CaSc2O4 hosted upconversion and downshifting luminescence

Abstract

The special position of scandium (Sc) in the periodic table implies unique chemical and physical features of Sc-based compounds, particularly the relatively small Sc³⁺–Sc³⁺ distance in the corresponding crystal structures. Herein, we report our discoveries on the dual luminescent emissions of lanthanide-doped scandates, i.e., CaSc₂O₄:Yb/Ln (Ln = Tb, Eu) where a strong and nearly pure green upconversion emission with the green to red intensity ratio as high as 45 was obtained in CaSc₂O₄:Yb/Tb (5/0.1 mol%), and at a much lower doping concentration than those conventionally utilized, e.g., NaYF₄:Yb/Er (18/2 mol%). Meanwhile, downshifting emissions were also realized in both CaSc₂O₄:Yb/Tb and CaSc₂O₄:Yb/Eu at their characteristic working wavelengths (280 nm for Tb³⁺ and 395 for Eu³⁺), making them competitive candidates for multi-channel luminescent materials in terms of both excitation and emission wavelength modulation. Such decent optical performance is due to the relatively low photon energy, robust thermal stability, and rigid framework of CaSc₂O₄ defined by the ScO₆ octahedra, which allows efficient energy transfer.