Observation of green emission from Ce-doped gadolinium oxide nanoparticles

Green emission at around 500 nm is observed in Gd₂O₃:Ce³⁺ nanoparticles and the intensity is highly dependent on the concentration of Ce³⁺ in the nanoparticles. The luminescence of this emission displays both picosecond (ps) and millisecond (ms) lifetimes. The ms lifetime is over four orders of magnitude longer than typical luminescence lifetimes (10-40 ns) of Ce³⁺ in traditional Ce³⁺ doped phosphors and therefore likely originates from defect states. The picosecond lifetime is shorter than the typical Ce³⁺ value and is also likely due to defect or surface states. When the samples are annealed at 700 °C, this emission disappears possibly due to changes in the defect moieties or concentration. In addition, a blue emission at around 430 nm is observed in freshly prepared Gd₂O₃ undoped nanoparticles, which is attributed to the stabilizer, polyethylene glycol biscarboxymethyl ether. On aging, the undoped particles show similar emission to the doped particles with similar luminescence lifetimes. When Eu³⁺ ions are co-doped in Gd₂O₃:Ce nanoparticles, both the green emission and the emission at 612 nm from Eu³⁺ are observed.