  Cathodoluminescence (CL) experiments at low temperature have been undertaken
on various bulk and exfoliated hexagonal boron nitride (hBN) samples. Different
bulk crystals grown from different synthesis methods have been studied. All of
them present the same so-called S series in the 5.6--6 eV range, proving its
intrinsic character. Luminescence spectra of flakes containing 100 down to 6
layers have been recorded. Strong modifications in the same UV range are
observed and discussed within the general framework of 2D exciton properties in
lamellar crystals.
