  Recently hBN has become an interesting platform for quantum optics due to the
peculiar defect-related luminescence properties. Concomitantly, hBN was
established as the ideal insulating support for realizing 2D materials device,
where, on the contrary, defects can affect the device performance. In this
work, we study the light emission properties of hBN flakes obtained by
mechanical exfoliation with particular focus on extended defects generated in
the process. In particular, we tackle different issues as the light emission in
hBN flakes of different thicknesses in the range of hundreds of nm, revealing a
higher concentration of deep level emission in thinner area of the flake. We
recognize the effect of crystal deformation in some areas of the flake with an
important blue-shift (130 meV) of the room temperature near band edge emission
of hBN and the concurrent presence of a novel emission at 2.36 eV related to
the formation of array of dislocations. We studied the light emission
properties by means of cathodoluminescence and sub-bandgap excitation
photoluminescence of thickness steps with different crystallographic
orientations, revealing the presence of different concentration of radiative
centers. CL mapping allows to detect buried thickness steps, invisible to the
SEM and AFM morphological analysis.
