Effect of starting materials and sintering temperature on microstructure and optical properties of Y203:Yb^(3+)5 at%transparent ceramics

Y2O3:Yb^(3+)5 at%ceramics have been synthesized by the reactive sintering method using different commercial yttria powders(Alfa-Micro,Alfa-Nano,and ITO-V)as raw materials.It has been shown that all Y2O3 starting powders consist from agglomerates up to 5-7 μm in size which are fonned from 25-60 nm primary particles.High-energy ball milling allows to significantly decreasing the median particle size D50 below 500 nm regardless of the commercial powders used.Sintering experiments indicate that powder mixtures fabricated from Alfa-Nano yttria powders have the highest sintering activity,while(Y0.86La0.09Yb0.05)2O3 ceramics sintered at 1750℃for 10 h are characterized by the highest transmittance of about 45%.Y2O3:Yb^(3+)ceramics have been obtained by the reactive sintering at 1750-1825℃using Alfa-Nano Y2O3 powders and La2O3+Zr02 as a complex sintering aid.The effects of the sintering temperature on densification processes,microstructure,and optical properties of Y2O3:Yb^(3+)5 at%ceramics have been studied.It has been shown that Zr^(4+)ions decrease the grain growth of Y2O3:Yb^(3+)ceramics for sintering temperatures 1750-1775℃.Further increasing the sintering temperature was accompanied by a sharp increase of the average grain size of ceramics referred to changes of structure and chemical composition of grain boundaries,as well as their mobility.It has been determined that the optimal sintering temperature to produce high-dense yttria ceramics with transmittance of 79%-83%and average grain size of 8μm is 1800℃.Finally,laser emission at〜1030.7 nm with a slope efficiency of 10%was obtained with the most transparent Y203:Yb^(3+)5 at%ceramics sintered.

Energy transfer and luminescent properties of Tb^(3+)and Tb^(3+),Yb^(3+)doped CNGG phosphors

In this work,calcium niobium gallium garnet(Ca_(3)Nb_(1.6875)Ga_(3.1875)O_(12)-CNGG)ceramic samples singledoped with Tb^(3+)and co-doped with Tb^(3+)and Yb^(3+)ions were sintered by the solid-state reaction method.The structural characterization of the samples was carried out by X-ray diffraction measurements.The optimal concentration of Tb^(3+)ions corresponding to the maximum luminescence in the green spectral range in CNGG:x at%Tb(x=0.1,0.5,1,2,3,4,and 5)was determined to be 4 at%.The timeresolved luminescence of the^(5)D_(4)level(Tb^(3+))in the CNGG:x at%Tb samples was analysed to explore the quenching mechanisms involved in the Tb^(3+)green emission.Co-doped CNGG:4 at%Tb,y at%Yb(y=0.5,2,4,6,8,and 10)ceramics were prepared and investigated.It is shown that CNGG:4 at%Tb,y at%Yb phosphors exhibit intense green luminescence under ultra-violet(UV),visible(VIS),and near-infrared(NIR)excitation,thus demonstrating the presence of simultaneous down-conversion(DC)and upconversion(UC)processes.The dependence of the UC luminescence intensity on the diode laser pumping power was measured and the results indicate a two-photon process based on cooperative energy transfer(CET).Under UV excitation,the lifetime of the^(5)D_(4)(Tb^(3+))level slowly increases with increase of Yb^(3+)concentration,suggesting the energy transfer from Yb^(3+)to Tb^(3+)ions,while under NIR excitation,the lifetime of the^(5)D_(4)(Tb^(3+))level decreases with increase of Yb^(3+)ions concentration,indicating the presence of a strong energy transfer from Tb^(3+)to Yb^(3+)ions.The highest energy transfer efficiency ofη_(ET)≈42%was determined for the CNGG:4 at%Tb,10 at%Yb sample.The obtained results indicate that CNGG:(Tb^(3+),Yb^(3+))could be efficient new yellowish-green-emitting phosphors.