Luminescent nanoparticles of MgAl2O4:Eu, Dy prepared by citrate sol-gel method

MgAl2O4:Eu, Dy nanoparticles were prepared by citrate sol-gel method and thermally treated at 600, 700, 800 and 900 degrees C. The trivalent europium ion is partially reduced to the divalent state at 700 and 800 degrees C. Infrared spectra of the phosphors showed bands around 700 and 520 cm(-1) corresponding to the AlO6 groups. X-ray diffraction patterns present sharp reflections of samples heated from 700 to 900 degrees C indicating the MgAl2O4 spinel phase. Grain size in the range 20-30 nm were observed by measurement of transmission electron microscopy (TEM). The emission spectra of the phosphors show a broadened band at 480 nm assigned to the 4f(G)5d -> 4f(7) (S-8(7/2)) transition of Eu2+ ion overlapped to the F-4(9/2) -> H-6(15/2) transition of the Dy3+ ion. Besides, the F-4(9/2) -> H-6(13/2) transition (579 nm) of Dy3+ ion is overlapped with the D-5(0) -> F-7(0) (578 nm) and D-5(0) -> F-7(1) (595 nm) transitions from the Eu3+ ion. Excitation spectra of the sample heated at 900 degrees C monitoring the excitation at 615 nm of D-5(0) -> F-7(2) transition of Eu3+ ion exhibit a broad band assigned to the O -> Eu3+ ligand-to-metal charge-transfer states (LMCT) around 280 nm. The samples present green persistent luminescence after exposure to UV radiation. The chromaticity coordinates were obtained from the luminescence emission spectrum. (C) 2008 Elsevier B.V. All rights reserved.