Cerium-activated rare-earth orthophosphate and double-phosphate scintillators for x-and gamma-ray detection

When activated with an appropriate rare-earth ion (e.g., Ce or Nd), rare-earth orthophosphates of the form REPO4 (where RE = a rare-earth cation) and alkali rare-earth double phosphates of the form A3RE(PO4)2 (where A = K, Rb, or Cs) are characterized by light yields and decay times that make these materials of interest for radiation-detection applications. Crystals of the compound Rb3Lu(PO4)2 when activated with ∼0.1 mol % Ce exhibit a light yield that is ∼250% that of BGO with a decay time on the order of ∼40 nsec. The cerium-activated rare-earth orthophosphate LuPO4:Ce is also characterized by a high light yield and a relatively fast decay time of ∼25 nsec. Additionally, the rare-earth orthophosphates are extremely chemically, physically, and thermally durable hosts that recover easily from radiation damage effects. The properties of the rare-earth orthophosphates and double phosphates that pertain to their use as X- and gamma-ray detectors are reviewed. This review includes information related to the use of Nd-doped LuPO4 as a scintillator with a sufficiently energetic, short-wavelength output (λ = 90 nm) so that it can be used in conjunction with appropriately activated proportional counters. Information is presented on the details of the synthesis, structure, and luminescence properties of lanthanide double phosphates that, when activated with cerium, are efficient scintillators with output wavelengths that are sufficiently long to be well matched to the response of silicon photodiode detectors.