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

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.