Atomic-Like Uv Emission Generated in Hexagonal Boron Nitride Single Crystals by Thermal Annealing

A series of atomic-like photoluminescence (PL) emission peaks in UV region near 4.0 eV were created by thermal annealing hexagonal boron nitride (h-BN) single crystals in air. The pristine h-BN did not have these peaks, emitting strong phonon-assisted band edge PL with peaks at 5.78 and 5.89 eV. After annealing the h-BN crystals in ambient air, a new atomic-like sharp emission in UV region at 4.09 eV with a line width of 0.2 nm appeared along with its phonon replicas at 3.89 and 3.69 eV in the low temperature (8 K) PL measurement. Further testing demonstrated that annealing the h-BN samples in the temperature window of 700-950 degrees C for 60 min generated the atomic-like emission. The peak position of the emission line is stable with the temperature and PL excitation power. Our study also suggests that the defect responsible for the atomic-like emission resides in the surface region.