A universal fast and easy access at room temperature to transparent sols of nanoscopic Eu and Tb doped CaF, SrF and BaF particles via the fluorolytic sol-gel synthesis route is presented. Monodisperse quasi-spherical nanoparticles with sizes of 3-20 nm are obtained with up to 40% rare earth doping showing red or green luminescence. In the beginning luminescence quenching effects are only observed for the highest content, which demonstrates the unique and outstanding properties of these materials. From CaF:Eu10 via SrF:Eu10 to BaF:Eu10 a steady increase of the luminescence intensity and lifetime occurs by a factor of ≈2; the photoluminescence quantum yield increases by 29 to 35% due to the lower phonon energy of the matrix. The fast formation process of the particles within fractions of seconds is clearly visualized by exploiting appropriate luminescence processes during the synthesis. Multiply doped particles are also available by this method. Fine tuning of the luminescence properties is achieved by variation of the Ca-to-Sr ratio. Co-doping with Ce and Tb results in a huge increase (>50 times) of the green luminescence intensity due to energy transfer Ce → Tb. In this case, the luminescence intensity is higher for CaF than for SrF, due to a lower spatial distance of the rare earth ions.

Easy upscaleable one-pot synthesis method at room temperature for ultra small sized Eu3+- and Tb3+-doped CaF2 nanoparticles.

An efficient, fast and easy construction kit using the fluorolytic sol–gel synthesis of rare-earth-doped alkaline earth fluoride core–shell nanoparticles at room temperature is presented, capable of synthesizing several hundred grams to kilograms of core–shell particles in one batch.

Nanocrystalline Sr 1−x Y x F 2+x samples (0 ≤ x ≤ 0.50) were prepared by fluorolytic sol−gel and mechanochemical syntheses using anhydrous HF or NH 4 F as fluorinating agents. This way, we compare the generated nanoparticular nonstoichiometric phases synthesized by two different routes. The obtained nonstoichiometric fluorite-type phases were studied using 19 F magic-angle spinning (MAS) and 19 F− 89 Y CP MAS NMR techniques and applying the superposition model. The 19 F spectra of these phases can be fully explained by the distribution of Sr 2+ and Y 3+ cations around fluoride ions. These samples can serve as model compounds for a better structural understanding of fluorescent up-and down-converting systems.

Two systems of suspended nanoparticles have been studied with near-ambient pressure x-ray photoelectron spectroscopy: silver nanoparticles in water and strontium fluoride-calcium fluoride core-shell nanoparticles in ethylene glycol. The corresponding dry samples were measured under ultra high vacuum for comparison. The results obtained under near-ambient pressure were overall comparable to those obtained under ultra high vacuum, although measuring silver nanoparticles in water requires a high pass energy and a long acquisition time. A shift towards higher binding energies was found for the silver nanoparticles in aqueous suspension compared to the corresponding dry sample, which can be assigned to a change of surface potential at the water-nanoparticle interface. The shell-thickness of the core-shell nanoparticles was estimated based on simulated spectra from the National Institute of Standards and Technology database for simulation of electron spectra for surface analysis. With the instrumental set-up presented in this paper, nanoparticle suspensions in a suitable container can be directly inserted into the analysis chamber and measured without prior sample preparation.