**3.2 Ultraviolet-visible spectroscopy study**

The optical transmittance measurements of LDPE/silica nanocomposite substrate films were carried out with a UV–Vis–NIR spectrophotometer (UV Spectrophotometer A560AOE instruments) at normal incident of light in the wavelength range of 200–1100 nm. **Figure 4** shows the transmittance spectra of the samples. The UV spectra show that the composite substrates (0.5, 1, 2.5, 5, and 7.5 wt% SiO2) have no significant effect on the transmittance. On the other hand, a significant decrease in the transmittance is observed with a mixture ratio of 10 wt% SiO2 compared to the LDPE without mixing. This decrease is addressed in Section 3.
