Optical and structural analysis of the charge transfer of Ce3++ e- →Ce4+ ion in the cerium oxide (CeO2)

Abstract

Cerium oxide (CeO2(s)) is prepared by Chemical Bath Deposition (green chemistry) at ~23.0 °C and subsequent thermal annealing treated (TAT) at ~1000 °C. This manuscript continues with previous research examining the spectra situated at UV–Vis-region to investigate the 4fds→4fds electronic intra-transitions of CeO2. The in-plane and out-of-plane strains are located at εc ~1.1 × 10−3, ~− 3.0 × 10−4 and εa ~− 1.2 ×10−3, ~4.0 × 10−4, dislocation density were ~3.87×1014 lines/m2 and ~4.31×1016 lines/m2 for the As-grown and the CeO2-TAT nanocrystals, respectively. As a first approximation, we consider that the inorganic nanomaterial has intrinsic native crystalline defects. It is supposed that the strain is caused by native point defects (vacancies and interstices). According to the d(DO)/dE equation, absorption band associated at Ce3+ + e-→Ce4+, assigned to 5d→4f electronic intra-transitions (~2.48 eV) at Vis-region. Deconvolution of the observed absorbance spectra shows that the emissions bands originating from the F0 centers prevail over those of F+ centers of V0. For CeO2-TAT nanocrystals, the band gap energy was at ~289 nm (~4.29 eV), whereas the As-grown was found at ~304 nm (~4.07 eV). In As-grown nanocrystals, three optical signals can be seen ~277 nm (~4.47 eV), ~330 nm (~3.75 eV), and ~393 nm (~3.15 eV). The absorption band at ~3.15 eV is relatively narrow and assigned to Ce3+ + e-→Ce4+ charge transfer. Calculations of Urbach energy were Eu~1.54 eV for As-grown and Eu~0.52 eV for CeO2-TAT nanocrystals, respectively.