Tailoring Optical Bandpass Filters in Sodium Silicate Glass: Impact of CuO Incorporation

The research aims to characterize a melt-quenched sodium silicate glass doped with different concentrations of copper oxide (CuO) as an optical filter material. Sodium oxide (Na₂O) was fixed at 45 mol%, whereas CuO was introduced to the glass network at the expense of Na₂O, from 0.2 to 0.8 mol%. The silicate network comprises Si–O–Si vibrations in symmetrical and assymmetrical modes, with the formation of non-bridging oxygens (NBOs) as a result of the presence of the modifiers NaO₆ and distorted tetragonal CuO₆ units. The optical transmittance was zero in the UV region and in the visible region starting from 600–900 nm, depending on the glass composition and the CuO ratio. The glass containing 0.6 mol% CuO had a maximum transmittance peak (T = 0.64) at 450 nm, whereas the glass containing 0.8 mol% CuO exhibited a low transmittance peak (T = 0.28) at 450 nm. The optical parameters were discussed in terms of the effect of CuO, in which the optical band gap varied from 3.168 eV to 2.819 eV as the CuO changed from 0 to 0.8 mol%. Other important parameters like Urbach energy, refractive index, and their related variables were determined and discussed. The glass density of sodium silicate glass is 2.478 g/cm³, which has been slightly increased to 2.491 g/cm³ due to the effect of the CuO dopant. Furthermore, as the CuO content increased, the optical basicity increased from 1.222 to 1.237, indicating that the glass was thermodynamically stable.