Oxidation State Of Manganese In Zinc Pyrophosphate: Probed By Luminescence And EPR Studies

摘要

Zn_2P_2O_7: Mn was synthesized by wet chemical route and characterized by X-ray diffraction (XRD), photoluminescence (PL) and electron paramagnetic resonance (EPR) techniques. Photoluminescence spectrum shows two bands, one at 500 nm (green emission), which is attributed to the ~4T_1(~4G)-~6A_1 (~6S) transition of Mn~(2+) and other centered at 686 nm (red emission) is attributed to the electronic transition between ~2E and ~4A_2 of Mn~(4+) accompanied with vibronic transitions. EPR spectroscopic studies also confirmed the presence of both Mn2+ and Mn4+ ions in zinc pyrophosphate with difference in the number of fine transitions and g values (Mn~(4+), S=3/2, three fine transitions and g < 2.00; Mn~(2+) S=5/2, five fine transitions and g =2.00).Mn2+ is attributed to presence of Mn at 6-ccordinated Zn~(2+) site whereas Mn~(4+) is due to presence substitution of Mn~(4+) at Zn~(2+) site thereby invoking charge compensation by presence of interstitial oxygen ions around Mn~(4+) ion or due to substitution of manganese at distorted 5-coordinated zinc site.