Aphen-derived N-doped white-emitting carbon dots with room temperature phosphorescence for versatile applications

For most of the carbon dots (CDs), solid-state fluorescence and room temperature phosphorescence (RTP) are difficult to achieve due to self-quenching and intersystem crossing (ISC) limitations. Here, nitrogen-doped CDs-1 showing both fluorescence and RTP was obtained by hydrothermal reaction from polyvinyl alcohol (PVA) and 5-amino-1,10-phenanthroline (Aphen). The CDs-1 emits blue-green fluorescence in aqueous solution, while emits white fluorescence and yellow-green RTP in the solid state with a RTP lifetime up to 103 ms, exhibiting a long afterglow with a duration of 3 s, which is visible to the naked eyes. The RTP of the CDs-1 is derived from the CeN/C=N in Aphen and C=N/CN in Aphen and C=O produced during the carbonization process with a small energy gap between the singlet and triplet states, which helps to realize the ISC. At the same time, the hydrogen bonds between the C=N/CN or CO bonds and O-H of the not completely carbonized PVA chains on the CDs-1 surface have the advantages of moisture resistance, oxygen barrier and improving the rigidity of CDs-1. Eventually, non-radiative transitions can be suppressed. Based on the decent fluorescence properties, the aqueous solution of CDs-1 can be used to detect TNP and is responsive to pH with a good linear relationship between acid and alkali. In addition, the RTP of CDs-1 can be utilized as banknote anti-counterfeiting material under a long excitation wavelength. This work provides a possibility to realize the multi-mode illumination regulation of CDs by facile one-step strategy.