Chalcogenide glass and optical elements

Abstract

To provide chalcogenide glass and optical elements with excellent thermal stability. [Solution] A chalcogenide glass having a Ga content of 2.0 to 40.0 mass%, an Sb content of 20.0 to 75.0 mass%, an S content of 15.0 to 40.0 mass%, a total content of Na, K, Rb, and Cs R[Na+K+Rb+Cs] of 0.05 mass or more, and a total content of Cl, Br, and I X[Cl+Br+I] of 0.01 mass or less.

Description

Technical Field

[0001] The present invention relates to chalcogenide glass and optical elements.

Background Art

[0002] In recent years, technologies and products using infrared rays have been attracting attention. For example, the demand for security devices and authentication devices using infrared cameras, infrared sensors, etc. has been increasing, and far-infrared imaging is also expected in in-vehicle night vision. Optical elements that transmit infrared rays are used in infrared cameras, infrared sensors, etc. Such optical elements are required to have excellent infrared transmittance and, further, excellent productivity that can meet the recent expanding demand.

[0003] Conventionally, crystalline materials such as germanium, silicon, zinc sulfide, and selenium sulfide have been used as materials for optical elements that transmit infrared rays. However, these crystalline materials are inferior in workability and are difficult to process into complex shapes such as aspherical lenses. On the other hand, chalcogenide glass containing a chalcogen element as a main component has been proposed as an infrared transmitting material with excellent workability.

[0004] As chalcogenide glass, Patent Document 1 discloses infrared transmitting glass suitable for mold molding.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Reference 1 (Journal of Optoelectronics and Advanced Materials Vol. 9, No. 12, December 2007, pp. 3751-3755) discloses that glass containing cesium halides such as CsCl has poor water resistance. From this, it can be inferred that among the glasses disclosed in Patent Document 1, glass containing both Cs (cesium) and halogens has poor water resistance. Furthermore, it is feared that such halogen-containing glass may corrode molten glass containers made of quartz glass or other materials during manufacturing, or that molten glass or volatile substances leaking out may corrode production equipment, thus resulting in poor productivity.

[0007] As a result of diligent research by the inventors, it was found that the thermal stability of chalcogenide glass can be improved by introducing alkali metals without adding halogens, which may impair water resistance or productivity. Patent Document 1 discloses glass containing both halogens and alkali metals, but does not propose glass in which the halogen content is sufficiently reduced and alkali metals are included, and the thermal stability of such glass has not been verified. If glass has poor thermal stability, problems arise such as difficulty in molding molten glass and difficulty in press molding such as reheat press molding and mold molding.

[0008] Therefore, the present invention aims to provide chalcogenide glass and optical elements with excellent thermal stability. [Means for solving the problem]

[0009] The gist of this invention is as follows: (1) The Ga content is 2.0 to 40.0% by mass, The Sb content is 20.0 to 75.0% by mass. The sulfur content is 15.0 to 40.0% by mass. The total content of Na, K, Rb, and Cs, R[Na+K+Rb+Cs], is 0.05% by mass or more. A chalcogenide glass in which the total content of Cl, Br, and I, X[Cl+Br+I], is 0.01% by mass or less.

[0010] (2) The Ga content is 0.5 to 30.0% by mass, The Ge content is 5.0% by mass or less. The sulfur content is 15.0 to 40.0% by mass. The total content of Na, K, Rb, and Cs, R[Na+K+Rb+Cs], is 0.05% by mass or more. A chalcogenide glass in which the total content of Cl, Br, and I, X[Cl+Br+I], is 0.01% by mass or less.

[0011] (3) An optical element made of the chalcogenide glass described in (1) or (2) above. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide chalcogenide glass and optical elements with excellent thermal stability. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic representation of a differential scanning calorimetry curve (DSC curve). [Modes for carrying out the invention]

[0014] In this specification, the content of glass components can be identified and quantified by known methods, such as ICP emission spectrometry (ICP-AES), atomic absorption spectrometry (AAS), ICP mass spectrometry (ICP-MS), ion chromatography, and non-dispersive infrared absorption spectrometry (ND-IR).

[0015] In this specification, the glass composition is expressed in mass%. Mass% is the mass percentage when the total content of all elements contained in the glass is set to 100%. The content of the glass components and the total content are based on mass percentage unless otherwise specified, and "%" means "mass%". Further, when the content of a constituent component is 0.00%, it means that this constituent component is not substantially contained, and it is allowed that the component is contained at an inevitable impurity level.

[0016] In this specification, when it is said that the glass has excellent thermal stability, it means that crystals are hardly deposited when forming the glass in a molten state, or that crystals are hardly deposited when the softened glass solidifies. Specifically, it means that the liquidus temperature LT is low, and the difference between the crystallization peak temperature Tc and the glass transition temperature Tg is large. When the liquidus temperature LT of the glass is low, the liquid-phase viscosity becomes high, and glass can be easily obtained without depositing crystals. Further, when the difference between the crystallization peak temperature Tc and the glass transition temperature Tg is large, the temperature range in which press molding can be performed without crystal deposition becomes wide. Further, water resistance means that the transmittance of the glass hardly decreases even when the glass is exposed to water.

[0017] Hereinafter, the chalcogenide glass according to the present invention will be described by dividing it into a first embodiment and a second embodiment.

[0018] First Embodiment The chalcogenide glass according to the first embodiment is the content of Ga is 2.0 to 40.0%, the content of Sb is 20.0 to 75.0%, the content of S is 15.0 to 40.0%, the total content R[Na+K+Rb+Cs] of Na, K, Rb, and Cs is 0.05% or more, the total content X[Cl+Br+I] of Cl, Br, and I is 0.01% or less.

