Observation of green emission from Ce³-doped gadolinium oxide nanoparticles

Green emission at around 500 nm is observed in Gd₂O ₃: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 (1040 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 Gd ₂O₃:Ce nanoparticles, both the green emission and the emission at 612 nm from Eu³ are observed.