Spectroscopic properties of alkali alkaline earth borate glasses doped with Fe3+ ions

Abstract

Iron oxide–doped lithium calcium borate glasses with composition (in mol%) of 25Li2O–15CaO–(60-x) B2O3: xFe2O3 (0 ≤ x ≤ 1) (LCBF) have been synthesized by melting and quenching technique. The physical and spectroscopic properties were accomplished using XRD, density, UV-Visible, EPR, FTIR and Raman spectroscopic techniques. XRD patterns have not revealed any crystalline peaks indicating the non-crystalline or amorphous characteristic of the glass samples. The density of the studied glasses increased with increasing iron ion concentration from 0 to 0.8 mol% (insteps of 0.2 mol%), and further, it is found to decrease. This may be due to the metamorphosis transformation of some tetrahedral Fe3+ (Th) to octahedral Fe3+ (Oh). The refractive index shows small variation with the iron ion concentration. In optical absorption spectra, only one absorption band exists at around 452 nm analogous to the 6A1g (S) → 4A1g (G); 4Eg (G) transition and is a peculiarity of iron ions in octahedral symmetry. The absorption edge shifts towards the greater wavelength with enhancing Fe3+ ion concentration. The optical band gap energy (Eopt) and Urbach energy (ΔE) are deliberated from their UV absorption edges. The EPR spectra exhibit three resonance signals at g ≈ 8.033, 4.282 and 2.0032. The resonance signal at g ≈ 8.033 is imputed to Fe3+ ions at axial symmetry sites whereas the resonance signal at g ≈ 4.282 is ascribed to isolated Fe3+ ions at rhombic symmetry site. The resonance signal at g ≈ 2.0032 is attributed to Fe3+ ions coupled by exchange interaction. The FTIR and Raman spectral studies divulge that iron ions accompanied to structural changes through the conversation of BO3 into BO4 and thereby diminishing the number of non-bridging atoms. The non-linear variations of several structural and optical properties portray a brawny structural consequence of iron ions on the LCB glass system.