Enhanced upconversion emission in Er3+/Yb3+-codoped Al2Mo3O12 microparticles via doping strategy: Towards multimode visual optical thermometer

To explore highly sensitive luminescent materials , a series of Er 3+ /Yb 3+ -codoped Al 2 Mo 3 O 12 microparticles were prepared through a high-temperature solid-state reaction method. The phase structure, light harvest ability, morphology, and upconversion (UC) emission characteristics of these synthesized microparticles were investigated systematically. Excited at 980 nm, glaring visible UC emissions are gained in the developed specimens, in which the optimal doping content for Yb 3+ is 7 mol% and the two-photon absorption process contributes to the UC emission mechanism. Based on the fluorescence intensity ratio technology, the thermometric properties of resultant microparticles are studied by analyzing the temperature-dependent green UC emissions of Er 3+ arising from the thermal coupling energy levels. The maximum absolute and relative sensitivities of final products are 0.011 K -1 and 1.09% K −1 , respectively, and they are barely influenced by Yb 3+ contents. Besides, via exploring the lifetimes of 2 H 11/2 and 4 S 3/2 levels of Er 3+ at various temperatures, the relative sensitivities of resultant microparticles are determined to be 0.27% and 0.26% K −1 , respectively. Furthermore, the newly developed microparticles can be adopted to fabricate fluorescent ink to realize optical anti-counterfeiting and visual temperature monitoring. Our studies demonstrate that Er 3+ /Yb 3+ -codoped Al 2 Mo 3 O 12 microparticles with strong UC emissions possess great potential for multimode visual optical thermometry applications.