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

Abstract

MgAl2O4: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 AlO6 groups. X-ray diffraction patterns present sharp reflections of samples heated from 700 to 900 °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 4f65d → 4f7 (8S7/2) transition of Eu2+ ion overlapped to the 4F9/2 → 6H15/2 transition of the Dy3+ ion. Besides, the 4F9/2 → 6H13/2 transition (579 nm) of Dy3+ ion is overlapped with the 5D0 → 7F0 (578 nm) and 5D0 → 7F1 (595 nm) transitions from the Eu3+ ion. Excitation spectra of the sample heated at 900 °C monitoring the excitation at 615 nm of 5D0 → 7F2 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.