Spectroscopic investigations on SrAl2O4 polymorphs

Nominally undoped and Eu3+ or Eu3+-Dy3+ doped SrAl2O4 powders are prepared using source chemicals of standard grade (99-99.99%) by solid state and sol-gel procedures, in order to vary the proportions of monoclinic (P21) and hexagonal (P63 and P6322) polymorphs in the compounds. Electron spin resonance reveals systematic contamination of the compounds by transition metal ions. The emission properties of the materials are investigated at 77 K upon UV and blue excitations. The optical features are ascribed, for the essential, to Mn4+ ions. The spectroscopy of this ion in conjunction with X-ray diffraction data and theoretical considerations is used to individuate P6322, P63 and P21 phases in the doped and undoped SrAl2O4 powders.