I am trying to evaporate a 1mm thick CsI:Tl scintillator. It works fine with CMOS, while it unusually increases its radioluminence around 1-3% when X-ray is giving. The temperature effect was excluded. I also tried other material under same device. CsI pure crystal has somehow similar raising but quickly reach a platform, CsCuI crystal looks stable and don't raise at all. What will be the possible reason of this radioluminence increase? and how I should eliminate that?