Towards substitution of rare-earth ions in scintillator materials

Scintillator materials are playing a major role in many applications where ionizing radiation detection is needed. Several excellent crystalline scintillators, in parallel with novel nano-scintillators and nano-composite systems, are being engineered. The intense research activity in this field is triggered by the needs of modern medical imaging and radiotherapy techniques, as well as by high energy physics, homeland security, and environmental applications. Most of these applications require high density scintillators with an intense and fast optical response in the nanosecond time scale. Such requirements are often pursued by employing rare-earth ions (RE) both as constituents of the host matrix and as luminescent activators. Single crystals and optical ceramics based on lutetium, yttrium, gadolinium mixed oxides doped with cerium or praseodymium are deeply investigated and in many cases they are already present in the market. These systems all display intense and fast scintillation responses thanks to the allowed 5d-4f transition of Ce or Pr featuring a decay time of few tens of ns. RE replacement in scintillators can be planned having clearly in mind application requirements and some examples of on-going research are proposed. In such cases high density is pursued by involving RE-free hosts like hafnates and tungstates; fast and efficient scintillation responses due to intrinsic, defect related, or ns2 ions related optical transitions are considered.