Correlation between the structural properties and upconversion emission of Ho3+ in AZrO3 (A = Ca, Sr, and Ba) nanocrystals

Abstract We investigated the luminescent properties of Ho3+ and Yb3+ co-doped AZrO3 (A = Ca, Sr, and Ba) perovskite nanocrystals synthesized using a combustion method. X-ray diffraction measurement revealed that these nanocrystals exhibited differences in their structural symmetries, varying from orthorhombic in CaZrO3 to cubic in BaZrO3, with an increase in their grain sizes and an enhanced degree of crystallinity along increased post-annealing temperatures. Under near-infrared excitations, we observed strong green (545 nm) and weak red (660 nm) emissions from the Ho3+ ions. Interestingly, the smaller the sizes of the A ions, the stronger were the upconversion emissions and the greater was the increase in the emission intensity due to post-annealing. We found that the crystal symmetry and the degree of crystallinity of the host play an important role in determining the luminescent behavior of Ho3+ ions in perovskite nanocrystals.