Optical Spectra of Chromium in Mixed Alkali Silicate Glasses

Abstract

As an approach to the mixed alkali effect in glass, the optical absorption spectra of Cr3+ were determined in mixed alkali silicate glasses. The values of the crystal field strength Dq and the Racah parameters B and C for the glasses were calculated from the observed band positions. The crystal field strength Dq is plotted in Fig. 1 against alkali concentration ratio, R1/(R1+R2) where (R1, R2)=(Li, Na), (Na, K) or (K, Li). The curves in Fig. 1 show that Dq deviates downwards from linearity predicted by combining the values for the end members, i.e., there is a minimum for Dq. The behavior in the glasses shown by curves in Fig. 1 may be interpreted based on the presence of mixed alkali effect.