Elucidating the structure and optimising the photoluminescence properties of Sr2Al3O6F: Eu3+ oxyfluorides for cool white-LEDs

Abstract

Herein, Sr2Al3O6F in hexagonal symmetry was synthesized via a solid-state methodology. The X-ray diffraction pattern of Sr2Al3O6F was refined by the Rietveld refinement with lattice parameters a = 17.8232(1) Å and c = 7.2168(0) Å. The stability of the crystal structure is further confirmed from the results of bond valence sums and the global instability index. The theoretical calculations of the electronic and optical behaviors of the Sr2Al3O6F were analyzed by density functional theory and the obtained results of the lattice parameters and direct bandgap were found close to the experimental data. The chemical states and elemental composition of Sr2Al3O6F were also authenticated by X-ray photoelectron spectroscopy (XPS). To evaluate the suitability of the Sr2Al3O6F structure as high efficient red phosphor, a series of Eu3+ doped Sr2-xEuxAl3O6F (x = 0.0 to 0.10) were synthesized, which showed intense red-orange emission (5D0→7F1,2) at UV and blue excitations. The photoluminescence intensity corresponding to 5D0→7F2 transition decreased significantly for x = 0.10 due to the luminescence quenching. Nevertheless, further enhancement in photoluminescence of Sr1.9Al3O6F: Eu0.1 sample was realized with the substitution of 0.1 mol Ba2+ ion for 0.1 mol Sr2+ ion. The various radiative properties of the emission bands were also analyzed through the Judd-Ofelt theory. The optimized Sr1.8Al3O6F: Ba0.1/Eu0.1 phosphor showed high red color purity (>95%), and moderate thermal stability of around 72% at 150 °C, suggesting that it could be an ideal red component for white-LEDs. A white-LED comprising the commercial yellow phosphor and the optimized sample showed bright white light having the CRI of 80.5%, CCT of 5510 K, and CIE of (0.33, 0.36) indicating that Sr1.8Al3O6F: Ba0.1/Eu0.1 phosphor is an appropriate red component for cool white-LEDs.