Synthesis and characterizations of Eu2O3 nanocrystallites and its effect on optical investigations of Eu3+, Eu2+: SiO2 nanopowder

Red and blue solid luminescent nanopowder due to presence of Eu3+/Eu2+ ion doped in SiO2 matrix has been successfully synthesized using sol gel method. Europium activated silica nanophosphors were produced by drying the precursor gels at room temperature followed by annealing at 500 °C and 1000 °C in ambient air. The phase and morphology of the nanopowder was determined by X-ray diffraction, FTIR and TEM. Transformation from amorphous to monoclinic phase of europium oxide has been observed due to annealing and its effect on optical properties is discussed at length. Optical properties were studied using Uv-Vis and PL spectroscopy. Red shift has been observed in absorption band edge due to annealing and band gap energy is also decreased. Luminescent Eu3+ species in silica matrix show intense red emission at 614 nm by exciting the nanopowder at λex. = 394 nm. Due to the crystalline phase of Eu2O3, temperature quenching/agglomeration occurs at 1000 °C which reduces the luminescence output particularly at 614 nm. In contrast to this, significant blue emission has been observed when nanopowder was excited by ultraviolet light λex. = 310 nm which confirms the presence of Eu2+ ions in silica powder. For the first time, the reduction of Eu3+ -- Eu2+ under ambient conditions has been observed in silica nanopowder containing Eu2O3 nanocrytallites as an activator.