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

Abstract

Cooperative performance of mixed-valent Eu(2+) /Eu(3+) in single-compound phosphors offers significant advantages in color rendering and luminescence efficiency, but their synthesis is challenging because of Eu(2+) 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 Eu(2+) /Eu(3+) with a controlled ratio. These materials exhibit rich photoluminescence, including intrinsic- and sensitized-emissions of Eu(2+) and Eu(3+) , 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 Eu(2+) /Eu(3+) emissions provides outstanding properties for applications as self-calibrated luminescent thermometers with a wide working temperature range. Further incorporation of Tb(3+) into the MOFs results in white light, utilizing all Eu(2+) ,Tb(3+) , and Eu(3+) emissions in a single crystalline lattice.

Lanthanide‐Based Thermometers: At the Cutting‐Edge of Luminescence Thermometry

“…Recent examples on Tb 3+ /Eu 3+ ‐doped systems not discussed in these reviews and deserving remark are the works of Liu et al and Li et al The first paper reported an in situ reduction and crystallization route for preparing Eu 2+ /Eu 3+ ‐doped MOFs. The materials exhibit intrinsic‐ and sensitized‐emissions of Eu 2+ and Eu 3+ ions, besides a long‐lived luminescence from ligand‐to‐metal charge transfer.…”

“…The materials exhibit intrinsic‐ and sensitized‐emissions of Eu 2+ and Eu 3+ ions, besides a long‐lived luminescence from ligand‐to‐metal charge transfer. A ratiometric luminescent thermometer was demonstrated based on the linear relation between temperature and the intensity ratio of Eu 3+ (at 618 nm) and Eu 2+ (at 427 nm) emissions between 9 and 293 K . The second example described a MOF‐based thermometer based on Eu 3+ ‐to‐ligand back energy transfer and operative over a wide temperature range, including the physiological (12–320 K), upon excitation with visible light (450 nm) …”

Eu3+‐Activated Gd8V2O17: Energy Transfer, Luminescence, and Temperature‐Dependence Characteristics

“…In particular, the 5 D 0 state is a single level without any Stark splitting in any hosts. This can avoid the convolution of overlapping luminescence lines from different energy levels …”

“…Recently,w eh ave investigatedt he preparation, luminescence characteristics, and thermal stability of an ew phosphor of Gd 8 4 ] 3À with at etrahedral symmetry (T d ), aknown luminescence center,has the efficiento pticala bsorption of the charge transfer (CT) in the near-UVregion. [6] The self-activated emission is ab road peak at l = 400-750 nm.…”

“…This can avoid the convolution of overlapping luminescence lines from different energy levels. [8][9][10] Brusset et al [11,12] firstly reported the rare-earth vanadate T 8 V 2 O 17 ,where Trepresents aREi on site. However,the detailed structure is still controversial.…”