| Rare earth-doped fluorescent polymer composites which have the advantages of characteristic luminescence in rare earth ions and easy to processing molding in polymer, are widely used in the detector, biological medicine and catalysis fields. The emission of mineral thenardite shows white light under UV excitation. Sm3+ doped thenardite phosphors poss the strong monochromaticity and the high light conversion rate. The problem that phosphor was vulnerable to the factors such as external humidity, p H value, can be solved by the formation of new composite functional materials based on LDPE matrix. Aimed at the application requirement of composite material, we took the treatment of acid immersion and gamma irradiation on the material respectively. The positron annihilation technique, fluorescence spectrum analysis methods were took to character the the change of microstructure and luminescence performance in the polymer composites.This paper simply introduces the preparation process of Na2SO4:Sm3+ phosphors doped LDPE matrix. According to the application of agriculture, we formulate the simulated acid solution which is consistent with the natural acidic composition. The composite materials were immersed in the acid solution for different regime or under different doses of gamma irradiation. The characterization of the luminescence properties, free volume properties and microscopic structure on the LDPE–20%Na2SO4:Sm3+ composite material of acid immersion or gamma irradiation treatment, were conducted by positron annihilation technique, X-ray diffraction and fluorescence analysis. And the experimental results were analyzed to explore the luminescence performance, the free volume properties and microscopic structure in the composite material.1) The relative luminescence intensity of the composites decreases with the immersion time in the simulated acid solution. This can be due to that part of the branched chain rupture in the case of the acid immersion and the NaSm××electron hole that is formed in the process of Sm3+ replace Na+ in the typed phosphors is easy to break, the relative concentrations of phosphors luminescence center Sm3+ decline. This conclusion can be consistent with the XRD data. It is namely that the swelling of polymer was occurred by solution uptake and parts of the cationic were spread to the molecular gap as anucleating agent in order to replace the holes. As a result, the crystallinity of the composite increase for the enhancement of polymer chain arrangment.2) It appears the carbonyl C=O in the composites by different doses of gamma irradiation. The ultraviolet absorption spectroscopy shows that the optical band gap gE decreases with the increase of irradiation dose. The more material crosslinking structure, the smaller optical band gap. The crosslinking dominated the influence of irradiation when it compared with chain scission and the improvement of crystallinity shows the increase of the hardness composites.3) The positron lifetime spectra of composite materials with acid immersion show that the concentration of free volume hole increases assigned to the wide chain gap caused by swelling and water uptake. The water molecules and acid radical ion began to occupy the free volume holes and size of free volume decreases with immersion time. The concentration of free volume decreases obviously that can be ascribed to occurrence of oxygen free radicals with electron affinity and inhibition of the o-Ps positronium formation in composites by Gamma irradiation. Doped fluorescent particles cannot be well filled in LDPE polymer network structure, which can be result in a decline in the luminescence properties of the composites. |
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