Synthesis And Surface Modification Of Transition Metal Mn⁴⁺ Doped Nb-Ta-based Luminescent Materials

White light-emitting diodes（WLEDs）made of blue light chips（InGaN）combined with yellow phosphor Y₃Al₅O₁₂:Ce³⁺(YAG:Ce³⁺)have the advantages of low energy consumption,long life and environmental friendliness,and are considered a new generation of green energy.However,this kind of WLED has some disadvantages such as low color rendering index（Ra<70）and high color temperature（CCT>6000 K）.In order to improve the performance of WLEDs and broaden their application range,it is necessary to introduce a new type of phosphor that emits red light appropriately.The transition metal Mn⁴⁺doped red phosphors can improve the color reproducibility of WLEDs,so they have received broad research interest due to the outstanding optical properties,low cost and thermal stability.However,the poor moisture resistance of this type of phosphor limits its application range.Therefore,this thesis is dedicated to finding a new Mn⁴⁺doped Nb-Ta-based red phosphor with excellent moisture resistance.The main research contents are as follows:The Nb-based fluoride phosphor K₂Nb F₇:Mn⁴⁺was synthesized by a simple co-precipitation method.The effects of the amount of KF,the concentration of Mn⁴⁺and the K source on the luminescence performance of the phosphor were explored,and the mechanism of concentration quenching was analyzed.Using methyl silicone oil（PDMS）to modify the surface of K₂Nb F₇:Mn⁴⁺shows that coating the surface of K₂Nb F₇:Mn⁴⁺with methyl silicone oil layer can effectively improve the moisture resistance and enhance luminescence.Using K₂Nb F₇:Mn⁴⁺@PDMS phosphor as the red light component,warm white LEDs assembled with yellow powder YAG:Ce³⁺and InGaN blue chips have a lower color temperature（CCT=3526 K）and a higher color rendering index（Ra=84.9）.A new type of high-efficiency Nb-based oxyfluoride phosphor K₃（Nb OF₅）（HF₂）:Mn⁴⁺was synthesized by a simple co-precipitation method.The effect of Mn⁴⁺concentration on the luminescence performance was explored,and the mechanism of concentration quenching was analyzed.The humidity resistance of Nb-based oxyfluoride phosphor K₃（Nb OF₅）（HF₂）:Mn⁴⁺and Nb-based fluoride phosphor K₂Nb F₇:Mn⁴⁺was compared.Finally,warm white LED with excellent performance（CCT=3430 K,CRI=87.3）was obtained by combining red phosphor K₃（Nb OF₅）（HF₂）:Mn⁴⁺,yellow powder YAG:Ce³⁺and Ga N blue chip.The Ta-based fluoride phosphor K₂Ta F₇:Mn⁴⁺was synthesized by the co-precipitation method,super water-resistant K₂Ta F₇:Mn⁴⁺crystals were obtained by hydrothermal treatment,and at the same time,the K₂Ta F₇:Mn⁴⁺powder was surface-modified with oleic acid to obtain a more stable K₂Ta F₇:Mn⁴⁺@OA.The humidity resistance and their application in warm white LEDs of K₂Ta F₇:Mn⁴⁺powder,K₂Ta F₇:Mn⁴⁺crystal and K₂Ta F₇:Mn⁴⁺@OA were compared.The results show that K₂Ta F₇:Mn⁴⁺crystal not only has excellent moisture resistance and luminescence performance,but also can greatly improve the performance of WLEDs.