JP2011057509A - Optical glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phosphate optical glass having a high refractive index, high dispersibility and high permeability, as having a refractive index n<SB>d</SB>of 1.9 or higher, an Abbe number ν<SB>d</SB>of 20 or lower and a wavelength λ<SB>70</SB>of 520 nm or shorter at which the glass has 70% spectral transmittance without a heat treatment after melting and cooling, and having a low liquid phase temperature and excellent devitrification resistance near the softening point, and suitable for reducing a size or thickness of an optical element. <P>SOLUTION: The optical glass contains, by mass% on an oxide basis, 15 to 35 of P<SB>2</SB>O<SB>5</SB>, 35 to 60 of Nb<SB>2</SB>O<SB>5</SB>, 6 to 20 of TiO<SB>2</SB>, 0.1 to 15 of WO<SB>3</SB>, 0.1 to less than 1.0 of B<SB>2</SB>O<SB>3</SB>, 0.1 to 10 of K<SB>2</SB>O, 0.1 to less than 5.5 of Na<SB>2</SB>O, 0 to 3 of Li<SB>2</SB>O, 0 to 3 of SiO<SB>2</SB>, 0 to less than 5.0 of Bi<SB>2</SB>O<SB>3</SB>, and substantially no BaO, and has a refractive index n<SB>d</SB>of 1.9 or higher, an Abbe number ν<SB>d</SB>of 20 or lower, and a wavelength λ<SB>70</SB>of 520 nm or shorter at which the glass has 70% spectral transmittance. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a phosphate optical glass having a high refractive index, a high dispersibility, a high transparency, a low liquidus temperature, and an excellent devitrification resistance near the softening point.

If Patent Document 1, the refractive index _{n d} 1.9 Although _{P 2 O} 5 -TiO 2 -based glass of the Abbe number [nu _d is 20 or less of the high refractive index and high dispersion have been proposed, which is not heat treated Has a wavelength of λ ₇₀ (hereinafter also simply referred to as λ ₇₀ ) giving a 70% spectral transmittance, which is colored purple, and the transmission characteristics are poor at 620 nm or more. Further, devitrification occurs inside the glass due to the heat treatment for improving the transmission characteristics, and the desired transmission characteristics may not be maintained. In addition, there is a risk of process complexity and non-uniform transmittance.

In Patent Document 2, a refractive index _{n d} is 1.9 or more, an Abbe number [nu _d is 20 or less _P 2 _O 5 having a high refractive index and high dispersion _{-B 2 O 3 -Nb 2 O 5} -TiO 2 -based glass However, a glass having a good softening point devitrification has a liquid phase temperature as high as 1140 ° C. and has problems in terms of productivity and durability of glass forming equipment.

In Patent Document 3, Sb ₂ O ₅ having a high refractive index, a high dispersibility, and a high transmittance having a refractive index n _{d of} 1.9 or more, an Abbe number ν _{d of} 20 or less, and λ ₇₀ of 520 nm or less was added. , P ₂ O ₅ —B ₂ O ₃ —Nb ₂ O ₅ —TiO ₂ —BaO-based glass has been proposed, but there is a problem that the glass is devitrified near the softening point and the transmittance tends to decrease.

Patent Document 4 proposes an optical glass for press molding based on P ₂ O ₅ —Nb ₂ O ₅ —Bi ₂ O ₃ —TiO ₂ having a high refractive index and high dispersibility, but has a refractive index n _d ; 1. No. 9 or more and Abbe number ν _d ; 20 or less have not been proposed as a specific composition. Although Ti ions or Nb ions P ₂ O ₅ based glass contains Sb ₂ O ₃ to prevent the coloring is reduced, depending on its content there is a possibility that light transmittance is deteriorated.

JP-A-6-345481 JP-A-8-104537 JP 2005-206433 A JP 2003-160355 A

The present invention provides a high refractive index having a refractive index n _d of 1.9 or more, an Abbe number ν _d of 20 or less, and a wavelength λ ₇₀ of 70% or less giving a 70% spectral transmittance without heat treatment after melting and cooling, The purpose is to provide a phosphate-based optical glass that is highly dispersible and highly permeable, has a low liquidus temperature, has excellent devitrification resistance near the softening point, and is suitable for miniaturization and thinning of optical elements. To do.

