Patent ID: 7741238

Claim:
A spinel sintered body having a contrast ratio of 300 or more in the case of white light, where the contrast ratio is defined as the quotient obtained by dividing an amount of transmitting light in the case of being arranged between two polarizing plates, the polarizing directions of the two polarizing plates being parallel to each other, by an amount of transmitting light in the case of being arranged between two polarizing plates, the polarizing directions of the two polarizing plates being orthogonal to each other, wherein the spinel sintered body has a composition of MgO.nAl 2 O 3 , where n is 1.07 to 1.125, where with a thickness of 1 mm the spinel body exhibits an in-line transmittance of 78% or more with respect to a light ray having a wavelength of 500 nm, and where with a thickness of 1 mm the spinel body exhibits an in-line transmittance of 70% or more with respect to a light ray having a wavelength of 350 nm.