Synthesis of CeO2 phosphor, both un-doped and Pr3+ (1–11 mol %) doped, utilizing a solution combustion route with Tulsi extract as a bio-fuel, has been investigated. Characterization through X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and photoluminescence (PL) analysis reveals successful inclusion of Pr3+ at the Ce3+ /Ce4+ site, inducing defects and oxygen vacancies, while maintaining the crystal structure and expanding the CeO2 lattice. Energy Dispersive X-ray spectra confirm the composition with desired stoichiometry. Under 444 nm excitation, the phosphor exhibits intense orange-red emission at 613 nm, corresponding to the 3P0→3H6 transition. With a relative sensitivity of 2.65 % K−1 and an absolute sensitivity of 0.023 K−1, CeO2:5Pr3+ phosphor exhibits remarkable temperature sensor capabilities. Moreover, a transparent nanocomposite (NCs), fabricated using highly efficient phosphors and soluble poly vinyl alcohol (PVA), exhibits bright red emission upon UV 365 nm light, ensuring anti-counterfeiting (AC) performance. The sustainability, excellent flexibility, and foldability of these materials open up possibilities for diverse anticounterfeiting applications. Overall, the results highlight the potential of CeO2:Pr3+ phosphors as versatile luminescent platforms for optical thermometers, flexible films, lip prints (LPs) detection, and AC applications.