Lattice distortion and corresponding changes in optical properties of CeO2 nanoparticles on Nd doping

Doping of Nd distorts the lattice structure of CeO2, increases the lattice strain and expands the lattice. Oxygen vacancies and other ceria related defects contribute to the lattice strain. Shifting and broadening of the F2g Raman peak of doped sample, compared to pure CeO2, is indicative of local structure distortion on doping. Dopant induced enhancement of oxygen vacancies, in the CeO2 lattice, is further confirmed by the generation of a new Raman peak at 543 cm−1 that is otherwise absent in the pure one. UV–vis spectroscopy gives an understanding of the different types of f–f electronic transition of Nd in the crystalline environment of CeO2. Effective band gap of CeO2 reduces upto Nd concentration of 2.5%. The band gap, however, increases at 4% of Nd due to Burstein–Moss shift. Photoluminescence intensity of pure CeO2 decreases with Nd concentration owing to the increase in the number of non radiative oxygen vacancies. These vacancies act as luminescence quencher and reduce the emission intensity. Photoluminescence excitation spectra confirm the presence of these oxygen vacancies in the CeO2 nanocrystallites.

► Nd doping distorts the lattice structure of ceria and generates oxygen vacancies.
► F2g Raman peak of ceria is widened and red shifted on doping 4% of Nd.
► Nd3+ undergoes crystal field interaction with ceria and gives f–f absorption spectra.
► Nd doping increases non radiative centers and quenches the luminescence.