Low-temperature swift heavy ion irradiation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si68.svg" display="inline" id="d1e2215"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">CaF</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2<

This study investigates the efficacy of low temperature swift heavy ion (SHI) irradiation in modifying the structural and morphological features of calcium fluoride (CaF 2 ) films deposited on flexible graphite substrates. Rutherford backscattering spectrometry (RBS) confirmed the deposited thickness for all four films. Atomic force microscopy (AFM) images reveal the formation of cracks induced by swift heavy ions (SHI) which are more pronounced for room temperature irradiation. Raman studies show two bands, with the prominent G band indicating the presence of amorphous and graphite-like structures in the films for the two irradiation types. Depending on the irradiation temperature, the band intensities vary, indicating structural changes within the thin film structures exposed to radiation. The X-ray diffraction study revealed differences in peak intensities between room-temperature and low-temperature irradiation films, indicating variation in the crystallinity and crystallite size. UV–Vis spectroscopy showed that low-temperature irradiation increased absorbance and reduced the optical bandgap from 4.0 eV to 1.77 eV for the thickest film (100 nm) exposed to cryogenic conditions. These findings highlight the importance of irradiation temperature in defect stabilisation and property engineering, demonstrating that cryogenic SHI irradiation is a practical approach for designing functional wide-bandgap materials for advanced, flexible, and radiation-tolerant applications. • Effects of heavy ion room versus low temperature irradiations on CaF 2 deposited on flexible graphite were studied. • 20 MeV Cu-beam was employed at a constant irradiation dose. • Raman spectroscopy and AFM studies revealed changes, while irradiation induced peak broadening and frequency shifts associated with lattice disorder and the formation of calcium colloidal defects. • UV–V is studies showed decreases in the energy bandgap and the efficacity of low temperatures irradiation was observed.