Stationary and nonstationary absorption in lead silicate glasses with short-range order inversion

Abstract

The methods of stationary and pulsed absorption spectroscopy were used to study the optical properties of xPbO·(1– x)SiO 2 glasses produced by cooling of a molten mixture of chemically pure oxides. The spectral dependence of the absorption in the range of the short-wavelength edge obeys the Urbach rule. As the PbO concentration increases, a red shift of the optical transparency cutoff is observed. At x = 0.45–0.50 the amorphous matrix undergoes a structural inversion, which is due to a transition from a silicate to a lead–oxygen glass-forming network. This transition shows up as an abrupt change in the type of optical transitions, the width of the optical gap E g, and the Urbach energy E U. The short-range order inversion in the glass is accompanied by an increase in the atomic correlation radius R 0 characterizing the size of the medium-range order in the system. It was found empirically that R 0 has a linear relationship with a continuum-disorder parameter E U. It was found that pulsed electron irradiation produces short-lived color centers, which absorb at 1.65 and 2.30 eV. The relaxation of unstable absorption centers is characterized by microsecond kinetics. The nature of unstable absorption centers and their relationship with a short-range order inversion and the structure function of lead atoms have been discussed. The kinetic dependences have been interpreted in the context of a mechanism responsible for diffusion-controlled tunneling recombination of radiation-induced electronic and hole states of the matrix.