Cation Exchange Mediated Synthesis and Tuning of Bimodal Plasmon in Alloyed Ternary Cu3BiS3-xSex Nanorods

We report a robust methodology for synthesizing monodisperse alloyed Bi2S3-xSex nanorods (NRs) to tune optical properties with the variation of Se concentration. The intercalation of Cu(I) into the presynthetic Bi2S3-xSex NRs converted to ternary Cu3BiS3-xSex NRs via cation exchange process. The transformation was monitored through the formation of core/shell Bi2S3-xSex/Cu3BiS3-xSex nanorod heterostructures. Shape anisotropy results in near-infrared bimodal localized surface plasmon resonance (LSPR) in Cu3BiS3-xSex nanorod over a broad range from 600 to 3500 nm with increase of Se:S ratio. The LSPR sensitivity, defined as the change in the LSPR peak wavelength per unit change in the refractive index (RI) of the medium, was estimated to be 250-350 nm/RI unit, much higher than other copper chalcogenides like Cu2S/Cu2Se. A fast photodetector was fabricated by Cu3BiS3-xSex NRs with high photocurrent gain value (similar to 125) with Se alloying. The intrinsic Cu vacancies and the effective mass of charge carriers play important roles to manipulate optical and electrical properties of Cu3BiS3-xSex NRs.