[0019] In the chalcogenide glass according to the first embodiment, the content of Ga is 2.0 to 40.0%. The lower limit of the content of Ga is preferably 2.2%, more preferably 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, 4.2%, 4.4%, 4.6%, 4.8%, 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9% in this order. The upper limit of the content of Ga is preferably 38.0%, more preferably 36.0%, 34.0%, 32.0%, 30.0%, 29.0%, 28.0%, 27.0%, 26.0%, 25.0%, 24.0%, 23.0%, 22.0%, 21.0%, 20.0%, 19.0%, 18.0% in this order.

[0020] Ga is a network-forming component of the glass and is also an expensive raw material. By setting the content of Ga within the above range, the thermal stability of the glass can be improved and an increase in raw material costs can be suppressed. On the other hand, if the content of Ga is too low, the thermal stability of the glass may decrease and the glass may not be able to be formed. If the content of Ga is too high, the absorption edge on the long wavelength side may shift to the short wavelength side, the wavelength range of the light transmitted through the glass may become narrow, the liquid-phase viscosity may decrease, and the raw material costs may soar.

[0021] In the chalcogenide glass according to the first embodiment, the content of Sb is 20.0 to 75.0%. The lower limit of the content of Sb is preferably 21.0%, more preferably 22.0%, 23.0%, 24.0%, 25.0%, 26.0%, 27.0%, 28.0%, 29.0%, 30.0%, 31.0%, 32.0%, 33.0%, 34.0%, 35.0%, 36.0%, 37.0%, 38.0%, 39.0%, 40.0% in this order. The upper limit of the content of Sb is preferably 74.0%, more preferably 73.0%, 72.0%, 71.0%, 70.0%, 69.0%, 68.0%, 67.0%, 66.0%, 65.0%, 64.0%, 63.0%, 62.0%, 61.0% in this order.

[0022] Sb is a network-forming component in glass. By keeping the Sb content within the above range, the thermal stability of the glass can be improved. On the other hand, if the Sb content is too low, the thermal stability of the glass may decrease, and it may also become impossible to mold the glass.

[0023] In the chalcogenide glass according to the first embodiment, the sulfur content is 15.0 to 40.0%. The lower limit of the sulfur content is preferably 16.0%, and more preferably in the order of 17.0%, 18.0%, 19.0%, 20.0%, 21.0%, 22.0%, 23.0%, 24.0%, and 25.0%. The upper limit of the sulfur content is preferably 39.0%, and more preferably in the order of 38.0%, 37.0%, 36.0%, 35.0%, 34.0%, 33.0%, 32.0%, and 31.0%.

[0024] By setting the sulfur content within the above range, the thermal stability of the glass can be improved. On the other hand, if the sulfur content is too low, the absorption edge on the short-wavelength side may shift to the long-wavelength side, and the absorption edge on the long-wavelength side may shift to the short-wavelength side, potentially narrowing the wavelength range of light transmitted through the glass. This could reduce the thermal stability of the glass and make it impossible to mold the glass.

[0025] In the chalcogenide glass according to the first embodiment, the total content R[Na+K+Rb+Cs] of Na, K, Rb, and Cs is 0.05% or more. The lower limit of the total content R is preferably 0.06%, and further preferably 0.08%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0. The percentages are most preferably 95%, 1.00%, 1.10%, 1.20%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, 1.80%, 1.90%, 2.00%, 2.10%, 2.20%, 2.30%, 2.40%, 2.50%, 2.60%, 2.70%, 2.80%, 2.90%, and 3.00%. Furthermore, the upper limit of the total content R is preferably 35.0%, and more preferably in the order of 34.0%, 33.0%, 32.0%, 31.0%, 30.0%, 29.0%, 28.0%, 27.0%, 26.0%, 25.0%, 24.0%, 23.0%, 22.0%, 21.0%, and 20.0%.

[0026] Alkali metals such as Na, K, Rb, and Cs are components that lower the liquidus temperature LT. By setting the total content R within the above range, the liquidus temperature LT is lowered and the liquidus viscosity increases, improving moldability. Furthermore, the thermal stability of the glass can be improved, and the absorption edge on the shorter wavelength side can be shifted to even shorter wavelengths, widening the wavelength range of light transmitted through the glass. If the total content R is too high, the thermal stability may decrease, and it may become impossible to obtain glass. Conversely, if the total content R is too low, the liquidus temperature LT may not decrease sufficiently, the increase in liquidus viscosity may be insufficient, and the desired thermal stability and moldability may not be achieved.

[0027] In the chalcogenide glass according to the first embodiment, the total content X[Cl+Br+I] of Cl, Br, and I is 0.01% or less. The upper limit of the total content X is preferably 0.009%, and more preferably in the order of 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002%, and 0.001%. It is preferable that Cl, Br, and I are substantially absent.

[0028] Halogen elements such as Cl, Br, and I shift the absorption edge on the short-wavelength side to even shorter wavelengths, but they worsen the water resistance of glass. Furthermore, they can corrode molten glass containers, such as those made of quartz glass, during manufacturing, and leak molten glass or volatile substances can corrode production equipment, potentially reducing productivity. By keeping the total content X within the above range, the deterioration of the glass's water resistance can be suppressed, and the desired productivity can be achieved.

[0029] In the chalcogenide glass according to the first embodiment, the upper limit of the Ge content is preferably 2.0%, and more preferably in the order of 1.8%, 1.6%, 1.4%, 1.2%, 1.0%, 0.8%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, and 0.1%. The lower limit of the Ge content is preferably 0.0%.

[0030] Ge is a network-forming component of glass. From the viewpoint of improving the thermal stability of the glass, it is preferable to keep the Ge content within the above range. On the other hand, if the Ge content is too high, the absorption edge on the long-wavelength side may shift to the short-wavelength side, narrowing the wavelength range of light transmitted through the glass, and since Ge is very expensive, raw material costs may skyrocket.

