Preparation and characterization of NaYF4:Er3+,Tm3+@NaYF4:Ce3+,Tb3+ microcrystals with dual-mode emissions at the single-particle level

Abstract Under hydrothermal environment, we synthesized lanthanide ions doped sodium yttrium fluoride (NaYF4:Er,Tm@NaYF4:Ce,Tb) luminescent microcrystals via an epitaxial growth technique. The structure and morphology of these microcrystals were examined by SEM, TEM, EDS and XRD measurements. These particles show dual-mode emissions with red upconversion (UC) and green down conversion (DC) as single particles level. The mean length and diameter of these microparticles increases from 0.43 to 2.26 μm and from 1.33 to 1.86 μm, respectively. Most interestingly, the photoluminescence properties of NaYF4:Er,Tm@NaYF4:Ce,Tb phosphor crystals are highly dependent on the crystallite size. The microcrystals fluoresce emit dual-mode emissions when they are solid or dispersed in solvents. Benefiting its intensive fluorescence and uniform morphology, these materials hold great potential for security and anti-counterfeiting applications.