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.