Determination of strain, site occupancy, photoluminescent, and thermoluminescent-trapping parameters of Sm3+-doped NaSrB5O9 microstructures

Monoclinic NaSrB5O9:Sm3+ phosphors were synthesized by a conventional solid-state reaction method in air. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies revealed that the Sm3+ ions preferably occupy Sr2+ cation sites in the NaSrB5O9 host lattice. The doping-dependent crystallite size and lattice strain on the X-ray peak broadening of the NaSrB5O9:Sm3+ phosphor was determined by the Scherrer and Williamson-Hall (W-H) methods. Trigonally and tetrahedrally coordinated boron atoms in the phosphors were confirmed by confocal Raman analysis. Under near-UV excitation (402 nm), the NaSrB5O9:Sm3+ phosphors emitted reddish-orange light at 604 nm that corresponds to the 4G5/2→6H7/2 transition. The concentration quenching mechanism between the two Sm3+ ions within the host was proved to be the dipole-dipole interaction, and the critical distance was found to be 22.29 Å. The fitted luminescence decay curves in terms of a second-order exponential model suggest that the Sm3+ ions possess two different kinds of environments in the host lattice, which was supported by XPS analysis. The defects acting as trapping centers were investigated by thermoluminescence glow curves. The γ-irradiated NaSrB5O9:Sm3+ phosphors show two major dosimetric glow peaks centered at about 188.83 and 378.66 °C, indicating two different kinds of trapping centers in the phosphors.