Phenylenediamine-derived near infrared carbon dots: The kilogram-scale preparation, formation process, photoluminescence tuning mechanism and application as red phosphors

Kilogram-scale preparation of near infrared (NIR) carbon dots (C-dots) from o-phenylenediamine (o-PDA) with over 96% yield was reported in this study, and the estimated cost for each gram of C-dots was only $ 0.1. The formation process of the C-dots was elucidated and the structural model was also proposed in which the key intermediates were revealed. Excitingly, the optical properties of the C-dots could be reversibly tuned via a facile protonation-deprotonation process. Upon protonation, fluorescence emission wavelength of the C-dots could be red shifted for 47 nm, and deprotonation could enhance the photoluminescence quantum yield by three times. These optical alterations were attributed to stabilization of the excited electrons by the surface protons, and diagrams showing the electronic transition states of the C-dots were proposed according to the calculated band gaps. The as prepared C-dots demonstrated themselves as cheap and readily available phosphors for the assembling of red LEDs.