The present invention concerns scintillator compositions comprising gadolinium halide and a dopant. The gadolinium halide and dopant material (e.g., GdI3:Ce) has surprisingly good characteristics including high light output, high gamma-ray stopping efficiency, fast response, low cost, good proportionality, and minimal afterglow, thereby making the material useful for various applications including, for example, gamma-ray spectroscopy, medical imaging, nuclear and high energy physics research, diffraction, non-destructive testing, nuclear treaty verification and safeguards, and geological exploration. The timing resolution of the scintillators of the present invention also provides compositions suitable for use in imaging applications, such as positron emission tomography (e.g., time-of-flight PET) and CT imaging.