an improved minimum light reflectivity , light transmissive vitreous member and method of fabrication in which an ion implanted , buried ion phase layer is provided within the light transmissive member closely spaced from the light output surface . this buried phase layer has an index of refraction greater than the index of refraction of the vitreous member such that the optical impedance of the buried phase layer and the vitreous material are closely watched to minimize reflectivity from the light output surface of the vitreous member .