Intense UV absorbers in fluorite-type rare-earth cerates for sunscreen formulations

Intense UV absorbers are developed in fluorite-type rare-earth cerate solid solutions: RE2O3 + 2CeO(2) = RE2Ce2O7 (RE = La, Gd, and Y) by the conventional ceramic route. X-ray diffraction analysis corroborates the formation of fluorite structure with lattice expansion from Y to La compound. Further, Raman analysis elucidates that the defect oxygen vacancies increased in concentration from Y- to Gd-substituted ones. The defect concentration of Ce3+ is dependent on the rare earth used and it is more for Y than the other two. The UV-vis spectra exhibit strong absorption in the UVA and UVB wavelength regions (210-400 nm) due to an increased polarizability of oxygen ions bound to cerium in the order of La > Gd > Y. The absorption edge is sharp, and the absorbance of La compound is 2.5 times higher than that of the existing titania UV absorber and is also far higher than that of the pure CeO2. Additionally, methylene blue photodegradation and photoluminescence studies show negligible photocatalytic activity for these compositions. Thus, the rare-earth cerates can be considered possible sun screen formulations that can be blended with other organic products to provide effective, safe, and desirable UV protection without surface coatings to shield the photocatalysis.