Carbothermal Reduction Synthesis Of Nitride Phosphor And The Removal Of Residual Carbon By Low Temperature Plasma

In the synthesis of nitrides phosphors, carbothermal reduction nitridation（CTRN）method is recognized to be the most practical value in industry owing to its advantages of abundant and low cost raw material as well as simple equipment. However, the residual carbon of CTRN has serious impacts on the appearance and luminescent properties of phosphor, which limit the practical application of CTRN in industry. In this thesis, the Eu²⁺-doped red nitride phosphors Sr₂Si₅N₈ and Ca Al Si N3 were prepared by CTRN. The influence of carbon reducing agent（graphite） content on the performances of phosphors was discuss to clarify the degradation approach of residual carbon for the luminescent properties of phosphors. And then, residual carbon in nitrides phosphors is removed by the dielectric barrier discharge（DBD） atmosphere plasma The influence of plasma parameters on the removal effect of residual carbon and the removal mechanism as well as the damage effect for DBD decarbonization technology. In addition, we compared DBD decarbonization technology with high-temperature oxidation decarbonization technology to interpretation the superiority of DBD. The main achievements of this thesis are summarized as follows:1. Sr₂Si₅N₈:Eu²⁺ and CaAl Si N3:Eu²⁺ phosphors were synthesized by CTRN method using all oxide materials. The main crystal phases of the prepared samples are identified as Sr₂Si₅N₈ and Ca Al Si N3 respectively. Sr₂Si₅N₈:Eu²⁺ and Ca Al Si N3:Eu²⁺ phosphors emit red light at 630 nm and 660 nm, under the excitation of 460 nm blue light. Because of the absorption effect of the residual carbon, the luminescence intensity of phosphor was found to decrease with the increase of residual carbon content.2. Dielectric barrier discharge（DBD） atmosphere plasma was employed to remove the residual carbon in above prepared nitrides phosphors. The influence of discharge voltage,discharge current and discharge time of DBD on the removal ratio was investigated. The removal mechanism of residual carbon is discussed. Plasma is rich in strong oxidation active particles, including free radical, excited state atom, molecule and others. The removal mechanism is identified to the oxidation of residual carbon into gaseous CO or CO₂, resulting from the physical and chemical interaction between active particles and residual carbon.Comparing with the serious damage effect of high-temperature oxidation decarbonization technology, DBD atmospheric plasma decarbonization technology is hard to decrease the crystallinity of the phosphor. As a result, DBD atmospheric plasma decarbonization technology avoided effectively the damage effect, which was announced obviously in traditional high-temperature oxidation decarbonization technology.3. The damage effect of DBD atmospheric plasma decarbonization technology was studied.By comparing the phase structure and luminescence properties for the phosphors before and after DBD treatment, we found that the crystallinity of the phosphor powder did not change significantly after DBD plasma treatment, but the luminescence intensity and efficiency of phosphor were found to be decreasing. The reason for this is ascribed to the appearance of the defect resulted by the bombardment of high energy particle on the surface of phosphor. The appearance of the defect is the origin of performance degradation for phosphor.