Synthesis and luminescence properties of Sm-doped LDPE–Na2SO4 composite material

• Sm-doped LDPE–Na2SO4 composites were successfully achieved for the first time.
• XRD, SEM, PALS and photoluminescence (PL) measurements were carried out.
• The composites show better PL efficiency with the increasing of phosphor content.
• LDPE–20%Na2SO4:Sm3+ composite shows the highest PL efficiency.

A series of Sm-doped LDPE–Na2SO4 composites were successfully achieved by melt mixing and hot pressing methods. Their morphology, structure and luminescent properties were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and photoexcitation (PE), photoluminescence (PL) spectra, respectively. The sizes and concentrations of free volume cavities in composites were studied by positron annihilation lifetime spectroscopy (PALS). SEM micrographs showed that Na2SO4:Sm3+ particles were well-distributed in the polymer matrix. XRD analyses revealed that the addition of Na2SO4:Sm3+ had no effect on the original crystal structure of LDPE. The dominant photoexcitation peak was observed at about 402 nm. The photoluminescence spectra consisted of four main peaks at 563, 598, 644 and 706 nm which could be associated to the transitions 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2 and 11/2, respectively) within the 4f5 electronic configuration of Sm3+. The effect of different doping concentration of Na2SO4:Sm3+ on the luminescent properties of the composites was investigated. The luminescent intensity of the composites increased with phosphor concentration.