Calcination temperature tuning of RTP and TADF with wide range of emission color from carbon dots confined in Al2O3

The room temperature afterglow (RTA) of carbon dots (CDs) and their wide-ranging application prospects have attracted significant attention. However, most of the synthesis and regulation methods for multicolor CDs-based RTA materials are complex. Therefore, it is still a challenge to obtain a series of CDs-based RTA materials with broad and tunable emission wavelengths via a simple preparation method using the same organic precursor and matrix. In this study, a series of CDs@Al2O3 materials with ultra-broad afterglow emission range (376 ∼ 619 nm) were prepared by regulating the reaction temperature through a one-step calcination method. High-temperature consumption led to a decrease of surface functional groups and conjugation size of CDs, resulting in the gradually blue-shifted emission from red to UV region. We also discovered a unique phenomenon where the afterglow emission mode of the material shifted from room temperature phosphorescence (RTP) to thermally activated delayed fluorescence (TADF) as the temperature increased, attributed to the stabilization of the excited triplet state from the strengthened crystallinity of Al2O3 matrix. Furthermore, a continuous emission at ∼ 471 nm attributed to the oxygen defects of the matrix was observed. Multiple anti-counterfeiting, information encryption, and fingerprint detection are demonstrated based on the unique RTA properties of CDs@Al2O3.