Origins of photoluminescence bands induced by ultraviolet photons in polyethylene

Photoluminescence (PL) spectra in low-density polyethylene (LDPE) and crosslinked polyethylene (XLPE) induced by irradiation of ultraviolet photons are examined. The samples were pre-irradiated by the ultraviolet photons under different atmospheres (air, O/sub 2/, and vacuum) in order to induce photochemical reactions. Two PL bands appear around 3.6 and 4.2 eV in LDPE. Their intensities decrease with the progress of the pre-irradiation regardless of the irradiation atmosphere. The two PLs are considered to be due to conjugated double bonds present in the antioxidant and impurities. A new PL band appears at 2.9 eV in LDPE if the sample was pre-irradiated in vacuum. This PL is considered to be due to photoinduced conjugated double bonds. In XLPE, a PL band different from the ones observed in LDPE appears at 3.1 eV. It is considered that the crosslinking byproducts are responsible for this band.