Composition comprising a three-dimensional amorphous trivalent network

A composition comprising a three-dimensional amorphous trivalent network, wherein the network defines a connected network comprising a plurality of vertices which are interconnected by cross members such that each cross member directly connects two vertices and the network comprises a plurality of trihedra, wherein each trihedron comprises a central vertex which is directly connected to three outer vertices such that each trihedron defines three skew angles, a skew angle being the angle between the normal of a plane, comprising the central vertex of the trihedron and two of the outer vertices, and between a cross member which directly connects the central vertex and the remaining outer vertex of the trihedron which does not form the plane, and any first and second trihedra comprising one shared cross member and two shared vertices define a dihedral angle which is the angle between the normal to a first plane, defined by a central vertex and two outer vertices of the first trihedron, wherein the two outer vertices which define the first plane do not comprise the second trihedron, and the normal to a second plane, defined by a central vertex and two outer vertices of the second trihedron, wherein the two outer vertices which define the second plane do not comprise the first trihedron, wherein the dihedral angle is greater than or equal to 90°, wherein at least 90% of the skew angles within the network define an angle between 70° and 110° and at least 90% of the dihedral angles within the network define an angle between 92° and 155° such that the amorphous trivalent network reduces within a particular frequency range (ωc±Δω) the number of modes of electromagnetic radiation passing through the network, wherein the amorphous trivalent network defines a band gap having a width of at least 5%.