Synthesis of spherical CeO₂:Eu³⁺ particles with enhanced sensor sensitivity for luminescence-based thermometry...

A hydrothermal approach was used in this study to prepare cerium dioxide phosphors doped by Eu³⁺ ions. Ethylenediaminetetraacetic acid (EDTA) was used as a chelating agent to synthesize the spherical particles of Ce_1-xEu_xO_2-δ. Small Ce_1-xEu_xO_2-δ spherical particles were observed in the samples synthesized at EDTA/Ce³⁺ molar ratio of 3: 1. The luminous efficiency of Ce_1-xEu_xO_2-δ phosphors was adjusted by varying the concentration of Eu³⁺ ions. The highest photoluminescence (PL) efficiency was obtained at the Eu³⁺ content of 7 mol%. Ce_1-xEu_xO_2-δ phosphors have photoluminescence emission spectra that include simultaneously the emissions (450-575 nm) from the host matrix as well as rare-earth ion emissions (590-700 nm). As the emission strength of the CeO₂ matrix and rare-earth ions varies with temperature, temperature-dependent emission spectra were observed in the range of 298-453 K. The variation in the fluorescence intensity ratio between the host and dopant emissions with temperature increase was used to evaluate the temperature-sensing performance of the Ce_0.93Eu_0.07O_2-δ phosphor. The absolute sensitivity of Ce_0.93Eu_0.07O_2-δ phosphors increased from 0.008 to 0.014 K^-1 as the temperature increased from 298 to 378 K and then dropped. Ce_0.93Eu_0.07O_2-δ phosphors showed a high relative sensitivity of 3.8% K^-1 at 298 K. According to obtained results based on high values of temperature sensitivity, minimal temperature uncertainty of 0.46 K at 378 K, negligible hysteresis loop, and excellent reversibility, Ce_0.93Eu_0.07O_2-δ phosphors are suitable for use in luminescence-based thermometry.