The present invention is a mass% based on oxide,
P ₂ O _5: 15~35,
Nb ₂ O _5: 35~60,
TiO _2: 6~20,
WO _3: 0.1~15,
B ₂ O ₃ : less than 0.1 to 1.0,
K ₂ O: 0.1~10,
Na ₂ O: 0.1 to less than 5.5,
Li ₂ O: 0 to 3,
SiO _2: 0~3,
Bi ₂ O ₃ : 0 to less than 5.0,
Provided is an optical glass that substantially does not contain BaO, has a refractive index n _d of 1.9 or more, an Abbe number ν _d of 20 or less, and a wavelength λ ₇₀ that gives 70% spectral transmittance of 520 nm or less. Unless otherwise specified, the “lower limit” in the numerical range of the chemical composition indicates “above” and the “upper limit” indicates “below”, respectively.

In the present invention, a refractive index n _d : 1. by using WO ₃ , K ₂ O and Na ₂ O as essential components in P ₂ O ₅ —Nb ₂ O ₅ —B ₂ O ₃ —TiO ₂ glass. It was found that an optical glass having a light transmittance of 9 or more and an Abbe number ν _{d of} 20 or less and having a wavelength λ ₇₀ of 520 nm or less that gives a 70% spectral transmittance without heat treatment after melting and cooling can be obtained.

In the present invention, by containing an appropriate amount of K ₂ O and using WO ₃ as an essential component, the liquidus temperature can be greatly lowered, and the redox state of the glass melt can be easily controlled. In addition, by controlling the alkali amount to an appropriate amount, devitrification (milky white) in the vicinity of the softening point, that is, a decrease in transmittance can be prevented. The optical glass of the present invention (hereinafter referred to as the present glass) can provide an optical element such as an optical lens that is optimal for miniaturization and thinning of optical products.

  The reason why each component range of the glass is set is as follows. In the present specification, “%” means “% by mass” unless otherwise specified. The chemical composition is based on oxide.

P ₂ O ₅ is an essential component, a main component (glass-forming oxide) that forms glass, and a component that increases the viscosity of glass. In the present invention, the P ₂ O ₅ content is too low, or the liquidus temperature is increased, or devitrification resistance softening temperature near to deteriorate. Therefore, the P ₂ O ₅ content of the present glass is 15% or more. The P ₂ O ₅ content is preferably 20% or more, and the P ₂ O ₅ content is more preferably 23% or more. On the other hand, if the P ₂ O ₅ content is excessive, the refractive index is less than 1.9. Therefore, the P ₂ O ₅ content of the present glass is 35% or less. The P ₂ O ₅ content is preferably 30% or less, and the P ₂ O ₅ content is more preferably 28% or less.

In the present glass, Nb ₂ O ₅ is an important essential component having an effect of increasing the refractive index of the glass. If the content is too small, the above effect will be insufficient, so in the present glass, the Nb ₂ O ₅ content is 35% or more. In the present glass, the Nb ₂ O ₅ content is preferably 38% or more, and the Nb ₂ O ₅ content is more preferably 40% or more. On the other hand, if the Nb ₂ O ₅ content is increased, the glass is not only easily colored but also difficult to vitrify, so the Nb ₂ O ₅ content of the present glass is 60% or less. The Nb ₂ O ₅ content is preferably 55% or less, and the Nb ₂ O ₅ content is more preferably 53% or less.

In the present glass, TiO ₂ is an important indispensable component that has a great effect in increasing the refractive index and increasing the dispersion of the glass. If the TiO ₂ content is too small, the effect is lowered, so the TiO ₂ content of the present glass is 6% or more. In the present glass, preferably the TiO ₂ content is more than 7%, more preferably TiO ₂ content is 8% or more.

On the other hand, in the present glass, when the TiO ₂ content is increased, the light transmission characteristics in the visible region are lowered, the glass becomes unstable, and the liquidus temperature is also increased. Therefore, the TiO ₂ content of the present glass is 20%. It is as follows. In the present glass, the TiO ₂ content is preferably 18% or less, and the TiO ₂ content is more preferably 16% or less.

