A series of phase-pure [(Gd 0.6 Lu 0.4 ) 0.99 Ce 0.01 ] 3 [Al 1- z (Mg/Si) z ] 5 O 12 ( z = 0-0.10) garnet phosphor powders were prepared via gel-combustion, which were then sintered into ceramics (up to 1550 °C) under atmospheric pressure. Dilatometry revealed that equimole of Mg 2+ /Si 4+ substitution for Al 3+ accelerates densification and lowers the activation energy for grain boundary diffusion in the intermediate stage of sintering (∼1150–1370 °C), which was assayed to be ∼353 kJ/mol for z = 0 and ∼289 kJ/mol for z = 0.10. The acceleration effects of Mg 2+ /Si 4+ on sintering and grain growth were further demonstrated by the results of ramp and holding sintering. Firing at 1550 °C for 4 h also produced ∼99 % dense ceramics for the Mg 2+ /Si 4+ codoped garnet powders. Through considering crystal splitting of the Ce 3+ 5d energy level, photon-phonon coupling, and crystal structure/microstructure, the influences of Mg 2+ /Si 4+ content and material form on Ce 3+ luminescence, including intensity, external/internal quantum efficiencies, emission wavelength, CIE color coordinates and decay time, were clarified in detail.
In this article, garnet-type Y 3 Al 5 O 12 (YAG) were doped with Mg 2+ -Si 4+ ionic pairs and its effect on the structure and the microwave dielectric properties was investigated. It was revealed that in ceramics Y 3 Mg x Al 5-2 x Si x O 12 ( x = 0, 0.5, 1.0, 1.5, 2.0), increasing doping concentration decreased the sintering temperature and time for the optimal densification. X-ray diffraction studies showed that the samples are isostructural to Al 5 Y 3 O 12 garnet. All sample were formed a single phase except for x = 2.0, where a secondary peak was detected. Excellent microwave dielectric properties of ε r = 10.56, Q × f = 67,571 GHz and τ f = -35.23 ppm/°C were obtained for Y 3 Mg 0.5 Al 4 Si 0.5 O 12 ceramics sintered at 1625 °C for 5 h. The factors influencing the microwave dielectric properties of Y 3 Mg x Al 5-2 x Si x O 12 ceramics were further discussed by considering the ionic polarization, packing fraction, average grain size and chemical bond valence theory.
Qinghong Meng,Yuning Zhang,Xiangming Li,Wanjun Yu,Zhijun Xu,Ji-Guang Li
Doping Gd 3 Ga 3 Al 2 O 12 :Cr 3+ with Mg 2+ /Si 4+ pair to develop Gd 3 Ga 3 – y Al 2 – 2 x Mg x Si x O 12 : y Cr 3+ ( x = 0–1.0; y = 0.005–0.05) new garnet solid solution was implemented for the regulation of structure and photoluminescence. Rietveld refinement, SEM/TEM, and UV-Vis-NIR/photoluminescence spectroscopy analysis clarified that Mg 2+ /Si 4+ incorporation increasing resulted in the enlargement of the unit cell, the expansion/larger distortion of [(Ga,Al,Mg,Cr)O 6 ] octahedron, the decrease of crystal field strength, red-shifting and broadening of emission band, and shortening decay times. The optimal Gd 3 Ga 2.97 MgSiO 12 :0.03Cr 3+ phosphor realized broadband NIR emission (centered at ∼760 nm, full-width at half-maximum ∼114 nm) under 450 nm light excitation and exhibited high quantum efficiency (IQE=71.0 %, EQE=29.4 %) and good thermal stability (78.5 %@423 K). The NIR pc-LED fabricated by combining this optimal phosphor with a 450 nm blue LED chip showed satisfactory output power (∼26.83 mW) and conversion efficiency (10.02 %) under a driving current of 100 mA, indicating that this phosphor has huge potential utilized in the construction of NIR pc-LED applied in night vision and noninvasive medical diagnosis.
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