| 摘要 |
An optical glass has optical constants of a refractive index (nd) within a range from 1.73 to less than 1.80 and an Abbe number (nud) within a range from 43 to 55, comprises SiO<SUB>2</SUB>, B<SUB>2</SUB>O<SUB>3</SUB>, Y<SUB>2</SUB>O<SUB>3</SUB>, La<SUB>2</SUB>O<SUB>3</SUB>, ZnO and Li<SUB>2</SUB>O as essential components, is substantially free of lead component, arsenic component and fluorine component, has a ratio of SiO<SUB>2</SUB>/B<SUB>2</SUB>O<SUB>3 </SUB>of 0.30 to 1.55 and a ratio of Y<SUB>2</SUB>O<SUB>3</SUB>/La<SUB>2</SUB>O<SUB>3 </SUB>of 0.15 to 1.00, and has a glass transition temperature (Tg) of 620° C. or below.
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