SrAl2O4: Eu2+(,Dy3+) Nanosized Particles: Synthesis and Interpretation of Temperature-Dependent Optical Properties

SrAl2O4 nanosized particles (NPs) undoped as well as doped with Eu2+ and Dy3+ were prepared by combustion synthesis for the discussion of their intensively debated spectroscopic properties. Emission spectra of SrAl2O4 : Eu2+(,Dy3+) NPs are composed by a green band at 19 230cm(-1) (520 nm) at room temperature, assigned to anomalous luminescence originated by Eu2+ in this host lattice. At low temperatures, a blue emission band at 22 520 cm(-1) (444 nm) is observed. Contrary to most of the interpretations provided in the literature, we assign this blue emission band very reliably to a normal 4f(6)(F-7(J))5d(t(2g))-> 4f(7)(S-8(7/2)) transition of Eu2+ substituting the Sr2+ sites. This can be justified by the presence of a fine structure in the excitation spectra due to the different F-7(J) levels (J = 0 ... 6) of the 4f(6) core. Moreover, Fano antiresonances with the I-6(J) (J = 9/2, 7/2) levels could be observed. In addition, the Stokes shifts (Delta E-s = 1 980 cm(-1) and 5 270 cm(-1) for the blue and green emission, resp.), the Huang-Rhys parameters of S = 2.5 and 6, and the average phonon energies of h omega = 480 cm(-1) and 470 cm(-1) coupled with the electronic states could be reliably determined.