Y₂Ti₂O7:Er³⁺/Yb³⁺ (EYYTO) phosphors co-doped with Li⁺ ions were synthesized by a conventional solid-state ceramic method. X-ray diffraction studies show that all the Li⁺ co-doped EYYTO samples are highly crystalline in nature with pyrochlore face centred cubic structure. X-ray photon spectroscopy studies reveal that the incorporation of Li⁺ ions creates the defects and/or vacancies associated with the sample surface. The effect of Li⁺ ions on the photoluminescence up-conversion intensity of EYYTO was studied in detail. The up-conversion study under B976 nm excitation for different concentrations of Li⁺ ions showed that the green and red band intensities were significantly enhanced. The 2 at% Li⁺ ion co-doped EYYTO samples showed nearly 15- and 8-fold enhancements in green and red band up-converted intensities compared to Li⁺ ion free EYYTO. The process involved in the up-conversion emission was evaluated in detail by pump power dependence, the energy level diagram, and decay analysis. The incorporation of Li⁺ ions modified the crystal field around the Er³⁺ ions, thus improving the up-conversion intensity. To investigate the sensing application of the synthesized phosphor materials, temperature-sensing performance was evaluated using the fluorescence intensity ratio technique. Appreciable temperature sensitivity was obtained using the synthesized phosphor material, indicating its applicability as a high-temperature-sensing probe. The maximum sensitivity was found to be 0.0067 K^-1 at 363 K.