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

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.