Transformation of crystal structure induced by the temperatures in carbon dots (CDs)-based composites with multicolor fluorescence for white Light-Emitting-Diode (WLED)

Regulation of the fluorescence through crystalizing from the matrix in the Carbon dots (CDs)-based solid-state materials has been verified to be one of the effective methods, yet there are not only challenges in preparing such materials efficiently, but also insufficient insight into their regulation mechanisms. Here, a one-pot solvothermal route to synthesize a series of CDs-based composites with crystalline matrix is reported. These crystals exhibited multicolor fluorescence with the feature of multi-peaks emissions with increasing temperatures from 140 ℃ to 220 ℃, in which the orange emitting O-CDs@PA and the yellow emitting Y-CDs@PA crystals obtained the FLQYs of 22% and 68% respectively due to relatively stable crystalline structures. After comparative analysis to both crystals in detail, the core and the groups associated with them on the interface between CDs and matrix were adjusted in size and species during structural transformation of the crystal matrix, which changes radically the energy band structures to influence fluorescent emitting of both crystals ultimately. In addition, the reasons resulting in higher FLQY for Y-CDs@PA were provided leveraging the schematic illustration presumed based on the PL properties of both crystals. Because of the optimal optical performances, these fluorescent materials promised to fabricate WLED devices and obtained a number of photometric parameters endowed these WLED devices with the feature of warm-white light.