Highly stable multicolor carbon dots created using o-phenylenediamine and terephthalic acid systems towards flexible emitting films

Multicolor carbon dots (CDs) with high stability are desired for various light emitting devices and bio-images. In this paper, the green and red emitting CDs were created by o-phenylenediamine and terephthalic acid (TA) as precursors at different temperatures via a solvothermal reaction. An efficient response surface methodology is developed to analyze the formation mechanism. Using optimized conditions, the green and red emitting CDs reveal photoluminescence quantum yields (PLQYs) of 34.0 and 26.8%, respectively. The result of response surface method indicates that temperature, precursor concentration, and TA amount significantly influence the PLQYs of the CDs. The formation mechanism of the CDs was proposed by analyzing solvatochromism phenomena, oxidation processes, and fluorescence lifetimes. Initially, green CDs with surface state luminescence were formed followed by the subsequent generation of red CDs exhibiting molecular and carbon core state emission during oxidation. These CDs reveal high stability, in which the PL intensity almost remained unchanged after 7 months. Furthermore, three-color CDs/polymer films (λem = 500, 536, and 568 nm) were successfully fabricated by using these two types of CDs. Sample 180-CDs/polystyrene film had photochromic properties, while other films had good photostability.