The synthesis of long-wavelength emission fluorescent carbon dots is not common, and it is even more difficult to quickly synthesize within 10 min. In this experiment, yellow, orange, and red B, N codoped fluorescent carbon dots were successfully synthesized using a microwave-assisted method with o-phenylenediamine as the carbon-nitrogen source, boric acid as the boron source, and potassium chloride as the catalyst in just 7 min. Based on the different contents of B, N element doping, there are differences in their surface structures, resulting in differences in the luminescence properties of the synthesized carbon dots. Long-wavelength carbon dots can avoid interference from the blue fluorescence of filter papers and have a clearer display in information encryption. Therefore, three types of carbon dots were mixed with PVP to produce fluorescent inks, and anticounterfeiting and encryption patterns were designed on the filter paper, displaying different fluorescence information under sunlight and UV light. In addition, the rich fluorescent colors were combined ingeniously to enable secondary encryption of information in the form of binary codes that increase the difficulty of decoding. These indicate that the three synthesized long-wavelength carbon dots have good application prospects in information encryption.