Nanocrystallization of lanthanide-doped KLu2F7–KYb2F7 solid-solutions in aluminosilicate glass for upconverted solid-state-lighting and photothermal anti-counterfeiting†
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(Lu0.5Yb0.5)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(Lu0.5Yb0.5)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.