Rare-earth incorporation in oxide scintillator crystals, glasses, and nanostructures: Optical emission and beyond

Rare earth ions (RE) are characterized by a great variety of optical transitions that make them very attractive as luminescent activators in many optical applications including lighting devices, lasers, solar energy materials, and ionizing radiation sensors. Moreover, several insulating oxide materials are considered good hosts for RE ions. After doping, the RE energy levels can lie within the host band-gap and confer an optical activity to otherwise transparent systems. In this lecture it will be shown that, besides optical functionalization, RE incorporation in a host can simultaneously give rise to other modifications (thermodynamic, morphological, and structural) that can be controlled in order to engineer a material for a specific application. This is for example the case of mixed Lu2xGd2−2xSiO5 scintillator crystals doped with Ce, in which Gd causes a lowering of the melting temperature, a subsequent reduction of anion defects and a clear improvement of scintillator performances [1]. In silica-based sol-gel glasses, RE incorporation allows to realize scintillating optical fibers [2]. However at concentrations above 1 mol%, RE ions tend to aggregate in the form of crystalline or amorphous clusters. These nano-structures are mostly non luminescent. An exception is the case of Eu doped SiO2 in which crystalline Eu2Si2O7 pyrosilicate nanocrystals are formed and display a very high luminescence efficiency [3]. Finally, incorporation of optically active RE (like Eu and Tb) above 5 mol% in nano-crystalline Hafnia gives rise to intense luminescence emission together with lattice simmetry modification from monoclinic to cubic, opening application perspectives to the material for the realization of nano-composites and ceramics [4]. 1. O. Sidletskiy et al., Phys. Rev. Appl. 4, 024009 (2015). 2. I. Veronese et al., Appl. Phys. Lett. 105, 061103 (2014). 3. A. Baraldi et al.,J. Phys. Chem. C 117, 26831 (2013). 4. A. Lauria et al., ACS Nano 7(8), 7041 (2013).