Preparation And Performance Analysis Of Eu³⁺-doped KGdF₄ Phosphor With Excellent Luminescence Thermal Stability

White light emitting diodes(WLEDs)is becoming popular lighting products due to their superior luminescence performance.One of the most important methods of commercial WLEDs to achieve white light emission is to mix red,green,blue or multi-color phosphors with UV/near-UV excitation to achieve white light emission.This approach can avoid the disadvantages of poor color rendering index,high color temperature and color reproduction due to the lack of red components in the traditional way and also has a color adjustment function,but there is a lack of suitable UV/near-UV excitation red phosphors in this solution.In addition,the operating temperature range of WLEDs is 150-180?.At this temperature,the the thermal quenching(TQ)phenomenon in the phosphor seriously affects the overall luminescence performance of WLEDs.Therefore,the development of phosphors with excellent luminescence stability is of both academic and practical application significance.Based on literature research,this thesis aims to develop high-temperature phosphors that can hopefully be used for UV/near-UV excited WLEDs.In this work,a series of UV-excited phosphors with high thermal stability of luminescence based on KGdF₄ were synthesized.KGdF₄:Eu³⁺,Sm³⁺@GQDs and KGdF₄:Eu³⁺,Yb³⁺@GQDs high-temperature red phosphors were prepared by chemical co-precipitation method,and KGdF₄:Eu³⁺,Tb³⁺@GQDs high-temperature red phosphors and KGdF₄:Tb³⁺high-temperature green phosphors were prepared by hydrothermal synthesis method.The details of the research result and innovations of this paper are as follows.1.A series of KGdF₄:Eu³⁺,Sm³⁺@GQDs phosphors were synthesized by the co-precipitation method,and the results of the analysis tests showed that:(1)the room temperature luminescence of Eu³⁺was significantly enhanced by the co-doping of Sm³⁺and the coating of GQDs,and the fluorescence intensity of the best sample(KGdF₄:0.20Eu³⁺,0.005Sm³⁺@GQDs _{1.5 mg/mol})had 1.81 times of the fluorescence intensity than that of the single-doped sample(KGdF₄:0.20Eu³⁺).(2)The coating of GQDs caused the sample to show negative TQ phenomenon,and the highest temperature point of the negative TQ was at 110?,at which the integrated luminescence intensity was 109.81%of the value at30?.Obtain an UV-excited red phosphor with good luminescence thermal stability;2.A series of KGdF₄:Eu³⁺,Yb³⁺@GQDs phosphors were synthesized by co-precipitation method and the characterization results showed that:(1)Both the co-doping of Yb³⁺and the coating of GQDs have enhanced the luminescence of Eu³⁺,and the luminescence intensity of the best sample(KGdF₄:0.20Eu³⁺,0.002Yb³⁺@GQDs _{2.0 mg/mol})is about 1.68 times that of the single-doped sample(KGdF₄:0.20Eu³⁺).(2)The co-doping of Yb³⁺caused the negative TQ phenomenon in the sample,and the co-doping of Yb³⁺and coating GQDs can further improve the negative TQ effect of the sample,and the highest temperature point of the negative TQ of the best sample is at 170?,at which the integrated luminescence intensity is 156.48%of the initial value at 30?.Obtain a red phosphor with good thermal stability of luminescence;3.A series of KGdF₄:Eu³⁺,Tb³⁺@GQDs phosphors were prepared by hydrothermal synthesis,and the results of the study indicated that:(1)The co-doping of Tb³⁺and the coating of GQDs resulted in a significant enhancement of the luminescence of Eu³⁺,and the luminescence intensity of the best red sample(KGdF₄:0.20Eu³⁺,0.06Tb³⁺@GQDs _{3.0 mg/mol})was 1.71 times that of the single-doped sample(KGdF₄:0.20Eu³⁺).(2)The Eu³⁺single-doped sample(KGdF₄:0.20Eu³⁺)prepared by hydrothermal synthesis showed negative TQ at high temperature,and the co-doping of Tb³⁺could increase the temperature of the highest point of negative TQ,and the thermal stability of the luminescence of the sample can be further optimized by coating GQDs with co-doped Tb³⁺,and the optimum red sample showed a monatonic increase in luminescence intensity within the measurement temperature without TQ,and the integrated luminescence intensity at 275?was 264.52%of the initial value of35?.(3)The Tb³⁺single-doped sample(KGdF₄:0.30Tb³⁺)prepared by hydrothermal synthesis method showed a monotonic increase in luminescence intensity in the measured temperature range and also did not TQ,and the luminescence intensity at 275? was 237.79%of the initial value of 35?.Obtain a red phosphor and green phosphor with excellent high-temperature fluorescence performance.