By the term ???phosphine cross-linking compound??? is meant, for purposes of the specification and claims to refer to a molecule that has at least one phosphine group (e.g., in the form of phosphine, phosphine oxide, or phosphonium) available for binding or chelating a metal such as Zn, Cd, or the like and/or a non metal such as Se, S or other non metals, or substrate containing such atoms, and ha