Color tunable upconversion luminescent perovskite fluoride with long /short lived emissions toward multiple anti counterfeiting
In contrast to simply static fluorescence, the introduction of time resolved visualized fluorescence in materials can significantly improve their anti counterfeiting performance; however, this remains challenging with photon upconversion (UC) luminescent materials. Herein, we demonstrate a color tunable UC luminescent perovskite fluoride KCdF3:Yb3+,Mn2+,Ln3+ (Ln3+ Er3+ Ho3+ Tm3+ with both long ~20 40 ms) and short ~0.4 2 ms) emission lifetimes. Under steady 980 nm laser excitation, color tunable steady UC fluorescence from yellow to red (or green) and yellow to blue (including UC white emission) could be easily achieved by tuning the doping concentration of Mn2+ and Ln3+ in the system; whereas, an unalterable yellow UC afterglow was observed by the naked eye when the excitation source was removed. Moreover, the upconversion nanoparticles (UCNPs) exhibited excellent pump power and temperature dependent luminescence stability. Static and dynamic photoluminescence analysis provided an understanding of the unique UC luminescence in this system, and a bidirectional energy transfer UC mechanism between Mn2+ (or Yb3+ Mn2+ dimer) and Ln3+ is presented. The multiple anti counterfeiting prototype using the unique UC luminescent materials demonstrated a high throughput authentication rate without the need for complex, time gated decoding instrumentation, suggesting their high potential for anti counterfeiting application, and also providing new insights for the design of photon UC luminescence materials.