Nonlinearity of the Upconversion Response of Er3+ in Y2TiO5:Er3+,Yb3+ Ceramics When Varying the Wavelength of Incident NIR Excitation Radiation

The upconversion response of Er³⁺ sensitized by Yb³⁺ in various crystalline hosts and illuminated with a laser light at around 980 nm revealed certain spectral shapes that are typical for each of the crystalline matrices containing the dopants. The purpose of this work was to measure the upconversion response of Er³⁺ as a dopant in Y₂TiO₅, sensitized by Yb³⁺, at different concentrations relative to the substituted Y³⁺ ion, and to reveal the subtleties of the mechanisms of the energy transfers between them and the lattice. Therefore, we synthesized Y₂TiO₅ ceramic samples doped with different concentrations of Er³⁺ and Yb³⁺, below 10% (mol), in order to minimize the distortion of the lattice. The oxide powders, obtained using the sol-gel method, as well as the ceramics were structurally and morphologically characterized using an X-ray diffraction analysis and scanning electron microscopy. When the ceramic samples were irradiated with an NIR laser light, it was found that, at a wavelength variation of only 2 nm of the incident radiation, from 973.5 nm to 975.5 nm, the upconversion spectra differed significantly. This nonlinearity is notable because it is not present in the case of other crystalline host matrices studied by us since the literature lacks information on this subject. We also correlated this effect with the simulated distribution of the average distances between Er³⁺ and Yb³⁺ ions in the host matrix.