  The study of hexagonal silicon polytypes attracts special attention due to
their unique physical properties compared to the traditional cubic phase of Si.
Thus, for some hexagonal phases, a significant improvement in the emission
properties has been demonstrated. In this work, the luminescent properties of
SiO2/Si structures irradiated with Kr+ ions at different doses and annealed at
800 {\deg}C have been systematically investigated. For such structures, a
photoluminescence line at ~ 1240 nm is observed and associated with the
formation of hexagonal 9R-Si phase inclusions. It is found that the variation
in the thickness of oxide film and the relative position of ion distribution
profile and film / substrate interface leads to a regular change in the
luminescence intensity. The nature of the observed dependencies is discussed as
related to the interplay between the desirable 3C-Si -> 9R-Si structural
transition and generation of nonradiative defects. The revealed regularities
suggest optimal ion irradiation conditions for synthesis of optically active
9R-Si phase in diamond-like silicon.
