Abstract
Optical waveguides have been formed in natural zircon crystals by MeV helium ion implantation to doses in excess of 4 x 10(16) ions/cm(2). Radiation damage formed by nuclear collisions at the end of the ion range destroys the crystallinity, reduces the refractive index and acts as an optical barrier to define the waveguide boundary. The amorphised region is stable to at least 800 degrees C but of particular interest is that within the damaged region there is rin apparent refractive index recovery for anneals made near 200 degrees C, even if made subsequent to high temperature annealing. This unusual annealing behaviour is interpreted as evidence for precipitation of metal colloids at 200 degrees C. Experiments to support the model are described.