JP2011051886A - Optical glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical glass which has excellent optical transmission characteristics, has optical constants of a refractive index n<SB>d</SB>of ≥2.0 and an Abbe's number ν<SB>d</SB>of ≤19 with a high dispersion and a high refractive index, is easily subjected to precision press molding, and can produce an optical element of high dimensional precision. <P>SOLUTION: The optical glass has a refractive index n<SB>d</SB>of ≥2.0, an Abbe's number ν<SB>d</SB>of ≤19 and a wavelength λ<SB>5</SB>for indicating an internal transmittance of 5% (10 mm) of ≤410 nm, and comprises Bi<SB>2</SB>O<SB>3</SB>, B<SB>2</SB>O<SB>3</SB>, TeO<SB>2</SB>and P<SB>2</SB>O<SB>5</SB>as essential components, wherein the optical glass preferably comprises, in terms of mol% of oxide, Bi<SB>2</SB>O<SB>3</SB>: 32-55; B<SB>2</SB>O<SB>3</SB>: 24-34; TeO<SB>2</SB>: 10-20; P<SB>2</SB>O<SB>5</SB>: 8-12; Nb<SB>2</SB>O<SB>5</SB>+Ta<SB>2</SB>O<SB>5</SB>: 0.1-4; TiO<SB>2</SB>: 0-10; and ZnO: 0-7. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a bismuth-based optical glass having a high refractive index, high dispersion (low Abbe number), excellent light transmittance, and capable of precision press molding.

  In recent years, with the widespread use of digital cameras, there has been a demand for higher performance in terms of miniaturization and color reproducibility. Therefore, in the optical glass constituting the lens, first, a high refractive index is required, but at the same time, in order to easily correct the problematic aberration, high dispersion (low Abbe number) is also required as an important characteristic. ing.

  Furthermore, high-refractive-index and high-dispersion lenses are also required to have excellent light transmission (hereinafter also referred to as high light transmission), like other lenses. However, high refractive index, high dispersion, and high light transmittance are generally in a trade-off relationship, and it is not always easy to achieve both. For example, the transmittance of optical glass having a high refractive index often decreases due to light absorption. This is because the wavelength at which strong light absorption starts (absorption edge) is closer to the visible wavelength range, the higher the refractive index, but the transmittance is reduced by the amount of light absorbed.

  Similarly, the dispersibility (Abbe number) is the wavelength dependence of the refractive index calculated at three specific wavelengths (486 nm, 588 nm, and 656 nm) in the visible light wavelength. The stronger the wavelength dependence, the smaller the Abbe number. Value (high dispersion). The closer the absorption edge is to these three wavelengths, that is, the visible wavelength, the stronger the wavelength dependency and the lower the Abbe number, but the transmittance decreases by the amount of the absorption. Accordingly, it is generally difficult to obtain an optical glass having a high refractive index, high dispersion, and excellent light transmission performance.

The light transmission characteristic is often expressed by a wavelength λ ₅ that exhibits an internal transmittance of 5% in a glass that is optically polished on both sides with a thickness of 10 mm. It can be said that the shorter the wavelength λ ₅ that shows the internal transmittance 5%, the shorter the absorption edge, and the better the light transmission characteristics. For example, when the wavelength λ ₅ showing internal transmittance of 5% is 420 nm or more, strong yellow coloring is observed in the glass.

In addition, lead glass is known as a high refractive index and high dispersion optical glass, but a glass containing no lead is required from the viewpoint of reducing environmental burden. Patent Document 1 proposes niobium phosphate glass as an optical glass having a high refractive index and high dispersion while not containing lead, although the light transmission characteristics are good, but the disclosed implementation. refractive index n _d of the example, none greater than 2.0, not necessarily sufficient in terms of refractive index.

Patent documents 2 to 4 propose a glass mainly composed of bismuth oxide and having a refractive index n _d of 2.0 or more. However, Patent Document 2 does not propose anything about high dispersion and high light transmittance. Further, in the glass mainly containing bismuth oxide shown in Patent Document 3, an example in which the refractive index _nd is 2.0 or more and the Abbe number ν _d is 19 or less is proposed, but λ ₅ is An example of 410 nm or less has not been proposed. That is, there is no proposal for an optical glass that balances the three characteristics of high refractive index, high dispersion, and high light transmittance, which is to be provided in the present application.

