A new type of solid state photon detector will be developed based on TlBr and TlCl. Crystals grown with these materials will be produced with graded bandgaps matched to the emission range of inorganic scintillator particle detectors. Higher photon detection efficiency will result. This in turn can lead to significant resolution improvement of such particle detectors because limitations from photon counting statistics will be removed. Improved performance of such detectors can impact nuclear monitoring and radiation medicine.