The effects of different x values on the dielectric properties in the Ba6-3xSm8+2xTi18O54 microwave dielectric ceramics(0.3≤x≤0.7) were studied. The results showed that the major crystal phase was BaSm2Ti4O12 and th...The effects of different x values on the dielectric properties in the Ba6-3xSm8+2xTi18O54 microwave dielectric ceramics(0.3≤x≤0.7) were studied. The results showed that the major crystal phase was BaSm2Ti4O12 and the sintering temperature of the ceramics was 1340 ℃ when the x value was 0.67. The dielectric properties were better: εr≈79, tanδ≈1×10-4(1 MHz); εr≈80, Q·f=9230 GHz(3.97 GHz), τf=-17 ppm·℃-1.展开更多
采用传统的高温固相法制备一种新型的红色荧光粉Ba_(6)Gd_(2)Ti_(4)O_(17):Sm^(3+),并通过X射线衍射(X-ray diffraction,XRD)、扫描电子显微镜(scanning electron microscope,SEM)、荧光(photoluminescence,PL)光谱及色坐标表征系列样...采用传统的高温固相法制备一种新型的红色荧光粉Ba_(6)Gd_(2)Ti_(4)O_(17):Sm^(3+),并通过X射线衍射(X-ray diffraction,XRD)、扫描电子显微镜(scanning electron microscope,SEM)、荧光(photoluminescence,PL)光谱及色坐标表征系列样品的物相、形貌和发光性能.PL光谱表明该荧光粉可以被近紫外光有效激发,在407 nm近紫外光激发下,发射光谱由四个发射峰组成,最强发射峰位于616 nm处,归结为Sm^(3+)的^(4)G_(5/2)→^(6)H_(7/2)跃迁.随着Sm^(3+)掺杂量的增加,荧光粉的发光强度先增大后减小,最佳掺杂比例(物质的量分数)为3%.系列掺杂比例荧光粉的色坐标基本不变,均位于红光区.研究结果表明,该荧光粉是一种具有应用前景的新型白光发光二极管(light-emitting diode,LED)用红色荧光粉.展开更多
The Er3+doped double perovskite Ba_(2)CaWO_(6) crystal is a promising ratiometric thermometer based on the fluorescence intensity ratio(FIR) of transitions from ^(2)H_(11/2) and ^(4)S_(3/2) to the lowered ^(4)I_(15/2)...The Er3+doped double perovskite Ba_(2)CaWO_(6) crystal is a promising ratiometric thermometer based on the fluorescence intensity ratio(FIR) of transitions from ^(2)H_(11/2) and ^(4)S_(3/2) to the lowered ^(4)I_(15/2) level.However,the Ca^(2+) vacancy defect caused by the charge difference between rare-earth ions and the substituted alkaline-earth ions gives rise to the non-radiative probability and limits the thermal sensitivity.Here,the up-conversion luminescence and thermometric performance of Er^(3+),Yb^(3+) dopedBa_(2)CaWO_(6) are tuned by tri-doping with alkaline ions.The Ca^(2+) vacancy defect can be eliminated by the introduction of Na^(+),which occupies the Ca^(2+) site when it is doped into Ba_(2)CaWO_(6) with Er^(3+) and Yb^(3+).On the contrary,the doping of Cs^(+) into Ba_(2)CaWO_(6) with Er^(3+) and Yb^(3+) enhances the defect concentration because it occupies the site of Ba^(2+).Thus,the tri-doping of Na^(+) reduces the non-radiative probability and enhances the quantum efficiency of Er^(3+),leading to the improvement of the thermometric sensitivity of Ba_(2)CaWO_(6).As a result,we get an excellent thermometric Ba_(2)CaWO_(6):8%Yb^(3+),3.5%Er^(3+),6%Na^(+) powder with a luminescence lifetime of 515 μs and maximum thermal sensitivity(S_(r)) of 1.45%/K,which is more than three times higher than that of the BCWO:Er^(3+) powder.展开更多
