Manganese-Doped Nanocrystals for Smartphone-Based X-ray Imaging and Optical Storage

Lanthanide-doped materials suffer from intrinsically narrow emission bands, limiting their spectral matching efficiency with visible light-based cameras in a smartphone. To improve luminescence performance and practical applicability, we introduce a manganese metal doping strategy, synthesizing Gd3+, Mn2+ codoped NaYF4 nanocrystals via a hydrothermal approach. The crystal phase of the nanocrystal can be regulated by doping Mn and Gd to adjust the emission wavelength within the range of 526–570 nm under X-ray excitation, precisely matching both the human eye's sensitivity range and the peak detection efficiency of commercial CMOS sensors in smartphone cameras. The doped Gd3+ acts as an energy-trapping center and significantly enhances the luminescence intensity of Mn2+ by an energy transfer process. Furthermore, we embedded the nanocrystalline material in a flexible PDMS film to achieve smartphone-based X-ray imaging and a thermally stimulated system for information storage. The NaYF4:Gd3+, Mn2+ nanoparticles developed here could advance research on lanthanide–transition metal codoped fluoride systems, while enabling new cost-effective luminescent applications.