Molten Salt Synthesis, Characterization And Luminescence Of Y₂0₂S:Eu³⁺ And CaW0₄:Eu³⁺ Nanophosphors

Rare earth doped fluorescent materials are widely applied in lighting, display devices, sensors, high-energy physics, biomedical and other fields. The synthesis of nanomaterials with different morphology is the most attractive and active fields of nanoscience and technology. Both the gas state and the liquid state approach can direct the growth of the crystal, but they have the disadvantages in complex operation, serious pollution and producing inappositely in the factory. On the contrary, molten salt synthesis has the advantages in high efficiency, simple operation, little pollution and low power wasting. So we applied molten salt approach to synthesize of the Y₂O₂S:Eu³⁺ and CaWO₄:Eu³⁺ red nanophosphors. Meanwhile, we discuss synthesis mechanism and the influence of yttrium salt, molten salt,molten salt dosage and sodium dodecyl sulfate （SDS） on fluorescence intensity and morphology. Compared with the products obtained by the solid-state reaction, the fluorescence intensity of Y₂O₂S:Eu³⁺ and CaWO₄:Eu³⁺phosphors have a significant improvement. The as-prepared powders have been characterized by X-ray powder diffraction （XRD）, scanning electron microscopy （SEM） and fluorescence spectrophotometer. Specific conclusions are as follows:1, We prepared Y₂O₂S:Eu³⁺ red nanofluorescent materials by molten salt method. Through the use of different eutectic molten salt, and explored the influence on the morphology and fluorescence, we choosed the best molten salt NaCl-Na₂CO₃. In addition, we also explored the influence of molten salt dosage and different yttrium salt on the morphology and fluorescence of phosphor powder. Research shows that: Many small-sized Y₂O₂S sphere-like particles ranging from 100 nm to 200 nm were prepared by using YNO₃ as yttrium salts, the phosphors could be regarded as mono-dispersed and non-aggregated. After using YCl₃ as starting yttrium salt, the morphologies and sizes of Y₂O₂S changed a lot. The obtained samples were hexagonal discotic particles ranging from lum to 2um. By the fluorescence performance test, fluorescent powder prepared from YNO₃ fluorescence properties was strongest. When molten salt and yttrium salt mole ratio was 30 （R=30）, it could be observed that Y₂O₂S:Eu³⁺ spherical particles were more and more small-sized and homogeneous, however, due to surface defects, its fluorescence is the weakest, so we added a small amount of surfactant sodium dodecyl sulfate （SDS）, can effectively improved its fluorescence properties. Finally, we used the sample of the molten salt method compared with the method of solid-state reaction, the results showed that the luminescence intensity of molten salt method increased 20% than solid-state reaction.2, Molten salt method was applied to the preparation of CaWO₄:Eu³⁺ red nanofluorescent materials. Through the use of different molten salt, and explored the influence on the morphology, In addition, we also explored the influence of molten salt dosage and different calcium salt on the morphology and fluorescence of phosphor powder. Research shows that:Under the different calcium salt, the prepared phosphor particle minimum, and more uniform by use CaCl₂ as calcium salt. Many small-sized CaWO₄ sphere-like particles ranging from 100 nm to 200 nm were prepared by using KCl as molten salt, however, the obtained samples were nanorods of 2 nm diameter by using K₂SO₄ as molten salt. By using different dosage of molten salt, found that the more dosage of molten salt, the smaller particles, the weaker fluorescence properties. Finally, we used the sample of the molten salt method compared with the method of solid-state reaction, the results showed that the luminescence intensity of molten salt method increased 20% than solid-state reaction.