Controlled synthesis of the monoclinic and orthorhombic polymorphs of Sr2SiO4 activated with Ce3+ or Eu2+

Abstract

Phase-pure orthorhombic and monoclinic Sr₂SiO₄ and its Ce³⁺- or Eu²⁺-activated versions were synthesized using H₃BO₃ or SrCl₂ fluxes. The effects of the type of dopant and its concentration, as well as the type of flux on the crystallization were revealed and discussed. The luminescence properties of the phase-pure Ce³⁺- or Eu²⁺-activated powders were characterized both at 30 K and 300 K. The presence of two luminescent sites was proved in both types of structures and in the case of both activators, and their characteristic excitation and emission spectra were presented. Energy transfer from ions emitting at higher energies to those giving luminescence at lower energies was shown to take place in both polymorphs and in the case of each of the dopants. Eu²⁺ emissions of both sites in both structures were located fully in the visible part of the spectrum, while part of the Ce³⁺ luminescence occurred in the long-wavelength UV. Room-temperature radioluminescence spectra showed that only the site emitting at longer wavelengths, in both structures and for both dopants, is active in the scintillation process. For the first time, for both dopants, luminescence from the two sites in both polymorphs of Sr₂SrO₄ has been spectroscopically characterized at 30 K and at room temperature.