Fluoride phosphate (FP) and phosphate (P) glasses were doped with CuO in low (25 - 1.000 ppm Cu) and high (10.000, 20.000, and 287.000 ppm Cu) concentrations, and melted under normal, strong oxidizing, and strong reducing conditions. The redox behavior of copper in glass was investigated quantitatively depending on concentration, temperature, time, and host glass by absorption and luminescence spectrosco-py, optical and electron microscopy. In the VUV and UV region two charge transfer bands of Cu~(1+) centered at 175 nm and 230 nm, and of Cu~(2+) at 185 nm and 230 nm were found. The calculated individual absorption coefficients are very high. For Cu~(2+) a broad d-d transition band was found at 830 - 870 nm causing a blue or green color together with the UV absorption band. Cu°, Cu_2O colloids, and metallic copper crystals were observed too in glasses melted under reducing conditions. In high doped glasses Cu_2O and Cu° were aggregated on the sample surface.
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