A positron annihilation spectroscopic investigation of europium-doped cerium oxide nanoparticles

Abstract

Doping in ceria (CeO2) nanoparticles with europium (Eu) of varying concentrations (0, 0.1, 0.5, …, 50 atom%) is studied using complementary experimental techniques and novel observations were made during the investigation. The immediate observable effect was a distinct reduction in particle sizes with increasing Eu concentration attributed to the relaxation of strain introduced due to the replacement of Ce(4+) ions by Eu(3+) ions of larger radius. However, this general trend was reversed in the doping concentration range of 0.1-1 atom% due to the reduction of Ce(4+) to Ce(3+) and the formation of anion vacancies. Quantum confinement effects became evident with the increase of band gap energy when the particle sizes reduced below 7-8 nm. Positron annihilation studies indicated the presence of vacancy type defects in the form of vacancy clusters within the nanoparticles. Some positron annihilation was also seen on the surface of crystallites as a result of diffusion of thermalized positrons before annihilation. Coincidence Doppler broadening measurements indicated the annihilation of positrons with electrons of different species of atoms and the characteristic S-W plot showed a kink-like feature at the particle sizes where quantum confinement effects began.

Synthesis, Structural and Optical Properties of Mn-Doped Ceria Nanoparticles: A Promising Catalytic Material

“…(0.097 nm). The introduced additional lattice perturbation and structural stress cause extrinsic defects both near the grain boundaries and on the plane surface [19]. facilitated substitution free of strain as ionic radius of Ce 3?…”

Shape dependence of nanoceria on complete catalytic oxidation of o-xylene

“…The longest component, τ 3 , with the lowest intensity, was generally due to the annihilation of ortho-positronium atoms in the large voids present in the sample. In previous studies, 42,[47][48][49] the shortest one (τ 1 ) within a wide range of 172-247 ps, was observed over nanoceria, attributed to free annihilation of positrons (τ 1 ∼ 172-187 ps) or annihilation of positrons in small oxygen vacancies, such as single oxygen vacancies in CeO 2 (τ 1 ∼ 188-247 ps). In our case, the values of τ 1 were 181 ps for cubes, 183 ps for rods, and 202 ps for particles.…”

Eu-Doped Cerium Oxide Nanoparticles Studied by Positron Annihilation

“…4b). This has happened at around the same particle size below which a characteristic blue shift had been observed in the optical absorption spectra and a corresponding increase in the band gap energy [8]. A deterministic process that…”