Subgap photoluminescence spectroscopy of nanocrystalline diamond films

Abstract

We report on the effect of ambient conditions and UV irradiation on the subgap photoluminescence of nanocrystalline diamond prepared by microwave plasma enhanced chemical vapour deposition. We measured the photoluminescence of self-supporting membranes of thickness about 290 nm with the grain size up to 40 nm under variable ambient conditions – pressure, temperature, air, nitrogen and helium atmospheres. We have found that intensity of photoluminescence of samples kept under low pressure increases during the time. The photoluminescence intensity of samples under low pressure depends on sample temperature with maximum at about 260 K. The photoluminescence increase can be enhanced substantially by UV irradiation (325 nm) of the sample under certain conditions: temperature greater than ~ 280 K, low pressure of ambient atmosphere. We interpret the experimental results in terms of desorption of water molecules and their interaction with the of individual diamond nanocrystals in the membrane.