Defect-assisted photoluminescence in hexagonal boron nitride nanosheets
Junkai Ren, Luigi Stagi, Carlo Maria Carbonaro, Luca Malfatti, Maria Francesca Casula, Pier Carlo Ricci, Antonio Esaú Del Río Castillo, Francesco Bonaccorso, Laura Calvillo, Gaetano Granozzi, Plinio Innocenzi
Abstract
Abstract The development of functional optoelectronic applications based on hexagonal boron nitride nanosheets ( h -BNNs) relies on controlling the structural defects. The fluorescent emission, in particular, has been observed to depend on vacancies and substitutional defects. In the present work, few-layer h -BNNs have been obtained by sonication-assisted liquid-phase exfoliation of their bulk counterpart. The as-prepared samples exhibit a weak fluorescent emission in the visible range, centred around 400 nm. Tailored defects have been introduced by oxidation in air at different temperatures. A significant increase in the fluorescent emission of the oxidated h -BNNs has been observed with maximum emissive intensity for the samples treated at 300 °C. A further increase in temperatures (>300 °C) determines a quenching of the fluorescence. We investigated, by means of detailed microscopic and spectroscopic analysis, the relationship between the optical properties and defects of h -BNNs. The investigation of the optical properties as a function of treatment temperature highlights the critical role of hydroxyl groups created by the oxidation process. Only h -BN exfoliated in water allows introducing OH groups with consequent enhancement of fluorescence emission. Quantum chemical calculations support the experimental findings.