Optical glass
An optical glass that is an oxide glass having a very high refractive index in spite of its low-dispersion property, having excellent glass stability and having less susceptibility to coloring.
1. An optical glass that is an oxide glass and that comprises, by cationic %,
0 to 30% of Si 4+ ,
10 to 50% of B 3+ ,
less than 5% of total of Li + , Na + and K + ,
less than 1% of total of Mg 2+ , Ca 2+ and Sr 2+ ,
0 to 8% of Ba 2+ ,
0.1 to 15% of Zn 2+ ,
10 to 50% of La 3+ ,
0.1 to 20% of Gd 3+ ,
0 to 15% of Y 3+ ,
0 to 10% of Yb 3+ ,
0 to 20% of Zr 4+ ,
0.1 to 22% of Ti 4+ ,
0 to 20% of Nb 5+ ,
0 to 8% of Ta 5+ ,
0 to 5% of W 6+ ,
0 to 4% of Ge 4+ ,
0 to 10% of Bi 3+ , and
0 to 10% of Al 3+ ,
the cationic ratio of the content of Si 4+ to the content of B 3+ , Si 4+ /B 3+ , being less than 1.0, the optical glass having a refractive index nd of 1.930 to 2.2, an Abbe's number νd of 26 to 45, and a glass transition temperature Tg of 630° C. or higher.
2. The optical glass of claim 1 , which has a coloring degree λ70 of less than 470 nm.
3. The optical glass of claim 1 , which has a partial dispersion ratio Pg,F and an Abbe's number νd which satisfy the relationship of the following expression (1),
Pg,F≦− 0.0017 ×νd+ 0.660 (1).
4. The optical glass of claim 1 , wherein the total content of Nb 2 O 5 and Ta 2 O 5 as oxides is determined so as to achieve a liquidus temperature of 1,220° C. or lower.
5. The optical glass of claim 1 , which contains 22% cationic % or more of La 3+ .
6. The optical glass of claim 1 , which contains none of Mg 2+ , Ca 2+ and Sr 2+ .
7. The optical glass of claim 1 , which contains less than 1% of Ba 2+ .
8. The optical glass of claim 1 , which contains 1% or more of Gd 3+ .
9. The optical glass of claim 1 , which contains 0 to 1% of Ge 4+ .
10. The optical glass of claim 1 , wherein the content of Ba 2+ is less than 1%, the content of Gd 3+ is 1% or more and the content of Ge 4+ is 0 to 1%.
11. A press-molding glass gob formed of the optical glass recited in claim 1 .
12. An optical element which is formed of the optical glass recited in claim 1 .
13. A process for producing an optical element blank to be completed into an optical element by grinding and polishing, which comprises softening the press-molding glass gob recited in claim 11 by heating, and press-molding it.
14. A process for producing an optical element blank to be completed into an optical element by grinding and polishing, which comprises melting a glass raw material and press-molding the thus-obtained molten glass to produce an optical element blank formed of the optical glass recited in claim 1 .
15. A process for producing an optical element, which comprises grinding and polishing the optical glass blank recited in claim 13 .
16. A process for producing an optical element, which comprises grinding and polishing the optical glass blank recited in claim 14 .