Spectral characterization of long-lived luminescence in h-BN powder under UV excitation

Abstract

Long-lasting luminescence in excited solid-state composites is of considerable interest as an inner light source for perspective materials capable to generate self-induced photoactivity after external irradiation turn-off. The corresponding slow ultraviolet (UV) and visible (Vis) emissions in hexagonal boron nitride can be caused by technology induced impurities (oxygen, carbon etc.) which form the complex system of electron and/or hole capturing levels within the energy gap. As result the created charge traps substantially influence on functional properties and optoelectronic characteristics of developed heterostructures based on h-BN. In this paper we study the photoluminescence (PL) peculiarities of nanostructured crystalline h-BN powder with C and O content< 0.5 wt% in the range of 200–600 nm in millisecond time window. The spectral and kinetic regularities of observed PL excitation and emission spectra have been quantitatively analyzed. Using delay time variation from 0.05 to 25 ms it has been demonstrated more than 2 times increase of Vis/UV luminescence intensities ratio under band-to-band excitation. This behavior is confirmed by two-exponential decay kinetics with τ2 = 1.5 – 10.6 ms time constant for a slow emission component in the powder studied. The observable luminescence is established to be due to recombination processes involving impurity ON and CN centers, as well as nitrogen VN vacancies and related complexes.