Optical Characterization on Perovskite Zirconate Nanocrystals

Abstract

We performed an optical study on the electronic properties of perovskite zirconate AZrO(3) (A = Ca and Ba) nanocrystals (NCs), which depend strongly on the size of A ion as well as the post-annealing process. The zirconate NCs were synthesized in the combustion method, which was found to be quite effective for synthesizing highly orthorhombic CaZrO3 NCs in the sense that their grain sizes are relatively larger and as-synthesized NCs do not include any raw material phase in the XRD pattern, compared with the cubic BaZrO3 NCs.The room-temperature visible emission is commonly quite strong in both NCs. Interestingly, the dominance of the green-yellow emission over the violet-blue emission with increasing the post-annealing temperature (T-anneal) appears to be in agreement with the formation of the mid-gap state identified in the absorption spectra. While the optical bandgaps of NCs increased with increasing T-anneal, a systematic trend that the optical bandgap in the AZrO(3) NCs decreased with the increasingly larger size of the A ion occurred. We discuss our findings in relation to the oxygen vacancy formation, lattice distortion, and size effect.