[0031] The following are non-limiting examples of the content and ratio of glass components other than those mentioned above in the chalcogenide glass according to the first embodiment.

[0032] In the chalcogenide glass according to the first embodiment, the lower limit of the Na content is preferably 0.00%, and more preferably in the order of 0.05%, 0.06%, 0.08%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, and 0.95%. Furthermore, the upper limit of the Na content is preferably 35.0%, and more preferably in the following order: 34.0%, 33.0%, 32.0%, 31.0%, 30.0%, 29.0%, 28.0%, 27.0%, 26.0%, 25.0%, 24.0%, 23.0%, 22.0%, 21.0%, 20.0%, 19.0%, 18.0%, 17.0%, 16.0%, 15.0%, 14.0%, 13.0%, 12.0%, 11.0%, 10.0%, 9.0%, 8.0%, 7.0%, 6.0%, 5.0%, 4.0%, and 3.0%.

[0033] Na is a component that lowers the liquidus temperature LT. From the viewpoint of lowering the liquidus temperature LT and increasing liquidus viscosity to improve moldability, and from the viewpoint of improving the thermal stability of the glass and further shifting the absorption edge on the short wavelength side to the shorter wavelength side, it is preferable to keep the Na content within the above range. If the Na content is too high, the thermal stability may decrease, and it may become impossible to obtain glass. If the Na content is too low, the liquidus temperature LT may not decrease sufficiently, the increase in liquidus viscosity may be insufficient, and the desired thermal stability and desired moldability may not be obtained.

[0034] In the chalcogenide glass according to the first embodiment, the lower limit of the K content is preferably 0.00%, and more preferably in the order of 0.05%, 0.06%, 0.08%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, and 0.95%. Furthermore, the upper limit of the K content is preferably 35.0%, and more preferably in the order of 34.0%, 33.0%, 32.0%, 31.0%, 30.0%, 29.0%, 28.0%, 27.0%, 26.0%, 25.0%, 24.0%, 23.0%, 22.0%, 21.0%, 20.0%, 19.0%, 18.0%, 17.0%, 16.0%, 15.0%, 14.0%, 13.0%, 12.0%, 11.0%, 10.0%, 9.0%, 8.0%, 7.0%, 6.0%, 5.0%, and 4.0%.

[0035] K is a component that lowers the liquidus temperature LT. From the viewpoint of lowering the liquidus temperature LT and increasing the liquidus viscosity to improve moldability, and from the viewpoint of improving the thermal stability of the glass and further shifting the absorption edge on the short wavelength side to the shorter wavelength side, it is preferable to keep the K content within the above range. If the K content is too high, the thermal stability may decrease, and it may become impossible to obtain glass. If the K content is too low, the liquidus temperature LT may not decrease sufficiently, the increase in liquidus viscosity may be insufficient, and the desired thermal stability and desired moldability may not be obtained.

[0036] In the chalcogenide glass according to the first embodiment, the lower limit of the Rb content is preferably 0.00%, and more preferably in the order of 0.05%, 0.06%, 0.08%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, and 0.95%. Furthermore, the upper limit of the Rb content is preferably 35.0%, and more preferably in the order of 34.0%, 33.0%, 32.0%, 31.0%, 30.0%, 29.0%, 28.0%, 27.0%, 26.0%, 25.0%, 24.0%, 23.0%, 22.0%, 21.0%, 20.0%, 19.0%, 18.0%, 17.0%, 16.0%, 15.0%, 14.0%, 13.0%, 12.0%, 11.0%, and 10.0%.

[0037] Rb is a component that lowers the liquidus temperature LT. From the viewpoint of lowering the liquidus temperature LT and increasing liquidus viscosity to improve moldability, and from the viewpoint of improving the thermal stability of the glass and further shifting the absorption edge on the short wavelength side to the short wavelength side, it is preferable to keep the Rb content within the above range. If the Rb content is too high, the thermal stability may decrease, and it may become impossible to obtain glass. If the Rb content is too low, the liquidus temperature LT may not decrease sufficiently, the increase in liquidus viscosity may be insufficient, and the desired thermal stability and desired moldability may not be obtained.

[0038] In the chalcogenide glass according to the first embodiment, the lower limit of the Cs content is preferably 0.00%, and more preferably in the order of 0.05%, 0.06%, 0.08%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.00%, 1.10%, 1.20%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, 1.80%, 1.90%, and 2.00%. Furthermore, the upper limit of the Cs content is preferably 35.0%, and more preferably in the order of 34.0%, 33.0%, 32.0%, 31.0%, 30.0%, 29.0%, 28.0%, 27.0%, 26.0%, 25.0%, 24.0%, 23.0%, 22.0%, 21.0%, 20.0%, 19.0%, and 18.0%.

[0039] Cs is a component that lowers the liquidus temperature LT. From the viewpoint of lowering the liquidus temperature LT and increasing liquidus viscosity to improve moldability, and from the viewpoint of improving the thermal stability of the glass and further shifting the absorption edge on the short wavelength side to the shorter wavelength side, it is preferable to keep the Cs content within the above range. If the Cs content is too high, the thermal stability may decrease, and it may become impossible to obtain glass. If the Cs content is too low, the liquidus temperature LT may not decrease sufficiently, the increase in liquidus viscosity may be insufficient, and the desired thermal stability and desired moldability may not be obtained.

[0040] In the chalcogenide glass according to the first embodiment, the upper limit of the content of In, Bi, and Te is preferably 30.0%, and more preferably in the order of 25.0%, 20.0%, 15.0%, 10.0%, and 5.0%. The lower limit of the content of In, Bi, and Te is preferably 0.0%. In, Bi, and Te are components that improve the thermal stability of the glass. From the viewpoint of improving the thermal stability of the glass, it is preferable to set the content of In, Bi, and Te within the above ranges.

