Optical properties and chemical composition analyses of mixed rare earth oxyorthosilicate (R₂SiO₅, R=La, Gd and Y) doped Dy³⁺ phosphors prepared by urea-assisted solution combustion method

Dysprosium (Dy³⁺) doped lanthanum gadolinium oxyorthosilicate (LaGdSiO₅), lanthanum yttrium oxyorthosilicate (LaYSiO₅) and gadolinium yttrium oxyorthosilicate (GdYSiO₅) phosphors (in powder form) were synthesized by urea-assisted combustion method. The X-ray diffractometer analysis confirmed that the LaGdSiO₅, LaYSiO₅ and GdYSiO₅ crystalized in monoclinic phases. The chemical composition of the phosphors was analyzed by measuring the atomic and molecular ionic species using the time of flight secondary ion mass spectroscopy (ToF SIMS). In addition, ToF SIMS imaging technique was used to determine the distribution of the Dy³⁺ dopant ions on the surface on the phosphors. The average crystallite sizes and lattice strains of the phosphor were increased by Dy³⁺ doping. The field emission scanning electron microscope images showed that the powders were made up of an agglomeration of particles with no regular shape. The photoluminescence data showed narrow line emission peaks at the wavelengths of 485 nm (minor emission) and 573 nm (major emission) associated with the f→f transitions of Dy³⁺. The photoluminescence (PL) measurements showed that the emission peak of LaGdSiO₅:Dy³⁺ was ~3× more intense than those of LaYSiO₅:Dy³⁺ and GdYSiO₅:Dy³⁺ when excited using monochromatic xenon lamp with a wavelength of 241 nm. However, when the powders were excited using a 325 nm He-Cd laser, the highest PL emission intensity was observed from GdYSiO₅:Dy³⁺.