CaSiO3:Eu2+, Er3+, BaSiO3:Eu2+, Er3+ and SrSiO3:Eu2+, Er3+ phosphors: molten salt synthesis, optical and thermal studies

Abstract

In this study, thermal and optical behaviors of CaSiO3:Eu2+, Er3+, BaSiO3:Eu2+, Er3+ and SrSiO3:Eu2+, Er3+ phosphors synthesized by molten salt synthesis technique are investigated. The doped phosphors activated with Eu2+ and Er3+ ions with varying doping concentrations of 0 mol% to 1 mol% were subjected to structural, optical, and thermal analyses. The powder X-ray diffraction analysis confirms the triclinic structure of CaSiO3: Eu2+, Er3+, orthorhombic structure of BaSiO3: Eu2+, Er3+, and monoclinic structure of SrSiO3: Eu2+, Er3+ phosphors with good homogeneity and phase purity. The morphological and topographical traits are studied via field emission scanning electron microscopy and transmission electron microscopy analyses. These analyses indicate the irregular shape and size of particles along with agglomeration that occurred as a result of prolonged heat treatment processes. The thermal behavior studied by thermogravimetric (TG) analysis confirms the thermal stability of these phosphors with less weight loss occurring while heating the phosphors from room temperature to 700 °C. The study of thermoluminescent spectra of ultraviolet (UV) and gamma-irradiated phosphors confirms deep trapping that occurred in the synthesized phosphors along with second-order kinetics. The trap depth analysis indicates the trapping of electrons in deep trap centers and hence high activation energy (~ 3 eV) is required to vacate the trapped electrons. Doping of conjugate rare earth pair Eu2+ and Er3+ in the host lattice leads to formation of more defects and hence enhances the trapping mechanism. The gamma-irradiated phosphors exhibit increased TL intensity, efficient trapping in much deeper trap centers, and improved fading characteristics in comparison to the UV-irradiated phosphors.