Faraday effect of sodium borate glasses containing divalent europium ions

Faraday effect measurements have been carried out at room temperature for some sodium borate glasses containing Eu2+ ions prepared under a reducing atmosphere. The wavelength dependence of the Verdet constant is analyzed in terms of a theory derived by Van Vleck and Hebb to obtain effective transition wavelength of the 4f7→4f65d transition which causes the Faraday effect of Eu2+ in the visible range. The effective transition wavelength increases with an increase in the optical basicity of glass. This phenomenon is explained in terms of the crystal field theory; because the splitting of 5d levels is larger in the glass with larger optical basicity, the energy required for the 4f7→4f65d transition decreases as the optical basicity of glass increases. The magnitude of Verdet constant increases with an increase in the effective transition wavelength when the concentration of EuO remains constant.