Synthesis Mechanism and High Temperature Chemical Stability of CaZrO3

CaZrO3 powder was prepared using CaO,CaCO3 and Ca(OH)2 as calcium source,nano m-ZrO2 powder,micron m-ZrO2 powder,micron CaO partially stabilized ZrO2(Ca-PSZ)powder as zircon source,through high temperature solid reaction.Effect of the calcination temperature(800,900,1000,1100,1200,1300,1400,1500,and 1600℃)and the holding time(3,4,and 5 h)on the phase composition change was studied to research the synthesis mechanism.The synthesized CaZrO3 powder was mixed with CaO,MgO,Al2O3,Cr2O3,SiO2,and ZrO2 powder separately and fired at 1500℃for 3 h to prepare specimens to research the high temperature chemical stability of CaZrO3 with different reaction mediums.The results show that during the synthesis process,the CaZrO3 content does not always increase with the increasing calcination temperature or the prolonging holding time,CaZrO3 decomposes resulting from the diffusion of Ca2+and O2-in CaZrO3 to m-ZrO2 or c-ZrO2.At high temperatures,when CaZrO3 is in alkaline environment(such as environment containing CaO or MgO),the high temperature chemical stability is high,but when CaZrO3 is not in alkaline environment(such as environment containing Al2O3,Cr2O3,SiO2 or ZrO2),the high temperature chemical stability is low.

Enhanced afterglow performance of CaAl_(2)O_(4):Eu^(2+),Nd^(3+) phosphors by co-doping Gd^(3+)

In order to effectively improve the afterglow properties of CaAl_(2)O_(4):Eu^(2+),Nd^(3+) phosphors,a series of Ca_(0.982-x)Al_(2)O_(4):0.012 Eu^(2+),0.006 Nd^(3+),xGd^(3+)(x=0,0.012,0.024,0.036,0.048,0.060 mol) phosphors were prepared by a high-temperature solid-phase approach.Crystalline composition and microstructure were characterized by XRD,TEM,HRTEM,and XPS,luminescence properties were systematically analyzed by fluorescence spectra,afterglow decay curves and TL glow curve.Results show that all of Ca_(0.982-x)Al_(2)O_(4):0.012 Eu^(2+),0.006 Nd^(3+),xGd^(3+)phosphors belong to monoclinic CaAl_(2)O_(4),without other cystalline phase.The blue emission at 442 nm is observed,which is assigned to the 4f^(6)5 d→4f^(7) transition of Eu^(2+) ions.Doping with appropriate amount of Gd^(3+) ions(x=0.036 mol) significantly improves the afterglow properties of phosphors,but the excessive doping of Gd^(3+) induces the fluorescent quenching.The doping of moderate Gd^(3+) changes the traps states,the trap depth varies from 0.598 to 0.644 eV and the trap concentration is also greatly improved,thus significantly improving afterglow performance.