Study On K 2 TiF 6 :Mn 4+ Red Phosphor For White Light LED Synthesis Without HF Method

White light emitting diodes(WLEDs)have attracted much attention due to their incomparable advantages such as low energy cost,high energy conversion efficiency,environment friendly and so on.Hence WLEDs have been considered as the fourth generation of green lighting source.Currently,the main commercial technique of producing phosphor converted WLEDs is based on the combination of blue In Ga N chip and yellow phosphor Y3Al5O12: Ce3+(YAG: Ce3+)in the market.Unfortunately,this kind of WLEDs suffers many weaknesses,for instance low color rendering index and high color temperature because of the absence of red component.To solve this issue,the discovery of efficient red emitting phosphors is essential.Recently,the Mn4+ activated fluoride red phosphors have attracted much attention because of their advantages such as high color purity,excitation by blue light/near ultraviolet light,cheap raw materials and so on,which has become a hot spot in current research.However,HF solution was necessary for the preparation of Mn4+ activated phosphors.HF solution is hypertoxic,which may cause fatal damages for human body and pollution of the environment.This topic focuses on research HF-free synthetic technology of K2 Ti F6:Mn4+ red phosphor for WLEDs,innovation and optimization of synthetic methods,to achieve the green synthesis of fluoride phosphors and study the phosphor luminescent properties.The results can be listed as follows:(1)Employ HCl(37wt %)instead of HF to synthesize phosphors,the phosphors under the different HCl/H2 O volume ratios are all pure K2 Ti F6 phases,and the phosphors preferentially grow along the(002)crystal plane.Under 200-500 nm light excitation,the phosphor have not emitting light,the reason contribute to this phenomenon is that the Mn4+ions was reduced to Mn2+ ions by HCl.(2)Employ H2SO4(98wt %)as raw material,as the H2SO4/H2 O volume ratios in8/42-16ml/34 ml range,a single pure phase K2 Ti F6 can be obtained,outside this range,KHSO4 impurity phase will appear.Appropriately increasing the H2SO4/H2 O volume ratio can increase the phosphors emission intensity.When the volume ratio is 12ml/38 ml,the phosphor emits the strongest light.(3)Employ HNO3(65wt %)as raw material,the phosphors synthesized under different HNO3/H2 O volume ratios are all pure phases,the phosphor emission intensity gradually increases with the increase of HNO3/H2 O volume ratios and reaches the maximum at40ml/10 ml,then decreases.The content of Mn ions in the phosphor matrix gradually decreased with the increase of HNO3/H2 O volume ratio,which is inconsistent with emission intensity changes,indicated that the change of emission intensity is not caused by the Mn4+ions doped concentration.With the increase of HNO3/H2 O volume ratios,the phosphor Phosphor particle size is more uniform,more evenly dispersed and surface is more smooth(4)Employ different H3PO4(85wt %)and different HNO3(65wt %)/H3PO4(85wt %)to synthesize phosphors,the synthesized phosphors are all pure phase.Appropriate increases the HNO3/H2 O volume ratio and HNO3/H3PO4 volume ratio will promoted Mn4+to enter the matrix and lead to emission intensity increases.When HNO3(65wt %)/H3PO4(85wt %)volume ratio is 20ml/30 ml,the luminescence intensity,morphology particle size,and thermal decomposition ability of the prepared phosphor are superior to other phosphors under the other synthesis conditions.Therefore,when the volume ratio of HNO3/ H3PO4 volume ratio is20ml/30 ml,it is the best choice to replace corrosive HF.(5)Based on the optimal volume ratio of HNO3/H3PO4,the luminescent properties of the phosphor are optimized by controlling Ti/F,reaction temperature,reaction time,and Mn4+ion doped concentration.The strongest excitation and emission peaks of K2 Ti F6: Mn4+phosphors are located at 470 nm and 633 nm,respectively.The optimum phosphor quantum yield is measured to be 82%,the emission intensity of K2 Ti F6: Mn4+ at 425 K remains about85% of its initial intensity(300 K).In the temperature range of 300-475 K,the color shift of the phosphor was lower than that of the commercial Ca Al Si N3:Eu2+red phosphor,the color purity of the phosphor was higher than the commercial Ca Al Si N3:Eu2+ red phosphor.The above shows that the employ HNO3/H3PO4 instead of corrosive HF can produce K2 Ti F6:Mn4+phosphors with excellent luminescence properties,which are demonstrating K2 Ti F6:Mn4+may be a potential red emitting phosphor for WLEDs.