New cadmium and rare earth metal tungstates with the formula Cd0.25RE0.50 0.25WO4 （RE=Nd, Sin, Eu, Gd, D-statistical distrib- uted vacancies in cation sublattice） were synthesized by the solid-state reaction between...New cadmium and rare earth metal tungstates with the formula Cd0.25RE0.50 0.25WO4 （RE=Nd, Sin, Eu, Gd, D-statistical distrib- uted vacancies in cation sublattice） were synthesized by the solid-state reaction between CdWO4 and corresponding RE2W209. The obtained phases crystallize in the scheelite type structure. The Cd0.25RE0.5 0.25WO4 compounds were characterized by X-ray diffractometer （XRD）, （DTA-TG）, infrared （IR） and EPR methods.展开更多
The trivalent dysprosium-doped yellow phosphor is an important component for realizing single-matrix white light.However,concentration quenching and thermal quenching greatly limit its application.White light phosphor...The trivalent dysprosium-doped yellow phosphor is an important component for realizing single-matrix white light.However,concentration quenching and thermal quenching greatly limit its application.White light phosphors,Li_(3)Ba_(2)Gd_(3)(WO_(4))_(8):Dy^(3+),Tm^(3+),with a stratified scheelite structure were prepared via a high-temperature solid-reaction.Calculated using the Kubelka–Munk model,the band gap of the host is 3.71 eV,which is suitable for near-ultraviolet white LEDs.展开更多
Novel scheelite structures of Li_(2)Ca(WO_(4))_(2),Li_(2)Ca_(2)(WO_(4))(SiO_(4)),and LiCa_(2)(WO_(4))(PO_(4))fluorescent materials were successfully prepared using a high-temperature solid-phase process.The compounds ...Novel scheelite structures of Li_(2)Ca(WO_(4))_(2),Li_(2)Ca_(2)(WO_(4))(SiO_(4)),and LiCa_(2)(WO_(4))(PO_(4))fluorescent materials were successfully prepared using a high-temperature solid-phase process.The compounds were characterized by X-ray diffraction and energy dispersive spectroscopy.The tests revealed that the substitution of[WO_(4)]^(2-)by[SiO_(4)]^(4-) or [PO_(4)]^(3-) tetrahedron in tungstate had no significant influence on the crystal structure of the Li_(2)Ca(WO_(4))_(2).When Dy^(3+) ions were introduced as an activator at an optimum doping concentration of 0.08 mol%,all of the as-prepared phosphors generated yellow light emissions,and the emission peak was located close to 576 nm.Replacing[WO_(4)]^(2-) with [SiO_(4)]^(4-) or [PO_(4)]^(3-) tetrahedron significantly increased the luminescence of the Li_(2)Ca(WO_(4))_(2) phosphors.Among them,the LiCa_(2)(WO_(4))(PO_(4)):0.08Dy^(3+) phosphor had the best luminescence properties,decay life(r=0.049 ms),and thermal stability(87.8%).In addition,the as-prepared yellow Li_(2)Ca(WO_(4))_(2):0.08Dy^(3+),Li_(2)Ca_(2)(WO_(4))(SiO_(4)):0.08Dy^(3+),and LiCa_(2)(WO_(4))(PO_(4)):0.08Dy^(3+) phosphor can be used to fabricate white light emitting diode(LED)devices.展开更多
The low dielectric constant(ε_(r)<15)is the key to improving the signal transmission speed of microwave communication devices.However,the resonant frequency temperature coefficient(τf)of most low-ε_(r) microwave...The low dielectric constant(ε_(r)<15)is the key to improving the signal transmission speed of microwave communication devices.However,the resonant frequency temperature coefficient(τf)of most low-ε_(r) microwave dielectric ceramics is usually negative.Aiming to modify the large negativeτf of scheelite CaWO_(4) and explore the underlying mechanism between the structure and microwave dielectric properties,a series of Ca_(1-x)(Li_(1/2)Eu_(1/2))_(x)WO_(4)(x=0.1−1.0)(CLEWOx)ceramics were prepared at low sintering temperatures(750−875℃).Theε_(r) increased from 10.46 to 18.55,and the Q×f decreased from 39,032 GHz-7425 GHz,mainly due to the enhanced rattling effect of Li+.Theτf rapidly increased from negative(−19.91×10^(−6)℃^(−1))to abnormally positive(+162.15×10^(−6)℃^(−1)),influenced by the reduced temperature coefficient of ion polarizability(ταm)caused by the rattling Li+cation.The CLEWO0.15 sample has good comprehensive performance(ε_(r)=12.28,Q×f=28,027 GHz,andτf=−0.5×10^(−6)℃^(−1))and compatibility with the Ag electrode,showing the potential of LTCC applications.Additionally,a dielectric resonator antenna based on CLEWO0.15 ceramic was designed with a bandwidth of 254 MHz at 4.504−4.758 GHz and a gain of 4.87 dBi at 4.62 GHz,indicating that CLEWO0.15 may be a potential candidate for dielectric resonator antennas.展开更多
文摘New cadmium and rare earth metal tungstates with the formula Cd0.25RE0.50 0.25WO4 （RE=Nd, Sin, Eu, Gd, D-statistical distrib- uted vacancies in cation sublattice） were synthesized by the solid-state reaction between CdWO4 and corresponding RE2W209. The obtained phases crystallize in the scheelite type structure. The Cd0.25RE0.5 0.25WO4 compounds were characterized by X-ray diffractometer （XRD）, （DTA-TG）, infrared （IR） and EPR methods.
