Provided is a phosphate glass that has a low melting point and has excellent water resistance while maintaining a glass structure. This phosphate glass PGS has a glass transition temperature Tg lower than 490° C. and contains, in oxide-based mol %, 55-65 [mol %] of P.sub.2O.sub.5, 10-27 [mol %] of ZnO, 0.5-7 [mol %] of R.sub.2O.sub.3 ((R.sub.2O.sub.3 is at least one of Al.sub.2O.sub.3, Ga.sub.2O.sub.3, and Y.sub.2O.sub.3), 0.5-3.5 [mol %] of a lanthanoid oxide L.sub.2O.sub.3(L.sub.2O.sub.3 is at least one of La.sub.2O.sub.3, Ce.sub.2O.sub.3, Pr.sub.2O.sub.3, Nd.sub.2O.sub.3, Pm.sub.2O.sub.3, Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Tb.sub.2O.sub.3, Dy.sub.2O.sub.3, Ho.sub.2O.sub.3, Er.sub.2O.sub.3, Tm.sub.2O.sub.3, Yb.sub.2O.sub.3, and Lu.sub.2O.sub.3), and 4-15 [mol %] of X.sub.2O (X.sub.2O is at least one of Li.sub.2O, Na.sub.2O, K.sub.2O, Rb.sub.2O, Cs.sub.2O, and Fr.sub.2O).

Provided is a phosphate glass that has a low melting point and has excellent water resistance while maintaining a glass structure. This phosphate glass PGS has a glass transition temperature Tg lower than 490° C. and contains, in oxide-based mol %, 55-65 [mol %] of P.sub.2O.sub.5, 10-27 [mol %] of ZnO, 0.5-7 [mol %] of R.sub.2O.sub.3 ((R.sub.2O.sub.3 is at least one of Al.sub.2O.sub.3, Ga.sub.2O.sub.3, and Y.sub.2O.sub.3), 0.5-3.5 [mol %] of a lanthanoid oxide L.sub.2O.sub.3(L.sub.2O.sub.3 is at least one of La.sub.2O.sub.3, Ce.sub.2O.sub.3, Pr.sub.2O.sub.3, Nd.sub.2O.sub.3, Pm.sub.2O.sub.3, Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Tb.sub.2O.sub.3, Dy.sub.2O.sub.3, Ho.sub.2O.sub.3, Er.sub.2O.sub.3, Tm.sub.2O.sub.3, Yb.sub.2O.sub.3, and Lu.sub.2O.sub.3), and 4-15 [mol %] of X.sub.2O (X.sub.2O is at least one of Li.sub.2O, Na.sub.2O, K.sub.2O, Rb.sub.2O, Cs.sub.2O, and Fr.sub.2O).

A near-infrared cut filter includes a transparent substrate having a first and a second surfaces, opposite to each other; and a dielectric multilayer film disposed on a side of the first surface. The dielectric multilayer film reflects light within a wavelength range of 700-750 nm. A mean regular transmittance T.sub.1 within a wavelength range of 700-750 nm measured when light is incident in the normal direction from the side of the second surface is 20% or less. A mean regular transmittance T.sub.2 within a wavelength range of 600-680 nm measured when light is incident in the normal direction from the side of the second surface is 65% or more. A mean regular reflectance R.sub.1 within a wavelength range of 700-750 nm measured when light is incident at an angle of 5° with respect to the normal direction from the side of the second surface is 80% or less.

Glass compositions include phosphorus oxide (P.sub.2O.sub.5), niobia (Nb.sub.2O.sub.5), barium oxide (BaO) and potassium oxide (K.sub.2O) as essential components and may optionally include titania (TiO.sub.2), calcium oxide (CaO), sodium oxide (Na.sub.2O), lithium oxide (Li.sub.2O), bismuth oxide (Bi.sub.2O.sub.3), strontium oxide (SrO), tungsten oxide (WO.sub.3) and other components. The glasses may be characterized by high refractive index at 587.56 nm at comparably low density at room temperature.

Disclosed herein are glasses that present several advantages over traditional glass compositions used in optical applications. The glasses disclosed herein have a low devitrification tendency and can be processed by melt quenching and formed into macroscopic components. The glasses have high glass thermal stability indices and are chemically durable. The glasses disclosed herein are transparent when heat treated in air or oxygen and have high refractive indices and low density, as well, making them suitable for optical applications.

Disclosed herein are glasses that present several advantages over traditional glass compositions used in optical applications. The glasses disclosed herein have a low devitrification tendency and can be processed by melt quenching and formed into macroscopic components. The glasses have high glass thermal stability indices and are chemically durable. The glasses disclosed herein are transparent when heat treated in air or oxygen and have high refractive indices and low density, as well, making them suitable for optical applications.

A near-infrared cut filter glass has: an average transmittance in a wavelength range of 400-550 nm of 50-92%; a transmittance at a wavelength of 700 nm of 40-92%; an average transmittance in a wavelength range of 850-950 nm of 0.0001-70%; and an average transmittance in a wavelength range of 1200-2500 nm of 0.0001-60%.

A near-infrared cut filter glass has: an average transmittance in a wavelength range of 400-550 nm of 50-92%; a transmittance at a wavelength of 700 nm of 40-92%; an average transmittance in a wavelength range of 850-950 nm of 0.0001-70%; and an average transmittance in a wavelength range of 1200-2500 nm of 0.0001-60%.

Provided is an optical glass having a composition including, by mol %: 0% to 15 % B.sub.2O.sub.3; 25% to 40% P.sub.2O.sub.5, the total content of B.sub.2O.sub.3 and P.sub.2O.sub.5 being 35% to 45%; 0% to 10% Al.sub.2O.sub.3; 5% to 15% Li.sub.2O; 0% to 15% Na.sub.2O; 0% to 5% K.sub.2O; 0% to 35% MgO; 0% to 35% CaO, the total content of MgO and CaO being 20% or more; 0% to 5 % ZnO; 0% to 3% ZrO.sub.2; 0% to 3% Y.sub.2O.sub.3; 0% to 3% La.sub.2O.sub.3; and 0% to 3% Gd.sub.2O.sub.3. The composition does not contain SrO and BaO.

Provided is an optical glass having a composition including, by mol %: 0% to 15 % B.sub.2O.sub.3; 25% to 40% P.sub.2O.sub.5, the total content of B.sub.2O.sub.3 and P.sub.2O.sub.5 being 35% to 45%; 0% to 10% Al.sub.2O.sub.3; 5% to 15% Li.sub.2O; 0% to 15% Na.sub.2O; 0% to 5% K.sub.2O; 0% to 35% MgO; 0% to 35% CaO, the total content of MgO and CaO being 20% or more; 0% to 5 % ZnO; 0% to 3% ZrO.sub.2; 0% to 3% Y.sub.2O.sub.3; 0% to 3% La.sub.2O.sub.3; and 0% to 3% Gd.sub.2O.sub.3. The composition does not contain SrO and BaO.