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The effects of TiO 2 and CaF 2 on the crystallization kinetics, microstructure, phase evolution and microhardness of Y 2 O 3 -Al 2 O 3 -SiO 2 glass ceramics were investigated by differential scanning calorimetric (DSC), field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. The results show that the addition of TiO 2 is effective to promote crystallization by decreasing the activation energy, refining the grain size and increasing the microhardness. However, the CaF 2 plays an opposite role by increasing the activation energy, coursing the grain size and decreasing the microhardness. Furthermore, the addition of TiO 2 induces bulk crystallization of Y 2 O 3 -Al 2 O 3 -SiO 2 glass. On the contrary, the addition of CaF 2 leads to surface crystallization and decreasing of thickness of surface crystallized layer. [ABSTRACT FROM AUTHOR]

Upconversion luminescence materials have gained extensive attentions owing to their unique luminescence characteristics of converting near-infrared excitation to visible light emission. However, how to improve the doping concentration of activator (usually <3 mol%) in traditional sensitizer-activator system is still a great challenge due to the luminescence quenching effect. In this work, NaErF 4 crystals with diverse crystal phases and morphologies were prepared by simple hydrothermal method, constructing a 100% doping concentration system of activator (Er3+). With the increase of F− content, the phase of NaErF 4 transfers from cubic to hexagonal, and the morphology changes from nanospheres to hexagonal microflakes, meanwhile, the upconversion luminescence intensity also increases gradually. In addition, in order to further inhibit the luminescence quenching effect of NaErF 4 bare core, a series of NaErF 4 @SiO 2 core-shell samples with different SiO 2 shell thickness were successfully prepared. Compared with NaErF 4 bare core, the morphology and structure of the NaErF 4 @SiO 2 core-shell samples have no obvious change, but the UC luminescence intensity is significantly enhanced. Interestingly, the change of NaErF 4 crystal phase and SiO 2 shell thickness can both bring about multicolor luminescence. In addition, different from the traditional NaYF 4 :Yb, Er co-doping system, the as-prepared hydrophilic NaErF 4 and NaErF 4 @SiO 2 samples showed a greater red to green ratio (R/G > 1), which may expand their potential applications in biological imaging and sensing fields. [ABSTRACT FROM AUTHOR]

CaO–Al 2 O 3 –SiO 2 –TiO 2 glass ceramic filler with high crystallinity was used for joining alumina ceramic. The influence of joining temperature and crystallization treatment on the microstructure and flexural strength of joints was studied. The results demonstrated that a joining temperature higher than the melting temperature of crystals was essential to obtain dense joints. Furthermore, the formation of CaAl 2 Si 2 O 8 at the alumina/glass filler interface decreased the flexural strength of joints due to the mismatch of coefficient of thermal expansion (CTE) between CaAl 2 Si 2 O 8 and substrate. The maximum flexural strength of 256 MPa at room temperature was achieved when the joining temperature was 1260 °C. After crystallization treatment, a large number of fine CaTiSiO 5 was precipitated in the brazing seam. The flexural strength of joints after crystallization at room temperature was 221 MPa, and increased to 242 MPa at 800 °C. These results can be attributed to the change of CTE value of the brazing seam. [ABSTRACT FROM AUTHOR]