Synthesis and experimental and theoretical characterization of rare earth doped garnets and nano-garnets at extreme conditions

Resumen

Garnets have very interesting physicochemical properties like hardness, high optical transparency and good mechanical and chemical stability. In the last decades, the garnet structure is being used as rare earth host matrix for different further applications. The rare earths are characterized by their excellent magnetic and spectroscopic properties. From the optical point of view, the combination of the great luminescence properties of rare earths and the crystal stability of the garnets makes them useful for the development of new lasers, sensing and imaging in biomedicine and as an alternative to quantum dots in photonics and optoelectronic devices for engineering. The high pressure and temperature studies play an important role in the understanding of the properties of these mineral garnets and nanometer size grain powder garnets. The knowledge of pressure dependent optical properties of these materials and nano-materials is important for future application as pressure sensors in extreme conditions experiments, as alternative to ruby. In this work the Y3Ga5O12 (YGG) and Lu3Ga5O12 (LuGG) single crystal and nanocrystalline garnets are studied in detail in order to carry out a complete and exhaustive study of their structural, electronic and stability properties under high pressure from a theoretical and experimental point of view. Ab initio calculations were performed within the Density Functional Theory with the VASP package using the PAW and GGA approximations. The structural, electronic and elastic properties and lattice dynamics and mechanical stability are analyzed up to 90 GPa. The YGG and LuGG structures have a high stability since they become unstable above 84 and 87 GPa respectively. Experimentally, the optical and vibrational characterization of the Er3+-doped YGG and pure YGG and LuGG nano-garnet were carried out through optical spectroscopy (OS) and Raman scattering (RS) measurements up to 60 GPa. OS experiments were developed at The Laser Spectroscopy and High Pressure Laboratory at The University of La Laguna while the RS were performed at the Technical University of Valencia. As a general conclusion, there is an excellent agreement between the results obtained by theoretical calculations and these by experiments.