In the present glass, WO ₃ is an important indispensable component that has a great effect in increasing the refractive index and increasing the dispersion of the glass. Further, possible substitutions at TiO ₂ component, high refractive index, while maintaining a high dispersion, the glass excellent in devitrification resistance is obtained. In the present glass, if the content of WO ₃ is too small, the above effect is lowered, so that the content of WO ₃ is 0.1% or more. In the present glass, the WO ₃ content is preferably 1% or more, and the WO ₃ content is more preferably 2% or more.

On the other hand, in the present glass, if the content of WO ₃ is increased, the light transmission characteristics in the visible region are lowered and the glass becomes unstable. Therefore, the content of WO ₃ is 15% or less. The glass has a WO ₃ content of preferably 14% or less, and more preferably a WO ₃ content of 12% or less.

In the present glass, B ₂ O ₃ is an essential component that forms a glass and can be obtained with a great effect in lowering the liquidus temperature by adding a small amount. In the present glass, the B ₂ O ₃ content is 0.1% or more. The B ₂ O ₃ content of the present glass is preferably 0.2% or more, and the B ₂ O ₃ content is more preferably 0.25% or more. On the other hand, if the content of B ₂ O ₃ is too large, the devitrification resistance near the softening point is significantly deteriorated, so the B ₂ O ₃ content of the present glass is less than 1.0%. The B ₂ O ₃ content is preferably 0.97% or less, and the B ₂ O ₃ content is more preferably 0.94% or less.

In the present glass, K ₂ O is an effective component for lowering the liquidus temperature without deteriorating the devitrification property near the softening point and suppressing the coloring of the glass due to the reduction of Ti ions and Nb ions. And an important essential ingredient. For this effect, the K ₂ O content of the present glass is 0.1% or more. Preferably the content of _{K 2} O of the glass is at least 1%, more preferably content of _{K 2} O is 1.5% or more. The K ₂ O content is particularly preferably 2% or more. On the other hand, if the K ₂ O content is excessive, the refractive index is less than 1.9, so the K ₂ O content of the present glass is 10% or less. The glass has a K ₂ O content of preferably 9% or less, and more preferably a K ₂ O content of 8% or less.

In the present glass, Na ₂ O is an effective component that lowers the liquidus temperature and suppresses the coloring of the glass, and is an essential component. If the Na ₂ O content is small, the liquidus temperature may increase, so the Na ₂ O content of the present glass is 0.1% or more. The Na ₂ O content of the present glass is preferably 1% or more, and the Na ₂ O content of the present glass is more preferably 2% or more. On the other hand, if the Na ₂ O content is excessive in the present glass, the devitrification resistance near the softening point is deteriorated. Therefore, the Na ₂ O content of the present glass is less than 5.5%. The Na ₂ O content of the present glass is preferably 5.4% or less.

Li ₂ O is a component that is effective for lowering the liquidus temperature, but it is also a component that deteriorates devitrification resistance near the softening point, and is not an essential component in the present glass. The content in the case of containing Li ₂ O is preferably 3% or less because the devitrification resistance near the softening point is deteriorated. It is more preferable that the Li ₂ O content of the present glass is less than 0.3%, and it is particularly preferable that the present glass does not substantially contain Li ₂ O.

Further, in the present glass, it is preferable to balance the contents of K ₂ O, Na ₂ O and Li ₂ O in order to achieve both devitrification resistance near the softening point and a low liquidus temperature. Specifically, Na ₂ O and Li ₂ O total amount of the mass ratio of the relative _{K 2 O (K 2 O /} (Na 2 O + Li 2 O), hereinafter, the mass ratio is also referred to as K-NaLi ratio), It is preferable that it is 3.5 or less, and it is further more preferable that K-NaLi ratio is 3 or less. In the present glass, it is particularly preferably 2.5 or less. On the other hand, in this glass, in order to maintain a low liquidus temperature, the K-NaLi ratio is preferably 0.43 or more. More preferably, the K-NaLi ratio of the present glass is 0.44 or more. It is particularly preferable that the K-NaLi ratio of the present glass is 0.4 or more.

SiO ₂ is a glass-forming component, a component that can be added when adjusting the viscosity, and is not an essential component in the present glass. Since the refractive index SiO ₂ content is too large falls below the 1.9, SiO ₂ content of the glass when it contains is less than 3%. The SiO ₂ content of the present glass is preferably less than 0.5%, and more preferably the SiO ₂ content is less than 0.3%.

