Glowing kaolinite intercalated with N-Methyl imidazole and Eu³⁺/Tb³⁺ salts and potential application in UV-to-red light conversion

Kaolinite, one of the most ubiquitous clay minerals on the earth, is a hydrated aluminum disilicate with the composition of Al₂Si₂O₅(OH)₄, 1:1 dioctahedral and structurally asymmetric layers. This type of lamella mineral provides a platform to create artificially functional materials. Herein, we present a facile approach to prepare the glowing Kaolinites via a stepwise of intercalation of Kaolinite with N-Methyl imidazole (abbr. NMI) and Eu³⁺/Tb³⁺ nitrate salts in sequence, which are labeled as K-NMI-Eu and K-NMI-Tb, respectively, and characterized by microanalysis, thermogravimetric (TG), IR spectroscopy, powder X-ray diffraction techniques. Under ultraviolet irradiation, K-NMI-Eu and K-NMI-Tb emit the characteristic luminescence of Eu³⁺/Tb³⁺ ion with quantum yields of 25.5% (Eu³⁺) and 16.3% (Tb³⁺), respectively. We further fabricated the composite films of K-NMI-Eu with polyvinylidene fluoride (PVDF), K-NMI-Eu@PVDF-X (X = 1, 2, 5 and 10%, representing the mass percentage of K-NMI-Eu in film). The mechanical performances of composite films are almost the same as that of the pure PVDF film even if the X value is up to 10%. K-NMI-Eu@PVDF-10% emits intense red luminescence under ultraviolet irradiation at ambient condition, indicating that K-NMI-Eu is a good ultraviolet-converted-red light material potentially used for the agricultural light conversion film.