Optical properties of zinc bismuth phosphate glass

Optical properties were studied on ternary zinc bismuth phosphate glasses, which have two distinct glass-forming regions; low-P2O5 region and high-P2O5 region. Orthophosphate and isolated phosphate structures are dominant in the former region and metaphosphate and pyrophosphate structures are dominant in the latter region. Refractive index of the low-P2O5 glass (nd > 1.82) was relatively higher than that of the high-P2O5 glass (nd < 1.74). Factors of additive law of the molar refraction were calculated from the refractive index, molar fraction of each component and density according to Lorentz–Lorenz formula. The factors of ZnO and P2O5 for the high-P2O5 glass were almost the same as those for the low-P2O5 glass. The factor of Bi2O3 of the low-P2O5 glass was, however, smaller than that of the high-P2O5 glass, although the refractive index of the former was higher than that of the latter. The discrepancy between the refractive index and the factor of Bi2O3 was due to the molar volume of glasses, that is, the refractive index was affected by the packing density much more than the molar refraction in zinc bismuth phosphate glasses. Absorption edge and reflection peak of the low-P2O5 glass were situated at lower energies than those of the high-P2O5 glass, which was consistent with the difference in resonance energy of the wavelength dispersion of the factor of Bi2O3 in molar refraction. The existence of a Raman band at 160 cm−1 in the low-P2O5 glass, which was not observed in the high-P2O5 glass, suggested the difference in the BiO bonding state between two glasses.