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This study reports on effects of dopant concentration and crystal size on some of the scintillation properties of SrI2:Eu2+. For example, the emission shifts to longer wavelengths as the dopant concentration is increased. It also results in scintillation decays getting slower: a 620 ns decay time constant observed for a small 0.5% Eu sample increases to 1650 ns for a 10%Eu sample. Similar changes in the time constant values were also observed when the crystal size was being increased. It also appears that larger samples yielded somewhat less light. These effects are attributed to radiation trapping, in which the scintillation light is multiple time absorbed and consequently emitted by the dopant. [ABSTRACT FROM AUTHOR]

Abstract: The high-performance inorganic scintillator, SrI2:Eu2+, when activated with divalent europium in the concentration range of 3–6%, has shown great promise for use in applications that require high-energy-resolution gamma-ray detection. We have recently grown and tested crystals in which other alkaline-earth ions have been partially substituted for strontium ions. Specifically, europium-doped single crystals have been grown in which up to 30at% of the strontium ions have been substituted for by barium, magnesium, or calcium ions. In the case of the strontium iodide scintillator host, a material that is characterized by an orthorhombic crystal structure, three other column IIA elements are obvious choices for investigations intended to realize potential improvements in the performance of SrI2:Eu2+-based scintillators via the replacement of strontium ions with Mg2+, Ca2+, or Ba2+. Light yields up to 81,400photons/MeV with an associated energy resolution of 3.7% (fwhm for 662keV gamma rays) have been observed in the case of partial substitution of Ba2+ for Sr2+. The measured decay times ranged from 1.1 to 2.0μs, while the peak emission wavelengths ranged from 432 to 438nm. [Copyright &y& Elsevier]

Abstract: Europium-doped barium and strontium iodide crystals are high light yield scintillator materials with excellent energy resolution. In this communication, BaI2:Eu and SrI2:Eu single crystals with space groups of Pnma () and Pbca () respectively were grown from the vertical Bridgman method. The crystals were investigated with polarized Raman spectroscopy at temperatures varied from 77 to 300 K. The observed Raman-active modes for each crystal were assigned with the help of group theory analysis. It is found that the absence of the site symmetry leads to splitting of a spectral line in Pnma structure into two lines in the Pbca structure. Structural defects including dark spots formed during crystal growth and new species produced from hydration were characterized. [Copyright &y& Elsevier]

Composite phosphor ceramics for warm white LED lighting were fabricated with K 2 SiF 6 :Mn 4+ (KSF) as both a narrowband red phosphor and a translucent matrix in which yellow-emitting Y 3 Al 5 O 12 :Ce 3+ (YAG) particles were dispersed. The emission spectra of these composites under blue LED excitation were studied as a function of YAG loading and thickness. Warm white light with a color temperature of 2716 K, a high CRI of 92.6, and an R9 of 77.6 was achieved. A modest improvement in the thermal conductivity of the KSF ceramic of up to 9% was observed with the addition of YAG particles. In addition, a simple model was developed for predicting the emission spectra based on several parameters of the composite ceramics and validated with the experimental results. The emission spectrum can be tuned by varying the dopant concentrations, thickness, YAG loading, and YAG particle size. This work demonstrates the utility of KSF/YAG composite phosphor ceramics as a means of producing warm white light, which are potentially suitable for higher-drive applications due to their increased thermal conductivity and reduced droop compared with silicone-dispersed phosphor powders.