Ultrahigh Room‐Temperature Photoluminescence from Few to Single Quintuple Layer Bi₂Te₃ Nanosheets

Abstract Owing to its narrow indirect bandgap, bulk bismuth telluride (Bi₂Te₃) exhibits exceptionally low room‐temperature photoluminescence (PL). Consequently, it remains challenging to achieve promising optical and optoelectronic performance from Bi₂Te₃. Moreover, due to the lack of plasmonic materials and available modulation methods, it is challenging to effectively control the surface plasmon resonance intensities in the visible region. Herein, thickness‐dependent photoluminescence studies unveil ultrahigh (282‐fold) room‐temperature photoluminescence (visible) from 20 quintuple layer Bi₂Te₃ nanosheets (NSs) compared to 200 quintuple layer NSs, attributable to a significant bandgap opening. Intriguingly, considerable photoluminescence quenching is observed beyond the thickness of 20 quintuple layer Bi₂Te₃. The PL emission is further optimized with reference to the number of quintuple layers, and the mechanism possibly responsible for such PL behavior is elucidated. Moreover, the thickness modulation is put forward as an effective strategy to control visible surface plasmon resonance energy modes and their intensities. Bi₂Te₃ nanosheets with large area and high crystallinity are fabricated on various silicon substrates by a facile hot‐pressing strategy, which facilitates investigation of intrinsic properties of 2D Bi₂Te₃. It is believed that these findings hold paramount importance in understanding the optical response of Bi₂Te₃ toward nanoscale variations and help build next‐generation transparent and flexible optoelectronic/plasmonic devices.