Temperature-dependent phase evolution of the Gd3+ doped strontium compounds: Structural and optical properties

Mixed-phases of the SrCO 3 /Sr 3 Al 2 O 6 /SrAl 2 O 4 /SrAl 4 O 7 /SrAl 12 O 19 (hereafter called SSSSS) doped with Gd 3+ (SSSSS: 0.05 % Gd 3+ ) nanopowders were prepared using the citrate sol–gel method. The effect of annealing temperature (T a ) on the structure, morphology, and photoluminescence (PL) properties was investigated. The T a was varied in a range of 600–1300 °C, while the dopant concentration was kept constant at 0.05 % Gd 3+ . X-ray diffraction (XRD) results revealed that the prepared nanopowders consist of a mixture of orthorhombic (SrCO 3 ), cubic (Sr 3 Al 2 O 6 ), monoclinic (SrAl 2 O 4 and SrAl 4 O 7 ), and hexagonal SrAl 12 O 19 structures. It was noted that increasing the phase composition depends on the T a . The Fourier-transform infrared spectroscopy (FTIR) shows several peaks at around 529, 874, 1181, 1442, 2947, and 3421 cm −1 . The Energy dispersive spectroscopy (EDS) confirmed the elementary composition of the Sr, C, O, and Al. The scanning electron microscope (SEM) images showed that the phase composition highly depends on the T a . Transmission electron microscope (TEM) showed that the particle sizes are in the nanoscale. The ultraviolet–visible (UV–vis) diffuse reflection spectroscopy results showed that the absorption peaks below 300 nm are influenced by the T a . The PL results showed three emission peaks located around 431, 541, and 657 nm when excited at 272 nm. These emission peaks were attributed to SrCO 3 , SrAl 2 O 4 , and Sr 3 Al 2 O 6 crystal lattice, respectively. The results showed that the luminescence intensity and lifetime of the prepared samples depends on the T a . The chromaticiy coordinate showed that all samples emit in a blue region and the color purity was influenced by the T a .