Molten Salt Synthesis and Upconversion of Cubic ZrO2 Submicron Phosphors for Temperature Sensor and Anticounterfeit Applications

Zirconia (ZrO2) is an excellent host material in the luminescent materials field because of its low phonon energy. Nevertheless, owing to a very high melting point of 2715 °C, preparation of cubic ZrO2 by the solid-state reaction must be done at high temperatures (>1400 °C). Here, we report a molten salt method (MSS) process to obtain rare earth-doped cubic ZrO2 phosphors in an air environment at 1200 °C, which has a relatively low preparation temperature with submicrometer size and fine control over the crystal morphology. Consequently, we successfully synthesized upconverting multicolor ZrO2 submicron phosphors by tuning the activators with a Yb3+ sensitizer under 980 nm excitation. Additionally, the submicron phosphors exhibit multifunctional applications, notably in temperature sensor and anticounterfeiting fields.