Correlation between the crystal structure and upconversion emission of Ho 3+ in AHfO 3 (A = Ca, Sr, and Ba)

We investigated the substitution-site dependence of the emission properties of the Ho3+ and the Yb3+ co-doped AHfO3 (A = Ca, Sr, and Ba) perovskite series using ultraviolet (UV) and near-infrared (NIR) photoexcitation. We measured the X-ray diffraction patterns of our samples and found that the crystal symmetry changed from orthorhombic in CaHfO3 and cubic in BaHfO3. Under both UV and NIR excitation, we observed dominant big green (550 nm) and very weak red and near-infrared (660 and 760 nm) emissions from Ho3+ ions. These emission properties depended strongly on the substitution site, i.e., A-site or B-site, in the ABO3-type perovskite, as well as the crystal symmetry of the host materials, which was discernible in the upconversion emission spectra obtained using the NIR photoexcitation. Our results suggest that the substitution site and the crystal symmetry of host materials should play crucial roles in determining the emission property of Ho3+ ions in perovskite hafnates.