[0041] In the chalcogenide glass according to the first embodiment, the upper limit of the Sn content is preferably 30.0%, and more preferably in the order of 28.0%, 26.0%, 24.0%, 22.0%, 20.0%, 18.0%, 16.0%, 14.0%, 12.0%, 10.0%, 9.0%, 8.0%, 7.0%, 6.0%, 5.0%, 4.0%, 3.0%, and 2.0%. The lower limit of the Sn content is preferably 0.0%. Sn is a component that improves the thermal stability of the glass. From the viewpoint of improving the thermal stability of the glass, it is preferable to set the Sn content within the above range.

[0042] In the chalcogenide glass according to the first embodiment, the upper limit of the Li content is preferably 5.0%, and more preferably in the order of 4.0%, 3.0%, 2.0%, 1.0%, and 0.5%. The lower limit of the Li content is preferably 0.0%. If the Li content is too high, the thermal stability will decrease, and it may not be possible to obtain glass. Therefore, it is preferable to keep the Li content within the above range.

[0043] In the chalcogenide glass according to the first embodiment, the upper limit of the Zn content is preferably 10.0%, and more preferably in the order of 9.0%, 8.0%, 7.0%, 6.0%, 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. The lower limit of the Zn content is preferably 0.0%. If the Zn content is too high, the thermal stability will decrease, and it may not be possible to obtain glass. Therefore, it is preferable to keep the Zn content within the above range.

[0044] In the chalcogenide glass according to the first embodiment, the upper limit of the La content is preferably 30.0%, and more preferably in the order of 25.0%, 20.0%, 15.0%, 10.0%, 9.0%, 8.0%, 7.0%, 6.0%, 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. The lower limit of the La content is preferably 0.0%. La has the function of shifting the absorption edge on the short wavelength side to an even shorter wavelength side and improving thermal stability. On the other hand, if the La content is too high, the thermal stability will decrease and it may not be possible to obtain glass. For this reason, it is preferable to keep the La content within the above range.

[0045] In the chalcogenide glass according to the first embodiment, the upper limit of the Cu content is preferably 10.0%, and more preferably in the order of 9.0%, 8.0%, 7.0%, 6.0%, 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. The lower limit of the Cu content is preferably 0.0%. If the Cu content is too high, the thermal stability will decrease, and it may not be possible to obtain glass. Therefore, it is preferable to keep the Cu content within the above range.

[0046] In the chalcogenide glass according to the first embodiment, the upper limit of the Ca content is preferably 10.0%, and more preferably in the order of 9.0%, 8.0%, 7.0%, 6.0%, 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. The lower limit of the Ca content is preferably 0.0%. If the Ca content is too high, the thermal stability will decrease, and it may not be possible to obtain glass. Therefore, it is preferable to keep the Ca content within the above range.

[0047] In the chalcogenide glass according to the first embodiment, the upper limit of the Sr content is preferably 15.0%, and more preferably in the order of 14.0%, 13.0%, 12.0%, 11.0%, 10.0%, 9.0%, 8.0%, 7.0%, 6.0%, 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. The lower limit of the Sr content is preferably 0.0%. If the Sr content is too high, the thermal stability will decrease, and it may not be possible to obtain glass. Therefore, it is preferable to keep the Sr content within the above range.

[0048] In the chalcogenide glass according to the first embodiment, the upper limit of the Ba content is preferably 15.0%, and more preferably in the order of 14.0%, 13.0%, 12.0%, 11.0%, 10.0%, 9.0%, 8.0%, 7.0%, 6.0%, 5.0%, 4.0%, 3.0%, 2.0%, and 1.0%. The lower limit of the Ba content is preferably 0.0%. If the Ba content is too high, the thermal stability will decrease, and it may not be possible to obtain glass. Therefore, it is preferable to keep the Ba content within the above range.

[0049] In the chalcogenide glass according to the first embodiment, the upper limit of the Ti content is preferably 1.0%, and more preferably in the order of 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, and 0.1%. The lower limit of the Ti content is preferably 0.0%. Ti has the function of bonding with oxygen in the glass and preventing oxygen from bonding with other elements. On the other hand, if the Ti content is too high, it may not be possible to obtain glass. Therefore, it is preferable to keep the Ti content within the above range.

[0050] In the chalcogenide glass according to the first embodiment, the upper limit of the Si content is preferably 1.0%, and more preferably in the order of 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, and 0.1%. The lower limit of the Si content is preferably 0.0%. Si has the function of bonding with oxygen in the glass and preventing oxygen from bonding with other elements. However, Si-O has a strong absorption peak in the wavelength range of light transmitted through the chalcogenide glass. Therefore, it is preferable to set the Si content within the above range.

[0051] In the chalcogenide glass according to the first embodiment, the upper limit of the C content is preferably 5.0%, and more preferably in the order of 4.5%, 4.0%, 3.5%, 3.0%, 2.5%, 2.0%, 1.5%, 1.0%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, and 0.1%. The lower limit of the C content is preferably 0.0%. C has the function of bonding with oxygen in the glass and preventing oxygen from bonding with other elements. However, if the C content is too high, the absorption edge on the short wavelength side may shift to the long wavelength side, or the absorption edge on the long wavelength side may shift to the short wavelength side, which may reduce the maximum transmittance. For this reason, it is preferable to keep the C content within the above range.

[0052] In the chalcogenide glass according to the first embodiment, the upper limit of the Al content is preferably 1.0%, and more preferably in the order of 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, and 0.1%. The lower limit of the Al content is preferably 0.0%. Al has the function of bonding with oxygen in the glass and preventing oxygen from bonding with other elements. On the other hand, if the Al content is too high, it may not be possible to obtain glass. Therefore, it is preferable to keep the Al content within the above range.

