Low-temperature sintered Pr3+/Er3+codoped Bi2Mo2O9 microcrystals for multimode optical thermometry and anti-counterfeiting

Lanthanide-doped oxide materials generally require high sintering temperatures for optical applications such as temperature sensing and anti-counterfeiting. In this work, the highly crystalline 1%Pr3+/1%Er3+ co-doped Bi2Mo2O9 phosphor is reported with a low sintering temperature of 923 K. Pr3+ in the Bi2Mo2O9 host has a narrow emission band of 3P0-3H6 transition at 624 nm due to the suppressed broadening of electronic transitions in the homogeneous crystal field. Multimode temperature sensing is realized based on the upconversion and downshifting emissions as well as the luminescence lifetimes of the as-prepared phosphor. The temperature sensing based on the downshifting emission bands of this phosphor at 530 and 624 nm achieves the maximum absolute and relative sensitivities of 0.693 K-1 at 568 K and 1.88% K-1 at 483 K, respectively. For anticounterfeiting applications, this phosphor can display bright yellow fluorescence at the liquid nitrogen cooling temperature, rather than white or pale colors. The white-color emission of this phosphor excited by 254 nm can also be used for lighting. The lanthanide-doped Bi2Mo2O9 can achieve favorable luminescence performance at much lower sintering temperature than most oxide phosphors, and is not only stable but also has the potential for in-situ sintering on materials that are not resistant to high temperature.