NaYF4:Ln3+, due to its outstanding upconversion characteristics, has become one of the most important luminescent nanomaterials in biological imaging, optical information storage, and anticounterfeiting applications. However, the large specific surface area of NaYF4:Ln3+ nanoparticles generally leads to serious nonradiative transitions, which may greatly hinder the discovery of new optical functionality with promising applications. In this paper, we report that monodispersed nanoscale NaYF4:Ln3+, unexpectedly, can also be an excellent persistent luminescent (PersL) material. The NaYF4:Ln3+ nanoparticles with surface-passivated core–shell structures exhibit intense X-ray-charged PersL and narrow-band emissions tunable from 480 to 1060 nm. A mechanism for PersL in NaYF4:Ln3+ is proposed by means of thermoluminescence measurements and host-referred binding energy (HRBE) scheme, which suggests that some lanthanide ions (such as Tb) may also act as effective electron traps to achieve intense PersL. The uniform and spherical NaYF4:Ln3+ nanoparticles are dispersible in solvents, thus enabling many applications that are not accessible for traditional PersL phosphors. A new 3-dimensional (2 dimensions of planar space and 1 dimension of wavelength) optical information-storage application is demonstrated by inkjet-printing multicolor PersL nanoparticles. The multicolor persistent luminescence, as an emerging and promising emissive mode in NaYF4:Ln3+, will provide great opportunities for nanomaterials to be applied to a wider range of fields.

Persistent luminescence (PersL) materials containing deep traps have attracted great attention in the field of optical information storage. However, the lack of nanomaterials with satisfactory light storage ability has become one of the main obstacles to the practical applications. In this work, NaMgF3:Tb3+@NaMgF3:Tb3+ nanoparticles are reported which exhibit excellent light storage ability into deep traps upon X‐ray irradiation and controllable photon emissions under thermal stimulation. A surface passivation strategy by constructing a core–shell structure is adopted, which is proved valid to greatly enhance the PersL efficiency. To understand the possible mechanism on the light storage and thermally stimulated PersL in the NaMgF3:Tb3+@NaMgF3 nanoparticles, an energy level diagram is built and the electronic transition processes are clarified. According to the proposed mechanism, the Tb3+ ions possibly serve as both emitting centers and trap centers in the NaMgF3 host during the X‐ray irradiation. Due to the excellent dispersibility and stability in water, luminescent inks containing the nanoparticles are successfully prepared and the applications to inkjet printing optical information storage and information decryption are demonstrated. The developed NaMgF3:Tb3+@NaMgF3 PersL nanoparticles may inspire further research on lanthanide‐activated fluoride PersL nanoparticles and provide new opportunities to the next‐generation information storage and biomedical technologies.