Governing the incorporation of rare earth ions in sol-gel silica: from microscopic mechanisms of nano-cluster formation to the realization of scintillating optical fibres

The recent progresses in the development of scintillating rare-earth (RE) doped silica fibres for real time in-vivo medical dosimetry applications and high energy physics detectors are described. First, the incorporation features of RE3+ ions in sol-gel silica are reviewed considering dopant concentrations and synthesis parameters. Structural (TEM, XRD) and vibrational (Raman, FTIR) studies, coupled to optical investigations, have allowed to find the most suitable RE concentrations and synthesis conditions for optimizing both radioluminescence efficiency and RE dispersion, avoiding the formation of aggregates [1, 2]. Nano-aggregates are indeed formed for RE concentrations exceeding 1 mol%. Amorphous clusters are detected for Gd, Tb, and Yb dopings. Moreover, cluster formation turns out to be sensitive to glass sintering conditions: amorphous Ce-based clusters are detected in Ce-doped glass sintered in reducing conditions, while CeO2 nanocrystals are formed under oxidizing conditions. In the case of Eu doping cristalline and highly luminescent Eu2Si2O7 nanoaggregates are formed [3, 4 and references therein]. After a general description of advantages and challenges for the use of optical fibre based dosimeters during radiation therapy treatment and diagnostic irradiations, recent results obtained by using cerium and europium doped silica optical fibres in medical applications are reviewed [5]. Finally, the perspectives and open problems for the employment of doped silica fibres in high energy physics detectors are discussed.