Photochromic behavior of tungsten ions in sodium metaphosphate glass and effect of oxidizing condition assessed by spectroscopic analysis

Glasses based on sodium metaphosphate doped with WO3 were prepared in both normal and oxidizing conditions. Optical, FTIR, and ESR spectral studies were carried out to justify the photochromic behavior of such glasses. Spectral data of studied samples reveal strong UV absorption band that is linked to mandatory trace iron impurities while WO3-doped samples under ordinary melting conditions show an additional UV band is linked to hexavalent tungsten ions and also reveal two broad visible bands related to lower valence states of tungsten (W5+, W4+). FTIR spectral data reveal nearly repetitive vibrational bands due to constitutional main meta phosphate building units with minor variations that are attributed to the presence of tungsten ions. ESR data of ordinary melted WO3-doped glasses confirm the presence of paired hexavalent tungsten ions with no distinct signals. The lower valences of tungsten ions are generated within oxidized samples and possess unpaired electrons giving characteristic ESR Signals.