Samples of cellulose nitrate polymer (CN-85) were annealed at 100 °C, 120 °C, and 140 °C for 15 min before and after irradiation with alpha particles emitted from a241Am source. Irradiation was performed at room temperature for 5 min. The changes in the optical and structural properties of CN-85 NTD, due to annealing and irradiation, were studied by using ultraviolet-visible spectroscopy (UV-VIS), and Fourier transform infrared spectroscopy (FTIR). Direct and indirect energy gap values, the number of carbon atoms, carbon clusters, and Urbach's energy values were determined. The UV-VIS analysis showed a shift in the absorption edge of the CN-85 polymer toward long wavelengths. The FTIR results revealed the changes in some bonds and the structural decomposition of CN-85 due to irradiation. The direct band gap energy was slightly decreased from 4.13 eV to 4.09 eV when the pristine samples were heated to 140 °C and irradiated. The indirect band gap energy was decreased from 3.9 eV to 3.8 eV under the same conditions. The Urbach's energy values showed a fluctuating rise with increasing annealing temperature for the irradiated and heated samples. When the pristine samples irradiated and heated, the band gap energy is reduced from 4.13 eV to 4.06 eV and from 3.90 eV to 3.84 eV for the direct and indirect transition, respectively. In conclusion, this technique showed promising benefits for a wide range of applications such as optoelectronics and microelectronic devices.