[0053] In the chalcogenide glass according to the first embodiment, the upper limit of the Ag content is preferably 20.0%, and more preferably 15.0%, 10.0%, and 5.0%, in that order. The lower limit of the Ag content is preferably 0.0%. From the viewpoint of suppressing increases in raw material costs, it is preferable to set the Ag content within the above range.

[0054] In the chalcogenide glass according to the first embodiment, the upper limit of the Gd content is preferably 20.0%, and more preferably 15.0%, 10.0%, and 5.0%, in that order. The lower limit of the Gd content is preferably 0.0%. From the viewpoint of suppressing increases in raw material costs, it is preferable to set the Gd content within the above range.

[0055] In the chalcogenide glass according to the first embodiment, the upper limit of the Y content is preferably 20.0%, and more preferably 15.0%, 10.0%, and 5.0%, in that order. The lower limit of the Y content is preferably 0.0%. If the Y content is too high, the thermal stability will decrease, and it may not be possible to obtain glass. Therefore, it is preferable to keep the Y content within the above range.

[0056] In the chalcogenide glass according to the first embodiment, the upper limit of the Cr content is preferably 20.0%, and more preferably 15.0%, 10.0%, and 5.0%, in that order. The lower limit of the Cr content is preferably 0.0%. If the Cr content is too high, the thermal stability will decrease, and it may become impossible to obtain glass. Therefore, it is preferable to keep the Cr content within the above range.

[0057] In the chalcogenide glass according to the first embodiment, the upper limit of the Mn content is preferably 20.0%, and more preferably 15.0%, 10.0%, and 5.0%, in that order. The lower limit of the Mn content is preferably 0.0%. If the Mn content is too high, the thermal stability will decrease, and it may not be possible to obtain glass. Therefore, it is preferable to keep the Mn content within the above range.

[0058] The chalcogenide glass according to the first embodiment is preferably composed mainly of the above-mentioned glass components, namely Ga, Sb, S, Na, K, Rb, Cs, Ge, In, Sn, Bi, Te, Zn, La, Cu, Ca, Sr, Ba, Ti, Al, Ag, Gd, Y, Cr, and Mn. The total content of the above-mentioned glass components is preferably 95% or more, more preferably 98% or more, even more preferably 99% or more, and particularly preferably 99.5% or more.

[0059] The chalcogenide glass according to the first embodiment is preferably composed of the above-mentioned glass components, but it may also contain other components as long as it does not hinder the effects of the present invention. Furthermore, the present invention does not exclude the inclusion of unavoidable impurities.

[0060] (Glass properties) <Light transparency> The chalcogenide glass according to the first embodiment exhibits excellent transmittance of light with wavelengths of 0.4 to 14 μm. Specifically, the transmission limit wavelength on the short wavelength side (maximum transmission wavelength in the visible range) is preferably 1.0 μm or less, more preferably 0.9 μm or less, and more preferably 0.8 μm or less. The transmission limit wavelength on the long wavelength side (maximum transmission wavelength in the infrared range) is preferably 11.0 μm or more, more preferably 11.5 μm or more, 12.0 μm or more, and more preferably 12.5 μm or more. The maximum transmission wavelength in the visible range is the wavelength at which the transmittance measured by ultraviolet-visible spectroscopy (UV-Vis) for a glass sample with a thickness of 1.5 mm becomes 50%. The maximum transmission wavelength in the infrared range is the wavelength at which the transmittance measured by Fourier transform infrared spectroscopy (FT-IR) for a glass sample with a thickness of 1.5 mm becomes 50%.

[0061] <Glass transition temperature Tg> In the chalcogenide glass according to the first embodiment, the lower limit of the glass transition temperature Tg is preferably 150°C, and more preferably in the order of 160°C, 170°C, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, and 220°C. The upper limit of the glass transition temperature Tg is preferably 500°C, and more preferably in the order of 490°C, 480°C, 470°C, 460°C, 450°C, 440°C, 430°C, 420°C, 410°C, 400°C, 390°C, 380°C, 370°C, 360°C, 350°C, 340°C, 330°C, 320°C, 310°C, 300°C, and 290°C.

[0062] <Crystallization peak temperature Tc> In the chalcogenide glass according to the first embodiment, the lower limit of the crystallization peak temperature Tc is preferably 300°C, and more preferably 310°C and 320°C in that order.

[0063] The chalcogenide glass according to the first embodiment includes glass that does not exhibit a crystallization peak temperature Tc because crystallization does not occur even when heated to 500°C. Such glass, in which no crystallization peak is observed even when heated to 500°C, has excellent thermal stability, excellent press formability, and excellent productivity.

[0064] <Thermal stability> In the chalcogenide glass according to the first embodiment, the thermal stability during press forming can be expressed as the difference between the crystallization peak temperature Tc and the glass transition temperature Tg [Tc-Tg]. In the press forming method, it is necessary to heat the glass to a temperature above the glass transition temperature Tg in order to soften it. On the other hand, it is preferable to soften the glass at a temperature as low as possible below the crystallization peak temperature Tc so that crystals do not precipitate in the glass. That is, the larger the difference between the crystallization peak temperature Tc and the glass transition temperature Tg, the wider the temperature range in which the glass can be softened without crystal precipitation. By increasing the difference between the crystallization peak temperature Tc and the glass transition temperature Tg, it is possible to widen the viscosity range of the glass that can be press-formed without generating crystals when the glass is softened. Therefore, it is easy to obtain suitable press forming conditions with excellent productivity. Regarding this, for example, Patent Document 2 (Patent No. 6808543) states that when [Tc-Tg] is high, crystallization can be sufficiently suppressed during mold forming, while when [Tc-Tg] is low, crystallization may proceed during mold forming. Furthermore, Patent Document 1 states that a large [Tc-Tg] means that the glass has high thermal stability and good moldability. In other words, these documents also state that the larger the [Tc-Tg], the better the thermal stability.

