The present invention relates to an optical glass containing, in terms of mass % on the basis of oxides, B 2 O 3 : 10 to 20%, SiO 2 : 0.5 to 12%, ZnO: 5 to 19%, Ta 2 O 5 : 2.5 to 17%, Li 2 O: 0.2 to 3%, ZrO 2 : 0.6 to 4.9%, WO 3 : 1 to 20%, La 2 O 3 : 25 to 50%, Gd 2 O 3 : 0 to 13%, and Y 2 O 3 : 0.2 to 20%, provided that La 2 O 3 +Gd 2 O 3 +Y 2 O 3 is 35 to 60%, in which the optical glass does not substantially contain Nb 2 O 5 , and has a refractive index (n d ) of 1.82 to 1.86, an Abbe's number (ν d ) of 37 to 44 and a glass transition point (T g ) of 630° C. or lower.
1. An optical glass comprising, in terms of mass % on the basis of oxides:
B 2 O 3 : 10 to 20%,
SiO 2 : more than 2 to 12%,
ZnO: 5 to 19%,
Ta 2 O 5 : 2.5 to 17%,
Li 2 O: 0.2 to 3%,
ZrO 2 : 0.6 to 4.9%,
WO 3 : 1 to 20%,
La 2 O 3 : 25 to 50%,
Gd 2 O 3 : 0 to 13%, and
Y 2 O 3 : 0.2 to 20%,
provided that La 2 O 3 +Gd 2 O 3 +Y 2 O 3 is 35 to 60%,
wherein the optical glass does not substantially comprise Nb 2 O 5 , and has a refractive index (n d ) of 1.82 to 1.86, an Abbe's number (ν d ) of 37 to 44 and a glass transition point (T g ) of 630° C. or lower.
2. The optical glass according to claim 1 , having a liquidus temperature (T L ) of 1130° C. or lower.
3. The optical glass according to claim 2 , wherein, at the liquidus temperature (T L ) or lower of the optical glass, a plurality of devitrified substances do not precipitate and only LaBO 3 precipitates.
4. The optical glass according to claim 1 , having a liquidus temperature viscosity (η TL ) of 5 dPa·s or more.
5. The optical glass according to claim 1 , wherein a mass % fraction of a content of La 2 O 3 to a total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3 and Yb 2 O 3 is 0.67 to 0.90.
6. A preform for precision press molding, comprising the optical glass according to claim 1 .
7. An optical element obtained by subjecting the optical glass according to claim 1 to precision press molding.
8. The optical glass according to claim 1 , wherein the mass % on the basis of oxides is:
B 2 O 3 : 12 to 19.5%,
SiO 2 : more than 2 to 10%,
ZnO: 6.5 to 17%,
Ta 2 O 5 : 8 to 13%,
Li 2 O: 0.5 to 2%,
ZrO 2 : 1.5 to 4.5%,
WO 3 : 8 to 16%,
La 2 O 3 : 30 to 46%,
Gd 2 O 3 : 2 to 12%, and
Y 2 O 3 : 1 to 15%,
provided that La 2 O 3 +Gd 2 O 3 +Y 2 O 3 is 43 to 55%.
9. An optical glass comprising, in terms of mol % on the basis of oxides:
B 2 O 3 : 20 to 40%,
SiO 2 : 8.3 to 30%,
ZnO: 10 to 34%,
Ta 2 O 5 : 0.8 to 8%,
Li 2 O: 0.5 to 15%,
ZrO 2 : 0.5 to 10%,
WO 3 : 3 to 15%,
La 2 O 3 : 10 to 25%,
Gd 2 O 3 : 0 to less than 5%, and
Y 2 O 3 : 0.1 to 15%,
provided that La 2 O 3 +Gd 2 O 3 +Y 2 O 3 is 15 to 30%,
wherein the optical glass does not substantially comprise Nb 2 O 5 , and has a refractive index (n d ) of 1.82 to 1.86 and an Abbe's number (ν d ) of 37 to 44 and a glass transition point (T g ) of 630° C. or lower.