Cao Renping,Cheng Xinyu,Zhang Fangteng,Su Lei,Chen Ting,Ao Hui,Yu Xiaoguang,Ruan Wen
A series of MgTiO 3 :Mn 4+ , MgTiO 3 :Mn 4+ , Ge 4+ , and MgTiO 3 :Mn 4+ , B 3+ phosphors are prepared by the high temperature solid-state reaction method in air. X-ray powder diffraction (XRD) patterns confirm that there is only pure phase in all samples. The samples are composed of microparticles with irregular shapes. Their excitation spectra monitored at 658 nm may be observed in the range of 200–600 nm and their emission spectra with excitation at 330 nm cover the region from 600 to 800 nm due to the 2 E → 4 A 2 transition of Mn 4+ ion. The chromaticity coordinate is (0.7233, 0.2767). The optimal Mn 4+ content is ~ 0.3% in MgTiO 3 :Mn 4+ phosphor. The luminescence intensity and quantum efficiency of MgTiO 3 :Mn 4+ phosphor may be obviously improved by adding Ge 4+ ion and H 3 BO 3 . The experimental results are helpful for the luminescence property improvement of other Mn 4+ doped materials.
Kang Du,Chang-Zhi Yin,Jia-Qing Yang,Wei Luo,Xiao-Chuan Wang,Wen-Zhong Lu,Wen Lei
Novel BaZr(Si 1- x Ge x ) 3 O 9 (0 ≤ x ≤ 1.0) microwave dielectric ceramics were prepared by solid-state reaction sintering at 1200–1450 °C for 5 h Ge 4+ ions occupied the Si 4+ positions, and BaZr(Si 1- x Ge x ) 3 O 9 solid solutions were obtained. The BaZr(Si 1- x Ge x ) 3 O 9 (0 ≤ x ≤ 1.0) ceramics exhibited hexagonal structures with P -6 c 2 space groups and octahedral layers and [Si/Ge 3 O 9 ] 6- rings. Owing to these structural characteristics, the ceramics exhibited low permittivity. With an increase in x , the relative permittivity ( ε r ) values of the BaZr(Si 1- x Ge x ) 3 O 9 (0 ≤ x ≤ 1.0) ceramics increased from 7.68 ( x = 0) to 9.45 ( x = 1.0), while their quality factor ( Q × f ) values first increased and then decreased. The Q × f value (10,300 GHz at 13.43 GHz) of the BaZrSi 3 O 9 ( x = 0) ceramic improved with the substitution of Si 4+ by Ge 4+ . A high Q × f value (36,100 GHz at 13.81 GHz) was obtained for the BaZr(Si 1- x Ge x ) 3 O 9 ( x = 0.2) ceramic, and the Q × f values of the BaZr(Si 1- x Ge x ) 3 O 9 ceramics could be controlled by varying the Si/Ge-site bond valence. The temperature coefficient of resonance frequency (τ f ) values of the BaZr(Si 1- x Ge x ) 3 O 9 ceramics were mainly affected by the O2-site bond valence, and the optimum τ f value (−22.8 ppm/°C) was achieved for the BaZrSi 3 O 9 ceramic. The BaZr(Si 1- x Ge x ) 3 O 9 ( x = 0.2) ceramic showed the optimum microwave dielectric properties ( ε r = 8.36, Q × f = 36,100 GHz at 13.81 GHz, and τ f = −34.5 ppm/°C).
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