Coloration of Fluorophosphate Glasses Containing Fluorescein Molecules by Heat Treatment or Gamma Ray Irradiation

The 70SnF2·30P2O5 glasses containing 25-500 ppm of fluorescein exhibit change in color from light yellow to reddish orange (absorption maximum, λ=500 nm) when heated at 240° C for 120-180 min. The fluorophosphate glasses also change the color from light yellow to reddish brown (λ=480 nm) when irradiated with 60Co γ-rays of 5×104 Gy. The P-F stretching mode observed in the Fourier transformed infrared (FT-IR) spectra showed an increase in peak intensity along with the coloration, suggesting a cleavage of the weak chemical bond between fluoride ions ( F-) and fluorescein molecules. The coloration is ascribed to change of the molecular structure of fluorescein from non-crystalline to crystalline type. ESR spectra of γ-ray irradiated 70SnF2·30P2O5 glasses showed a poorly resolved doublet, which was ascribed to a hole-trapped PO3F- center produced by electron scattering: PO3F2-→PO3F-+e-.