Study On The Preparation Of Molten Salt Of K₂SiF₆:Mn⁴⁺ Red Phosphor With High Luminescence Property And Its Improvement Of Water Resistance

Compared with the traditional incandescent lamp and fluorescent lamp,white light emitting diode（LED）has the advantages of long life,high efficiency,low cost and energy saving,which is considered as a new generation of solid-state lighting technology.At present,the white LED on the market mainly realizes the effect of white light illumination through the combination packaging of commercial YAG:Ce³⁺yellow phosphor and blue LED chip.Due to the lack of red light,this combination leads to the low color rendering index and high color temperature of the white LED device,which limits its wide application.Among them,Mn⁴⁺doped fluoride red phosphors have attracted much attention because of their excellent narrow-band red emission under blue light excitation and mild preparation method.However,the preparation process of the red phosphor needs to consume a large amount of highly toxic HF aqueous solution and the poor water resistance of the product greatly limits its application.In this paper,through regulating the ratio of reactants in the process of preparation step was synthesized with high water resistance and excellent luminescent properties K₂SiF₆:Mn⁴⁺red phosphors,and then improve the preparation methods,innovation to introduce NH₄HF₂ molten salt as a reaction to the environment,and prepared at low temperature has water resistance and high luminous performance Mn⁴⁺doped fluoride red phosphors.The main research contents are as follows:（1）Taking KHF₂,KMnO₄,MnF₂ and SiO₂ as raw materials,K₂SiF₆:Mn⁴⁺red phosphor was synthesized in HF aqueous solution by simple co-precipitation method.The water resistance of K₂SiF₆:Mn⁴⁺red phosphor can be effectively improved by adjusting the SiO₂ raw material added at the initial reaction stage at the expense of some luminescent properties.According to the test results,different proportions of SiO₂raw materials can regulate the process of reverse substitution of Mn⁴⁺by Si⁴⁺in the reaction process,and eventually form a K₂SiF₆ protective layer on the surface of the phosphor to improve the water resistance.When the molar ratio of KMnO₄ is 14%and MnF₂ is21%,the phosphors obtained by stirring for 4 hours have the best properties.After soaking in water at room temperature for 24 hours,the phosphors obtained can still maintain 81.9%of the initial luminescence intensity,and when the temperature is up to200℃,they can still maintain 86.1%of the initial luminescence intensity.A warm white LED with high color rendering index（Ra=86.7）,low color temperature（CCT=3857K）and high lumen efficiency（141.49lm/W）was obtained.（2）K₂SiF₆:Mn⁴⁺red phosphor with water resistance was synthesized by a new green preparation method of HF-free aqueous solution.In the preparation process,NH₄HF₂ molten salt is used to replace the highly toxic HF solution to provide an acidic environment and a rich F^-ion environment.The redox reaction of MnF₂ and KMnO₄ is used to produce Mn⁴⁺to replace the K₂MnF₆ precursor.The resulting product was cleaned with H₂O₂ for the incomplete reaction of KMnO₄.When the molar ratio of KMnO₄ is 10%,MnF₂ is 15%,the addition amount of NH₄HF₂ is twice that of the raw material,and the reaction time is 140℃for 4 hours,the optimal reaction conditions are obtained.After the products were immersed in water for 24 hours,the luminescence properties of the phosphors almost did not change.Meanwhile,the luminescence intensity of the phosphors remained unchanged at 125℃compared with that at room temperature.Its quantum efficiency at room temperature is 47.3%.The warm white LED devices are packaged with K₂SiF₆:Mn⁴⁺red phosphor and commercial YAG:Ce³⁺yellow phosphor to obtain a color rendering index of 87.1,a relative color temperature of 3536K,and a lumen efficiency of 116.99lm/W.