Construction and multifunctional applications of carbon dots/PVA nanofibers with phosphorescence and thermally activated delayed fluorescence

Fluorescence of carbon dots (CDs) has grown well for substantial applications, but the long-lived photoluminescence, such as room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF), still catch less attention due to the serious deactivation of triplets under ambient conditions, leading to extremely low radiative efficiency. Herein, we simultaneously achieved both of them by incorporating CDs into poly(vinyl alcohol) (PVA) with the assistance of electrospinning technology. Through systematic investigation, ordered mesoporous structure from the electrospun CDs/PVA nanofibers can effectively stabilize the triplet states of CDs, thus enabling the reverse intersystem crossing (RISC) process for TADF and realizing the first example in CDs/polymer system. RTP is closely related to the triplet excited states of the carbonyls located at the surface of CDs and PVA molecule can rigidify these groups with hydrogen bonds, which can prevent quenching from atmospheric oxygen to promote the RTP and TADF behaviors in the air atmosphere. The afterglow spectrum of these nanofibers exhibits dual emission centered at 456 nm and 569 nm, originated from TADF and RTP, respectively. By changing the excitation wavelength or by adjusting the temperature of measurement, the color of the photoluminescence (PL) can be systematically tailored, the white-light emitting is promising. Moreover, these nanofibers show a long average afterglow lifetime of 1.61 s with visually recognizable period of 9 s. Moreover, CDs/PVA composites (nanofibers, solution, film, and aerogel) demonstrate potentialities in optical imaging, writing, anti-counterfeiting, temperature sensing.