Long-wavelength emission room-temperature phosphorescent carbon dots activated by an ortho-carboxyl substitution strategy and employed for achieving tunable LED

While room temperature phosphorescence (RTP) associated with carbon dots (CDs) has been widely achieved, obtaining long-wavelength emission RTP, especially while mitigating the quenching effect of water or dissolved oxygen, remains a challenging yet desirable goal. We synthesized three types of phosphorescent CDs with varying luminescent properties by using three precursors with carboxyls positioned differently. The formation process of these CDs resulted in a well-ordered and compact structure, effectively inhibiting molecular vibrations and reducing non-radiative transitions. Consequently, it successfully prevented the quenching effect of dissolved oxygen on the RTP of CDs in an aqueous environment. Significantly, PA-AIBN synthesized with phthalic acid, rather than iso-phthalic acid and terephthalic acid, exhibited long-wavelength emission RTP, with the phosphorescent emission center reaching as far as 640 nm. To be specific, the ortho-substituted carboxyls played a critical role in boosting the formation of intramolecular hydrogen bonds. Simultaneously, an increase in the doping levels of both nitrogen (N) and phosphorus (P) in PA-AIBN facilitated the long-wavelength emission RTP. The increased sp2 conjugated carbon core of PA-AIBN narrowed the optical band gap, contributing to the long-wavelength emission. Taken together, these factors cooperatively promoted the long-wavelength emission of RTP. Importantly, the PA-AIBN synthesized in this study exhibited a broad half-peak width and long-wavelength emission. It was successfully used in the preparation of white-light-emitting diodes without the need for commercial phosphor powder, demonstrating its enormous potential for practical lighting devices.