Preparation method and application of red phosphor for silicyl nitride

Light emitting diode (LED) as a new efficient solid light source, with high efficiency, energy saving, environmental protection, long life, safety, rich color, small size, fast response and other significant advantages and has been widely studied. At present, phosphor conversion method (pc-LED) is the main way to realize white LED, that is, Ga(In) N-based blue light chip and yellow YAG:Ce3+ phosphor which can be effectively excited by blue light are packaged into white light diode, which has been successfully commercialized and applied in People’s Daily life. However, the white LED obtained by this method has low luminous efficiency and poor uniformity. In addition, due to the lack of red light in the spectrum components, the color rendering index is low and the color temperature is high, so the development of efficient red phosphor has become a research hotspot in recent years.
To overcome the shortcomings of white leds, many red phosphors have been developed, such as sulfide systems, manganese tetro-doped aluminum (gallium) ate systems and alkaline earth-transition metal composite oxide systems. But all face a variety of problems: sulfide red phosphor in the process of use, sulfur is easy to precipitate, europium is easy to be oxidized and light decline; Alum (gallium) deep red phosphors cannot be excited effectively by violet and ultraviolet light; Alkaline earth-transition metal composite oxide red phosphors are not water resistant enough, the emission wavelength of Mr 630nm. Silicon-based nitrogen (oxygen) phosphors represented by M2Si5Ns:Eu, CaAlSiN3:Eu and MSi202N2:Eu are a new type of red phosphors developed in recent years. Their structure is composed of SiN4 tetrahedron as the basic unit, which is connected through common points, common sides and coplanes, etc., forming a three-dimensional network structure like chain, layer or frame. Compared with traditional LED phosphors, rare earth doped nitrogen (oxygen) compound phosphors have excellent properties such as high structural stability, wide excitation wavelength range, adjustable emission wavelength, high thermal stability, high luminous efficiency, non-toxic, mild luminous color, and insensitive to the change of driving current, so it has attracted great attention from the scientific community and LED industry.
However, the synthesis conditions of silicon-based nitride phosphor are harsh, and it needs to be synthesized at high temperature for a long time under the protection of high pressure and atmosphere, which not only has high energy consumption, but also has high requirements for equipment, and domestic equipment is difficult to meet the corresponding requirements. Us patent US6649946 reports the preparation of nitride red phosphors with the chemical formula MxSiyNz:Eu2+ using pure metal nitride compounds such as strontium nitride, calcium nitride, europium oxide and silicon nitride as raw materials. In this method, the raw materials are expensive and active, and need to be operated in glove box, resulting in high cost. At present, there is a lot of progress in the synthesis of nitride phosphor, among which carbothermal reduction is a common method. CN104327850A is directly used as a reducing agent, which will lead to additional steps of carbon removal, more carbon residue, difficult to remove, and will seriously weaken the luminescence intensity; CN102260500A uses one or several gases as reducing agents, such as N2/H2, CH4, NH3, C0, H2, etc., which are faced with safety problems.
Including the following specific steps: alkali earth metal carbonate, Si3N4, rare earth metal oxide and solid non-carbon reducing agent mixed evenly, roasting under inert atmosphere atmospheric pressure to obtain silicyl nitrite red phosphors.
The solid non-carbon reducing agent mentioned above may be at least one of urea, anhydrous citric acid, dicyandiamine and melamine.
Preferably, the above solid non-carbon reducing agent is at least one of urea, dicyandiamine and melamine.
The above alkali earth metal carbonates can be at least one of MgC03, CaC03, SrC0#P BaCO 3.
The molar ratio of alkaline earth metal carbonate, Si3N4 and rare earth metal oxides used can be adjusted according to actual needs.
The molar ratio of the alkali earth metal carbonate, Si3N4, and rare earth metal oxides used is 1.176:1:0.012 οοοοοοοοοοοοοοοοοοοοο
The above mixture is preferably ground with a mortar at 20? 30 minutes.
The above inert atmosphere is preferred to be nitrogen atmosphere.
The above roasting is preferably divided into two stages in a tubular furnace. The first stage of roasting makes the reducing agent completely carbonized, and the second stage of roasting is a carbothermal reduction reaction.
The heating rate of the first stage roasting above is 10? 20 degrees Celsius, at 700? At 1000°C, the roasting time is 2? 4h ; The heating rate of the second stage roasting above is 2.5? 10°C at 1450? 1650°C, roasted for 3? 6h.
In order to better realize the invention, the calcined product is preferably cooled, ground, pickling, washing, drying, etc., and purified silicyl nitride red phosphors are obtained.
The above cooling preferred means cooling to room temperature.
The above acid may be one of nitric, hydrochloric or sulfuric acid, preferably nitric acid with a volume fraction of 10%.
The chemical formula of the red phosphors of silicyl nitride mentioned above can be M2xSi5Ns :xRE, in which 0 < x < 2, south of China are at least one of the alkaline earth metals Ca, Sr and Ba, RE is at least one of the rare earth elements Eu, Tm and Dy.
The silicon nitride red phosphor has low carbon content, which greatly reduces the production cost of the nitride phosphor and guarantees the luminescence performance of the material. It is especially suitable for application in high-quality white LED.
Example 1 Preparation of fauSiAz0.04Eu phosphor
According to the stoichiometric ratio of chemical formula Ca1.96Si5Ns:0.04Eu, 0.196mol of CaC03(99.99 %), 0.167mol of Si3N4(99.9 %), 0.002mol of Eu203(99.99 %),0.098mol of solid non-carbon reducing agent urea were accurately weighed. Add an appropriate amount of alcohol into the agate mortar as the grinding medium, grind for 30min to make the raw materials evenly mixed, and then put them in a drying oven at 60°C to dry lh and put them into boron nitride crucible.