Similarly, Patent Document 4 is an optical glass containing bismuth oxide as a main component. Although an example in which the refractive index _nd is 2.0 or more and the Abbe number ν _d is 19 or less is proposed, λ ₅ Is 429 nm, and an optical glass that balances the three characteristics of high refractive index, high dispersion, and high light transmittance, to be provided in the present application, has not been proposed.

  In addition, high refractive index, high dispersion optical glass is often solarized (light transmittance is reduced) by ultraviolet irradiation. There are various causes of solarization, but various defects induced by light absorption form a level in the vicinity of the band gap and can be roughly explained by forming a new absorption band in the vicinity of the absorption edge. Since an optical glass having a high refractive index and high dispersion has an absorption edge in the vicinity of a short wavelength in the visible region, this ultraviolet-induced absorption band affects the visible region, resulting in a decrease in light transmittance. When strong solarization occurs, the wavelength dependence of the transmission spectrum changes before and after the ultraviolet irradiation. For example, when applied to a lens, the color of the image changes and there is a problem in color reproducibility.

  As can be seen from the above, high optical transparency, high refractive index, and high dispersion are in a trade-off relationship, and therefore, no optical glass that has achieved these three characteristics at a practical level has been proposed. . Furthermore, any optical glass having solarization resistance to ultraviolet rays (hereinafter also simply referred to as solarization resistance) while satisfying these three characteristics can be applied to practical optical equipment having environmental durability.

JP 2005-206433 A JP 2002-201039 A JP 2006-327926 A Japanese Patent Laid-Open No. 2007-070156 WO2009 / 107612 A1

The present invention has excellent light transmission characteristics, a refractive index _nd of 2.0 or more, an Abbe number ν _d of 19 or less, an optical constant having a high dispersion and a high refractive index, and a solarization resistance. Provide glass. According to the present invention, it is possible to provide an optical glass capable of producing an optical element that is easy to mold, has high dimensional accuracy, and has high durability against ultraviolet irradiation.

In the present invention, Bi ₂ O ₃ , B ₂ has a refractive index n _d of 2.0 or more, an Abbe number ν _d of 19 or less, and a wavelength λ ₅ showing an internal transmittance of 5% (10 mm) of 410 nm or less. An optical glass containing O ₃ , TeO ₂ , and P ₂ O ₅ as essential components is provided.

The present invention is preferably mol% based on oxide, Bi ₂ O ₃ : 35 to 55, B ₂ O ₃ : 24 to 35, TeO ₂ : 5 to 20, P ₂ O ₅ : 8 to 12, Nb Provided is an optical glass containing ₂ O ₅ + Ta ₂ O ₅ : 0.1-4, TiO ₂ : 0-10, ZnO: 0-7.

The optical glass of the present invention (hereinafter, referred to as the present glass) is, _Bi 2 _{O 3} having an effect on the high refractive index as an essential _component, and to include TeO _2, the refractive index _{n d} of 2.0 or more, an Abbe's number As v _d is 19 or less, a high refractive index and a low Abbe number can be realized. The present _glass, Bi ₂ O 3, in addition to TeO _2, to include B 2 _{O 3,} excellent resistance to devitrification, yet chemically, thermally stable optical glass is obtained. Furthermore, since P ₂ O ₅ is contained as an essential component, it is excellent in high light transmittance.

In the present glass, in order to improve the light transmission characteristics, it is particularly preferable to adjust the molar ratio to P ₂ O ₅ / (Bi ₂ O ₃ + B ₂ O ₃ + TeO ₂ ) = 0.08 to 0.15. High refractive index, high dispersion (low Abbe number) and high light transmission characteristics, which were difficult to achieve with optical glass, can be achieved in a balanced manner. Further, by satisfying P ₂ O ₅ / (Bi ₂ O ₃ + B ₂ O ₃ + TeO ₂ ) = 0.08 to 0.15 in a molar ratio and limiting the amount of TeO ₂ to 6 mol% or less, particularly solarization Optical glass having high refractive index, high dispersion, and high light transmittance with improved resistance can be obtained.

  By using this glass, a lens having excellent light transmission characteristics, high performance, easy aberration correction, and high color reproducibility can be produced. In addition, the degree of freedom in lens design is greatly improved, such as being able to be used for a large diameter and thick lens, or by combining a plurality of lenses.

