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The structural and vibrational properties of nanocrystalline yttrium orthoaluminate perovskite (YAlO3) under compression have been experimentally studied. Experimental results have been compared to ab initiosimulations of bulk YAlO3in the framework of the density functional theory. Furthermore, they have been complemented with an ab initiostudy of its elastic properties at different pressures. Calculated total and partial phonon density of states have allowed us to understand the contribution of the different atoms and structural units, YO12dodecahedra and AlO6octahedra, to the vibrational modes. The calculated infrared-active modes and their pressure dependence are also reported. Finally, the pressure dependences of the elastic constants and the mechanical stability of the perovskite structure have been analyzed in detail, showing that this phase is mechanically stable until 92 GPa. In fact, experimental results up to 30 GPa show no evidence of any phase transition. A previously proposed possible phase transition in YAlO3above 80 GPa is also discussed.

The effects of pressure on the behavior of optical microspherical resonators, prepared from Nd^3+ doped, barium titanium silicate glass, have been studied up to 5 GPa inside a diamond anvil cell using silicone oil as the hydrostatic transmission medium and ruby emission lines as the pressure gauge. The optical resonances, known as whispering gallery modes, were observed within the broad emission band of the Nd^3+ ions, and the resonances were identified as a function of pressure. By means of simulations, it was found that the average wavelength position of both transverse electric and magnetic modes depended on the radius and refractive index of the sphere, but not on the refractive index of the pressure transmitting medium under the experimental conditions. This was used to define the average sensitivity of the resonant modes with the pressure. Therefore, a value of 6.5×10^−4  GPa^−1 has been obtained for this sensitivity, which is higher than the value for ruby, the most conventional pressure sensor.

Luminescence of Mn2+ in A sites in natural and synthetic MgAl2O4 spinel has been studied. In the near perfect structure of the natural crystals the degenerate levels of the Mn2+ are splitted due to a symmetry lower than tetrahedral. In synthetic crystals the structure of the spectra is lost as a consequence of the superposition of partial spectra related to Mn2+ ions perturbed by the cationic disorder of the lattice. Thermal annealing modifies the spectra of natural crystals making them similar to those of the synthetic ones due to an order-disorder transition.

A study of the optical properties of the Eu3+ ions in borate glasses and their correlation with the local environment of the ions is presented. From luminescence spectra and emission decay curves with narrow band excitation of the 5Do level, the Judd-Ofelt parameters are calculated as a function of the excitation wavelength. In codoped glasses the non radiative energy transfer process from Eu to Ho has been studied; the energy transfer parameter is also found to depend on the wavelength excitation.