Pressure characters of defects in hexagonal boron nitride flakes

We have measured the pressure-dependent photoluminescence (PL) spectra of hBN flakes at low temperature by using diamond anvil cell (DAC) device. It is found that the absolute values of pressure coefficients of discrete PL emission lines are all below 15 meV/GPa which are much less than 36 meV/GPa, the pressure-induced red-shift rate of hBN bandgap. These PL emission lines are originated from the atom-like localized defect levels confined within the band gap of hBN flakes. The experimental results of pressure-dependent PL emission lines present three different types of pressure response, corresponding to red-shift (negative pressure coefficient) and blue-shift (positive pressure coefficient), or even a sign change from negative to positive.