Achieving a blue-excitable yellow-emitting Ca-LMOF phosphor 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(tcbpe-F)(HO)] (1, LMOF-411) has been constructed from calcium (Ca) and 1,1,2,2-tetrakis(4-(4-carboxyphenyl)phenyl)ethene (Htcbpe-F). Compound 1 features a three-dimensional framework with a 10-nodal net topology. Due to the relatively high hydration energy of Ca, compound 1 readily transforms into a new phase formulated as [Ca(Htcbpe-F)(HO)] (1') upon exposure to water. Combining experimental characterization and theoretical calculations, we elucidated the mechanism of HO-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 ( = 490 nm) under UV excitation, while compound 1' emits bright yellow light ( = 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).