Mg_0.25-xAl_2.57O_3.79N_0.21:xMn Study On The Preparation And Properties Of Transparent Ceramic Phosphor

WLED,a new generation of lighting source,is paid much attention because of its excellent performance,such as environment-friendliness,energy saving,high efficiency and so on.Duo to poor thermal properties of organic-based encapsulants,high-power WLED could not been realized.Therefore,inorganic solid phosphor conversion materials come up.Owing to high optical transparency and low cost,the transparent ceramic phosphors composed of transparent ceramic and activator ions have gained more and more attention.However,the research of transparent ceramic phosphors is mainly focused on yellow-emitting ceramic phosphors at present.It is necessary to develop green-emitting or red-emitting transparent ceramic phosphors for high-power and high color rendering WLED.Spinel-type MgAlON transparent ceramic with excellent optical and thermal-mechanical properties is a potential host material for solid phosphor converters.As a common activator ion,Mn²⁺is sensitive to the surrounding crystal-field environment.In spinel-type matrix materials,Mn²⁺preferentially resides in tetrahedron acting as a green-emitting fluorescence center.Thus,it is possible to functionalize MgAlON transparent ceramic with green-emitting fluorescence by doping of Mn²⁺.In this work,Mg_0.25Al_2.57O_3.79N_0.21 was functionalized with fluorescence by doping of Mn²⁺.Single phase Mn²⁺doped MgAlON[Mg_0.25-xAl_2.57O_3.79N_0.21:xMn?x=0.01-0.07?]phosphor powder with a narrow size distribution were synthesized by solid state reaction at first.By the characterizations of XPS and EPR,it is demonstrated that Mn ions in divalent state occupied the tetrahedral sites of spinel-type structure.A crystal structure model was established based on the results of XPS and EPR,and the crystal structure of phosphor powder was analyzed by the Rietveld method using the Fullprof program.According to the excitation and emission spectra,MgAlON:Mn phosphor powder has green-light emission under blue-light excitation,and the optimum doping content of Mn²⁺is x=0.05-0.06.Transparent MgAlON:Mn ceramic phosphors with high transparency were obtained by pressureless sintering of these powder followed by hot isostatic pressing?HIP?.The result of MgAlON:Mn with different Mn²⁺contents under different sintering temperature shows that the more Mn²⁺-doped content,the better sintering performance MgAlON:Mn phosphor powder have.After HIP treatment of MgAlON:Mn bodies obtained under optimized pre-sintering condition,MgAlON:Mn transparent ceramic phosphors with lower Mn²⁺contents?x=0.01-0.04?show better optical transparency?⁸0%at 800 nm?,while those with higher Mn²⁺contents?x=0.05-0.07?show lower optical transparency.Fluorescence measurements show that MgAlON:Mn transparent ceramic phosphors have strong green emission peak at 512-520 nm under 445 nm blue-light excitation.Meanwhile,MgAlON:Mn ceramic phosphor?x=0.04?exhibits higher green color purity,higher internal quantum efficiency?47%?and lower thermal quenching compared with its powder counterpart.Based on the rigid lattice of MgAlON ceramic-matrix,MgAlON:Mn transparent ceramic phosphors retain excellent thermal-mechanical properties in comparison to glass-ceramic phosphors:thermal conductivity is 10.9 W/?m·K?,thermal expansion coefficient is 7.9×10^-6/K,and Vickers hardness is 14.62 GPa.This novel MgAlON:Mn green transparent ceramic phosphor will be a candidate color converter usable in high-power WLEDs to improve its color rendering.The relationship between the composition,structure and properties of Mn²⁺doped MgAlON transparent ceramics was studied in this work,which could provide a reference for the doping of other activator ions in MgAlON transparent ceramics.