It has been observed that only a part of the AlxGa1-xAs graded- gap layer with the energy gap gradient g gt 20 eV/cm is active as a X-ray luminescence source. The thickness of the active layer is 30-50 mum. To increase the detectors optical response efficiency, the following methods are proposed and tested: 1. Reflection of the X-ray luminescence light, generated in the bulk AlxGa1-xAs layer, inside the total reflection angle theta; 2. Optical stimulation of the electron-hole radiative recombination.