stopped gradually from propagating into the bulk crystal by necking. The UV-vis transparency of the crystal region having best crystalline perfection was found to be higher. Photoluminescence (PL) spectra revealed that a crystal region that was found to contain vacancy (point) defects by HRXRD yielded the maximum PL intensity because of color centers at the vacancies. The dielectric properties were also studied over a wide range of frequency.