Recently SrI2, a scintillator patented by Hofstadter in 1968, has been rediscovered and shown to possess remarkable
scintillation properties. The light output of SrI2:Eu2+ has been measured to be even higher than previously observed and
exceeds 120,000 photons/MeV, making it one of the brightest scintillators in existence. The crystal also has excellent
energy resolution of less than 3% at 662 keV. The response is highly linear over a wide range of gamma ray energies.
The emission of SrI2:Eu2+ and SrI2:Ce3+/Na+ is well-matched to both photomultiplier tubes and blue-enhanced silicon
photodiodes. While SrI2:Eu2+ is relatively slow, SrI2:Ce3+/Na+ has a fast response. SrI2 crystals with many different
dopant concentrations have been grown and characterized. In this presentation, crystal growth techniques as well as the
effects of dopant concentration on the scintillation properties of SrI2, over the range 0.5% to 8% Eu2+ and 0.5% to 2%
Ce3+/Na+, will be discussed in detail.
The growth and scintillating properties of undoped and Eu2+ doped Strontium Iodide indicate
excellent potential for gamma ray spectroscopy. Energy resolution at 662 keV was found to be as
good as 2.7% at 662 keV. The effect of purification by zone refining was also studied and crystal
growth of SrI2 by the Bridgman technique was found to be less subject to cracking compared to the
growth of lanthanum halide scintillators.
We find that the high-Z crystal Barium Iodide is readily growable by the Bridgman growth technique and is less
prone to crack compared to Lanthanum Halides. We have grown Barium Iodide crystals: undoped, doped with
Ce3+, and doped with Eu2+. Radioluminescence spectra and time-resolved decay were measured. BaI2(Eu)
exhibits luminescence from both Eu2+ at 420 nm (~450 ns decay), and a broad band at 550 nm (~3 μs decay)
that we assign to a trapped exciton. The 550 nm luminescence decreases relative to the Eu2+ luminescence
when the Barium Iodide is zone refined prior to crystal growth. We also describe the performance of BaI2(Eu)
crystals in experimental scintillator detectors.
Ceramic and single crystal Lutetium Aluminum Garnet scintillators exhibit energy resolution with bialkali
photomultiplier tube detection as good as 8.6% at 662 keV. Ceramic fabrication allows production of garnets that
cannot easily be grown as single crystals, such as Gadolinium Aluminum Garnet and Terbium Aluminum Garnet.
Measured scintillation light yields of Cerium-doped ceramic garnets indicate prospects for high energy resolution.