Effect of annealing on luminescence of Eu3+- and Sm3+-doped Mg2TiO4 nanoparticles

This work explores the influence of annealing temperature on the structure and luminescence of 2 at% Eu3+ and 1 at% Sm3+-doped Mg2TiO4 nanopowders produced via Pechini-type polymerized complex route. Mg2TiO4 samples were annealed at 7 different temperatures (400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C and 700 °C) to determine the temperature range in which cubic inverse spinel structure is stable and to follow the changes of material luminescence properties. X-ray diffraction revealed that crystallization of both Eu3+ and Sm3+-doped Mg2TiO4 nanopowders starts at 400 °C, and that Sm3+ doped Mg2TiO4 starts to decompose at 650 °C, while Eu3+ doped Mg2TiO4 starts to decompose at 700 °C. Samples annealed at higher temperatures show higher crystallinity and larger crystallite size. Mg2TiO4 powder annealed at 600 °C is composed of ~5 nm size nanoparticles agglomerated in micron-size and dense chunks. The emission spectra of nanoparticles are composed of emissions from defects in Mg2TiO4 host and characteristic emissions of Eu3+ (5D0→7FJ) and Sm3+ (4G5/2→6HJ) ions. The stronger emission and longer emission decays are observed with samples annealed at high temperatures. In the case of the Eu3+ ions emission intensity increased one order of magnitude between samples annealed at 400 °C and 650 °C.