Matrix-free nitrogen-doped carbon dots with room temperature phosphorescence for information encryption and temperature detection

Matrix-free nitrogen-doped carbon dots (n-CDs) with room temperature phosphorescence were successfully prepared by a simple one-step hydrothermal method. The as-prepared n-CDs exhibit good biocompatibility and water solubility and show blue fluorescence and green phosphorescence. More importantly, the n-CDs exhibit a stable phosphorescence and their phosphorescence lifetime is 139 ms. Owing to vibration, the phosphorescence intensity of the n-CD powder linearly decreases with increasing temperature. The as-prepared n-CD test paper can be applied in temperature monitoring as a probe; the monitoring results are consistent with those of a traditional thermometer. Furthermore, the n-CD solution can also be used in the field of advanced information security as an encryption ink.