Functional design and implementation of multilayer Ce:YAG/Cr:YAG composite transparent ceramics by tape casting for white LEDs/LDs

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.