Metal–Organic Framework-Assisted Rational Design of Multicolor Solid-State Fluorescent Carbon Nanodots and Its Application for LEDs

Carbon nanodots (CDs) are a new type of carbon-based fluorescent nanomaterials, but they are limited in many applications due to the inherent fluorescence weakening and quenching problems suffered in solid state. Herein, ZIF-8, a class of metal–organic framework (MOF) is employed as a matrix to immobilize fluorescent CDs, resulting in the strong luminescence of CDs achieved in solid state. The as-synthesized CDs@ZIF-8 fluorescent powders possess blue, green, and red emissions with the main emission at ≈495, 528, and 600 nm, and the corresponding photoluminescence quantum yields (PLQYs) are as high as 25.89%, 52.24%, and 15.42%, respectively. It is found that the encapsulation of ZIF-8 with CDs will increase the excitation dependence of the product fluorescence, which may be attributed to the carrier effect of ZIF-8 as a carrier of CDs and some surface defects or surface functional groups change of the CDs introduced by ZIF-8. In addition, the encapsulation of CDs with ZIF-8 may result in the charge transfer. Importantly, the prepared CDs@ZIF-8 phosphors present a promising application in the fabrication of monochromatic light-emitting diodes (LEDs). The synthesis design is expected to provide technical support for future solid-state fluorescent CDs preparation and applications.