Preparation And Optical Performance Of Red Nitride Phosphor In Low Melting Point Glass

In recent years,people's requirements of the fluorescent materials applied for high power LED and LDP?Laser phosphor display?are increasingly higher.In traditional LED and LDP technology,phosphor is usually mixed directly with organic resins.However,due to heat radiation from the LED chip and high power blue laser,organic resins degrade,and become yellow and phosphor decompose after a period of operation,which leads to lumen loss and chromaticity shift.The PiG?phosphor in-glass?prepared by low-temperature co-sintering phosphor and glass power is becoming a most promising candidate to solve the above problems.In order to achieve warm white LED and high quality display of LDP,it is very imperative to produce red PiG.Red nitride phosphor with high quantum efficiency,thermal stability and chemical resistance,is suited well for preparing PiG.Nevertheless,there are some questions of red nitride PiG needed to be solved,such as the influence factors of luminous property of red nitride PiG and measures to reduce the adverse impact of glass phase on phosphor crystalline phase.Among the red nitride phosphors,CaAlSiN₃:Eu²⁺ has these advantages of prominent quantum efficiency and heat-resistance.In this paper,a series of Ca_1-xAlSiN₃:xEu²⁺ phosphors have been successfully synthesized by gas-pressure-sintering and characterized X-ray diffraction?XRD?,scanning electronic microscope?SEM?and fluorescence spectrophotometer?PL?.The experiment results indicated that the phosphor,which was obtained under the condition that sintering temperature was 1700?,sintering pressure was 0.65 MPa,the concentration of Eu²⁺ was 2 mol%,and quenching temperature was 1200?,had a well crystalline and strong luminescent intensity.Interestingly,the wavelength of emission peak could be tuned between 637-646 nm only by altering the quenching temperature,which was a new means to adjust the emitting color of phosphor.After acid washing,surface of the phosphor particles became smooth and the luminous intensity of the emission peak were also promoted by 9.3%.For the sake of figuring out the influence factors of luminescence property of red nitride PiG,different kinds of low melting glass matrix PiG were prepared by the low-temperature co-sintering technology.The experimental results showed that the content of phosphor and sintering temperature had a important impact on the luminous properties of red nitride PiG.Silicate glass,SBB?SiO₂-B₂O₃-BaO?,owned a high melting temperature.When the sintering temperature was 700?,the glass phase reacted with phosphor crystalline phase to form SiO₂ and Ca₆?SiO4_?(Si₃O₁₀)and the emission intensity of the PiG reduced seriously.Although tellurite glass,TBZNA?TeO₂-B₂O₃-ZnONaO-Al₂O₃?possessed a low melting temperature,its chemical character was very active,enabling the phosphor to degrade at sintering temperature of 425?.Bismuthate glass,BBAZ?Bi₂O₃-B₂O₃-Al₂O₃-ZnO?,had a moderate melting temperature and the luminous property was quite good at sintering temperature of 550?.Taking various factors into consideration,BBAZ was the optimum glass matrix to prepared red nitride PiG.To reduce the negative influence from glass phase on the phosphor,a plan of coating SiO₂ on the surface of phosphor particles was tried.The results suggested that a uniform nano-sized amorous SiO₂ layer deposited on the surface of phosphor particles after the analysis of FE-SEM?EDX and XRD.The reflection spectrum confirmed that a little of SiO₂ had almost no effect on the light absorption of phosphor.PL spectra showed that the emission intensity had a slight increase with a little of SiO₂,while the emission intensity dropped down seriously with a large of SiO₂.PiG prepared by SiO₂ coated had the following superiority: compact microstructure,high extraction efficiency of red light,emission intensity and internal quantum efficiency.Therefore,it was an effective mean to reduce the adverse impact of glass phase on phosphor crystalline phase by coating SiO₂ on the surface of phosphor particles.