Carbothermal Reduction Synthesis And Removal Of Residual Carbon For Nitride Phosphor

Nitride phosphors have favorable luminescence properties,which can effectively solve the problem of insufficient light intensity in the red part of the existing white LEDs,thereby improving the color rendering index of the device,and it have received wide attention and research in the field of semiconductor lighting.Traditional high-temperature solid-phase synthesis of nitride phosphors requires expensive nitride starting materials and complex anhydrous,oxygen-free operation procedures,high temperature and high-pressure synthesis conditions.The carbothermal reduction nitridation method uses low-cost oxides as raw materials,can operate in an atmospheric environment and has a relatively low synthesis temperature,so it has a potential application value in the field of preparing synthetic nitride phosphors.In order to ensure that the oxide raw material is fully reduced,the carbothermal reduction process usually need to add an excessive amount of reducing agent.The residual carbon leads the phosphor's luminescence performance to a decline sharply,which is the key technical bottleneck for limiting the carbothermal synthesis of phosphor materials.In response to this problem,this dissertation has carried out research on the synthesis of Sr Al Si₄N₇:Eu²⁺and Y₃Si₆N₁₁:Ce³⁺ two kinds of nitride phosphors by carbothermal reduction synthesis,and adopts two processes of non-thermal plasma oxidation and high temperature oxidation to eliminate residual carbon.The main contents of this article are as follows:1.Study on the synthesis of Sr Al Si₄N₇:Eu²⁺ red nitride phosphor via carbothermal reduction.Red nitride phosphor Sr Al Si₄N₇:Eu²⁺ was synthesized by carbothermal reduction nitridation under normal pressure,and the effects of different amounts of reducing agent on the phase,morphology and luminescence properties were studied.The optimized preparation conditions were determined:the pure phase target products can be synthesized at 1600? for 8 hours when C/O ratio was 1.15.As the C/O ratio increases,the emission spectra will gradually shift to red.When the amount of carbon reducing agent exceeds the optimal concentration,the luminescence intensity of the material decreases significantly due to the sharp increase of the residual carbon content in the synthesized phosphor.Combined with the results of thermogravimetric analysis,the synthesis mechanism of Sr Al Si₄N₇:Eu²⁺ red nitride phosphor synthesized by carbothermal reduction was preliminarily discussed.2.Study on the effect of non-thermal plasma oxidation and high temperature oxidation on carbon removal.The research object is the Sr Al Si₄N₇:Eu²⁺ red nitride phosphor synthesized by carbothermal reduction nitridation in the previous chapter.The phase,morphology and luminescence properties of the phosphor material were compared for the non-thermal plasma oxidation and high temperature oxidation by the effect of carbon removal.For the high temperature oxidation,as the temperature rises during carbon removal,the luminescence intensity of the phosphor is enhanced,and no new phase was produced,it shows a high residual carbon removal efficiency.For the non-thermal plasma oxidation,the luminescence intensity of the phosphor increases with the treatment time,it also shows that it has excellent carbon removal effect.The reaction mechanism of carbon removal by non-thermal plasma oxidation was preliminarily explained.The active particles such as free radicals,excited atoms and molecules generated by the discharge of non-thermal plasma in the air atmosphere oxidized with the residual carbon and then removed in the form of CO or CO₂.3.Research on Y₃Si₆N₁₁:Ce³⁺ yellow nitride phosphor preparation process of carbothermal reduction and residual carbon.The carbothermal reduction preparation process of Y₃Si₆N₁₁:Ce³⁺ yellow nitride phosphor was studied,and the effects of different preparation conditions on the phase,morphology and luminescence properties of the samples were discussed.The optimized preparation conditions were determined:Pure phase target products can be synthesized at 1625? for 7 hours when C/O ratio was 1.80.The thermal stability of Y₃Si₆N₁₁:Ce³⁺ was studied.The luminescence intensity drops sharply after the test temperature rises,and the abnormal thermal quenching phenomenon is caused by the small energy difference between the 5d energy level of the excited state of Ce³⁺ and the host lattice conduction band,which is partially caused photoionization process.After that,the residual carbon in the prepared phosphor was removed by non-thermal plasma oxidation and high-temperature oxidation carbon removal,and the effects of different treatment conditions on the sample performance were compared.The effect of atmospheric conditions on non-thermal plasma oxidation carbon removal was discussed.The carbon removal efficiency was higher under O₂ atmosphere and lower under N₂ atmosphere.