  Cadmium selenide nanocrystal quantum dots (NC-QDs) are site-selectively
synthesized by sequential ion beam implantation of selenium and cadmium ions in
a SiO2 matrix through sub-micron apertures followed by a rapid thermal
annealing step. The size, areal density and optical emission energy of the
NC-QDs are controlled by the ion fluence during implantation and the diameter
of implantation aperture. For low fluences and small apertures the emission of
these optically active emitters is blue-shifted compared to that of the bulk
material by $>100\,{\rm meV}$ due to quantum confinement. The emission exhibits
spectral diffusion and blinking on a second timescales as established also for
solution synthesized NC-QDs.
