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

Abstract MgAl 2 O 4 :Eu, Dy nanoparticles were prepared by citrate sol–gel method and thermally treated at 600, 700, 800 and 900 °C. The trivalent europium ion is partially reduced to the divalent state at 700 and 800 °C. Infrared spectra of the phosphors showed bands around 700 and 520 cm −1 corresponding to the AlO 6 groups. X-ray diffraction patterns present sharp reflections of samples heated from 700 to 900 °C indicating the MgAl 2 O 4 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 6 5d → 4f 7 ( 8 S 7/2 ) transition of Eu 2+ ion overlapped to the 4 F 9/2  →  6 H 15/2 transition of the Dy 3+ ion. Besides, the 4 F 9/2  →  6 H 13/2 transition (579 nm) of Dy 3+ ion is overlapped with the 5 D 0  →  7 F 0 (578 nm) and 5 D 0  →  7 F 1 (595 nm) transitions from the Eu 3+ ion. Excitation spectra of the sample heated at 900 °C monitoring the excitation at 615 nm of 5 D 0  →  7 F 2 transition of Eu 3+ ion exhibit a broad band assigned to the O → Eu 3+ 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.