Highly efficient photoluminescence from isolated Eu3+ ions embedded in high-charge mica

Abstract

Incorporation of lanthanide ions in synthetic clay minerals is a promising approach to combine the efficient sharp-line emission of lanthanides with the unique structural stability and high adsorption capacity of high-charge micas. These aluminosilicate hosts are synthetic exchanger layered-clays which have demonstrated a unique selectivity in heavy metal and radionuclide capture. A phosphor based on the emission of Eu³⁺ ions homogeneously distributed in the dispersing inorganic-host high-charge mica Na₂[Mg₆]^VIII[Si₆Al₂]^IVO₂₀F₄ is reported. Eu³⁺ cations act as an ideal luminescent probe to study the physical–chemical adsorption mechanisms of the contaminants in the aluminosilicate. Despite the forbidden nature of the f–f transition involved, well-resolved Eu³⁺ luminescence is observed from both the ⁵D₀ and the ⁵D₁ Eu³⁺ states in the high-charge mica, and, in contrast to previous results, the use of an antenna for light absorption and transfer to the lanthanide is not required. The fluorinated nature and the absence of iron impurities, together with the homogeneous dispersion of lanthanide ions provided by Al³⁺, makes the high-charge mica a biocompatible host as an optical sensor or drug delivery material. Further evidence of the homogeneous distribution and isolation of Eu³⁺ cations in the hexagonal cavities of the mica is provided by spectroscopic luminescence and lifetime measurements.