[0065] In the chalcogenide glass according to the first embodiment, the difference between the crystallization peak temperature Tc and the glass transition temperature Tg [Tc-Tg] is preferably 100°C or higher, and more preferably in the order of 102°C or higher, 104°C or higher, 106°C or higher, 108°C or higher, 110°C or higher, 112°C or higher, 114°C or higher, 116°C or higher, 118°C or higher, 120°C or higher, 122°C or higher, 124°C or higher, 126°C or higher, and 128°C or higher. From the viewpoint of stably press-forming the glass, it is preferable to set the difference between the crystallization peak temperature Tc and the glass transition temperature Tg [Tc-Tg] within the above range.

[0066] As described above, the chalcogenide glass according to the first embodiment includes glass in which no crystal precipitation is observed even when heated to 500°C, that is, glass in which the crystallization peak temperature Tc cannot be measured even when heated to 500°C. Such glass has a wide temperature range in which it can be stably press-molded without crystal precipitation, and can be said to have excellent thermal stability.

[0067] <Liquidus temperature LT> In the chalcogenide glass according to the first embodiment, the upper limit of the liquidus temperature LT is preferably 700°C, and more preferably in the order of 690°C, 680°C, 670°C, 660°C, 650°C, 640°C, 630°C, 620°C, 610°C, 600°C, 590°C, 580°C, 570°C, 560°C, and 550°C. By setting the liquidus temperature LT within the above range, a glass with excellent thermal stability can be obtained. Furthermore, by setting the liquidus temperature LT of the glass within the above range, the liquidus viscosity is increased, and glass can be easily obtained without precipitation of crystals from the melt.

[0068] In the present invention and this specification, "liquid phase temperature LT" is determined by the following method. Using a differential scanning calorimeter, when a glass sample is heated to 500-600°C at a heating rate of 10°C / min in a nitrogen atmosphere while flowing nitrogen at a flow rate of 50 mL / min, the liquidus temperature LT is defined as the endpoint of the endothermic peak that occurs when crystals in the glass formed during the heating process melt in a temperature range higher than the glass transition temperature Tg and crystallization peak temperature Tc. Figure 1 is a schematic diagram of the differential scanning calorimetry curve (DSC curve). The horizontal axis represents temperature, with higher temperatures to the right and lower temperatures to the left. The vertical axis corresponds to the exothermic and endothermic processes of the sample, with exothermic processes occurring above the baseline (dotted line) and endothermic processes occurring below. The exothermic peak corresponds to the crystal precipitation during the heating process, and the endothermic peak corresponds to the melting of the precipitated crystals. The liquidus temperature LT is the temperature at which all the crystals melt and become liquefied. The liquidus temperature LT is determined as the temperature at the intersection of the tangent line on the high-temperature side of the endothermic peak and the baseline.

[0069] If the liquidus temperature LT is outside the measurement range of the differential scanning calorimeter, the glass can be vacuum-sealed in a quartz ampoule, heated to a predetermined temperature in an electric furnace and held for 2 hours, then removed and rapidly cooled. The resulting sample can then be observed under a microscope to determine the lowest temperature at which crystals do not precipitate as the liquidus temperature LT.

[0070] (Glass manufacturing) The method for producing chalcogenide glass according to the first embodiment is not particularly limited, but for example, it can be produced by vacuum-sealing a predetermined amount of raw materials in a quartz ampoule so as to obtain the desired glass composition, and then vitrifying the contents by heat treatment. Alternatively, it can be produced by filling a crucible made of, for example, quartz, carbon, or alumina with a predetermined amount of raw materials so as to obtain the desired glass composition, and then heating and melting it in an inert gas and reducing gas atmosphere containing sulfur gas. When vitrifying, it is preferable to heat-treat at a heating temperature of 500 to 1000°C, and more preferably at a heating temperature of 700 to 950°C. The heat treatment temperature and time should be such that the contents are sufficiently vitrified.

[0071] The raw materials are not particularly limited, but individual glass components, sulfides, or other compounds can be used. In the chalcogenide glass according to the first embodiment, the total content of Cl, Br, and I X[Cl+Br+I] is 0.01% by mass or less, so it is preferable not to use raw materials that mainly consist of Cl, Br, and I.

[0072] (Manufacturing of optical elements) The chalcogenide glass according to the first embodiment has excellent thermal stability and is suitable for press molding. When press molding, the glass is heated to a temperature above its glass transition temperature Tg to achieve a desired softened state, and then molded into a desired shape by, for example, sandwiching it between an upper and lower mold and pressing it.

[0073] Optical elements that can be manufactured by press molding, particularly mold molding, are not particularly limited, but examples include aspherical lenses, lens arrays, microlens arrays, and diffraction gratings, which are required to transmit infrared light. These are useful as optical elements used in infrared cameras and various sensors that use infrared light.

[0074] Second Embodiment The chalcogenide glass according to the second embodiment is The Ga content is 0.5-30.0%. The Ge content is 5.0% or less. The sulfur content is 15.0-40.0%. The total content of Na, K, Rb, and Cs, R[Na+K+Rb+Cs], is 0.05% or more. The total content of Cl, Br, and I, X[Cl+Br+I], is 0.01% or less.

[0075] In the chalcogenide glass according to the second embodiment, the Ga content is 0.5 to 30.0%. The lower limit of the Ga content is preferably 0.6%, and more preferably in the order of 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, 4.2%, 4.4%, 4.6%, 4.8%, 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, and 5.9%. Furthermore, the upper limit of the Ga content is preferably 29.0%, and more preferably in the order of 28.0%, 27.0%, 26.0%, 25.0%, 24.0%, 23.0%, 22.0%, 21.0%, 20.0%, 19.0%, 18.0%, and 17.0%.

