Investigation of defect related photoluminescence property of multicolour emitting Gd2O3:Dy3+ phosphor

Abstract

Multicolour emitting Gd₂O₃:Dy³⁺ phosphor is prepared by citrate based sol–gel method as a function of annealing temperature of the sample and its emission property dependence with lattice defects is elaborated. The annealed phosphors are characterized by X-ray powder diffraction (XRD), Raman spectroscopy, diffuse reflectance spectroscopy (DRS), photoluminescence (PL), fluorescence lifetime and positron annihilation lifetime spectroscopy (PALS). The phosphors annealed at different temperatures greatly influence the defect and emission intensities, as revealed from PL and PALS measurements, respectively. The efficient energy transfer (ET) from the Gd³⁺ ion to Dy³⁺ ion is schematically illustrated with the aid of an energy level diagram. The PL spectra clearly conclude that Dy³⁺ with an ionic radius close to the Gd³⁺ ion prefers to occupy the C₂ site in the Gd₂O₃ matrix. The positron lifetime spectroscopy qualitatively explains the concentration of defects (vacancy and voids) which are minimized with the increase in the annealing temperature. The correlation between PL emission and lattice defects is also reported in detail.