Tuning Mixed-Valent Eu2+/Eu3+ in Strontium Formate Frameworks for Multichannel Photoluminescence.

Cooperative performance of mixed-valent Eu2+/Eu3+ in single-compound phosphors offers significant advantages in color rendering and luminescence efficiency, but their synthesis is challenging because of Eu2+ oxidation. Using the tunable nature of the metal-ion nodes in metal-organic frameworks (MOFs), we present an in situ reduction and crystallization route for preparing MOFs and doping Eu2+/Eu3+ with a controlled ratio. These materials exhibit rich photoluminescence, including intrinsic- and sensitized-emissions of Eu2+ and Eu3+, and long-lived luminescence from charge transfer. Color rendering can be easily achieved by fine-tuning the valence states of Eu. A linear relation between temperature and the intensity ratio of Eu2+/Eu3+ emissions provides outstanding properties for applications as self-calibrated luminescent thermometers with a wide working temperature range. Further incorporation of Tb3+ into the MOFs results in white light, utilizing all Eu2+,Tb3+, and Eu3+ emissions in a single crystalline lattice. [ABSTRACT FROM AUTHOR]