Red emitting phosphors play a significant role in accelerating the improvement of illumination quality for white light emitting diodes(WLEDs).In this work,by using solid-state reaction method,an efficient novel Ba_(2)...Red emitting phosphors play a significant role in accelerating the improvement of illumination quality for white light emitting diodes(WLEDs).In this work,by using solid-state reaction method,an efficient novel Ba_(2)LuNbO_(6):Eu^(3+)phosphor with double-perovskite structure was successfully prepared.Here,a series of Ba_(2)LuNbO_(6):Eu^(3+)red phosphors can be efficiently pumped by the near-ultraviolet(UV)light and then present high-brightness at orange emission(598 nm,~5D_(0)→~7 F_(1))and red emission(610 nm,~5D_(0)→~7 F_(2)).The ratio values of 610 to 598 nm in Ba_(2)LuNbO_(6):Eu^(3+)phosphors exceed 1 when the content of Eu^(3+)is larger than 0.4 mol,because the occupation of Eu^(3+)ions is changed from Lu^(3+)ions with symmetric sites to Ba^(2+)ions with asymmetric sites.Besides,the optimized concentration of Eu^(3+)at the~5D_(0)→~7 F_(2)transitions is obtained when x=1,indicating that there is non-concentration quenching in Ba_(2)LuNbO_(6):Eu^(3+)phosphors.Moreover,the CIE chromaticity coordinates of Ba_(2)LuNbO_(6):Eu^(3+)was calculated to be(0.587,0.361),the color purity was calculated to be 72.26%and internal quenching efficiency(IQE)was measured to be 67%.Finally,the thermal stability of Ba_(2)LuNbO_(6):Eu^(3+)phosphors was also studied.Our work demonstrates that the novel double-perovskite red-emitting Ba_(2)LuNbO_(6):Eu^(3+)phosphors are prospective red emitting elements for WLEDs applications.展开更多
(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) ultra-fine powders were synthesized by a novel sol–gel route,and the mechanism of the reaction was discussed.SrCO_(3),BaCO_(3),oxalate niobium and citric acid were used to initiate the ...(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) ultra-fine powders were synthesized by a novel sol–gel route,and the mechanism of the reaction was discussed.SrCO_(3),BaCO_(3),oxalate niobium and citric acid were used to initiate the sol–gel process,and ethylene glycol(EG)was added to further polymerize the cross-linking structure.The evolution of the(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) phase,the reaction process and the microstructures were investigated by X-ray diffraction(XRD),Raman spectroscopy,Fourier transform infrared spectroscopy,DSC-TG and scanning electron microscopy.The synthesis temperature of the(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) powders reached as low as 1200℃,and the size and morphology of the powders were controlled by temperature.By adjusting the calcination temperature,we obtained(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) powders with uniform sizes of 20 nm to 500 nm.Then,dense(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) ceramics were successfully prepared using these ultrafine powders.Finally,an enhanced electrocaloric effect(ECE)value of 0.35℃ was obtained at 100 kV/cm.展开更多
文摘The effects of different x values on the dielectric properties in the Ba6-3xSm8+2xTi18O54 microwave dielectric ceramics(0.3≤x≤0.7) were studied. The results showed that the major crystal phase was BaSm2Ti4O12 and the sintering temperature of the ceramics was 1340 ℃ when the x value was 0.67. The dielectric properties were better: εr≈79, tanδ≈1×10-4(1 MHz); εr≈80, Q·f=9230 GHz(3.97 GHz), τf=-17 ppm·℃-1.
