Defect-induced blue luminescence of hexagonal boron nitride

• Defect-induced luminescence at 380 nm is observed for hBN powders.
• A phonon-assisted structure is characteristic for 380 nm luminescence.
• The defect-related excitation of 380 nm luminescence is at 340 nm and 265 nm.
• The 380 nm luminescence is caused by a recombination or an intra-center mechanism.
• The 380 nm luminescence is sensitive to oxygen gas environment.

Native defect-induced photoluminescence around 400 nm (blue luminescence - BL) was studied in hBN materials with different size and various origins. The following spectral characterizations were used: spectra of luminescence and its excitation, luminescence dependence on temperature, luminescence kinetics, optically stimulated luminescence and infrared absorption. It was found, that the BL is characteristic for all these materials, which were studied. The BL forms a wide, asymmetric and phonon-assisted emission band at 380 nm. This luminescence can be excited either through the exciton processes, or with light from two defect-induced excitation bands at 340 nm and 265 nm. It was found that the BL is caused by two luminescence mechanisms. One of them is intra-center luminescence mechanism (340 nm excitation), but the other one is recombination mechanism (265 nm excitation). It was considered that the most probable candidates for the defects, which cause the BL in hBN can be related to the nitrogen vacancy type-centers. It was certainly confirmed, that presence of oxygen gas is partly quenching the BL intensity, thus ranking the hBN material among the materials prospective for development of oxygen gas optical sensors.