Color Conversion Materials for High-Brightness Laser-Driven Solid-State Lighting

Transparent ceramics (TCs) are promising for high-power (hp) white light-emitting diode (WLED) and laser diode (LD) lighting. However, comfortable warm white light has not been achieved only using a single TC in hp-WLEDs/LDs. Herein, highly transparent Gd3Al4GaO12:Ce3+ (GAGG:Ce3+) TCs (transmittance, T = 55.9–80.2%) were prepared via a solid-state reaction. Ce3+ as a doped activator center in grains plays a positive role in luminescence based on the microstructural investigations by scanning electron microscopy and the cathodoluminescence system. T decreases upon increasing the Ce3+ concentration and/or the ceramic thickness, whereas the luminous efficacy of hp-WLEDs/LDs goes up. For blue hp-LEDs driven at 350 mA or LDs of 2 W, warm white light with a low correlated-color temperature of ∼3000 K was achieved by a single GAGG:Ce3+ TC, benefiting from its broad emission band (full width at half maximum, FWHM = 133–137 nm) and abundant red components (peaking at about 568–574 nm). The color-rendering index of...

Warm White Light with a High Color-Rendering Index from a Single Gd3Al4GaO12:Ce3+ Transparent Ceramic for High-Power LEDs and LDs

The development of high-power white light-emitting diodes demands highly efficient and stable all-inorganic color converters. In this respect, phosphor-glass/ceramic composites show great promise as they could combine the merits of high quantum efficiency of phosphors and high chemical and thermal stabilities of glass/ceramic matrices. However, strong interfacial reaction between phosphors and matrices at high temperature results in quantum efficiency loss of the embedded phosphors, and traditional solutions rely on high-pressure consolidation techniques. Here we report the intrinsic inhibition of interfacial reaction by using silica glass rather than multicomponent glasses as the matrix. The embedment of phosphors is achieved via a pressureless sintering method, rendering these color-tunable phosphor-glass composites not only accessible to three-dimensional printing technique, but also highly efficient (internal quantum efficiency >90.0%), thermally stable at 1200 °C and hydrothermally stable at 200 °C. Our results provide a facile and general strategy for developing all-inorganic functional composites. Phosphor-glass/ceramic composites are attractive for high-power white light-emitting diodes, but interfacial reaction leads to loss of quantum efficiency. Here the authors report a reduction sintering method for embedment of phosphors into silica glass with limited interfacial reaction.

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Highly efficient phosphor-glass composites by pressureless sintering

A series of YAG:Ce,Mn transparent ceramics were prepared via a solid-state reaction-vacuum sintering method. The effects of various Mn2+–Si4+ pair doping levels on the structure, transmittance, and luminescence properties were systematically investigated. These transparent ceramics have average grain sizes of 10–16 μm, clean grain boundaries, and excellent transmittance up to 83.4% at 800 nm. Under the excitation of 460 nm, three obvious emission peaks appear at 533, 590, and 745 nm, which can be assigned to the transition 5d→4f of Ce 3+ and 4T1→6A1 of Mn2+. Thus, the Mn2+–Si4+ pairs can effectively modulate the emission spectrum by compensating broad orange-red and red spectrum component to yield high quality warm white light. After the optimized YAG:Ce,Mn transparent ceramic packaged with blue light-emitting diode (LED) chips, correlated color temperature (CCT) as low as 3723 K and luminous efficiency (LE) as high as 96.54 lm/W were achieved, implying a very promising candidate for application in white light-emitting diodes (WLEDs) industry.

https://link.springer.com/content/pdf/10.1007/s40145-019-0346-0.pdf

Mingxiang Chen

Papers

Glass Ceramic Phosphors: Towards Long-Lifetime High-Power White Light-Emitting-Diode Applications–A Review