Engineering UV-emitting defects in h-BN nanodots by a top-down route

Hexagonal boron nitride (h-BN) nanodots of 10 nm have been synthesized via top-down route from bulk powders. A combination of ultrasonic and thermal treatments in phosphoric acid has been used to achieve edge etching and size reduction to the nanoscale. A new emission in the ultraviolet region, correlated to a characteristic infrared-active vibration, has been detected in the BN dots. The UV emission is stable in as-prepared samples but quenches after thermal treatments higher than 100 degrees C. Besides the UV band, the fluorescent emission of h-BN shows a broad band in the visible region, whose intensity reaches a maximum after thermal treatment at 200 degrees C. Structural and optical characterization techniques have been used to investigate the synthesis-properties relationship in h-BN and the hydroxyl covalent functionalization of the surfaces. The experiments show that the particular combination of ultrasonic treatment and etching in temperature is essential to achieve the UV fluorescent emission. Quantum chemistry calculations have been used to evaluate Stones-Wales defects as possible causes of the optical and vibrational properties.