The present invention has a refractive index n _d of 2.0 or more, an Abbe number [nu _d 19 below, excellent light transmission characteristics, and, for the purpose of providing a pliable optical glass, based on the a result of various studies is there. As a result of the study, the present glass is characterized by containing Bi ₂ O ₃ , B ₂ O ₃ , TeO ₂ and P ₂ O ₅ as essential components.

In addition to the above essential components, the present glass may contain at least one of Nb ₂ O _{5 and} Ta ₂ O ₅ from the viewpoint of a high refractive index. _Similarly, it may contain the components of TiO 2, ZnO.

On the other hand, in the present _{glass, SiO 2, Li 2 O,} Na 2 O, K 2 O, it is preferred not to substantially contain the components of Cs ₂ O. Although SiO ₂ contributes to glass stability, it is a component that decreases press formability, and each component of Li ₂ O, Na ₂ O, K ₂ O, and Cs ₂ O, which are alkaline components, has a decreased optical characteristic. It is an ingredient to do. In the present specification, “substantially does not contain” means that the content is not more than the impurity level. Specifically, if it is 0.1 mol% or less, “substantially does not contain”. It can be considered. In the present specification, hereinafter, mol% is abbreviated as% unless otherwise specified.

  The reason why each component range of the glass is set is as follows. The chemical composition is based on oxide.

In the present glass, Bi ₂ O ₃ is a glass forming component and an essential component. Furthermore, there is an effect of increasing the refractive index of the glass and softening the glass. If the content is too small, the above effects may be insufficient, so the Bi ₂ O ₃ content of the present glass is 32% or more. The Bi ₂ O ₃ content is preferably 36% or more, and the Bi ₂ O ₃ content is more preferably 40% or more. On the other hand, if the Bi ₂ O ₃ content is increased, the light transmission characteristics in the visible region are deteriorated and the glass becomes unstable. Therefore, the Bi ₂ O ₃ content of the present glass is 55% or less. The Bi ₂ O ₃ content is preferably 53% or less, and more preferably 50% or less.

In the present glass, B ₂ O ₃ is an essential component and a main component that forms the glass. When the content is too small because the glass may become unstable, B ₂ O ₃ content of the glass is more than 24%. The B ₂ O ₃ content is preferably 26% or more, and the B ₂ O ₃ content is more preferably 28% or more. On the other _hand, since the content of B 2 _{O 3} is too large, the refractive index is lowered, in the present _glass, the content of B 2 _{O 3} is 35% or less. The B ₂ O ₃ content is preferably 34% or less. The B ₂ O ₃ content is more preferably 32% or less, and the B ₂ O ₃ content is particularly preferably 30% or less.

In the present glass, TeO ₂ is a glass forming component and an essential component. Further, it has the effect of increasing the light transmission characteristics and increasing the refractive index of the glass. On the other hand, TeO ₂ is also a component that causes light absorption by ultraviolet irradiation. If the content is too small, the TeO ₂ content of the present glass is 5% or more from the viewpoint of the balance between the above effect being insufficient and the resistance to solarization. The TeO ₂ content is preferably 5.3% or more, and the TeO ₂ content is more preferably 5.5% or more. However, when the resistance to solarization is not so important, the TeO ₂ content of the present glass is preferably 10% or more in order to make the effect of addition sufficient. The TeO ₂ content is more preferably 10.5% or more, and the TeO ₂ content is particularly preferably 11% or more.

On the other hand, if the TeO ₂ content increases, the glass may become unstable, so the TeO ₂ content is 20% or less. The TeO ₂ content is preferably 19.5% or less, and the TeO ₂ content is more preferably 19% or less. When importance is attached to solarization resistance in the present glass, it is necessary to limit the TeO ₂ content. In that case, the TeO ₂ content is preferably 15% or less, and more preferably 10% or less. In order to suppress the maximum value of the decrease in transmittance due to solarization to 4% or less, the content of TeO ₂ is particularly preferably 6% or less.

In the present glass, P ₂ O ₅ is a glass forming component and an essential component. Furthermore, since it has a very great effect on improving the light transmission characteristics, it is important to contain it appropriately. In order to make the effect remarkable, the P ₂ O ₅ content is 8% or more. The P ₂ O ₅ content is preferably 8.5% or more, and the P ₂ O ₅ content is more preferably 8.7% or more. On the other hand, if the P ₂ O ₅ content is increased, the refractive index is lowered and the glass becomes unstable. Therefore, in the present glass, the P ₂ O ₅ content is 12% or less. When it is desired lowering of improvement and the Abbe number of the refractive index is _preferably the P 2 _{O 5} content is 11% or _less, further preferably P 2 _{O 5} content is less 10.5%.

