Fabrication of NIR-Vis Upconversion YO_1–<i>x</i>F_1+2<i>x</i>:Ln (Ln = Yb, Er, Ho, and Tm) Crystal Layers by Flux Coating and Investigation of Growth Manner

Abstract

High-quality upconversion YO_1–<i>x</i>F_1+2<i>x</i>:Ln (Ln = Yb, Er, Ho, and Tm) layers with good adhesion, comprising densely packed, plate-shaped idiomorphic crystals, were directly grown on stainless steel (SUS) substrates by flux coating. The LiNO₃–KNO₃ flux effectively promoted crystal growth. Additionally, the near-infrared-to-visible (NIR-vis) upconversion fluorescence properties of the YO_1–<i>x</i>F_1+2<i>x</i>:Ln crystal layers could be tuned by varying the type of dopant (Ln element). YO_1–<i>x</i>F_1+2<i>x</i>:Yb,Er, YO_1–<i>x</i>F_1+2<i>x</i>:Yb,Ho, and YO_1–<i>x</i>F_1+2<i>x</i>:Yb,Tm crystal layers showed red, green, and blue fluorescence, respectively, under 980 nm laser irradiation