  We investigate the quenching of the photoluminescence (PL) from the divacancy
defect in 4H-SiC consisting of a nearest-neighbour silicon and carbon
vacancies. The quenching occurs only when the PL is excited below certain
photon energies (thresholds), which differ for the four different inequivalent
divacancy configurations in 4H-SiC. Refined theoretical ab initio calculation
for the charge-transfer levels of the divacancy show very good agreement
between the position of the (0/-) level with respect to the conduction band for
each divacancy configurations and the corresponding experimentally observed
threshold, allowing us to associate the PL decay with conversion of the
divacancy from neutral to negative charge state due to capture of electrons
photoionized from other defects (traps) by the excitation. Electron
paramagnetic resonance measurements are conducted in dark and under excitation
similar to that used in the PL experiments and shed light on the possible
origin of traps in the different samples. A simple model built on this concept
agrees well with the experimentally-observed decay curves.
