INFLUENCE OF CRYSTALLOGRAPHIC POLARITY ON THE OPTICAL-PROPERTIES OF BI22SIO20 CRYSTALS

The optical properties of BSO crystals grown along [111], [(111) over bar], [112] and [(112) over bar] polar axes by the vertical Bridgman m ethod have been studied in the present paper. The corresponding relati onships of the optical properties to the growth direction, polar face etching pattern and SiO4 tetrahedra orientation have been established by etching experiments, piezoelectric measurements and structure analy sis. It was found that the [(111) over bar] and [(112) over bar] grown crystals showed a darker yellow colour and thus a decreased transmiss ion in the near blue-green region as compared with the [111] and [112] grown crystals. It can be inferred from the references and our presen t results that the Bisi absorption centres are preferentially segregat ed into the [(111) over bar] and [(112) over bar] grown crystals, main ly by a preferential adsorption mechanism.