基金Project supported by the National Natural Science Foundation of China (51972061,22109025,22171045,52072076)。
文摘The Er3+doped double perovskite Ba_(2)CaWO_(6) crystal is a promising ratiometric thermometer based on the fluorescence intensity ratio(FIR) of transitions from ^(2)H_(11/2) and ^(4)S_(3/2) to the lowered ^(4)I_(15/2) level.However,the Ca^(2+) vacancy defect caused by the charge difference between rare-earth ions and the substituted alkaline-earth ions gives rise to the non-radiative probability and limits the thermal sensitivity.Here,the up-conversion luminescence and thermometric performance of Er^(3+),Yb^(3+) dopedBa_(2)CaWO_(6) are tuned by tri-doping with alkaline ions.The Ca^(2+) vacancy defect can be eliminated by the introduction of Na^(+),which occupies the Ca^(2+) site when it is doped into Ba_(2)CaWO_(6) with Er^(3+) and Yb^(3+).On the contrary,the doping of Cs^(+) into Ba_(2)CaWO_(6) with Er^(3+) and Yb^(3+) enhances the defect concentration because it occupies the site of Ba^(2+).Thus,the tri-doping of Na^(+) reduces the non-radiative probability and enhances the quantum efficiency of Er^(3+),leading to the improvement of the thermometric sensitivity of Ba_(2)CaWO_(6).As a result,we get an excellent thermometric Ba_(2)CaWO_(6):8%Yb^(3+),3.5%Er^(3+),6%Na^(+) powder with a luminescence lifetime of 515 μs and maximum thermal sensitivity(S_(r)) of 1.45%/K,which is more than three times higher than that of the BCWO:Er^(3+) powder.
基金Project supported by the Excellent Youth Project of Yunnan Province Applied Basic Research Project(2019FI001)the National Natural Science Foundation of China(61775187,61965012,12064022)the Key Project of Yunnan Provincial Natural Science Foundation(202101AT070126)。
文摘Red emitting phosphors play a significant role in accelerating the improvement of illumination quality for white light emitting diodes(WLEDs).In this work,by using solid-state reaction method,an efficient novel Ba_(2)LuNbO_(6):Eu^(3+)phosphor with double-perovskite structure was successfully prepared.Here,a series of Ba_(2)LuNbO_(6):Eu^(3+)red phosphors can be efficiently pumped by the near-ultraviolet(UV)light and then present high-brightness at orange emission(598 nm,~5D_(0)→~7 F_(1))and red emission(610 nm,~5D_(0)→~7 F_(2)).The ratio values of 610 to 598 nm in Ba_(2)LuNbO_(6):Eu^(3+)phosphors exceed 1 when the content of Eu^(3+)is larger than 0.4 mol,because the occupation of Eu^(3+)ions is changed from Lu^(3+)ions with symmetric sites to Ba^(2+)ions with asymmetric sites.Besides,the optimized concentration of Eu^(3+)at the~5D_(0)→~7 F_(2)transitions is obtained when x=1,indicating that there is non-concentration quenching in Ba_(2)LuNbO_(6):Eu^(3+)phosphors.Moreover,the CIE chromaticity coordinates of Ba_(2)LuNbO_(6):Eu^(3+)was calculated to be(0.587,0.361),the color purity was calculated to be 72.26%and internal quenching efficiency(IQE)was measured to be 67%.Finally,the thermal stability of Ba_(2)LuNbO_(6):Eu^(3+)phosphors was also studied.Our work demonstrates that the novel double-perovskite red-emitting Ba_(2)LuNbO_(6):Eu^(3+)phosphors are prospective red emitting elements for WLEDs applications.
基金National Natural Science Foundation of China under Grant No.51202215Natural Science Foundation of Zhejiang Province under Grant No.LY15E02003Chinese National Basic Research Program under Grant No.2015CB654601.
文摘(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) ultra-fine powders were synthesized by a novel sol–gel route,and the mechanism of the reaction was discussed.SrCO_(3),BaCO_(3),oxalate niobium and citric acid were used to initiate the sol–gel process,and ethylene glycol(EG)was added to further polymerize the cross-linking structure.The evolution of the(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) phase,the reaction process and the microstructures were investigated by X-ray diffraction(XRD),Raman spectroscopy,Fourier transform infrared spectroscopy,DSC-TG and scanning electron microscopy.The synthesis temperature of the(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) powders reached as low as 1200℃,and the size and morphology of the powders were controlled by temperature.By adjusting the calcination temperature,we obtained(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) powders with uniform sizes of 20 nm to 500 nm.Then,dense(Sr_(0.5)Ba_(0.5))Nb_(2)O_(6) ceramics were successfully prepared using these ultrafine powders.Finally,an enhanced electrocaloric effect(ECE)value of 0.35℃ was obtained at 100 kV/cm.
