Facet-dependent nonlinear optical properties of bismuth oxychloride single-crystal nanosheets

Single-crystal nanosheets of BiOCl with preferentially exposed {001} and {010} facets were synthesized, and their third-order nonlinear optical performances were evaluated by Z-scan measurements. Both BiOCl{001} and BiOCl{010} exhibit reverse saturable absorption, with an effective nonlinear absorption coefficient of (8.17 ± 1.13) × 10−4 cm GM−1 for BiOCl{001} and (11.53 ± 1.30) × 10−4 cm GM−1 for BiOCl{010}. According to the measurements of photoluminescence and electron paramagnetic resonance, excited-state absorption is found to prevail over two-photon absorption during the nonlinear optical process, and the facet-dependent response of BiOCl nanosheets is attributed to the localization of excited carriers correlated with the defect density and size of the atomic slab.