Advances in solid state white lighting technologies witness the explosive development of phosphor materials (down-conversion luminescent materials). A large amount of evidence has demonstrated the revolutionary role of the emerging nitride phosphors in producing superior white light-emitting diodes for lighting and display applications. The structural and compositional versatility together with the unique local coordination environments enable nitride materials to have compelling luminescent properties such as abundant emission colors, controllable photoluminescence spectra, high conversion efficiency, and small thermal quenching/degradation. Here, we summarize the state-of-art progress on this novel family of luminescent materials and discuss the topics of materials discovery, crystal chemistry, structure-related luminescence, temperature-dependent luminescence, and spectral tailoring. We also overview different types of nitride phosphors and their applications in solid state lighting, including general ...

Down-Conversion Nitride Materials for Solid State Lighting: Recent Advances and Perspectives.

Y3 Al5 O12 :Ce3+ (YAG:Ce3+ ) transparent ceramic phosphors (TCPs) are regarded as the most promising luminescent converter for laser-driven (LD) lighting. High-quality YAG:Ce3+ TCPs are still urgent for high efficiency LD lighting devices. YAG:Ce3+ TCPs in a vacuum ambience by using nano-sized raw materials are prepared. Controlling defects by adding nano-sized MgO and SiO2 simultaneously enables a high transmittance nearly 80%. After annealing in air furthermore, the luminous efficiency is enhanced greatly from 106 to 223 lm W-1 , which is the best result reported now for LD lighting. These results demonstrate that the optimizing YAG:Ce3+ TCPs in a fitting strategy will brighten once again in the next-generation LD lighting. Based on scanning electron microscopy (SEM) coupled with a cathodoluminescence system, defects and Ce3+ distributions in grains are identified directly for the first time.

YAG:Ce3+ Transparent Ceramic Phosphors Brighten the Next-Generation Laser-Driven Lighting

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

Transparent ceramics have various potential applications such as infrared (IR) windows/domes, lamp envelopes, opto-electric components/devices, composite armors, and screens for smartphones and they can be used as host materials for solid-state lasers. Transparent ceramics were initially developed to replace single crystals because of their simple processing route, variability in composition, high yield productivity, and shape control, among other factors. Optical transparency is one of the most important properties of transparent ceramics. In order to achieve transparency, ceramics must have highly symmetric crystal structures; therefore, the majority of the transparent ceramics have cubic structures, while tetragonal and hexagonal structures have also been reported in the open literature. Moreover, the optical transparency of ceramics is determined by their purity and density; the production of high-purity ceramics requires high-purity starting materials, and the production of high-density ceramics requires sophisticated sintering techniques and optimized sintering aids. Furthermore, specific mechanical properties are required for some applications, such as window materials and composite armor. This review aims to summarize recent progress in the fabrication and application of various transparent ceramics.

Materials development and potential applications of transparent ceramics: A review

As a next-generation high-power lighting technology, laser lighting has attracted great attention in high-luminance applications. However, thermally robust and highly efficient color converters suitable for high-quality laser lighting are scarce. Despite its versatility, the phosphor-in-glass (PiG) has been seldom applied in laser lighting because of its low thermal conductivity. In this work, we develop a unique architecture in which a phosphor-in-glass (PiG) film was directly sintered on a high thermally conductive sapphire substrate coated by one-dimensional photonic crystals. The designed color converter with the composite architecture exhibits a high internal quantum efficiency close to that of the original phosphor powders and an excellent packaging efficiency up to 90%. Furthermore, the PiG film can even be survived under the 11.2 W mm-2 blue laser excitation. Combining blue laser diodes with the YAG-PiG-on-sapphire plate, a uniform white light with a high luminance of 845 Mcd m-2(luminous flux: 1839 lm), luminous efficacy of 210 lm W-1, and correlated color temperature of 6504 K was obtained. A high color rendering index of 74 was attained by adding a robust orange or red phosphor layer to the architecture. These outstanding properties meet the standards of vehicle regulations, enabling the PiG films with the composite architecture to be applied in automotive lighting or other high-power and high-luminance laser lighting.

Unique Color Converter Architecture Enabling Phosphor-in-Glass (PiG) Films Suitable for High-Power and High-Luminance Laser-Driven White Lighting.

Solid state laser lighting is a newly emerging technology that combines a blue laser diode (LD) with a yellow-emitting phosphor converter to generate high-brightness white light. Due to high flux irradiation as well as thermal attack from the incident laser, this technology draws a demanding requirement on the thermal performance of the color converter. In this work, we design a Al2O3–YAG:Ce phosphor ceramic with a unique composite structure, where yellow-emitting YAG:Ce particles are embedded in a non-luminescent Al2O3 matrix having high thermal conductivity. The large YAG:Ce particles (5–20 μm) show good crystallinity and a high external quantum efficiency of 76% (upon 460 nm excitation) while the fine Al2O3 grains (0.5–2 μm) contribute to the superior in-line transmittance of 55% at 800 nm by minimizing the birefringence related scattering. The phosphor ceramic exhibits a high thermal conductivity of 18.5 W m−1 K−1 and a remarkable improvement in thermal stability (only an 8% reduction at 200 °C). When irradiated under 445 nm blue laser diodes, the phosphor ceramic shows no luminescence saturation even under a high power density of 50 W mm−2, validating its suitability for high-power solid state laser lighting.

George Ouyang

Papers

Al2O3–YAG:Ce composite phosphor ceramic: a thermally robust and efficient color converter for solid state laser lighting