Research On The Structure And Luminescence Properties Of Sm³⁺-doped LDPE-N_a2SO₄Composite Material

The rare-earth luminescence materials which possess the sharp emission band,high colour purity, high conversion efficiency and other excellent properties have thewidespread application prospect in light, display devices, laser and many other fields.The luminescence properties of thenardite (Na2SO4) activated with rare earth ionshave received great research interest in the past few years due to their easypreparation, low cost and high quantum efficiency. However, the luminescenceproperties of phosphors are easily affected by the external factors in practicalapplications. Through the research, coating or dispersing the phosphor particles into apolymer or glass matrix can protect the surfaces of phosphor particles and prevent thedegradation of luminescent intensity.In this paper, high purity Na2SO4(99.99%) and SmF3(99.99%) were used as thestaring materials to prepare the Na2SO4:Sm3+phosphor using the high temperaturesolid-state method. The effects of different doping concentration of SmF3on thecrystal structure and luminescent properties of the Na2SO4:Sm3+phosphors wereanalyzed, and selected the appropriate raw materials ratio for the optimumluminescent intensity. LDPE–Na2SO4:Sm3+composites were successfully prepared bymelt-mixing the synthesized Na2SO4:Sm3+phosphor powders into LDPE matrix usingmelt mixing and hot pressing methods. Effects of doping concentration ofNa2SO4:Sm3+phosphor and gamma irradiation on the structure, morphology, freevolume properties and luminescence properties of LDPE–Na2SO4:Sm3+compositematerials were characterized by X-ray diffraction (XRD), scanning electronmicroscope (SEM), positron annihilation lifetime spectroscopy (PALS) andphotoluminescence (PL) spectra for the first time. The test results were furtheranalyzed and processed.Experimental results show that Na2SO4:Sm3+particles can be uniformlydistributed in the polymer matrix, and the addition of Na2SO4:Sm3+has no obviouseffect on the original crystal structure of LDPE. Under402nm excitation, theemission spectra of composite materials consist of four main peaks at563,598,644and706nm which could be associated to the transitions4G5/26HJ(J=5/2,7/2,9/2and11/2) within the4f5electronic configuration of Sm3+. The luminescent intensity ofthe composites increases with Na2SO4:Sm3+phosphor concentration. Irradiation effects are reflected in the increase of crystallinity and decrease of free volumefraction of samples. It can be considered that low-dose γ-ray-irradiation mainly causesthe cross-linking of LDPE. Meanwhile, we observe an additional peak at about686nm in the irradiated composites except four main peaks. Luminescence intensity ofthe Sm2+emission band linearly increases, while the luminescence intensity of Sm3+emission peaks linearly decreases with gamma irradiation doses, which can be owingto the conversion of Sm3+Sm2+in the composites caused by γ-ray-irradiation. Thereduction of luminescence intensity of Sm3+peaks may reduce the PL efficiency ofcomposites to some extent. However, the creation of Sm2+in the irradiated compositesmakes it have potential applications in some radiation detection systems and otheroptical devices.