Surface-Oxidation-Controlled Synthesis of Blue Fluorescence Wavelength-Tunable Mini-Size Carbon Nitride Nanosheet and Its Application

Developing highly efficient, stable, and saturated blue emitting polymer is essential in display and lighting applications and has long been a challenge. In this study, blue fluorescence wavelength-tunable mini-size carbon nitride nanosheets (MCNNSs) are successfully synthesized via surface oxidation polyethyleneimine (PEI) without introducing any external solvent. A simple closed container is constructed at high temperature for the controlled oxidation of PEI effectivelly. The obataind fluorescence quantum yields (QYs) of MCNNSs are up to 35% by using quinine sulfate (QY: 54%) in 0.10 M H₂SO₄ as a reference. More importantly, the tunable width of blue fluorescence emission wavelengths is about 50 nm ranging from 414 to 461 nm, which can be realized through change temperature. Additionally, an obvious blue fluorescence is found in PEI solutions at low temperature even at 50 ^oC under UV riddiation. According to surface oxidation of PEI, the MCNNSs have been applied in fluorescence image of HeLa cell. Meantime, a paper-based new information encryption strategy is developed using MCNNSs, and a correct code “2017” is visualized only after baking the encryption paper at 100 ^oC under 365 nm excitation. These investigations will shed light on the use of MCNNSs in bioimaging and information encryption, as well as blue light materials used in OLED.