Fig. 4: Applications of multicolor persistent luminescent nanoparticles to optical information storage

a–c Photographs of an inkjet printer (a), luminescent inks (b) and a quartz glass sheet with printed patterns (c) under natural light. d Photograph of the printed pattern under a fluorescence microscope. The size of a single printed pixel is ~60 μm. e PersL images of a printed pattern (emergency exit sign) with delay time from 0 to 600 s. The pattern was printed using the NaYF₄:Tb³⁺@NaYF4 ink and irradiated by the X-ray source for 5 min. f Schematic illustration of the application in 3-D optical information storage. The upper and lower figures illustrate the information write-in and readout processes, respectively. Three independent overlapping patterns were printed on a glass sheet. The luminescent patterns were activated after X-ray irradiation. Mixed information was read directly by an image sensor, and the patterns could be correctly decomposed by using specific optical filters. g, h The original images and monochromatic images after passing through 545BP, 570BP and 605LP filters. The transmittance spectra of the three optical filters are given in Figs. S21–S23. The scale bars are 100 μm in (d) and 10 mm in (e, g, and h), respectively.