Investigation on growth and defects of Ho³⁺:BaY₂F₈ crystals grown by Czochralski method

Large and heavily Ho³⁺-doped BaY₂F₈ single crystals were grown by the Czochralski method. X-ray powder diffraction was applied to analyze the phase of the crystal samples. Simultaneously, metallographic microscope, scanning electron microscopy and energy dispersive spectrometer were employed to observe and investigate defects in the as grown crystals. Two significant kinds of defects, namely cracking and impurities were discovered in the samples of Ho³⁺:BaY₂F₈ single crystals. Theoretical analyses suggested that mechanisms concerning the formation of the impurities such as bubbles and inclusions were considered to be closely related to the growth temperature and atmosphere while the former defect was primarily brought by the lattice distortion relating to the thermal stress and the impurities. Based on the results of experiments and theoretical analyses, the parameters of growth process were optimized and a crack free 20 mol% Ho³⁺:BaY₂F₈single crystal has been successfully obtained. Furthermore, the UV–Vis-IR (0.2–10 μm) absorption spectra of BaY₂F₈ single crystal and the crystal heavily doped with Ho³⁺ ions (20 mol%) have been investigated at room temperature. - Highlights: • Main reason of cleavages is the crystal lattice distortion caused by the impurities. • Lattice distortion was caused by carbon phases derived from the graphite crucible. • High quality crystal can be obtained by using CF₄ and high purity graphite crucibles. • The crystal exhibits the broader absorption band and larger absorption cross section