Furthermore, in the present glass, Bi ₂ O ₃ , which is an essential component, in order to achieve a good balance between high refractive index, high dispersion (low Abbe number) and high light transmittance while maintaining good glass stability, It was found that the content of the four components B ₂ O ₃ , TeO ₂ and P ₂ O ₅ should be kept in a certain relationship. That is, in mol _ratio, it is preferable that the _{P 2 O 5 / (Bi 2} O 3 + B 2 O 3 + TeO 2) = 0.08~0.15. Hereinafter, in this specification, the molar ratio of P ₂ O ₅ / (Bi ₂ O ₃ + TeO ₂ + B ₂ O ₃ ) is referred to as a phosphorus component ratio.

A phosphorus component ratio of 0.085 or more is more preferable in terms of a balance between high refractive index, high dispersion (low Abbe number) and high light transmittance, and a phosphorus component ratio of 0.09 or more is particularly preferable. On the other hand, the phosphorus component ratio is more preferably 0.14 or less for the same reason, and the phosphorus component ratio is particularly preferably 0.135 or less. Further, by satisfying P ₂ O ₅ / (Bi ₂ O ₃ + B ₂ O ₃ + TeO ₂ ) = 0.08 to 0.15 in a molar ratio and limiting the amount of TeO ₂ to 6 mol% or less, particularly solarization It is preferable because an optical glass having high refractive index, high dispersion, and high light transmittance with improved resistance can be obtained.

In this glass, Nb ₂ O ₅ and Ta ₂ O ₅ are effective components for increasing the refractive index while maintaining good light transmission characteristics, and are not essential components, but Nb ₂ O ₅ or Ta ₂ It is preferable that at least one of O ₅ is an essential component. When Nb ₂ O ₅ and Ta ₂ O ₅ are contained, if they are contained in large amounts, the stability of the present glass is significantly impaired. Therefore, it is preferable that the total (Nb ₂ O ₅ + Ta ₂ O ₅ is hereinafter referred to as Nb · Ta total amount) is 4% or less, and the Nb · Ta total amount of the present glass is 3% or less. Particularly preferred. On the other hand, when it contains, it is preferable in the Nb * Ta total amount of this glass being 0.1% or more.

In the present glass, TiO ₂ is a component effective for a high refractive index and a low Abbe number, but is not an essential component. On the other hand, when the content of TiO ₂ increases, the light transmission characteristics deteriorate. Therefore, the TiO ₂ content is preferably 10% or less, more preferably 7% or less, and particularly preferably TiO ₂ content is 4% or less. When contained, the TiO ₂ preferably 0.1% or more.

  In the present glass, ZnO is a component having an effect of stably forming the glass, but is not an essential component. When it contains ZnO, it is preferable to contain 0.5% or more, and it is further more preferable in ZnO content being 1% or more. On the other hand, since the refractive index decreases as the ZnO content increases, the ZnO content is preferably 7% or less, and more preferably 6% or less.

Although SiO ₂ is widely used as a glass forming component, it is desirable that the present glass does not substantially contain the glass because if it is contained, the solubility of the glass is remarkably deteriorated and the industrial productivity is lowered. An alkali component Li 2 _O, when containing Na 2 O, _K 2 _O, in addition to lower the light transmission characteristic and refractive index, thermal expansion coefficient of the optical glass is increased, it is difficult to give the dimensional accuracy during molding Therefore, it is preferable that the present glass does not substantially contain. In the present glass, it is more preferable that the glass does not substantially contain SiO ₂ , Li ₂ O, Na ₂ O, and K ₂ O in order to achieve a good balance between the three characteristics of high refractive index, high dispersion, and instep transmittance. .