Bi ₂ O ₃ has an effect of increasing the refractive index of the glass and softening the glass, but is not an essential component in the present glass. When the Bi ₂ O ₃ content is increased, the devitrification resistance near the softening point is decreased or the Abbe number ν _d is increased. Therefore, in the present glass, the Bi ₂ O ₃ content when added is 5%. The following is preferable. It is more preferable that the Bi ₂ O ₃ content is 1% or less, and it is particularly preferable that Bi ₂ O ₃ is not substantially contained.

In the present glass, Sb ₂ O ₃ is an effective component as a decoloring agent that suppresses coloring caused by the reduction of Ti ions and Nb ions in addition to acting as a clarifier during glass melting, but is an essential component is not. Hereinafter will be described the reason for defining the content of _Sb 2 _{O 3,} in the present specification, the content of _Sb 2 _{O 3} is described outside hanging display with 100% other components than _Sb 2 _{O 3} To do.

For the effect, the content of Sb ₂ O ₃ is preferably 0.03% or more, and more preferably 0.05% or more. On the other hand, if the content is too large, the light transmittance is deteriorated due to the absorption of Sb ions. Therefore, the content of Sb ₂ O ₃ is preferably 1% or less, more preferably 0.8% or less, and It is especially preferable that it is 5% or less.

  In the present glass, the total of the above components is preferably 95% or more because various properties can be balanced. More preferably, the total of the above components is 98% or more, and it is particularly preferable that the present glass is substantially composed of the above components. In the present specification, “consisting essentially of the above components” means “consisting of the above components except for inevitable impurities”.

  MgO, CaO, SrO, and ZnO are components that can lower the liquidus temperature of the glass and improve the devitrification resistance by adding appropriate amounts, but are not essential components in the present glass. On the other hand, these components are also components that make it difficult to lower the Abbe number νd. Therefore, even when it is added, the content is preferably 10% or less independently, more preferably 3.0% or less, and particularly preferably not contained. In order to achieve high dispersion, BaO is not contained in the present glass except for inevitable impurities.

In this glass, one or more of Al ₂ O ₃ , GeO ₂ , Ga ₂ O ₃ , ZrO ₂ , Gd ₂ O ₃ , La ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ is adjusted for optical properties. Although it can be added as a component for the purpose, it is not an essential component. However, since the glass becomes unstable and the raw materials are relatively expensive when the content increases, it is preferable to suppress the content of these elements as much as possible in the industry. Therefore, even when it is added, each content is preferably 10% or less alone, more preferably 3.0% or less, and particularly preferably not contained.

In addition, the present glass preferably does not contain PbO, TeO ₂ , F, As ₂ O ₃ apart from those inevitable impurities due to environmental impacts and the like.

For smaller and thinner optical element which is an object of the present invention, the refractive index n _d of the glass it is 1.9 or more. Refractive index _{n d} of the glass is preferably 1.91 or more, the refractive index _{n d} of the glass is more preferably 1.92 or more. On the other hand, the liquidus temperature, in order to maintain the light transmittance is preferably the refractive index n _d of the glass and 2.00 or less, more preferably 1.99 or less, the refractive index n _d of the glass Is particularly preferably 1.98 or less.

In the present glass, in order to correct the necessary chromatic aberration, the Abbe number ν _d is 20 or less in consideration of the balance between the liquidus temperature and the light transmission characteristics. The glass has an Abbe number ν _d of preferably 19 or less, and particularly preferably an Abbe number ν _d of 18 or less.

In general, high-dispersion optical glass has a poor transmission property in the ultraviolet region. Therefore, it is preferable that the wavelength λ ₇₀ that gives a spectral transmittance of 70% is as low as possible. Λ _{70 of the} present glass is 520 nm or less. Λ ₇₀ of the present glass is preferably 510 nm or less, and λ _{70 of} the present glass is particularly preferably 500 nm or less. Similarly, it is preferable that the wavelength λ ₅ giving 5% spectral transmittance is on the lower wavelength side. Λ _{5 of the} present glass is preferably 420 nm or less, λ ₅ is more preferably 415 nm or less, and λ _{5 of} the present glass is particularly preferably 410 nm or less.

The glass transition point T _g of the present glass, can be lowered molding temperature and is 700 ° C. or less is preferable because the thermal Call is reduced on molding apparatus and the molding die. T _g, more preferably 690 ° C. or less of the glass for the life of the production facilities, and particularly preferably T _g 680 ° C. of the glass.

