Enhancement of Sm3+ Luminescence in Sol-Gel Silica Matrix: Effect of Ligands Phenyl Phosphinic Acid and Trioctylphosphine Oxide.

Sol-gel silica matrices singly doped with Sm³⁺ and co-doped with ligands phenyl phosphinic acid (PPIA) and trioctylphosphine oxide (TOPO) were fabricated and studied for their structural and spectroscopic behaviour. Structural studies were done by x-ray diffraction (XRD) and Fourier transform infra-red (FTIR) absorption analysis whereas spectroscopic behaviour was studied by ultraviolet - visible (UV-Vis) absorption, photoluminescence (PL) excitation, emission and time-correlated decay analyses. XRD studies exhibit the amorphous nature of the samples and FTIR studies corroborate the presence of the ligands in the silica matrix. UV-Vis absorption and PL studies show significant enhancement in the radiative parameters in ligand co-doped samples compared to singly doped Sm³⁺ sample. Judd Ofelt parameters estimated from the absorption spectra possess higher values compared to popular hosts; revealing higher asymmetry and covalency around the active Sm³⁺ ions. An enhancement in PL intensity by 50.38 times and yield by 52.57 times with the co-doping of the ligands PPIA and TOPO is reported. These enhancement in the radiative output in ligand co-doped samples is attributed to the modification of the silica network with the incorporation of the ligands, energy transfer from ligands to nearby Sm³⁺ ions as well as due to the shielding of Sm³⁺ ions from the OH quenchers in the silica matrix. The improved PL behaviour especially corresponding to ⁴G_5∕2→⁶H_9∕2 transitions occurring at 643 nm suggests the potential of PPIA and TOPO co-doped Sm³⁺ silica matrix for diverge optical applications.