Prospects for dense, infrared emitting scintillators

We present results from an ongoing search for inorganic scintillators for X-ray and gamma-ray detection. We measure the scintillation properties (luminous efficiency, decay time, and emission wavelength) of powdered samples excited by brief X-ray pulses. To find scintillators that are compatible with silicon photodetectors, we have tested over 1,100 samples using a photomultiplier tube with a GaAs:Cs photocathode, which is sensitive to 200-950 nm emissions. Optical filters are used to block emissions that are observable with bialkali PMTs. Several lanthanide and transition metal ions, molecular complexes, and II-VI compounds are known to have strong emissions at wavelengths >500 nm. We find that several compounds exhibit emission intensities comparable to commercial phosphors in the 600-900 nm range, including Eu and Sm doped LuPO₄, ScPO₄, and YPO₄. Significant emissions are also observed from Tb, Dy, Er, Pr, and Tm doped phosphates, as well as several intrinsic compounds, notably Hg₂Cl₂. Scintillation characteristics of promising compounds (in powdered or small crystal form) are presented