Structural, optical and Judd-Ofelt parameters study on samarium and dysprosium ions doped calcium sulfate and magnesium sulfate ultra-phosphate glasses

Abstract

Trivalent rare earth (Dy3+ and Sm3+) doped calcium sulfophosphate, 20CaSO4-(80-x)P2O5-xDy2O3, 20CaSO4-(80-x)P2O5-xSm2O3 and magnesium sulfophosphate 20MgSO4-(80- x)P2O5-xDy2O3, 20MgSO4-(80-x)P2O5-xSm2O3 with 0.2 = x = 1.5 mol% of ultra-phosphate glass system were prepared using conventional melt-quenching method followed by annealing process at 300 ºC for 4 hours. The amorphous phase of glass samples were characterized by X-ray diffraction (XRD) method, while the structural features of the samples were measured using Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The optical properties of glass samples were characterized by ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy and photoluminescence (PL) spectroscopy. The infrared spectra revealed the bonding link of the host affected by modifier oxides (MgO, CaO) and intermediate oxides (SO4). Their linkages consist of P-O-P network, PO2 units, PO-, P=O, O-S-O and SO4 groups with no evidence of rare earth ions network as a result of the low concentrations of dopant. In addition, the similar tetrahedral arrangement was also shown by Raman spectra. The NMR spectra were used to identify the phosphate compositional change through conversion of Q3 (in P2O5) to Q2, Q1 and Q0 which follow the predictions of the Van Wazer’s model. The NMR spectra affirmed the presence of Q3, Q2, and Q1 groups, referring to existence of ultra-, meta- and pyrophosphate units, although the Q2 and Q1 are more predominant. Changes in Qn distributions in host phosphate networks are due to the breaking of P-O-P linkages to form P-O-M networks (where M is metal ions). The physical and nuclear properties such as density, molar volume, field strength, oxygen packing density, ionic packing density, inter nuclear distance, ion concentration and polaron radius were evaluated. The absorption characteristic presented by the UV-Vis-NIR spectra showed eight peaks from transition of Sm3+, and six peaks for transition of Dy3+ ions. All transitions correspond to the transition from ground state to excited state of Sm3+ and Dy3+ ions, respectively. The energy gap ranges from 4.090 – 4.185 eV, 4.517 – 4.612 eV and Urbach energy from 0.105 – 0.119, 0.155 – 0.135 eV with respect to the rare earth ions content. The photoluminescence spectra of Dy3+ ions illustrate three prominent bands around 481 nm (4F9/2->6H15/2), 577 nm (4F9/2->6H13/2), and 660 nm (4F9/2->6H11/2), and for Sm3+ ions five peaks were observed around 560 nm (4G5/2->6H5/2), 597 nm (4G5/2->6H7/2), 642 nm (4G5/2->6H9/2), 703 nm (4G5/2->6H11/2) and 735 nm (4G5/2->6H13/2). The absorption and emission spectra were used to evaluate the Judd-Ofelt parameters and radiative properties such as transition probabilities, radiative lifetimes and branching ratios of rare earth ions. Based on this study, calcium sulfophosphate glass and magnesium sulfophosphate glass doped with rare earth ions could be suggested as promising luminescent host material for solid-state lighting device application.