[0076] Ga is a network-forming component of glass and is also an expensive raw material. By keeping the Ga content within the above range, the thermal stability of the glass can be improved and the increase in raw material costs can be suppressed. On the other hand, if the Ga content is too low, the thermal stability of the glass may decrease, and it may become impossible to mold the glass. If the Ga content is too high, the absorption edge on the long-wavelength side may shift to the short-wavelength side, narrowing the wavelength range of light transmitted through the glass, and the liquid phase viscosity may decrease, and raw material costs may increase further.

[0077] In the chalcogenide glass according to the second embodiment, the Ge content is 5.0% or less. The upper limit of the Ge content is preferably 4.8%, and more preferably in the order of 4.6%, 4.4%, 4.2%, 4.0%, 3.8%, 3.6%, 3.4%, 3.2%, 3.0%, 2.8%, 2.6%, 2.4%, 2.3%, 2.2%, 2.0%, 1.8%, 1.6%, 1.4%, 1.2%, and 1.0%. The lower limit of the Ge content is preferably 0.0%.

[0078] Ge is a network-forming component in glass. By keeping the Ge content within the above range, the thermal stability of the glass can be improved. On the other hand, if the Ge content is too high, the absorption edge on the long-wavelength side may shift to the short-wavelength side, potentially narrowing the wavelength range of light transmitted through the glass. Furthermore, since Ge is very expensive, raw material costs may skyrocket.

[0079] In the chalcogenide glass according to the second embodiment, the sulfur content is 15.0 to 40.0%. The lower limit of the sulfur content is preferably 16.0%, and more preferably in the order of 17.0%, 18.0%, 19.0%, 20.0%, 21.0%, 22.0%, 23.0%, 24.0%, and 25.0%. The upper limit of the sulfur content is preferably 39.0%, and more preferably in the order of 38.0%, 37.0%, 36.0%, 35.0%, 34.0%, 33.0%, 32.0%, and 31.0%.

[0080] By setting the sulfur content within the above range, the thermal stability of the glass can be improved. On the other hand, if the sulfur content is too low, the absorption edge on the short-wavelength side may shift to the long-wavelength side, and the absorption edge on the long-wavelength side may shift to the short-wavelength side, potentially narrowing the wavelength range of light transmitted through the glass. This could reduce the thermal stability of the glass and make it impossible to mold the glass.

[0081] In the chalcogenide glass according to the second embodiment, the total content R[Na+K+Rb+Cs] of Na, K, Rb, and Cs is 0.05% or more. The lower limit of the total content R is preferably 0.06%, and further preferably 0.08%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0. The percentages are most preferably 95%, 1.00%, 1.10%, 1.20%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, 1.80%, 1.90%, 2.00%, 2.10%, 2.20%, 2.30%, 2.40%, 2.50%, 2.60%, 2.70%, 2.80%, 2.90%, and 3.00%. Furthermore, the upper limit of the total content R is preferably 35.0%, and more preferably in the order of 34.0%, 33.0%, 32.0%, 31.0%, 30.0%, 29.0%, 28.0%, 27.0%, 26.0%, 25.0%, 24.0%, 23.0%, 22.0%, 21.0%, and 20.0%.

[0082] Alkali metals such as Na, K, Rb, and Cs are components that lower the liquidus temperature LT. By setting the total content R within the above range, the liquidus temperature LT is lowered and the liquidus viscosity increases, improving moldability. Furthermore, the thermal stability of the glass can be improved, and the absorption edge on the shorter wavelength side can be shifted to even shorter wavelengths, widening the wavelength range of light transmitted through the glass. If the total content R is too high, the thermal stability may decrease, and it may become impossible to obtain glass. Conversely, if the total content R is too low, the liquidus temperature LT may not decrease sufficiently, the increase in liquidus viscosity may be insufficient, and the desired thermal stability and moldability may not be achieved.

[0083] In the chalcogenide glass according to the second embodiment, the total content X[Cl+Br+I] of Cl, Br, and I is 0.01% or less. The upper limit of the total content X is preferably 0.009%, and more preferably in the order of 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002%, and 0.001%. It is preferable that Cl, Br, and I are substantially absent.

[0084] Halogen elements such as Cl, Br, and I shift the absorption edge on the short-wavelength side to even shorter wavelengths, but they worsen the water resistance of glass. Furthermore, they can corrode molten glass containers, such as those made of quartz glass, during manufacturing, and leak molten glass or volatile substances can corrode production equipment, potentially reducing productivity. By keeping the total content X within the above range, the deterioration of the glass's water resistance can be suppressed, and the desired productivity can be achieved.

[0085] In the chalcogenide glass according to the second embodiment, the lower limit of the Sb content is preferably 0.0%, and more preferably in the order of 2.0%, 4.0%, 6.0%, 8.0%, 10.0%, 12.0%, 14.0%, 16.0%, 18.0%, 20.0%, 21.0%, 22.0%, 23.0%, 24.0%, 25.0%, 26.0%, 27.0%, 28.0%, 29.0%, 30.0%, 31.0%, 32.0%, 33.0%, 34.0%, 35.0%, 36.0%, 37.0%, 38.0%, 39.0%, and 40.0%. Furthermore, the upper limit of the Sb content is preferably in the following order: 84.0%, 82.0%, 80.0%, 78.0%, 76.0%, 75.0%, 74.0%, 73.0%, 72.0%, 71.0%, 70.0%, 69.0%, 68.0%, 67.0%, 66.0%, 65.0%, 64.0%, 63.0%, 62.0%, and 61.0%.

[0086] Sb is a network-forming component of glass. From the viewpoint of improving the thermal stability of the glass, it is preferable to keep the Sb content within the above range. On the other hand, if the Sb content is too low, the thermal stability of the glass may decrease, and it may also be impossible to mold the glass.

[0087] In the chalcogenide glass according to the second embodiment, the content of glass components other than those mentioned above can be the same as in the first embodiment described above.

