Nanocrystalline yttrium aluminium garnet (YAG, Y₃Al₅O₁₂) and Ce-doped YAG ceramics were synthesized by two ‘soft chemistry' sol–gel processes using (i) mixtures of inorganic salts or oxides and (ii) mixtures of alkoxides of the respective elements. In the first approach the metal ions, generated by dissolving metal oxides or nitrates in acetic acid and/or water, were complexed by ethylene glycol to obtain the precursors for pure and doped YAG samples. In the alkoxide route monolithic gels were obtained by hydrolysis and condensation of a compositional mixture of Al, Y and Ce alkoxides in a PrⁱOH solution. The molecular level mixing and the tendency of partially hydrolysed alkoxide species to form extended networks of cross-linked metal centers facilitates the structure evolution thereby lowering the crystallization temperature, in the latter case. The X-ray diffraction (XRD) patterns of the ceramic sintered at 700 °C were identical with the stoichiometric YAG composition which is the lowest temperature reported for the synthesis of crystalline and single phase Y₃Al₅O₁₂ while well developed YAG phases in the non-alkoxide synthesis were obtained only at 1000 °C. Cerium doped YAG powders (CeO₂ + Y₃Al₅O₁₂) were synthesized using [NH₄]₂[Ce(NO₃)₆] (8 mol%) and [Ce₃(OBu^t)₉(Bu^tOH)₂] (5 mol%), as dopants. A homogeneous distribution of cerium in the YAG lattice was achieved in both cases. The thermal behaviour, phase transformations, composition and microstructural features in the gels and polycrystalline samples were studied by TG/DTA, XRD, FT-IR, solid-state ²⁷Al MAS NMR spectroscopy, SEM, TEM, energy dispersive X-ray analysis and high resolution electron microscopy studies. The quality of the resulting products (homogeneity, crystallization temperature, grain size, grain size distribution, etc.) and economical aspects (synthetic skill, cost of precursors, etc.) of the two approaches are discussed.

Previous synthesis routes created apatites in low crystallinity and high crystallinity states, but a wider range will extend the design capabilities of apatites for hard tissue replacements. While high crystallinity apatites are more conventional, this work investigated lower crystallinity variations from an amorphous state to low crystallinity apatite. Carbonated hydroxyapatite was prepared by precipitating an amorphous phase followed by crystallization at 650 °C at slow (5 °C min⁻¹) and fast heating rates (60 °C min⁻¹). The effect of processing conditions on crystallinity and structural changes was evaluated by thermal analysis, X-ray diffraction, transmission electron microscopy, Fourier transform infrared and Raman spectroscopy. Furthermore, peak deconvolution of IR and Raman spectra resolved the carbonate and phosphate bands and revealed the carbonate and crystalline phase content in CHAp. Similar to precipitation of crystalline apatites, the crystallization at elevated temperature led to carbonate in both the phosphate and hydroxyl positions. Heating at 650 °C provided a nanosized spherical hydroxyapatite containing carbonate controlled by the heating rate. This creates a mechanism for creating a large range in crystallinity with a greater resorption capability for regenerative medicine.

A series of polycrystalline Li₃Ba₂La_3−xEu_x(MoO₄)₈ samples were prepared by the conventional solid-state reaction. The phase formation of the samples was investigated by X-ray diffraction measurements. The luminescence spectra and decay curves were studied as a function of Eu³⁺ concentration and temperature. It turned out that the optical band gap of the undoped molybdates is at 3.65 eV. The quantum efficiency (QE) of the Eu³⁺ doped luminescent materials increases with increasing Eu³⁺ concentration and almost 100% QE was obtained for those samples doped with 70, 80, or 90% Eu³⁺. A sample containing 100% Eu³⁺ showed solely a slight decrease in quantum efficiency. The luminous efficacy (LE) was 330 and 312 lm W_opt ⁻¹ for the 10 and 100% Eu³⁺ doped samples, respectively. The decrease of LE values is caused by a slight shift of the colour point to the red spectral range with increasing Eu³⁺ content. Temperature dependent measurements revealed that Li₃Ba₂Eu₃(MoO₄)₈ loses only 15% of efficiency up to 400 K, which demonstrates that the investigated phosphors are attractive for application in pcLEDs.