Surface Coating And Its Improvement Mechanism On Thermal Stability Of BaMgAl₁₀o₁₇:Eu²⁺ Phosphor

BaMgAl₁₀O₁₇:Eu²⁺ blue phosphor has been wildly used in all kinds of green lighting and flat panel display equipment for its high luminous efficiency and color purity.However,during the use process,it may happen obvious thermal degradation and influence the object application's quality and longevity.A large number of studies have shown that surface coating could improve its thermal stability,but the thermal degradation mechanism is not clear,and this lead to the reason why surface coating can improve thermal stability is also not clear.Thus,In this thesis,the thermal degradation was analyzed by process analysis and theoretical description as viewed from phosphor surface and phase microstructure aspects.And thermal degradation mechanism was put forward based on structure activity relationship.Then,the effect of surface coating on thermal stability was studied.Discussed surface coating improvement mechanism on thermal stability based on thermal degradation mechanism.In order to study thermal degradation mechanism of BaMgAl₁₀O₁₇:Eu²⁺,the phosphor was annealed at 600¹000? in this thesis.The structure distortion,surface chemical composition,defect feature and luminescent properties of phosphor with different heat treament were analyzed by XRD,XPS,thermalluminescent spectra and fluorescence spectra.The ralationship between thermal degradation and phosphor's surface and phase microstructure was established,then thermal degradation of surface structure corrosion mechanism was proposed.Results showed that:?1?The phase structure of BaMgAl₁₀O₁₇:Eu²⁺ was not changed obviously,but the lattice distortion could happen to some extent.?2?In emission spectra,the bule emission at 450 nm which belongs to Eu²⁺ transition was reduced and the characteristics of Eu³⁺ red light emission appeared with increase temperature.?3?The bonding patterns of Al-O₄-Al and Al-O₆-Ba/Mg increased and Al-O₆-Al decreased on the surface of phosphor,this indicated that structure distortion layer formed under the condition of heat treatment,and the distortion layer propagates inwards with increase temperature.?4?With the increase of heat temperature,oxygen vacancy gradually reduced in thermalluminescent spectra,and the group changes in FTIR was consistent with XPS.Comprehensive the above results,it is thought that the BaMgAl₁₀O₁₇:Eu²⁺ thermal degradation was caused by surface structure corrosion.On the one hand,the oxygen in the air reacted with surface defect and causing the oxidation of Eu²⁺ under the action of heat,on the other hand,under the action of heat,surface defect has formed surface structure distortion layer and expand to internal,affect the luminescence behaviors and properties of Eu²⁺.To study the micromechanism of surface coating improvement on thermal stability of BaMgAl₁₀O₁₇:Eu²⁺ phosphor.In this paper,heterogeneous precipitation method was adopted to coat a SiO₂ and MgO layer with different content.The phosphor was characterized by XRD,SEM-EDS,FTIR and luminescence properties tests.The affect of coating content on luminescence properties and thermal stability was investigated.Combined with the thermal degradation mechanism this paper has proposed,put forward surface defect /distortion repair mechanism of surface coating improvement thermal stability.Results indicated that:?1?A uniform density oxide film layer was coated on the phosphor successfully adopting heterogeneous precipitation method,and the layer did not change phase structure.?2?Surface coating can not obviously improve the luminescence properties of phosphor,but is able to improve its resistance to degradation performance.When the SiO₂ and MgO covering amount is 4%,phosphor has good thermal stability.Combining thermal degradation mechanism that surface coating can improve the thermal stability reason is: on the one hand,to prevent the entry of oxygen,protect luminous center Eu²⁺ ions from the oxidation;on the other hand,coating material has bonded with phosphors surface,repaired the surface defects,prevented the formation and extension of surface structure distortion layer.