[0088] In the chalcogenide glass according to the second embodiment, the glass properties can be the same as those of the first embodiment described above.

[0089] The manufacturing of the chalcogenide glass and the optical element according to the second embodiment can be carried out in the same manner as in the first embodiment described above. [Examples]

[0090] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the embodiments shown in the examples.

[0091] (Example 1) Glass samples having the glass composition shown in Table 1 were prepared using the following procedure and evaluated in various ways. In all glass samples, the content of Cl, Br, and I was 0.00% by mass. Furthermore, in all glass samples, the content of Ge was 0.00% by mass. In Comparative Example 1, glass samples were prepared so that the content of Na, K, Rb, and Cs was 0.00% by mass.

[0092] [Glass manufacturing] Quartz ampoules were prepared and washed with purified water. A rotary vacuum pump was operated to heat the quartz ampoules with a burner under vacuum to evaporate the moisture. The raw materials were mixed to achieve the glass composition shown in Table 1 and placed inside the quartz ampoules. After thoroughly vacuuming the inside of the ampoules with the rotary vacuum pump, the ampoules were sealed using an H2-O2 burner. The sealed quartz ampoules were heated to 950°C at a heating rate of 20°C / hour and held at the same temperature for 8 hours. They were allowed to cool to room temperature to vitrify the contents and obtain glass samples. In addition, glass samples were obtained by filling a carbon crucible with a predetermined amount of raw materials to obtain the glass composition shown in Table 1 and heating and melting it in an inert gas atmosphere containing sulfur gas. The melting temperature was 500-1200°C and the melting time was 1-12 hours. Similar glass was obtained when melted in quartz ampoules and when produced by heating in an inert gas atmosphere containing sulfur gas.

[0093] [Light transparency] To evaluate the transmittance from visible light to infrared light, the maximum transmittance wavelength in the visible range and the maximum transmittance wavelength in the infrared range were measured. The maximum transmittance wavelength in the visible range was defined as the wavelength at which 50% of the maximum transmittance measured for a 1.5 mm thick glass sample using a UV-Vis-Near-Infrared Spectrophotometer (Shimadzu Corporation, UV-3600i Plus, measurement wavelength range 350-2500 nm) occurred. The maximum transmittance wavelength in the infrared range was defined as the wavelength at which 50% of the maximum transmittance measured for a 1.5 mm thick glass sample using a Fourier Transform Infrared Spectrophotometer (Shimadzu Corporation, IRTracer-100, measurement wavelength range 2-16 μm) occurred. In this specification, "maximum transmittance" refers to the transmittance at the wavelength at which the transmittance is greatest, and is also called the highest transmittance.

[0094] [Glass transition temperature Tg, crystallization peak temperature Tc] The glass transition temperature (Tg) and crystallization peak temperature (Tc) were measured using a Rigaku differential scanning calorimetry analyzer (DSC8271) at a nitrogen flow rate of 50 mL / min and a heating rate of 10 °C / min, up to 500 °C.

[0095] The difference between the crystallization peak temperature Tc and the glass transition temperature Tg [Tc-Tg] was calculated to confirm thermal stability. Glass samples that did not exhibit crystal precipitation or a crystallization peak temperature Tc even when heated to 500°C were evaluated as having excellent thermal stability.

[0096] [Liquidus temperature LT] Using a differential scanning calorimeter, when a glass sample was heated to 500°C at a heating rate of 10°C / min while flowing nitrogen at a flow rate of 50 mL / min, the liquidus temperature LT was defined as the endpoint of the endothermic peak that occurs when crystals precipitated in the glass during the heating process melt in a temperature range higher than the glass transition temperature Tg and crystallization peak temperature Tc. The liquidus temperature LT was determined as the temperature at the intersection of the tangent on the high-temperature side of the endothermic peak and the baseline.

[0097] [water resistance] Glass samples were processed to a thickness of 1.5 mm and immersed in a sufficient amount of water at room temperature for 1 hour. The transmittance of light with wavelengths of 2 to 16 μm was measured for the glass samples before and after immersion in water using a Fourier transform infrared spectrophotometer (Shimadzu Corporation, IRTracer-100). Water resistance was evaluated as good if the maximum transmittance did not decrease by more than 10% between before and after immersion in water. All glass samples were confirmed to have good water resistance.

[0098] [Table 1]

[0099] (Example 2) The glass samples prepared in Example 14 were molded in a nitrogen atmosphere at 300°C to produce aspherical lenses, lens arrays, and microlens arrays. The glass samples exhibited excellent thermal stability and superior processability during mold forming, resulting in good aspherical lenses, lens arrays, and microlens arrays.

[0100] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended.

[0101] For example, by adjusting the composition described in the specification with respect to the glass composition exemplified above, a chalcogenide glass according to one aspect of the present invention can be produced. Furthermore, it is certainly possible to arbitrarily combine two or more items described as examples or preferred scopes in the specification.

Claims

1. The Ga content is 2.0 to 40.0% by mass. The Sb content is 20.0 to 75.0% by mass. The sulfur content is 15.0 to 40.0% by mass. The total content of Na, K, Rb, and Cs, R[Na+K+Rb+Cs], is 0.05% by mass or more. A chalcogenide glass in which the total content of Cl, Br, and I, X[Cl+Br+I], is 0.01% by mass or less.

2. The Ga content is 0.5 to 30.0% by mass. The Ge content is 5.0% by mass or less. The sulfur content is 15.0 to 40.0% by mass. The total content of Na, K, Rb, and Cs, R[Na+K+Rb+Cs], is 0.05% by mass or more. A chalcogenide glass in which the total content of Cl, Br, and I, X[Cl+Br+I], is 0.01% by mass or less.

3. An optical element made of chalcogenide glass according to claim 1 or 2.

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