A radiation detector device is disclosed that includes a scintillator including a scintillator crystal and a hybrid photodetector (HPD) coupled to the scintillator. The HPD includes an electron tube having an input window and a photocathode adapted to emit photoelectrons when light passing through the input window strikes the photocathode. Further, the hybrid photodetector includes an electron detector adapted to receive photoelectrons emitted by the photocathode. The electron detector comprises a semiconductor material characterized by a bandgap of at least 2.15 eV.