Green Synthesis And Luminescent Properties Of Novel Mn⁴⁺ Doped Fluoride Phosphors

White light emitting diodes?WLEDs?have become a new generation lighting sources due to their energy saving,high efficiency,long life and environmental friendliness.At present,merchant WLEDs are composed of In Ga N/Ga N chips and Y₃Al₅O₁₂:Ce³⁺(YAG:Ce³⁺)yellow phosphor.However,the disadvantages of WLEDs obtained by this method are high color temperature?CCT> 6000 K?and low color rendering index?Ra <70?,which is not conducive to indoor lighting.To solve this problem,researchers are working to find an excellent red phosphor to improve the performance of WLEDs.The transition metal Mn⁴⁺ doped fluoride red phosphor has the advantages of unique narrow-band red light emission,low production costs,and abundant raw materials.It is an ideal red emitting material.Unfortunately,the synthesis of these phosphors usually requires the toxic HF as a solvent,which will cause harm to the environment and the human body.Therefore,this work aims to find a green route to synthesis the Mn⁴⁺ doped fluoride red phosphors.The main research contents are as follows:The KZnF₃:Mn⁴⁺ were synthesized by using?NH₄F+HCl?instead of the toxic HF.The KZnF₃:Mn⁴⁺ can be effectively excited by blue light,which results in a series of narrow-band red light emission.The effects of reaction conditions on the optical performance of KZnF₃:Mn⁴⁺ phosphor was explored.In addition,the concentration quenching mechanism was analyzed.The WLED assembled with KZnF₃:Mn⁴⁺,YAG:Ce³⁺ and Ga N chip has low color temperature?CCT = 4974 K?,high color rendering index?Ra = 82.1?,and the luminous efficiency of 120.33 lm/W.The chrysanthemum-shaped K₂LiAlF₆:Mn⁴⁺ was synthesized by using?NH₄F+HCl?instead of toxic HF.Under 465 nm blue light excitation,the K₂LiAlF₆:Mn⁴⁺ can exhibits sharp red emitting.The effects of reaction conditions on the optical performance of K₂LiAlF₆:Mn⁴⁺ phosphor was investigated.The concentration quenching mechanism was analyzed.In addition,the Mn⁴⁺ has strong crystal field strength in the K₂LiAlF₆ host and its emission mechanism was discussed.A series of K₃ZrF₇:Mn⁴⁺ were prepared by using HAc,HCl and HNO₃ instead of the toxic HF,respectively.Under 468 nm blue light excitation,the K₃ZrF₇:Mn⁴⁺ exhibits sharp red emission.The strongest emission peak located at 632 nm,which belongs to the spin forbidden 2Eg?4A2g transition of Mn⁴⁺.The effects of surfactants on the luminescence properties of K₃ZrF₇:Mn⁴⁺ were studied.In addition,the concentration quenching mechanism was discussed.The results indicate the K₃ZrF₇:Mn⁴⁺ is a promising red material.The K₂SiF₆:Mn⁴⁺ was synthesized by using?NH₄F+HNO₃/HAc/H₃PO₄?instead of the toxic HF.The effects of potassium sources and surfactants on the luminescent properties of K₂SiF₆:Mn⁴⁺ were studied.The concentration quenching mechanism was discussed.The field strength and emission mechanism of Mn⁴⁺ in K₂SiF₆ host were analyzed.Finally,using K₂SiF₆:Mn⁴⁺ as the red material,a warm WLED with low color temperature?CCT=3816 K?,high color rendering index?Ra=87.7?and luminous efficiency of 139.51 lm/W was achieved.