Achieving a blue-excitable yellow-emitting Ca-LMOF phosphor via water induced phase transformation

Luminescent metal–organic frameworks (LMOFs) with diverse structural features and promising fluorescence-based applications have attracted wide attention in the past two decades. In this work, a LMOF with the formula [Ca(4)(tcbpe-F)(2)(H(2)O)(3)] (1, LMOF-411) has been constructed from calcium (Ca) and 1,1,2,2-tetrakis(4-(4-carboxyphenyl)phenyl)ethene (H(4)tcbpe-F). Compound 1 features a three-dimensional framework with a 10-nodal net topology. Due to the relatively high hydration energy of Ca(2+), compound 1 readily transforms into a new phase formulated as [Ca(H(2)tcbpe-F)(H(2)O)(2)] (1′) upon exposure to water. Combining experimental characterization and theoretical calculations, we elucidated the mechanism of H(2)O-induced phase transition from 1 to 1′. Notably, the water induced phase transformation can be detected visibly from the change in luminescence, which originates from the fluorescent linker. Compound 1 emits green light (λ(em) = 490 nm) under UV excitation, while compound 1′ emits bright yellow light (λ(em) = 550 nm) under blue excitation (450 nm). Compound 1′ represents the first Ca based LMOF yellow phosphor and its luminescence quantum yield reaches 68%. It can be coated directly onto a commercial blue light-emitting-diode (LED) chip to fabricate a white LED (WLED).