The yield point At the present glass, preferably a 750 ° C. or less for the same reason as the glass transition temperature T _g. The yield point At of the present glass is more preferably 740 ° C. or lower. The yield point At of the present glass is particularly preferably 730 ° C. or lower.

As the liquidus temperature L _T of the glass, from the viewpoint of durability productivity aspects and molding apparatus, is preferably 1100 ° C. or less. Preferred oxidation state redox state (Redox) of the melt by holding at a temperature slightly higher than the previous melt L _T to improve the transmittance of the glass to glass was flowing out to a plate molding or gob molding (For Ti, W, and Bi, the transmittance is high because the degree of coloring is small at large valences), and an optical lens with high transmittance can be obtained by suppressing the coloring of glass. More preferably, the liquidus temperature L _T of the glass is at 1080 ° C. or less, particularly preferably liquidus temperature L _T of the glass is at 1060 ° C. or less.

  Since this glass has the above-described component structure, it has excellent devitrification resistance near the softening point. In this specification, the devitrification resistance in the vicinity of the softening point is evaluated by the deterioration amount of the spectral transmittance (including surface reflection loss) after being held for 10 minutes at a temperature of yield point (At) + 80 ° C. The deterioration amount of the spectral transmittance is preferably 1% or less, and more preferably 0.5% or less. The deterioration amount of the spectral transmittance is particularly preferably 0.3% or less.

  In addition, when the common logarithm (hereinafter simply referred to as logarithm) of the viscosity (dPa · s) at the time of melting is less than 0.2 in the present glass, bubbles adhering to the interface between the internal bubbles and the crucible in the glass melt As a result, the foam quality was confirmed to be good. The higher the temperature when the logarithm of viscosity (dPa · s) is 0.2, the higher the refining temperature must be set, and the elution from a crucible such as Pt and Pt alloy tends to be mixed. Absorption of the eluted Pt ions becomes a factor that degrades the transmittance in the visible range.

Therefore, in order to obtain a glass having a good quality while suppressing the elution of impurities from the crucible, in the present glass, the temperature when the logarithm of the viscosity (dPa · s) is 0.2 (hereinafter T _{logη = 0). .2} ) is preferably 1300 ° C. or less, more preferably T _{log η = 0.2} is 1270 ° C. or less, and most preferably T _{log η = 0.2} is 1230 ° C. or less.

As described above, in order to maintain a low viscosity curve and keep the fining temperature low, the total amount of Li ₂ O, Na ₂ O and K ₂ O is preferably 3% or more in the present glass. More preferably, the amount is 5% or more. In the present glass, the total amount is particularly preferably 7% or more. On the other hand, if the total amount is too large, the devitrification resistance near the softening point is deteriorated. Therefore, in the present glass, the total amount is preferably less than 10%, more preferably 9.5% or less, The total amount is particularly preferably 9% or less.

The method for producing this glass is not particularly limited. For example, platinum, platinum, and the like are used by weighing and mixing raw materials used in ordinary optical glass such as oxides, hydroxides, carbonates, nitrates, and phosphates. crucible, a gold crucible, a quartz crucible was placed in a crucible for use in an alumina crucible or the like usually has an optical glass, 2 to 10 hours melted at about 1000 to 1400 ° C., clarified, stirred, slightly higher temperature than the liquidus temperature _{L T} In this case, the melt is held and cast into a mold preheated to 400 to 500 ° C., and then slowly cooled to produce.

  As a means to adjust the redox state of the glass melt, transition is achieved by sending gas into the melt and bugling it through a pipe made of a heat-resistant material such as ceramics. A metal can be in a high valence state and the transmittance can be improved. Examples of the oxidizing atmosphere gas include oxygen gas.

  Examples of the present invention will be described below. Examples 1 to 31 are examples of the present invention. In addition, this invention is limited to these Examples and is not interpreted. In the table, “-” indicates that there is no data.

[Chemical composition and sample preparation]
The raw materials were weighed so as to have chemical compositions (%) shown in Tables 1 to 5. As raw materials of the present invention, for P ₂ O ₅ , orthophosphoric acid (H ₃ PO ₄ ), metaphosphoric acid, etc. are used, and for other components, carbonates, nitrates, oxides, etc. Can be selected according to cost.

