Abstract
The optical properties of BSO crystals grown along 〈111〉, 〈1̄1̄1̄〉, 〈112〉 and 〈1̄1̄2̄〉 polar axes by the vertical Bridgman method have been studied in the present paper. The corresponding relationships of the optical properties to the growth direction, polar face etching pattern and SiO
4 tetrahedra orientation have been established by etching experiments, piezoelectric measurements and structure analysis. It was found that the 〈1̄1̄1̄〉 and 〈1̄1̄2̄〉 grown crystals showed a darker yellow colour and thus a decreased transmission in the near blue-green region as compared with the 〈111〉 and 〈112〉 grown crystals. It can be inferred from the references and our present results that the Bi
Si absorption centres are preferentially segregated into the 〈1̄1̄1̄〉 and 〈1̄1̄2̄〉 grown crystals, mainly by a preferential adsorption mechanism.