Multiple Confinement-Limited Activation and Defect Effect Co-Triggered the Ultra-Long Lifetime of Carbon Dots

The luminescence process of carbon dots (CDs) is typically influenced by spin-forbidden transition, triplet exciton quenching, and non-radiative transition. Thus, it faces great challenges to achieve efficient and ultra-long lifetime afterglow for CDs. The commonly employed strategy to obtain efficient afterglow performance of CDs is to encapsulate CDs into a rigid matrix to protect the afterglow signal from quenching. Generally, the ultra-long lifetime and excellent luminescent properties of inorganic RTP (room temperature phosphorescence) nanomaterials attribute to the slow release of electrons trapped in defect states of the surfaces. This capture-release mechanism has advanced afterglow lifetime of CDs towards longer levels via the design of defect states. Anchoring CDs onto a rigid matrix can preserve the rigid structure for the restrictive effect, and also can create structural defects. Herein, as-prepared RHCDs@SiO2 composite can exhibit an ultra-long afterglow lifetime of 7.76 s, which is the highest value achieved for CDs in silica matrix to date. This composite is also successfully applied in anti-counterfeiting and cell imaging fields. The synergistic multiple confinement effect and defect effect from the composite provides a universal strategy to design and achieve the ultra-long afterglow lifetime of CDs.