Impact of ligands on the performance of band-stop and bandpass optical filter of cobalt sodium zinc borate glass

A core glass of B2O3–ZnO–Al2O3–Na2O–CoO was prepared to be used as a UV-indigo band-stop and blue–green bandpass filter. The impact of Bi3+ ions as ligands on the filter behavior was extensively studied through inlaid the core glass by 5, 10, 15, and 20 mol% of Bi2O3. The role of Bi3+ ions inside the proposed core glass structurally studied through density and Fourier Transformation Infrared spectroscopy. It was found that Bi3+ ions reduce the disorder in the glass network through the formation of bridging oxygens BOs and CoO4. A stable octahedral (oh) and tetrahedral geometry of Co2+ and octahedral (oh) of Co3+ were formed inside the considered glass network. The band gap results, 1.56–1.7 eV, signified that the considered glasses have a semiconducting nature. UV-indigo band-stop filter in the region of 190–440 nm with a cut-off wavelength at 440 nm and blue–green bandpass filter in the region of 440–585 nm with a center at 515 nm were observed in the transmitted spectrum of the core glass. Bi3+ ions gradually reduced the band-stop region and expanded the bandpass region through shifting the cut-off wavelength toward the shorter wavelengths. Based on the obtained results, the studied glass is considered an excellent candidate for UV-indigo band-stop and blue–green bandpass filter applications and the applications that require glasses of a semiconducting nature.