Abstract
Abstract Newly explored two-dimensional (2D) materials have shown promising optical properties, owning to the tunable band gap of the layered material with its thickness. A widely used method to achieve tunable light emission (or photoluminescence) is through thickness modulation, but this can only cover specific wavelengths. This approach limits the development of tunable optical devices with high spectral resolution over a wide range of wavelengths. Here, we report wideband tunable light emission of exfoliated black phosphorus nanosheets via a pulsed thermal annealing process in ambient conditions. Tunable anisotropic emission was observed between wavelengths of 590 and 720 nm with a spectral resolution of 5 nm. This emission can be maintained for at least 11 days when proper passivation coupled with adequate storage is applied. Using hyperspectral imaging X-ray photoelectron spectroscopy (i-XPS), this tunable emission is found to be strongly dependent on the level of oxidation. We finally discuss the underlying mechanism responsible for the observed tunable emission and show that tunable emission is only observed in nanosheets with thicknesses of (70–125 nm) ± 10 nm with the maximum range achieved for nanosheets with thicknesses of 125 ± 10 nm. Our results shed some light on an emerging class of 2D oxides with potential in optoelectronic applications.
Highlights
New emerging two-dimensional (2D) materials have attracted significant attention in recent years due to their extraordinary mechanical, electrical, and optical properties at the nanoscale [1,2,3,4,5]
After the first cycle of pulsed thermal annealing, PL emission was observed at 720 nm
The tunable emission of pulsed thermally annealed black phosphorus nanosheets can be explained by examining black phosphorus oxide properties
Summary
New emerging two-dimensional (2D) materials have attracted significant attention in recent years due to their extraordinary mechanical, electrical, and optical properties at the nanoscale [1,2,3,4,5]. Among these materials, layered black phosphorus has played a key role in several applications. Phosphorene exhibits a layer-dependent band gap ranging from 0.3 to 1.7 eV for bulk to monolayer, respectively [6]. Phosphorene is desirable for light emission applications since the band gap depends only on the number of layers. Phosphorene still suffers from major obstacles including long-term stability in ambient conditions [13,14,15,16], which can be overcome by layer passivation or layer functionalization [17, 18]
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