基金financially supported by the National Natural Science Foundation of China(No.51902354 and 22061020)the Science and Technology Program of Jiangxi Province(No.20192BBEL50017and 20202ACBL203002)+2 种基金the Characteristic Innovation Projects in Colleges and Universities in Guangdong Province(No.2021KTSCX128)theGDAS’Project of Science and Technology Development(No.2022GDASZH-2022010104 and 2022GDASZH-2022030604-04)the Special Found Project of Institute of Rare Metals,Guangdong Academy of Sciences(No.XYS2020-02).
文摘The trivalent dysprosium-doped yellow phosphor is an important component for realizing single-matrix white light.However,concentration quenching and thermal quenching greatly limit its application.White light phosphors,Li_(3)Ba_(2)Gd_(3)(WO_(4))_(8):Dy^(3+),Tm^(3+),with a stratified scheelite structure were prepared via a high-temperature solid-reaction.Calculated using the Kubelka–Munk model,the band gap of the host is 3.71 eV,which is suitable for near-ultraviolet white LEDs.
基金supported by the National Natural Science Foundations of China(Grant Nos.51872269 and 51672257)the Fundamental Research Funds for the Central Universities(Grant Nos.2652018305 and 2652017335).
文摘Novel scheelite structures of Li_(2)Ca(WO_(4))_(2),Li_(2)Ca_(2)(WO_(4))(SiO_(4)),and LiCa_(2)(WO_(4))(PO_(4))fluorescent materials were successfully prepared using a high-temperature solid-phase process.The compounds were characterized by X-ray diffraction and energy dispersive spectroscopy.The tests revealed that the substitution of[WO_(4)]^(2-)by[SiO_(4)]^(4-) or [PO_(4)]^(3-) tetrahedron in tungstate had no significant influence on the crystal structure of the Li_(2)Ca(WO_(4))_(2).When Dy^(3+) ions were introduced as an activator at an optimum doping concentration of 0.08 mol%,all of the as-prepared phosphors generated yellow light emissions,and the emission peak was located close to 576 nm.Replacing[WO_(4)]^(2-) with [SiO_(4)]^(4-) or [PO_(4)]^(3-) tetrahedron significantly increased the luminescence of the Li_(2)Ca(WO_(4))_(2) phosphors.Among them,the LiCa_(2)(WO_(4))(PO_(4)):0.08Dy^(3+) phosphor had the best luminescence properties,decay life(r=0.049 ms),and thermal stability(87.8%).In addition,the as-prepared yellow Li_(2)Ca(WO_(4))_(2):0.08Dy^(3+),Li_(2)Ca_(2)(WO_(4))(SiO_(4)):0.08Dy^(3+),and LiCa_(2)(WO_(4))(PO_(4)):0.08Dy^(3+) phosphor can be used to fabricate white light emitting diode(LED)devices.
基金supported by Project of Scientific Research,Technical Exploitation Program of the Guangxi Zhuang Autonomous Region(No.AD24010021)Natural Science Foundation of Guangxi Zhuang Autonomous Region(No.2024GXNSFFA010013)the National Natural Science Foundation of China(Nos.52362017 and 52462016).
文摘The low dielectric constant(ε_(r)<15)is the key to improving the signal transmission speed of microwave communication devices.However,the resonant frequency temperature coefficient(τf)of most low-ε_(r) microwave dielectric ceramics is usually negative.Aiming to modify the large negativeτf of scheelite CaWO_(4) and explore the underlying mechanism between the structure and microwave dielectric properties,a series of Ca_(1-x)(Li_(1/2)Eu_(1/2))_(x)WO_(4)(x=0.1−1.0)(CLEWOx)ceramics were prepared at low sintering temperatures(750−875℃).Theε_(r) increased from 10.46 to 18.55,and the Q×f decreased from 39,032 GHz-7425 GHz,mainly due to the enhanced rattling effect of Li+.Theτf rapidly increased from negative(−19.91×10^(−6)℃^(−1))to abnormally positive(+162.15×10^(−6)℃^(−1)),influenced by the reduced temperature coefficient of ion polarizability(ταm)caused by the rattling Li+cation.The CLEWO0.15 sample has good comprehensive performance(ε_(r)=12.28,Q×f=28,027 GHz,andτf=−0.5×10^(−6)℃^(−1))and compatibility with the Ag electrode,showing the potential of LTCC applications.Additionally,a dielectric resonator antenna based on CLEWO0.15 ceramic was designed with a bandwidth of 254 MHz at 4.504−4.758 GHz and a gain of 4.87 dBi at 4.62 GHz,indicating that CLEWO0.15 may be a potential candidate for dielectric resonator antennas.