In addition, alkaline earth metal oxides MgO, CaO, and SrO are components that contribute to glass stabilization, but are components that reduce light transmission characteristics, and further increase the thermal expansion coefficient of optical glass. In the present glass, it is preferable that the glass is not substantially contained. In this glass, in order to realize the three properties of high refractive index, high dispersion, and instep transmittance in a balanced manner, SiO ₂ , Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, SrO, and BaO are substantially used. It is particularly preferred not to be contained in

In the present glass, each component of GeO ₂ , Ga ₂ O ₃ , or CeO ₂ is not an essential component, but can be contained to adjust optical characteristics. On the other hand, each of these components is relatively expensive as a raw material, which increases the raw material cost of the optical glass, so it is preferable to minimize it as much as possible. In the present glass, it is preferable for the above reason that the three components of GeO ₂ , Ga ₂ O ₃ and CeO ₂ are not substantially contained.

In the present glass, WO ₃ , ZrO ₂ , Gd ₂ O ₃ , La ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ are not essential components, but any one or more are arbitrarily selected in order to adjust optical properties Can be added as a component. Since the effect of adjusting optical properties is hardly obtained when the content is small, the content is preferably singly and the content is preferably 0.1% or more, and the content is 1% or more. More preferably, the content is particularly preferably 2% or more.

  On the other hand, since each of the components hardly contributes to the improvement of the light transmission characteristics, it is preferable to suppress the content as much as possible when the light transmission characteristics are important. Accordingly, it is preferably 10% or less each independently, more preferably 5% or less, and particularly preferably 4% or less.

Further, in this glass, PbO, F, that contains substantially no As ₂ O ₃ is preferable from the influence of the aspect and environmental surface of the forming temperature. In the present glass, Sb ₂ O ₃ is not an essential component, but can be added as a clarifier during glass melting. The content is preferably 1% or less, more preferably 0.5% or less, and particularly preferably 0.1% or less. In the present glass, the lower limit when adding is preferably 0.01% or more, more preferably 0.05% or more, and particularly preferably 0.1% or more.

Regarding the Abbe number ν _d , which is one of the optical constants, the present glass needs to have a low Abbe number and high dispersion, and the Abbe number ν _d of the present glass is 19 or less. The Abbe number ν _d of the present glass is preferably 18 or less, and more preferably, the Abbe number ν _d is 17 or less.

A high refractive index that is one of the optical constants, a refractive index _nd of 2.0 or more, is required. Preferably the refractive index _{n d} of the glass is 2.05 or more, more preferably a refractive index _{n d} is 2.1 or more.

As light transmission characteristics, since it is necessary to reduce yellow coloring, the wavelength λ ₅ indicating the internal transmittance of 5% of the present glass is 410 nm or less. Preferably the wavelength lambda ₅ showing the internal transmittance of 5% of the glass is less than 408 nm, more preferably the wavelength lambda ₅ showing the internal transmittance 5% and not more than 406nm of the glass, internal transmittance of this glass 5 It is more preferable that the wavelength λ ₅ indicating% is 403 nm or less.

Furthermore, in order to improve the transmittance in the entire visible range, the wavelength λ ₇₀ indicating the internal transmittance of the present glass is preferably 480 nm or less, and the wavelength λ ₇₀ indicating the internal transmittance of the present glass is 70%. It is more preferable that it is 470 nm or less, and it is especially preferable that wavelength (lambda) ₇₀ which shows the internal transmittance | permeability 70% of this glass is 460 nm or less.

For the present glass, the relationship between the refractive index _nd and the wavelength λ ₅ indicating the internal transmittance of 5% is expressed by Equation 1.
Refractive index n _d ≧ 0.0061 × λ ₅ −0.42 (Formula 1).
Similarly, when the relationship between the Abbe number ν _d and the wavelength λ ₅ indicating the internal transmittance of 5% is expressed, Equation 2 is obtained.
Abbe number ν _d ≦ −0.1 × λ ₅ +58.8 (Formula 2).
Therefore, in other words, the present glass satisfies the above formulas 1 and 2 at the same time, and well balances the three characteristics of high refractive index, high dispersion and high light transmittance.

  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. Put into a crucible usually used in optical glass such as crucible, gold crucible, quartz crucible, alumina crucible, etc., cast into a mold preheated from 300 to 450 ° C after melting, clarification and stirring at about 800-1200 ° C for 2-10 hours. It can be manufactured by slow cooling after squeezing.

  Further, the method of molding the present glass into an optical element is not particularly limited, but press molding is preferable because the characteristics of the material can be utilized.

