EPR, optical and physical studies on Cr3+ doped MgO–BaO–B2O3–TeO2 glasses

Physical, optical and Electron Paramagnetic Resonance (EPR) studies on 15MgO–15BaO–(59.8−x) B₂O₃–(10 + x) TeO₂–0.2Cr₂O₃ (x = 0,10,20,30 mol%) glass samples are reported. EPR spectra exhibited two resonance signals at g = 4.8 and g = 1.98. The resonance signal with large zero field splitting parameter (D) and E/D ≤ 1/3 at g = 4.8 is attributed to isolated Cr³⁺ centers in strongly distorted octahedral sites, whereas the resonance signal at g = 1.98 is assigned to Cr³⁺ centers at axially distorted octahedral sites. The resonance signal at g = 4.26 is assigned to Fe³⁺ ions, which are present in the glass matrix as unwanted impurities. The resonance signal at g = 1.91 indicates the Cr³⁺–Cr³⁺ exchange coupled pairs. The two observed broad optical bands in the optical absorption spectra 16,025 cm⁻¹ and 23,474 cm⁻¹ are assigned to ⁴A_2g(F)→ ⁴T_2g(F) and ⁴A_2g(F)→ ⁴T_1g(F) transitions, respectively. The site symmetry of Cr³⁺ is C_4v or C_3v. Racah parameters, crystal field (D_q) parameters and energy gap are evaluated from the optical spectra. Various other physical parameters like density etc. have also been reported.