Scratch-resistant optical multi-layer system applied to a crystalline substrate

A crystalline substrate comprising an optical multi-layer system thereon, which substrate is obtainable by

• (a) applying a first free-flowing composition which comprises nanoscale inorganic solid particles comprising at least one of a polymerizable and a polycondensable organic group to at least one surface of a crystalline substrate;
• (b) at least one of polymerizing and polycondensing the organic groups of the solid particles to form a first organically crosslinked layer on the at least one surface;
• (c) applying a second free-flowing composition which comprises nanoscale inorganic solid particles comprising at least one of a polymerizable and a polycondensable organic group to the organically crosslinked layer of (b), the second composition giving rise to a different refractive index than the first composition;
• (d) at least one of polymerizing and polycondensing the organic groups of the solid particles of the applied second composition to form a second organically crosslinked layer on the first organically crosslinked layer;
• (e) optionally, applying a further free-flowing composition which comprises nanoscale inorganic solid particles comprising at least one of a polymerizable and a polycondensable organic group to the organically crosslinked layer of (d) and at least one of polymerizing and polycondensing the organic groups of the solid particles of the further composition to form a further organically crosslinked layer on the second organically crosslinked layer;
• (f) optionally, repeating (e) one or more times to form one or more further organically crosslinked layers;
• and
• (g) single-stage thermal consolidation of the organically crosslinked layers present and burnout of organic constituents thereof;
• with the proviso that for the uppermost layer the nanoscale inorganic solid particles do not comprise a polymerizable or polycondensable organic group so that for the uppermost layer a polymerization or polycondensation of groups of the solid particles with formation of organic crosslinking does not take place before or during (g).