EPR, optical absorption and photoluminescence properties of MnO2 doped 23B2O3–5ZnO–72Bi2O3 glasses

Electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), optical absorption and photoluminescence (PL) spectroscopic measurements are performed on Mn2+ doped high bismuth containing zinc–bismuth–borate glasses. TEM images reveal homogeneously dispersed Bio nanoparticles (NPs) of spherical shape with size about 5 nm. EPR spectra exhibit predominant signals at g≈2.0 and 4.3 with a sextet hyperfine structure. The resonance signal at g≈2.0 is due to Mn2+ ions in an environment close to octahedral symmetry, where as the resonance at g≈4.3 is attributed to the rhombic surrounding of the Mn2+ ions. The hyperfine splitting constant (A) indicates that Mn2+ ions in these glasses are moderately covalent in nature. The zero-field splitting parameter D has been calculated from the allowed hyperfine lines. The optical absorption spectrum exhibits a single broad band centered at 518 nm (19,305 cm−1) is assigned to the 6A1g(S)→4T1g(G) transition of Mn2+ ions. The visible and near infrared (NIR) luminescence bands at 548, 652 and 804 nm have been observed when excited at 400 and 530 nm, respectively. These luminescence centers are supposed to be caused by the lower valence state of bismuth, such as Bi2+ and Bi+ ions, generated during melting process.