Effect of silver and antimony on optical properties of tungsten-phosphate glasses

Abstract

The effect of silver ions on the photochromic properties of tungsten phosphate glass is investigated. All samples when excited at 377 nm exhibit ~430 nm luminescence attributed to the charge transfer mechanism within the WO42−tungstate anions. The broad absorption band extending from ultraviolet to the visible region, between 500 and 1400 nm, of the NaPO3-WO3 (PW) base matrix due to the small-polarons(Wx5+W1−x6+O3) transferring charges between neighboring tungsten ions according to the following photon absorptionWA5++WB6++hvs→WA6++WB5+. The dual oxidation state of the antimony, Sb3+ and Sb5+, incorporated into the matrix at the 0.5−xNaPO3−0.5WO3−xSb2O3x=0…0.2mol% (PWS) ratio acts as a reducing element of the W5+ ions leading to the suppression of polarons as UV-VIS absorption centers. These results are confirmed by EPR measurements with scanned magnetic field between 2500 and 4500G. The most intense effect is observed for nominal doping aboveAgNO3≥10mol%. The temporal dynamics of luminescence at ~430 nm as a function of UV exposure time shows that both,Wx5+W1−x6+O3 for PW glasses as well as Ag+ for PWSA glasses act as traps for the charge generated by the excitedWO42− anions. Photodarkening due to continuous exposure to UV radiation reduces the pump transmission by ~12% of its initial value for PW and PWSA glasses. This is attributed to F-center formation (Ag+) which acts traps to the photoexcited electrons. This is attributed to oxidation of silver ions (Ag+) becoming metallic silver (Ag0). The effect when compared to PWS glass was observed to be reduced by only 2% over the same interval under the same pumping conditions.