Papers by Author: Lian Ping Chen

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Authors: Lian Ping Chen, Yuan Hong Gao
Abstract: It is hardly possible to obtain rare earth doped CaWO4 thin films directly through electrochemical techniques. A two-step method has been proposed to synthesize Tb3+-doped CaWO4 thin films. X-ray diffraction, energy dispersive X-ray analysis, spectrophotometer were used to characterize their phase, composition and luminescent properties. Results reveal that Tb3+-doped CaWO4 films have a tetragonal phase. The ratio of n(Tb)/[n(Ca)+n(Tb)+n(Na)] decreases with the increase of pH value of TbCl3 solutions. When the pH value (adjusted by NaOH) is higher than 5, Na element has been detected in CaWO4:Tb3+ thin films. Based on the analysis on the composition and luminescence, it can be concluded that the pH value of TbCl3 solutions must be no higher than 9.1, otherwise, no Tb3+-doped CaWO4 thin films can be obtained. Under the excitation of 237 nm, sharp emission peaks at 543 and 489 nm have been observed for Tb3+-doped CaWO4:Tb3+ thin films.
204
Authors: Lian Ping Chen, Yuan Hong Gao, Jian Xiong Yuan, Qing Hua Zhang, Yan Hong Yin, Chun Xiang Wang
Abstract: It is hardly possible to obtain rare earth doped CaWO4 thin films directly through electrochemical techniques. A novel post processing has been proposed to synthesize CaWO4:Eu3+ thin films at room temperature. X-ray diffraction, X-ray photoelectron spectrometry, spectrophotometer were used to characterize their phase, composition and luminescent properties. Results reveal that Eu3+-doped CaWO4 films have a tetragonal phase; the content of Eu in the near surface region is much higher than that of the bulk; under the excitation of 310 nm, a sharp emission peak at 616 nm has been observed for Ca0.9WO4:Eu0.13+ thin films.
2458
Authors: Lian Ping Chen, Yuan Hong Gao
Abstract: It is hardly possible to obtain rare earth doped CaWO4 thin films directly through electrochemical techniques. A two-step method has been proposed to synthesize CaWO4:(Eu3+,Tb3+) thin films at room temperature. X-ray diffraction, energy dispersive X-ray analysis, spectrophotometer were used to characterize their phase, composition and luminescent properties. Results reveal that (Eu3+,Tb3+)-doped CaWO4 films have a tetragonal phase. When the ratio of n (Eu)/n (Tb) in the solution is up to 3:1, CaWO4:(Eu3+,Tb3+) thin film will be enriched with Tb element; on the contrary, when the ratio in the solution is lower than 1:4, CaWO4:(Eu3+,Tb3+) thin film will be enriched with Eu element. Under the excitation of 242 nm, sharp emission peaks at 612, 543, 489 and 589 nm have been observed for CaWO4:(Eu3+,Tb3+) thin films.
170
Authors: Yuan Hong Gao, Jian Gao Yang, Bai Tao Su, Lian Ping Chen
Abstract: Hydrogen is widely used to prepare tungsten from tungsten oxides. Such a gas is combustible and strict measures must be taken. However, assisted by Mg or Li3N, tungsten can be prepared through the ball milling at room temperature. Al powder is supposed to be one of the proper reducers. Simulations on the loss of Gibbs energy of these reactions have been investigated. Studies reveal that the reduction of Na2WO4 is feasible when reducers such as Al, Mg and Li3N are used; and the intermediate tungsten oxides such as WO2, WO2.72 and WO2.9 can be seldom generated. In addition, the calculation favors that NH3 does not react with Na2WO4 or WO3 theoretically.
85
Authors: Lian Ping Chen, Yuan Hong Gao, Bai Tao Su
Abstract: Hydrogen is widely used to prepare tungsten from tungsten oxides. Such a gas is combustible and strict measures must be taken. However, assisted by Mg or Li3N, tungsten can be prepared through the ball milling at room temperature. The reduction of WO3 by Al powder is investigated thermodynamically. Simulations on the loss of Gibbs energy of these hypothetic reactions reveal that the reduction of WO3 and WO2(OH)2 (or H2WO4) is feasible when Al powder is used; and it is more difficult to generate the intermediate tungsten oxides such as WO2, WO2.72 and WO2.9. In addition, it is better to prepare tungsten powder in vacuum containers in view of economy.
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