Zhaohua Luo

Effect of Yb3+ on the Crystal Structural Modification and Photoluminescence Properties of GGAG:Ce3+

Gadolinium gallium aluminum garnet (GGAG) is a very promising host for the highly efficient luminescence of Ce(3+) and shows potential in radiation detection applications. However, the thermodynamically metastable structure would be slanted against it from getting high transparency. To stabilize the crystal structure of GGAG, Yb(3+) ions were codoped at the Gd(3+) site. It is found that the decomposition of garnet was suppressed and the transparency of GGAG ceramic was evidently improved. Moreover, the photoluminescence of GGAG:Ce(3+),xYb(3+) with different Yb(3+) contents has been investigated. When the Ce(3+) ions were excited under 475 nm, a typical near-infrared region emission of Yb(3+) ions can be observed, where silicon solar cells have the strongest absorption. Basing on the lifetimes of Ce(3+) ions in the GGAG:Ce(3+),xYb(3+) sample, the transfer efficiency from Ce(3+) to Yb(3+) and the theoretical internal quantum efficiency can be calculated and reach up to 86% and 186%, respectively. This would make GGAG:Ce(3+),Yb(3+) a potential attractive downconversion candidate for improving the energy conversion efficiency of crystalline silicon (c-Si) solar cells.

YAG phosphor with spatially separated luminescence centers

A micron size YAG:Ce/YAG:Cr core–shell structure was designed and accomplished via the urea homogeneous precipitation method using the YAG:Ce spherical core as the introduced second phase. A well dispersed gel like encapsulation structure can be achieved before the formation of YAG:Ce/YAG:Cr core–shell particles via a calcination process. As prepared YAG:Ce/YAG:Cr particles can emit a broad range of photons from 500 to 750 nm with excitation light of 433 nm. A schematic illustration showing the mechanism of excitation–emission of the core–shell particles is presented. The integral spectra are composed of three parts: emission photons of YAG:Cr, YAG:Ce, and emission light of YAG:Cr excited by the emission photons of the YAG:Ce core according to the proposed mechanism. The method accomplished in this work can significantly improve the exploration of full spectrum luminescent powder synthesis and spectra designation.

Fabrication of cerium-doped nonstoichiometric (Ce, Lu, Gd)3+δ(Ga, Al)5–δO12 transparent ceramics

Abstract Cerium-doped nonstoichiometric (Ce,Lu,Gd) 3+ δ (Ga,Al) 5– δ O 12 (LuGGAG) transparent garnet ceramic samples were fabricated via a solid state reaction method in this study. The ceramics were prepared via oxygen sintering followed by hot isostatic pressing (HIP). The phase and microstructure of the samples were analyzed by X-ray diffraction and scanning electron microscopy (SEM), respectively. The excitation, emission and transmission spectra were also measured. The total optical transmittance of the annealed LuGGAG ceramics with thickness of 3 mm reached 47% at the emission wavelength of 555 nm. The decay time was about 60 ns. Compact microstructure of polycrystalline grains with scale around 5 μm were gained according to scanning electron microscopy characterization. The successful preparation of the bulk ceramic material and implementation of the combined oxygen sintering-hot isostatic pressing treatment process provided an important method for the exploration of nonstoichiometric scintillator material.

Highly transparent cerium doped gadolinium gallium aluminum garnet ceramic prepared with precursors fabricated by ultrasonic enhanced chemical co-precipitation

Cerium doped gadolinium gallium aluminum garnet (GGAG:Ce) ceramic precursors have been synthesized with an ultrasonic chemical co-precipitation method (UCC) and for comparison with a traditional chemical co-precipitation method (TCC). The effect of ultra-sonication on the morphology of powders and the transmittance of GGAG:Ce ceramics are studied. The results indicate that the UCC method can effectively improve the homogenization and sinterability of GGAG:Ce powders, which contribute to obtain high transparent GGAG ceramic with the highest transmittance of 81%.

The Effects of Cation Concentration in the Salt Solution on the Cerium Doped Gadolinium Gallium Aluminum Oxide Nanopowders Prepared by a Co-precipitation Method

Cerium doped gadolinium gallium aluminum oxide (GAGG:Ce) nanopowders were prepared by a co-precipitation method with different cation concentrations of the mother salt solution, followed by calcination at different temperatures. The influence of cation concentrations (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mol/L) in the mother salt solution on GAGG:Ce nanopowders was investigated by thermal gravity-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL). The GAGG phase was formed after calcining at 950 degree C for 2 h for all samples. The primary particle sizes of powder calcined at the same temperature decrease with the increase of cation concentration, which is suggested by the analysis of SEM and specific surface area measurement. However, the nonuniformity of particle size was observed for samples prepared using the salt solutions with cation concentrations > 0.3 mol/L, especially for the 0.6 mol/L sample. The photoluminescence spectrum intensity indicates that the 0.2 mol/L and 0.3 mol/L samples have higher degree of crystal perfection than others. Considering all the factors above, samples synthesized by using salt solution with 0.3 mol/L cation concentration were chosen for ceramic scintillators preparation in our future work.

Investigation of interfacial bonding between Na2O–B2O3–SiO2 solder and silicon carbide substrate

Abstract The interfacial characteristics of the SiC/glass solder/SiC joining part were investigated by means of thermodynamic and wetting behaviour calculation, microstructure observation, chemical structure and element analysis. The results of wavelength dispersive spectroscopy linear scan across the joint showed a relatively low increase in sodium content at the interfaces, which indicated that the sodium silicates in glass could react with silicon carbide substrate at the joining temperature, but it is not the reason for the good bonding between SiC and the interlayer. The mechanism of the good interfacial bonding lies in the formation of oxycarbide phase at the interface.