Rapid aqueous-phase synthesis of highly stable K0.3Bi0.7F2.4 upconversion nanocrystalline particles at low temperature

Bismuth-based fluoride nanocrystalline materials are an emerging class of host matrixes for luminescent ions with promising applications in optoelectronic devices and medical diagnosis. However, rapid aqueous-phase synthesis of highly stable bismuth-based fluoride nanocrystals at low temperature (room temperature ∼ 90 °C) is still a significant challenge. Herein we report an ultrafast (1 min only) and economical aqueous method to synthesize lanthanide-doped K0.3Bi0.7F2.4 upconversion nanocrystalline particles at low temperature. The resultant materials show exceptional upconversion luminescence performance under the excitation of a 980 nm near-infrared laser. More importantly, these fluoride nanocrystalline particles show excellent stability against high temperature up to 200 °C, high excitation power density (80 W cm−2) and prolonged water soaking (60 days or more). The proposed simple synthesis route, rare-earth free fluoride matrix, commendable upconversion luminescence performance and excellent chemical and thermal stability opens the door to access these lanthanide-doped K0.3Bi0.7F2.4 upconversion nanocrystalline particles for anti-counterfeiting and other daily applications.