Effect of ZnO on the structure, optical properties and ESR studies of B2O3–Na2O–SrO–Fe2O3–ZnO glass system

Abstract

Iron oxide-doped borate glass with composition [(63-x)B₂O₃ – 10Na₂O – 25SrO – 2Fe₂O₃ – (x)ZnO; x = 0, 2, 4, 6, and 8 mol%] was prepared following melt-quench technique. The absence of sharp peaks in the X-ray diffraction (XRD) spectra confirmed the amorphous nature. Furthermore, Fourier transform infrared (FTIR) spectroscopy was employed to study the structure and subnetwork units inside the glass matrix. Moreover, the density and molar volume values were assessed for supplementary studies about the glass structure. Also, the present glass system's optical properties and electron spin resonance were considered. FTIR spectra showed that the basic structural units are trigonal BO₃ units, BO₄ tetrahedral coordinated units and nonbridging oxygens. Here, a tendency towards the back conversion of BO₄ units to BO₃ and nonbridging oxygen was also indicated for the further ZnO contents concurring with the optical band gaps and Urbach energy trends. Moreover, FTIR outcomes supported the presence of ZnO as a glass modifier in the form of octahedral coordinated units (ZnO₆). Furthermore, the optical band gaps (E_g) exhibit a decreasing trend with excessive ZnO contents which is attributed to the increase in optical basicity from 0.681 to 0.729 and the increase in electronic polarizability from 1.690 to 1.776 as well as the creation of nonbridging oxygen. In addition, the metallization criterion values decreased from 0.376 to 0.355 with more ZnO concentrations. Such behavior indicates it is favored towards metallic behavior. Furthermore, the decreased values of $E$_g and increased electronic polarizability increase the nonlinear properties of the present glasses. The electron spin resonance spectra show resonance signals at g = 4.12 and 2.04. The resonance signal at 4.12 associated with Fe³⁺ ions mainly located in rhombically distorted tetrahedral or octahedral coordination. The g = 2.04 resonance signal is ascribed to dipolar interactions. The obtained results suggest that the proposed glasses can be used in nonlinear optical applications.