Europium fluoride based luminescent materials: From hydrogels to porous cryogels, and crystalline NaEuF₄ and EuF₃ micro/nanostructures

Europium fluoride based hydrogels, porous cryogels, and crystalline NaEuF₄ and EuF₃ nanostructures were prepared by wet chemical route at room temperature by using NaF or NH₄F as the reactants and gelation agents, in the absence of any other additives. The phase, morphology and thus resultant photoluminescence properties of luminescent products are demonstrated on the basis of the formation and evolution of europium fluoride complexes (EuF₆^3-). The characteristic emission of Eu³⁺ ions is strongly dependent on their existing states and also the adopted fluorides (both cations and anions of NaF or NH ₄F). The amorphous NaF- and NH₄F-mediated cryogels with highly porous structure and uniform distribution of optically active Eu ³⁺ ions show much (one or two order) stronger luminescence intensity than their corresponding hydrogels and crystalline NaEuF₄ and EuF₃ nanostructures.