| Due to a series of advantages such as small size,high efficiency and long service life,white light-emitting diodes(w-LEDs)have become a new generation of light sources for display equipment and lighting systems.It has been a hot topic in the field of white LEDs to research and develop low-cost,stable and efficient narrow-band emitting red phosphors that can be efficiently excited by near UV/blue LEDs.Mn4+doped fluoride phosphors show multiple narrow-band red light emission in the range of 600-650 nm with high QEs.In addition,most of them can be prepared by simple synthetic methods at room temperature,which has attracted great attention.Due to these advantages,Mn4+-activated fluoride phosphors become a promising red component for high-efficiency and high color rendering index w-LED devices.Therefore,in this dissertation,a series of Mn4+ doped fluoride red phosphors have been prepared through different synthesis methods.The specific content is as follows:1)Combining solid phase method and hydrothermal method,a series of K2NbF7:Mn4+ phosphors were synthesized.The phase structure and morphology of the synthesized samples were analyzed,and their luminescence performances were improved by optimizing the concentration of Mn4+,the temperature of hydrothermal synthesis,and the acidity of the solution.The results show that the K2NbF7:Mn4+phosphor synthesized by the two-step method has excellent crystallinity.When the synthesis temperature is 120℃ and the doping amount of Mn4+ is 5 mol%,K2NbF7:Mn4+ phosphor has the best emission intensity.High-concentration HV solution is conducive to the incorporation of Mn4+.Under the excitation of～371 nm or～471 nm,K2NbF7:Mn4+ has multiple sharp emission peaks in the range of 600-650 nm.K2NbF7:Mn4+ has a strong zero-phonon line(ZPL)emission at 620 nm,and the internal quantum efficiency(IQE)is about 82%.The thermal quenching behavior of K2NbF7:Mn4+ red phosphor was studied.The reason for thermal quenching is the crossover relaxation process at high temperature.Combining K2NbF7:Mn4+ phosphor with commercial YAG:Ce3+yellow phosphor,a white light-emitting diode was fabricated with a lower correlated color temperature(CCT=3426 K)and a high luminous efficiency of 134.4 lm/W,which indicates that K2NbF7:Mn4+ could be a great potential red component for warm w-LEDs.2)A novel Mn4+-doped fluoride phosphor NaBaZrF7:Mn4+ was synthesized by the co-precipitation method.The phase structure and morphology of the sample,as well as its luminescence performances were analyzed.XRD results show that the as-prepared NaBaZrF7:Mn4+ is a single phase,and a small doping amount of Mn4+ does not change the crystal structure of NaBaZrF7.SEM images show that the as-synthesized NaBaZrF7:Mn4+ particles were irregular and fluffy with a size ranging from 0.3 to 1μm.The optimal doping concentration of Mn4+ is 1.0 mol%.NaBaZrF7:Mn4+ has a broad excitation band in the blue region and multiple sharp emission peaks in the range of 600-650 nm,which could be a potential candidate as a red phosphor for warm wLEDs.3)By using Mn(HPO4)2 as the source of Mn4+ and using H3PO4/KHF2 instead of toxic HF,K2SiF6:Mn4+ red phosphor was successfully synthesized under hydrothermal conditions,and its structure,morphology and luminescence properties were studied.The influence of hydrothermal reaction temperature on the luminescence intensity of K2SiF6:Mn4+ red phosphor was investigated.XRD analysis shows that the as-prepared K2SiF6:Mn4+ is a single phase with excellent crystallinity.K2SiF6:Mn4+ phosphor has broad excitation peaks at～350 nm and～460 nm,and under 460 nm excitation it produces multiple narrow-band red emission peaks in the range of 600-650 nm.The warm w-LED based on commercial YAG:Ce3+and K2SiF6:Mn4+ exhibits a low CCT of 3524 K,a high Ra of 80.5 and a high luminous efficiency of 113.2 lm/W. |
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