Radiation induced modifications on structural and luminescence properties of LDPE–Na2SO4:Sm3+ composites by γ-ray

• Gamma irradiation caused cross-linking in LDPE–20%Na2SO4:Sm3+ composites.
• The cross-linking increased the crystallinity of the samples.
• Gamma irradiation induced the conversion of Sm3+ → Sm2+ in composites.
• Concentrations of the Sm2+ centers linearly increased with irradiation doses.

A comparative study on the morphology, structure and luminescence modifications of LDPE–Na2SO4:Sm3+ composite induced by gamma irradiation was reported for the first time. The composites were irradiated with irradiation doses of 10, 30, and 50 kGy in air at room temperature. Modifications on structural and luminescence properties of LDPE–Na2SO4:Sm3+ composites were investigated by using several analytical methods. The X-ray diffraction (XRD) patterns revealed that the cross-linking improved the crystallinity of the composites. Scanning electron microscope (SEM) images illustrated the surface modifications of composites induced by irradiation. Results of positron annihilation lifetime spectroscopy (PALS) suggested that gamma irradiation affected the free volumes concentrations in the samples. The photoluminescence (PL) spectra of non-irradiated and irradiated composites consisted of four main peaks at 563, 598, 644 and 706 nm which could be assigned to the 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2 and 11/2, respectively) transitions within the 4f5 electronic configuration of Sm3+. Meanwhile, we observed an additional peak at about 686 nm in the irradiated composites, owing to the conversion of Sm3+ → Sm2+. Concentrations of the Sm2+ centers linearly increased with gamma irradiation doses, which partly accounted for the degradation of PL intensity of Sm3+ peaks.