Vibrational properties of anatase titanium dioxide single crystal are thoroughly investigated by means both of experimental and theoretical approaches. Polarized Raman-scattering experiments were carried out at room temperature in backscattering geometry on a microcrystalline anatase sample under different crystal orientations set by a micromanipulator. All the independent components of the polarizability tensor were separately obtained. In particular, it was possible to evidence, in turn, the different components of the A1g mode, thus unambiguously determining its peak wave number, and then, definitively resolve and identify the A1g and B1g modes of anatase. Moreover, ab initio calculations based on density-functional perturbation theory within the generalized gradient approximation have been performed to evaluate infrared (IR) and Raman modes, dielectric tensors, Born effective charges and TO-LO splitting of the IR modes. The agreement between computational and experimental results is much better than the one achieved in previous computational works.

Colloidal Er³⁺/Yb³⁺, Tm³⁺/Yb³⁺ and Ho³⁺/Yb³⁺ doped CaF₂ nanoparticles have been prepared by a one-pot hydrothermal procedure and their upconversion properties have been investigated.

Nanocrystalline Lu(3)Ga(5)O(12), with average particle sizes of 40 nm, doped with a wide variety of luminescent trivalent lanthanide ions have been prepared using a sol-gel technique. The structural and morphological properties of the powders have been investigated by x-ray powder diffraction, high resolution transmission electron microscopy and Raman spectroscopy. Structural data have been refined and are presented for Pr(3+), Eu(3+), Gd(3+), Ho(3+), Er(3+) and Tm(3+) dopants, while room temperature excited luminescence spectra and emission decay curves of Eu(3+)-, Tm(3+)- and Ho(3+)-doped Lu(3)Ga(5)O(12) nanocrystals have been measured and are discussed. The Eu(3+) emission spectrum shows typical bands due to 5D(0)-->7F(J) (J = 0, 1, 2, 3, 4) transitions and the broadening of these emission bands with the non-exponential behaviour of the decay curves indicates the presence of structural disorder around the lanthanide ions. Lanthanide-doped nanocrystalline Lu(3)Ga(5)O(12) materials show better luminescence intensities compared to Y(2)O(3), Gd(3)Ga(5)O(12) and Y(3)Al(5)O(12) nanocrystalline hosts. Moreover, the upconversion emission intensity in the blue-green region for the Tm(3+)- and Ho(3+)-doped samples shows a significant increase upon 647.5 nm excitation with respect to other common oxide hosts doped with the same lanthanide ions.