Influence of red lead on the intensity of green and orange emissions of Sm3+ and Ho3+ co-doped ZnO–SrO–P2O5 glass system

Abstract

In this study, we have attempted to amplify green and orange emissions of Sm3+ and Ho3+ ions due to co-doping in zinc strontium phosphate glasses by adding different concentrations of red lead. The preliminary structural investigations like EPR and optical absorption spectra of rare earth free glasses have indicated that the lead ions do exist in Pb3+ state and the covalent character of PbO bond gradually decreased with increase of Pb3O4. The optical absorption (OA) spectra of Sm3+ and Ho3+ individually doped glasses exhibited conventional bands in the visible and NIR regions. The spectra were characterized using J-O theory. The value of Ω2 exhibited decreasing trend with increase of Pb3O4 concentration up to 8.0 mol%. The photoluminescence spectra of Sm3+, Ho3+ and co-doped glasses were recorded at an excitation wavelength of 401 nm. The Sm3+ doped glasses exhibited feeble green and orange emission bands due to 4G5/2 → 6H52, 6H9/2 transitions in addition to strong 4G5/2 → 6H7/2 emission at about 600 nm. The visible emission spectra of Ho3+ doped glasses exhibited green and orange emission bands due to 5F4 + 5S2 → 5I8 and 5F5 → 5I8, respectively. These two bands observed to have been overlapped with 4G5/2 → 6H52 (green) and 4G5/2 → 6H9/2 (orange) bands of Sm3+ ions, respectively, in the co-doped glasses. The intensity of green and orange emission lines of co-doped glasses mixed with 8.0 mol% of Pb3O4 seemed to have been intensified nearly two times when compared with that of Sm3+ individually doped glasses. The increased efficiency of these two emissions is attributed to the decreasing covalent character of glass network due to the increasing concentration of Pb3O4 and the mutual energy transfer between the two co-dopant ions. The emission process is further analyzed using rate kinetic equations and the resultant emission intensities are found to be proportional to the life time of the corresponding excited state.