Exploration On Crystallization Habit Of Fluoride Crystal BaF₂Y₈

The up-conversion luminescence has been found for forty yearsand a good many up-conversion materials has been developed. TheBaF₂Y₈ crystal has such merits comparing with other laser crystalsas lower refracting power, lower phonon-energy and widerpenetrating rang. In this paper we investigate the growth method ofBaY₂F₈ crystal and the influences of the technique parameters tocrystal quality.BaY₂F₈ crystal belongs to monoclinic-symmetry class(biaxialcrystal, space group C 2/m , point group C 2h ). According to the phasediagram, the proportion of raw materials and the temperature ofcrystal growth were determined. We also studied the seed used incrystal growth, and made a conclusion that it was impossible to use aforeign seed for the growth.We tested different temperature gradient, rotation rate and pullingrate for the crystal growth. We found that, the crystal crashed whilethe temperature gradient was 100 ℃ / ㎝ . When the temperaturegradient was reduced to 70℃ /㎝ , the crystal was got successfully. Asthe temperature gradient reached to 30℃ /㎝ , the crystallization forcewas not enough to drive the growth, the crystal growth was interfered.In order to obtain the favorable interface, we set the rotation rate at alow level, because the convection of the BaY₂F₈ melt under thecrystallization temperature was fairly weak. At last the X-raydiffraction and absorption spectrum of the BaY₂F₈ crystal were alsomeasured.