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%Pr 3+ /1%Er 3+ co-doped Bi 2 Mo 2 O 9 phosphor is reported with a low sintering temperature of 923 K. Pr 3+ in the Bi 2 Mo 2 O 9 host has a narrow emission band of 3 P 0 – 3 H 6 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 anti-counterfeiting 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 Bi 2 Mo 2 O 9 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.