  The light emission properties of color centers emitting in 3.3-4 eV region
are investigated for hydrostatic pressures ranging up to 5GPa at liquid helium
temperature. The light emission energy decreases with pressure less sensitively
than the bandgap. This behavior at variance from the shift of the bandgap is
typical of deep traps. Interestingly, hydrostatic pressure reveals the
existence of levels that vary differently under pressure (smaller increase of
the emission wavelength compared to the rest of the levels in this energy
region or even decrease of it) with pressure. This discovery enriches the
physics of the color centers operating in the UV in hBN.
