Abstract: The crystals are sealed by either glass-to-metal seals or epoxy to prevent moisture degradation. Combined with the multiple moisture barriers, the new configurations are long lasting and provide long life for the modular detectors. The crystal geometry depends on the application. The crystal surfaces are shaped in such a way that provide minimum optical paths of the light photons. The cladding layers and the mirror system provide gas-free, high reflectivity crystal mirror surfaces. The mirrors can be specular or diffusive. Curved shapes at the photo detector sides provide the first step in focusing the light. Focused photon beams are easily translated into smaller photodetectors that have higher signal-to-noise ratio, are more compact in nature, are more economical. Crystals have upper and lower truncated conical or pyramidal portions and intermediate straight wall portions. The crystals have rounded bottoms and tops, and cladding on the crystals and mirrors on the cladding or on interior walls of a housing.