The present invention relates to an optical glass containing, in terms of mass % on an oxide basis, P 2 O 5 : from 10 to 18%; Bi 2 O 3 : from 37 to 64%; Nb 2 O 5 : from 5 to 25%; Na 2 O: from more than 4.1 to 10%; K 2 O: from 0 to 2%; Li 2 O: from 0 to 0.2%; WO 3 : from 0 to less than 20%; TiO 2 : from 0 to 3%; and B 2 O 3 : from 0 to 2%, and having a refractive index n d of 1.98 or more and an Abbe's number ν d of 20 or less.
1. An optical glass comprising, in terms of mass % on an oxide basis:
P 2 O 5 : from 10 to 18%;
Bi 2 O 3 : from 37 to 64%;
Nb 2 O 5 : from 5 to 25%;
Na 2 O: from more than 4.1 to 10%;
GeO 2 : from 0 to 5.0%;
K 2 O: from 0 to 2%;
Li 2 O: from 0 to 0.2%;
WO 3 : from 0 to less than 20%;
TiO 2 : from 0 to 3%; and
B 2 O 3 : from 0 to 2%,
wherein the optical glass has a refractive index n d of 1.98 or more and an Abbe's number ν d of 20 or less.
2. The optical glass according to claim 1 , wherein the optical glass contains substantially no BaO.
3. The optical glass according to claim 1 , wherein the optical glass comprises from 10 to less than 20 mass % of WO 3 .
4. The optical glass according to claim 1 , wherein the optical glass has a liquidus temperature of 905° C. or less.
5. The optical glass according to claim 1 , wherein the optical glass has λ 5 of 415 nm or less.
6. The optical glass according to claim 1 , wherein the optical glass comprises from 13% to 17.2% of P 2 O 5 .
7. The optical glass according to claim 1 , wherein the optical glass comprises from 13.5% to 15.8% of P 2 O 5 .
8. The optical glass according to claim 1 , wherein the optical glass comprises from 13% to 17.2% of P 2 O 5 and from 0% to 1.8% of B 2 O 3 .
9. The optical glass according to claim 1 , wherein the optical glass comprises from 13.5% to 15.8% of P 2 O 5 and from 0% to 1.8% of B 2 O 3 .
10. The optical glass according to claim 1 , wherein a sum of P 2 O 5 , B 2 O 3 and GeO 2 is from 15.44% to 17.77%.
11. The optical glass according to claim 1 , wherein the optical glass comprises from 0.1% to 3.0% of GeO 2 .
12. The optical glass according to claim 1 , further comprising from 0.01% to 1% of Sb 2 O 3 .
13. The optical glass according to claim 1 , further comprising from 0.05% to 0.1% of Sb 2 O 3 .
14. The optical glass according to claim 1 , wherein the optical glass has λ 70 of 485 nm or less.
15. The optical glass according to claim 1 , wherein the optical glass has a glass transition point of 520° C. or less.
16. The optical glass according to claim 1 , wherein the optical glass has a liquidus viscosity of 2.5 dPa·s to 20 dPa·s.
17. The optical glass according to claim 1 , wherein the optical glass has a liquidus viscosity of 4 dPa·s to 10 dPa·s.