Wang Guo,Jiquan Huang,Yue Lin,Qiufeng Huang,Binjie Fei,Jian Chen,Wenchao Wang,Fangyu Wang,Chaoyang Ma,Xuanyi Yuan,Yongge Cao
We study the dependence of the rheological properties of slurries, as well as hydration reaction of the oxide powders during fabricating the transparent Cr:YAG ceramics out of Al 2 O 3 /Y 2 O 3 /Cr 2 O 3 powders via slip casting shaping and vacuum sintering. We demonstrated that the dispersant can absorbed the Y(III) and Al(III) species that have dissolved in the slurry, absorbed them on the surface of the undissolved oxide powders, and changes the pH and rheological property of the slurry and therefore further affect process of the slip casting and the sintering of the ceramic. By adopting appropriate dispersants, we obtained Cr:YAG ceramic with average grain size of ∼6.2 μm and in-line transmittance > 84% at 1450 nm after sintering the green samples at 1800 °C under vacuum for 40 h.
The shortage of red-light emission in Ce 3+ :Y 3 Al 5 O 12 (Ce:YAG) luminescent ceramics is a bottleneck problem to realize the key applications of ceramics based white light-emitting diode (LED) and laser diode (LD) devices. However, the energy band-gap engineering for Ce 3+ ion via host substitution or red-emission ions co-doping always leads to its decrease of luminescence efficiency (LE), while a spectrum overlay strategy would be simple and effective. In this study, multilayer composite structure Ce:YAG/Cr:YAG transparent ceramics (TCs) with high color rendering index (CRI) were fabricated by tape casting and vacuum sintering. An organic tape casting protocol with low toxicity and environmental protection was developed and the amounts of dispersants, binders, and plasticizers were systematically optimized to produce good quality tapes with no defects. The transmittance of ceramic reached 78% at 800 nm. By using a 455 nm blue chip, the CRI of the Ce:YAG/Cr:YAG TCs based LED device was increased from 26.7 to 77.5, and the LE was decreased from 181.5 to 10.4 lm/W. Additionally, the optimized LE and CRI for LD device were 130.2 lm/W and 78.1, respectively. Therefore, this research displays that the design and implementation of ceramic functional layer to achieve the essential enhancement of CRI in TC based white lighting is a promising method through the tape casting forming technology.
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