The Effect Of Liquid Ammonia Treatment Of Metal Si/Ca/Eu On The Preparation And Properties Of Ca₂Si₅N₈:Eu²⁺ Phosphor

Ca₂Si₅N₈:Eu²⁺ phosphor have recently been a research focus of white light LED phosphors because of its excellent luminescence properties, thermal and chemical stability, as well as low energy consumption. The preparation and property of Ca₂Si₅N₈:Eu²⁺ phosphor have received considerable attention of numerous researchers, researches showed that the preparation have effect on the property of Ca₂Si₅N₈:Eu²⁺ phosphor, while the preparation is determined by the raw materials and mixing method. Whereas the the raw materials, mixing method and preparation are limited by the non-Oxygen in element composition. Hence it is crucial to choose suitable raw materials and appropriate mixing method in order to prepare Ca₂Si₅N₈:Eu²⁺ phosphor with excellent properties under atmosphere at lower temperature.In this paper amorphous silicon was used as silicon source instead of traditional Si3N4,Ca₂Si₅N₈:Eu²⁺ phosphor was prepared under atmosphere at lower temperature through liquid mixing. Furthermore, the influence of Eu doping content on the luminescence properties and crystal structure of Ca₂Si₅N₈:Eu²⁺ phosphor was investigated. The crystal structure was analyzed by X-ray diffraction（XRD）, the morphology was characterized by scanning electron microscope（SEM）, and luminescence properties were evaluated by Photoluminescence（PL）spectroscopy. The influencing mechanism of storage condition and liquid mixing process over the reduction of nitriding temperature of the phosphors was also preliminary discussed.Meanwhile, the suitable Eu2+doping content was determined. The conclusions are listed as follows:The effect of storage condition on the surface performance of amorphous silicon has been investigated. The amorphous silicon absorb moisture in air condition and NH3 in ammonia-nitrogen atmosphere. The amorphous silicon is oxidized much more in air condition,and combine NH3 to form Si-N or Si-N-O bond in ammonia-nitrogen atmosphere. The TG curves show that the nitriding temperature of the amorphous silicon in ammonia-nitrogen atmosphere is 400 °C and 500 °C in air condition. The nitriding speed in ammonia-nitrogen atmosphere is almost four times of the one in the other condition at 980 °C. Hence,ammonia-nitrogen atmosphere can not only hinder the amorphous silicon oxidation by O2, but also can be absorbed on the surface of amorphous silicon to change its surface properties to speed up nitriding, in preparation for the later mixing of raw materials and synthesis.The effect of liquid mixing process on the synthesis temperature of Ca₂Si₅N₈:Eu²⁺ phosphor has been investigated. Metal Ca and Eu are dissolved in liquid ammonia to form a metal amide solution, in which amorphous material is suspended. By the volatilization of ammonia, the solution become supersaturated,and precipitate metal amide on the surface of amorphous silicon. The liquid mixing prompt Ca₂Si₅N₈:Eu²⁺phosphor to synthesize at atmospheric pressure 1100 °C for 6 h. TG analysis and FTIR spectrum show that amorphous silicon react with N2 at 980 °C to form Si-N bond. The synthesized phosphor is spherical with good dispersion. Ca2Si5N8 crystal contains a small account of Eu in divalent state with wide broad band emission fluorescence characteristics. Excited at 467 nm the phosphor presented a single broad emission band peaking at 580 nm. The liquid mixing reduce the synthesis temperature of the phosphor from above1300 °C as reported in other papers to 1100 °C.The effect of Eu doping content on the crystal structure and luminescence properties has been investigated. With the increase of Eu doping content from 10 % to 30 %, the crystallinity of the product becomes better. No significant differences are found in the crystal structure. The emission intensity increases at first before reaching at the maximum for Eu doping content is15 %. With Eu doping content continues to increase, the luminous intensity decreases due to the concentration quenching. The emission peak position red-shifts with the increasing of Eu doping content. It is concluded that Ca₂Si₅N₈:Eu²⁺ phosphor prepared at atmospheric pressure 1100 °C for 6 h show the optimal luminescence properties at Eu content 15 %.