Luminescence properties of hexagonal boron nitride powders probed by deep UV photoluminescence spectroscopy.

Deep ultraviolet (UV) photoluminescence (PL) spectroscopy was employed to study the luminescence properties of hexagonal boron nitride (h-BN) crystal powders after annealing the samples at different temperatures in the range of 100-900 °C for 1 h in ambient air. The PL spectrum from the h-BN powder samples annealed around 700 °C showed strong luminescence intensity at 5.49 eV along with enhanced phonon-assisted band-edge emission at 5.90 eV. Additionally, it revealed sharp atomic-like emission lines in UV region at 4.10, 4.12, 4.14, and 4.16 eV with line widths less than 1 nm from the annealed samples which were not present in the unannealed samples. Power- and temperature-dependent PL measurements of the sharp atomic-like emission lines exhibited robust nature of the energy peak positions. Based on the theoretical reports, the sharp emission lines could be carbon-related defects.