X-ray-charged bright persistent luminescence in NaYF₄:Ln³⁺@NaYF₄ nanoparticles for multidimensional optical information storage

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.