The band gap of black phosphorus depends strongly on the number of layers and covers wavelengths from 720 to 4000 nm from monolayer to bulk, but only in discrete steps and suffering from poor photostability.
In our recent Optical Materials Express, we demonstrate tunable and stable infrared emission from defect states in few-layer BP. First, we engineer defects using laser exposure and photo-oxidation. The tunable emission spectrum continuously bridges the discrete near-infrared energies of few-layer BP for a decreasing number of layers. Second, using plasma-enhanced encapsulation, we report the creation and protection of such defects with peak emission energy between bilayer and trilayer black phosphorus. The emission is photostable and has an efficiency comparable to that of pristine layers.
Our results put forward defect engineering in few-layer BP as a flexible strategy for stable and widely tunable infrared sources and detectors in integrated spectrometers and hyperspectral sensors.