Dual-Mode Long-Lived Luminescence of Mn2+-Doped Nanoparticles for Multilevel Anticounterfeiting

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Luminescent nanoparticles with dual-mode long-lived luminescence are of great importance for their attractive applications in biosensing, bioimaging, and data encoding. Herein, we report the realization of up- and downconversion emission of Mn 2+ dopants in multilayer nanoparticles of NaGdF 4:Yb/Tm@NaGdF 4:Ce/Mn@NaYF 4 upon excitation at 980 and 254 nm, respectively. The dual-mode emission of the Mn 2+ dopants at 531 nm have a long-lived lifetime up to ∼30 ms as a result of the spin-forbidden optical transition of Mn 2+ within the 3d 5 configuration. After ceasing steady excitation at the two wavelengths, the long-lived feature of Mn 2+ luminescence allows a longer persistent time than lanthanide emissions, thereby enabling the ease of data decoding by a cell phone camera under a burst mode. The long-lived green upconversion emission also permits the generation of a long green tail emission upon dynamic excitation at 980 nm. These attributes make the as-prepared Mn 2+ -doped multilayer nanoparticles particularly attractive for multilevel anticounterfeiting.