The weighed raw materials are mixed, put into a quartz crucible having an internal volume of about 300 cc, melted at 1100-1300 ° C. for 1 to 3 hours, stirred, and then the glass crucible is replaced with a platinum crucible at 1050 ° C. at 1.0-0. The sample was held for 5 hours and cast into a rectangular mold of 100 mm length × 50 mm width preheated to about 600 ° C., and then slowly cooled at about 0.5 ° C./min to obtain a measurement sample. In the table, R ₂ O represents the total amount of alkali components (K ₂ O, Na ₂ O and Li ₂ O).

[Evaluation methods]
And refractive index, _{n d} is the refractive index with respect to helium d-line, refractometer (Kalnew Optical Industry Co., Ltd., trade name: KRP-2000) was measured with. The refractive index value was measured to the fifth decimal place and rounded to the fourth decimal place.
The Abbe number ν _d was calculated by ν _d = (n _d −1) / (n _F −n _C ), rounded to the first decimal place and rounded to the first decimal place. _However, n F, _{n C} is the refractive index for each of the hydrogen F line and C line.
Transmittance λ ₅ , λ ₇₀ ; The spectral transmittance (including surface reflection loss) of a 10 mm thick plate was measured according to Japan Optical Glass Industry Association Standard JOGIS02-2003.
- liquid phase temperature L _T is put glass of approximately 100g in a platinum crucible and cooled by natural cooling those held for 1 hour at 10 ° C. increments up to 1000 ° C. C. to 1100 ° C., respectively, the microscope the presence or absence of crystal precipitation The minimum temperature at which no crystal was observed was taken as the liquidus temperature.
The transmittance was measured in 1 nm increments for a sample that was polished on both sides to a thickness of 10 mm using a spectrophotometer (trade name: Lambda 950, manufactured by Perkin Elmer).
T _{log η = 0.2} ; rotating cylinder method? Was used to measure the temperature dependence of the viscosity η during melting, and the temperature at log η = 0.2 was determined.
・ Devitrification resistance in the vicinity of the softening point uses a sample of 100 mm × 100 mm × thickness 10 mm, 10 min. The spectral transmittance after holding and before heating was measured with the above spectrophotometer, and calculated from the amount of deterioration of transmittance before and after (simply described as simply the amount of deterioration in the table). The glass transition point Tg and the yield point At are obtained by processing each obtained glass into a rod shape, and using a thermal analyzer (trade name: TMA4000SA, trade name: TMA4000SA) by a thermal expansion method to increase the temperature rise rate 5 Measured at ° C / min.

  The present invention is an optical glass having a high refractive index, a high dispersibility, and a high transmittance, and is suitable for application to various optical elements such as optical lenses that are severely required to be downsized or thinned.

Claims (7)

% By mass based on oxide,
P ₂ O _5: 15~35,
Nb ₂ O _5: 35~60,
TiO _2: 6~20,
WO _3: 0.1~15,
B ₂ O ₃ : less than 0.1 to 1.0,
K ₂ O: 0.1~10,
Na ₂ O: 0.1 to less than 5.5,
Li ₂ O: 0 to 3,
SiO _2: 0~3,
Bi ₂ O ₃ : 0 to less than 5.0,
Optical glass which does not substantially contain BaO, has a refractive index n _d of 1.9 or more, an Abbe number ν _d of 20 or less, and a wavelength λ ₇₀ which gives 70% spectral transmittance is 520 nm or less. Bi ₂ O ₃ containing substantially no claim 1, wherein the optical glass. Sb ₂ O ₃ and containing 0.05 to 1.0 wt% in the outer hanging against the total amount of 100% of the other components according to claim 1 or 2, wherein the optical glass. The optical glass according to claim 1 liquidus temperature _{L T} is 1100 ° C. or less.   5. The optical glass according to claim 1, wherein the temperature when the common logarithm of the viscosity (dPa · s) of the glass melt is 0.2 is 1300 ° C. or less.   The optical glass according to any one of claims 1 to 5, wherein the amount of deterioration of spectral transmittance after holding at the yield point + 80 ° C for 10 minutes is less than 1%. The optical glass according to claim 1, wherein λ ₅ giving 5% spectral transmittance is 420 nm or less.