Potential of Nano-Sized Rare Earth Fluorides in Optical Applications

Abstract

Rare earth fluorides are a class of materials with a high potential for optical applications. Fluoride lattices allow high coordination numbers for the hosted rare earth ions, but the high ionicity of the rare earth to fluorine bond leads to a wide band gap and very low vibrational energies. These two essential factors, in particular, contribute to their practicality for use in optical applications based on vacuum ultraviolet (VUV) and near infrared (NIR) excitation. The preparation and optical characteristics of rare earth fluoride nanoparticles and their embedding in polymeric, glassy or porous matrices are very promising for the eventual manufacture of transparent hybrid materials. Recent attempts to control the size of these particles down to the nano-scale and, at the same time, maintaining the performance of their macroscopic counterparts, indicate accessibility of hitherto unrealized optical properties and applications.

Synthesis and optical characterization of rare earth nanofluorides

“…On the optical side, the feasibility of zeolites supported luminescence, in particular, has been demonstrated for ions, complexes and molecules [7][8][9][10]. However, most likely due to the high reactivity of the zeolite matrix towards fluorides, reports on the optical performance of encapsulated fluoride species have been presented only recently [11]. Fluorides encaged within the zeolites were obtained using either a direct synthesis by treating rare earth ion exchanged zeolite X [8] in vacuum with an excess of Ammoniumfluoride at elevated temperatures (10 equivalents of NH 4 F per rare earth ion, 250°C) or by decomposing fluoride containing precursor complexes, which were also prepared via the gas phase (typically at 150°C; trifluoracetic acid, H(tfa); hexafluoracetylacetone, H(hfa); bisperfluormethylsulfodiimine H(pms); see Fig.…”

Fluorescence enhancement of Ln3+ doped nanoparticles

“…Wide bandgaps and low phonon energies resulting from the high ionicity of Ln-fluorine bonds are expected for luminescent Ln 3+ ions especially emitting in the NIR region [37,38]. Therefore, it is not surprising that most of the core materials are fluoride complex in the study of core/shell configurations.…”