Large-Scale Black Phosphorus Ink Films for Multiplex Mid-Infrared Optoelectronics

Black phosphorus (bP) based ink with a bulk bandgap of 0.33 eV (<i>λ</i> = 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 (<i>λ</i> = 4.4 μm) to 0.8 eV (<i>λ</i> = 1.5 μm). Specifically, through the reduction of bP particle size distribution (i.e., lateral dimension and thickness), the optical bandgap systematically blueshifts, reaching up to 0.8 eV. Conversely, alloying bP with arsenic (bP_1−xAs_x) induces a redshift 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 a MWIR phosphor, a gas sensing system is demonstrated that selectively detects gases, such as CO₂ and CH₄ whose absorption band varies around 4.3 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.<br/><br/><b>Acknowledgments: </b>This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DE-AC02-05Ch11231 (Electronic Materials program). N.H. acknowledges support from JST PRESTO (JPMJPR23H7), Japan.