Structural, thermal and light emission properties of Eu, Sm, Dy, Er and Mn doped CaAl2O4 and SrAl2O4

1 mol% Re2O3/MnO ? 99 mol% MAl2O4 (Re = Eu, Sm, Dy, Er and M = Ca and Sr) powder samples were prepared by solid state sintering in the temperature range of 1386?1450 ?C and their structural, thermal and photoluminescence properties were compared. X-ray diffraction and Rietveld refinement studies of calcium aluminate samples confirm the formation of monoclinic CaAl2O4 along with a small concentration (1.9?4.6 wt %) of monoclinic CaAl4O7 while the strontium aluminate samples contain monoclinic SrAl2O4 and a small amount (0.7?3.5 wt %) of cubic Sr3Al2O6. The short-range structure of CaAl2O4 consists of CaO6, CaO9 and AlO4 structural units while that of SrAl2O4 contains SrO9 and AlO4 units. The Sr?O bond-lengths (2.32?3.58 ?) are longer than Ca?O bond-lengths (2.04?3.18 ?) and Al?O bond-lengths are of the range 1.35?2.12 ?. Differential scanning calorimetry studies reveal high thermal stability of calcium aluminates, while strontium aluminate samples show reversible monoclinic to - hexagonal structural phase transition at 688 ?C during heating cycle. Raman spectra exhibit Al?O vibrational modes. Photoluminescence studies show reddish-orange emission in Eu, Sm and Mn-doped samples, Er doped samples show green emission and Dy-doped samples emit yellow-white light. Calcium aluminate samples show significantly higher luminescence intensity and quantum yield than strontium aluminates.

Automated summary

Powder samples containing 1 mol% Re2O3/MnO and 99 mol% MAl2O4 (Re = Eu, Sm, Dy, Er and M = Ca and Sr) were prepared by solid state sintering at temperatures ranging from 1386 to 1450 ℃. The samples showed different structural, thermal, and photoluminescence properties, with calcium aluminate samples exhibiting higher luminescence intensity and quantum yield compared to strontium aluminates. Additionally, strontium aluminate samples displayed a reversible monoclinic to hexagonal structural phase transition during the heating cycle at 688℃.