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.

The emission band of the isoelectronic impurity Te in CdS is investigated with static uniaxial stress, σ, applied to the crystal. It is suggested that the bandshape is due to strong electron‐LA‐phonon interaction, the corresponding coupling constant and the effective phonon energy are determined. The measured peak shifts and stress‐induced polarization of the emission band for σ ‖ c and the band splitting for σ ⟂ c are interpreted on the basis of first order perturbation theory. The symmetry group of the defect and the irreducible representations of the electronic states involved in the optical transition are obtained and confirm the bound exciton model proposed in [5].

Here, we describe how to synthesise proton-conductive transition metal phosphates (TMPs) by direct thermal processing of precursor M-struvites, NH4MPO4·6H2O, with M = Ni2+, Co2+. In the as-derived TMP phases their...

The characterization of technical lignins is a key step for the efficient use and processing of this material into valuable chemicals and for quality control. In this study 31 lignin samples were prepared from different biomass sources (hardwood, softwood, straw, grass) and different pulping processes (sulfite, Kraft, organosolv). Each lignin was analyzed by attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopy. Statistical analysis of the ATR-FT-IR spectra by means of principal component analysis (PCA) showed significant differences between the lignins. Hence, the samples can be separated by PCA according to the original biomass. The differences observed in the ATR-FT-IR spectra result primarily from the relative ratios of the p-hydroxyphenyl, guaiacyl and syringyl units. Only limited influence of the pulping process is reflected by the spectral data. The spectra do not differ between samples processed by Kraft or organosolv processes. Lignosulfonates are clearly distinguishable by ATR-FT-IR from the other samples. For the classification a model was created using the k-nearest neighbor (k-NN) algorithm. Different data pretreatment steps were compared for k = 1 … 20. For validation purposes, a 5-fold cross-validation was chosen and the different quality criteria Accuracy (Acc), Error Rate (Err), Sensitivity (TPR) and specificity (TNR) were introduced. The optimized model for k = 4 gives values for Acc = 98.9 %, Err = 1.1 %, TPR = 99.2 % and TNR = 99.6 %.