Nanocrystallization of lanthanide-doped KLu2F7–KYb2F7 solid-solutions in aluminosilicate glass for upconverted solid-state-lighting and photothermal anti-counterfeiting

Abstract

In situ nanocrystallization of homogeneously distributed Lu–Ln (Lu = La–Lu, Sc) solid-solution potassium lanthanide fluorides inside the same aluminosilicate glass matrix is reported. These precipitated nanocrystals exhibit Ln³⁺ radius dependent phase structures, i.e., cubic K(Lu/Ln)₃F₁₀ for large-radius Ln³⁺ ions and orthorhombic K(Lu/Ln)₂F₇ for small-radius Ln³⁺ ones. Particularly, a Lu–Yb system shows the ability to completely substitute between Lu and Yb in the K(Lu/Yb)₂F₇ nanocrystals, and Er (2 mol%):K(Lu_0.5Yb_0.5)₂F₇@glass yields the best upconversion quantum yield of 0.7%, which is far higher that the value of well-known Yb/Er (20/2 mol%):NaYF₄@glass (0.13%). Taking Er/Tm:K(Lu_0.5Yb_0.5)₂F₇@glass as a color converter, a 980 nm laser-driven upconverted lighting device can be constructed to produce bright white-lighting with an optimal luminous efficiency of 0.53 lm W⁻¹ and an energy efficiency of 1.31%. In addition, Er:KYb₂F₇@glass shows a significant photothermal effect owing to 100% Yb³⁺ host ions, leading to 980 nm laser-power-sensitive upconversion luminescence colors. As a proof-of-concept experiment, a specially designed Er:KYb₂F₇@glass-based flower pattern with tunable upconversion colors is adopted to demonstrate its practical application in high-end anti-counterfeiting.