An investigation of the local distortions and the EPR parameters for Cu2+ in 40MgO–(10−x)PbF2–50SiO2–xCuO glasses

• Concentration dependences of d–d transition and EPR parameters are studied for MPSC glasses.
• [CuO6]10− clusters suffer tetragonal elongation distortions of 3% due to Jahn–Teller effect.
• Five-parameter Fourier type functions suitably reproduce observed concentration dependences.
• Concentration dependences are analyzed from overall decreasing Λ and reverse rule at x ≥ 0.7.

The local distortions and electron paramagnetic resonance (EPR) parameters for Cu2+ in 40MgO–(10−x)PbF2–50SiO2–xCuO (MPSC) glasses are theoretically studied at various impurity CuO concentrations x (= 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0 mol %) in a consistent way. Due to the Jahn-Teller effect, the [CuO6]10− clusters are found to experience the moderate tetragonal elongation distortions (characterized by the moderate relative tetragonal elongation ratios ρ ≈ 3%) along C4 axis. With only five adjusted coefficients a1, a2, b1, b2 and ω, the relevant model parameters (Dq, k, ρ, κ and H) are described by the Fourier type functions, which suitably reproduce the corresponding overall varying tendencies and fluctuations of the measured d–d transition bands and EPR parameters with x. The microscopic mechanisms of the varying rules of the relevant quantities with x are discussed in view of the whole decreasing ability of Si4+ to accept electrons and the reverse tendencies due to partial Cu2+ reduced to Cu+ at x ≥ 0.7 mol %. The monotonically increasing tendency of the calculated optical basicity reveals decreasing covalency of the whole glass systems with x.