Effect of annealing on photoluminescence of MgAl1.8Y0.14Eu0.06O4

Abstract

MgAl2O4 and MgAl1.8Y0.14Eu0.06O4 powders were prepared by sol–gel method and annealed at 600, 800, and 1000 °C. X-ray diffraction patterns confirm the cubic spinel phase with space group Oh7Fd3-m. Increasing the annealing temperature (Ta) resulted in increased octahedral bond lengths and bonding angles resulting in the crystalline phase of the samples. Scanning electron microscopy reveals the micron size flakes morphology and agglomerated grains. The presence of elements such as Mg, Al, Eu, and Y was confirmed by Energy dispersive x-ray spectra. Photoluminescence (PL) was not observed in MgAl2O4 but in the excitation spectra of MgAl1.8Y0.14Eu0.06O4 at emission wavelength 615 nm, both f orbital transitions of Eu3+ ions and charge transfer bands were observed. The intensity of the peak at 392 nm corresponding to the 7F0 → 5L6 transition is strongly dependent on annealing and it is increasing with Ta. Out of 5D0 → 7FJ(= 0, 1, 2, 3, 4) characteristic transitions of Eu3+ ions, the electric dipole transition - 5D0 → 7F2 (618 nm) is prominent in the PL emission spectra. Annealing has further increased the intensity of PL emission spectra. The presence of Eu2+ ions is evident from the broad peak observed around 340 nm (assigned to the 4f65d to 4f7 (8S7/2) transition) in the excitation spectra at emission wavelength 480 nm. The intensity of this peak is decreasing with increasing Ta.