Examples of the present invention will be described below. Examples 1 to 9 and Examples 11 to 20 are examples of the present invention, and Example 10 is a comparative example. Example 10 is the same as Example 18 described in Patent Document 5. The “phosphorus component ratio” in the table is a molar ratio of P ₂ O ₅ / (Bi ₂ O ₃ + TeO ₂ + B ₂ O ₃ ) as described above.

[Chemical composition and sample preparation]
The raw materials were weighed so as to have chemical compositions (mol%) shown in Tables 1 to 4. The raw materials for each glass are BPO ₄ in the case of P ₂ O ₅ , H ₃ BO ₃ or BPO ₄ in the case of B ₂ O ₃ , Al ₂ O ₃ , Bi ₂ O ₃ , TiO ₂ , TeO ₂ , ZnO. In the case of Nb ₂ O ₅ and Ta ₂ O ₅ , oxides were used. Weighed raw materials, put into a gold crucible with an internal volume of about 300 cc, melted, clarified and stirred at about 800-1000 ° C. for 1-3 hours, preheated to about 300-450 ° C. After casting into a rectangular mold, it was gradually cooled at about 1 ° C./min to prepare a sample. For reference, chemical compositions (mass%) are shown in Tables 5 to 8.

[Evaluation methods]
Refractive index n _d; a refractive index with respect to the helium d line, refractometer (Kalnew Optical Industry Co., Ltd., trade name: KPR-2) was measured in. The refractive index value was measured to the fifth decimal place and rounded to the fifth decimal place and listed as the fourth decimal place.
・ Abbe number ν _d ; calculated by ν _d = (n _d −1) / (n _F −n _C ) to the fifth decimal place, rounded to the first decimal place and listed as 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.
-Regarding the glass solubility, etc., as a result of visual observation at the time of the above sample preparation, it was confirmed that all the examples had no problem in solubility, and the obtained glass sample had no bubbles or striae. .
In Examples 10 to 20, the transmittance reduction characteristics due to solarization with respect to ultraviolet rays were evaluated as follows.
Measurement method of transmittance reduction by solarization: Both surfaces of a sample of 20 mm long × 20 mm wide × 2 mm thick were mirror-polished, and the light transmittance wavelength dependency was measured before and after UV irradiation. In the ultraviolet irradiation, a metal halide lamp is used as a light source, and the optical power irradiated to the sample is 80 mW / cm in a wavelength range of 254 to 436 nm. The wavelength at which the transmittance decrease is maximum is shown in the table as the maximum transmittance decrease wavelength. Similarly, the maximum transmittance reduction amount in that case is also shown.

  This glass is a high refractive index, highly dispersible optical glass with extremely excellent light transmission characteristics, and realizes the three characteristics of high refractive index, high dispersibility, and high light transmission properties in a well-balanced manner, and is precision press-molded. Useful as an optical glass. Furthermore, it can have solarization resistance to ultraviolet rays by adjusting the composition. Moreover, it is useful also for optical elements other than an optical lens, such as a dispersive element and a diffractive element subjected to fine processing.

Claims (7)

Bi ₂ O ₃ having a refractive index n _d of 2.0 or more, an Abbe number ν _d of 19 or less, and a wavelength λ ₅ showing an internal transmittance of 5% (10 mm) of 410 nm or less. _{, B 2 O 3, TeO 2} , optical glass and P 2 _{O 5} as an essential component. The optical glass according to claim 1, wherein at least one of Nb ₂ O _{5 and} Ta ₂ O ₅ is an essential component. In mol% of oxide basis,
Bi ₂ O _3: 32~55,
B ₂ O _3: 24~35,
TeO _2: 5~20,
P ₂ O _5: 8~12,
_{Nb 2 O 5 + Ta 2 O} 5: 0.1~4,
TiO _2: 0~10,
ZnO: 0 to 7,
The optical glass of Claim 2 containing. _{SiO 2, Li 2 O, Na} 2 O, K 2 O, the optical glass according to claim 1 which is substantially free of Cs ₂ O. in mol _{ratio, P 2 O 5 / (Bi} 2 O 3 + B 2 O 3 + TeO 2) = 0.08~0.15 optical glass according to any one of claims 1 to 4. The optical glass according to any one of claims 1 to 5, wherein a wavelength λ ₇₀ showing an internal transmittance of 70% (10 mm) is 470 nm or less.   The optical glass according to any one of claims 1 to 6, wherein the maximum value of transmittance decrease before and after ultraviolet irradiation is 4% or less.