Determination of the thermal expansion of Cr3+ sites in glasses

Abstract

High temperature optical spectra of Cr3+ in glasses show a systematic linear redshift of crystal-field transitions in the 300–800K range, giving them thermochromic properties. Linear thermal expansion coefficients of Cr3+ in glasses of about 15×10−6K−1 are derived from the spectroscopic data, using a point charge model. The values obtained are independent on glass composition and greater than the macroscopic thermal expansion coefficients of the glasses investigated. These observations help understand the structural evolution of glasses at high temperatures by a better comparison between thermal expansion processes in glasses and crystals.