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.
In the high-power white light LEDs/LDs area, obtaining phosphor-converted materials with high thermal stability and high luminous emittance with proper blue/yellow light ratio has been the main challenge in recent years. In this study, a group of (Ce x Y 1-x ) 3 (Sc y Al 1-y ) 5 O 12 transparent ceramics with high optical quality were proposed to rise to that challenge. Their spectra were regulated by incorporating Sc 3+ , showing blue shifted emission bands (peak position from 554 nm–538 nm), blue shifted excitation bands (462–445 nm) and narrowed full width at half maxima (120–112 nm). Significantly, the prepared Ce:YScAG transparent ceramics (TC) exhibited decent thermal quenching performance with the photoluminescence intensity at 150 °C maintaining 88.7% of its original value at room temperature. The Sc incorporation impacted the atoms’ occupation and distance, crystal field splitting and energy band structure . Under remote LD excitation mode, the luminous efficiency of the prepared Ce:YScAG TC can achieve 164.8 lm/W. And even if the Ce 3+ doping reaches 2.0 at%, the LE can still maintain 117.8 lm/W, exhibiting decent concentration quenching characteristic. Consequently, Ce:YScAG TCs have great potential as promising phosphor-converted materials in future high-power LED and LD white lighting.
Ce/Mn/Cr: Y 3 Al 5 O 12 transparent ceramics with a pure garnet structure and a high color rendering index were prepared by a solid-state reaction method. Mn 2+ and Cr 3+ enhance the emission between 500 and 700 nm and expand the conventional Ce: YAG phosphors spectrum. The Ce 3+ can work both, as activators and sensitizers, and the intense energy transfer from Ce 3+ to Mn 2+ /Cr 3+ is realized through the non-radiative and radiative processes. In the sample with the optimized doping concentration the high color rendering index (CRI) value of 75.3 can be achieved under a 450 nm laser diode excitation. The chromaticity coordinates can be tuned from (0.3125, 0.3232) to (0.2917,0.2851) by varying the doping concentration. With the increasing Mn 2+ /Cr 3+ doping concentration, the lifetime of Ce 3+ , quantum efficiency and luminous efficiency are all gradually decreased. This work effectively offers a scheme for realizing the high color rendering performance of phosphor-converted transparent ceramics in white LEDs/LDs.
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