Controlled and Tunable Light Emission of Heat Treated Black Phosphorus: Towards Tunable Optoelectronic Devices*

Layered black phosphorus (BP) has shown exceptional optical properties due to its layer-dependent band gap, which ranges from 0.3 to 1.7 eV for bulk to monolayer, respectively. However, instability of black phosphorus nanosheets can be a major hurdle in controlling this light emission and requires various passivation methods. Moreover, the tunablility of the emitted light can only be controlled by changing the nanosheet thickness, which in turns changes the band gap energy. Here, we show for the first time a well-controlled tunable light emission from heat treated black phosphorous nanosheets. We show tunable wideband photoluminescence (PL) between 590nm to 720nm, with a tunablilty resolution of 5nm. This tunable PL is found to be anisotropic and can last for at least 10 days when nanosheets are properly stored. We attribute the origin of this light emission to the formation of stable black phosphorus oxide on the surface of black phosphorus, as confirmed with i-XPSmeasurements. Our findings unlock doors for optoelectronic applications of layered black phosphorus nanosheets.