Multicolor Inks of Black Phosphorus for Midwave-Infrared Optoelectronics.

Black phosphorus (bP) based ink with a bulk bandgap of 0.33 eV (λ = 3.7 µm) has recently been shown to be promising for large-area, high performance mid-wave infrared (MWIR) optoelectronics. However, the development of multicolor bP inks expanding across the MWIR wavelength range has been challenging. Here we demonstrate a multicolor ink process based on bP with spectral emission tuned from 0.28 eV (λ ∼ 4.4 µm) to 0.8 eV (λ ∼ 1.5 µm). Specifically, through the reduction of bP particle size distribution (i.e., lateral dimension and thickness), the optical bandgap systematically blue-shifts, reaching up to 0.8 eV. Conversely, alloying bP with arsenic (bP 1- x As x ) induces a red-shift in the bandgap to 0.28 eV. The ink processed films are passivated with an infrared-transparent epoxy for stable infrared emission in ambient air. Utilizing these multicolor bP-based inks as an infrared light source, a gas sensing system is demonstrated that selectively detects gases such as CO 2 and CH 4 whose absorption band varies around 4.3 µm and 3.3 µm, respectively. The presented ink formulation sets the stage for the advancement of multiplex MWIR optoelectronics, including spectrometers and spectral imaging using a low-cost material processing platform. This article is protected by copyright. All rights reserved.