Lanthanide-doped Bi2SiO5@SiO2 Core-Shell Upconverting Nanoparticles for Stable Ratiometric Optical Thermometry

The development of nanomaterials with high sensitivity to external stimuli such as temperature, is critical to investigate the driving force of biological processes but also catalytic mechanisms in extreme environments. However, the instability of nano-objects at high temperatures and different environments is a serious drawback limiting often their real use. This is particularly severe in the case of bismuth-based compounds, making the development of highly stable bismuth-based nanosystems a challenge. Here, we report the synthesis of uniform crystalline lanthanide-doped Bi2SiO5 nanoparticles into a silica shell of a controlled thickness (Bi2SiO5:Ln@SiO2) for the design of a reliable ratiometric optical thermometer stable at high temperatures and extreme acid environments. The fine control of the SiO2 shell thickness is modelled based on a theoretical and experimental approach. The formation of the Bi2SiO5 single phase is triggered by the local reactivity between Bi2O3 and SiO2, in the Bi2O3@SiO2 system,...