Luminescence-Monitored Progressive Chemical Pressure Implementation Realized through Successive Y 3+ and Mg 2+ Doping into Ca 10.5 (PO 4 ) 7 :Eu 2 .

Chemical pressure generated through ion doping into crystal lattices has been proven to be conducive to exploration of new matter, development of novel functionalities, and realization of unprecedented performances. However, studies are focusing on one-time doping, and there is a lack of both advanced investigations for multiple doping and sophisticated strategies to precisely and quantitatively track the gradual functionality evolution along with progressive chemical pressure implementation. Herein, high-valent Y 3+ and equal-valent Mg 2+ is successively doped to replace multiple Ca sites in Ca 10.5 (PO 4 ) 7 :Eu 2+ . The luminescence evolution of Eu 2+ serves as an optical probe, allowing step-by-step and atomic-level tracking of the site occupation of Y 3+ and Mg 2+ , interassociation of Ca sites, and ultimately functionality improvement. The resulting Ca 8 MgY(PO 4 ) 7 :Eu 2+ displays a record-high relative sensitivity for optical thermometry. Utilization of the environment-sensitive emission of Eu 2+ as a luminescent probe has offered a unique approach to monitoring structure-functionality evolution in vivo with atomic precision, which shall also be extended to optimization of other functionalities such as ferroelectricity, conductivity, thermoelectricity, and catalytic activity through precise control over atomic diffusion in other types of substances.