Experimental study of copper–alkali ion exchange in glass

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Abstract
Copper–alkali ion exchange was performed by immersing different silicate glasses (soda-lime and BK7) in different molten eutectic salt baths ( CuSO 4 :Na 2 SO 4 and CuSO 4 :K 2 SO 4 ). The obtained optical waveguides were characterized by m -lines spectroscopy for the determination of refractive index profiles, and by secondary ion mass spectrometry for the concentration profiles of the ion species involved in the exchange process. The different oxidation states of copper inside the glass structure were studied by electron paramagnetic resonance and x-ray absorption techniques. Interdiffusion copper coefficients were also determined. The Cu–alkali exchange was observed to give rise to local structural rearrangement of the atoms in the glass matrix. The Cu + ion was found to mainly govern the exchange process, while competition between Cu–Na and K–Na exchanges occurred when a potassium sulfate bath was used. In this case, significant waveguide modal birefringence was observed.