Stable, Heat-Conducting Phosphor Composites for High-Power Laser Lighting

Abstract

Solid-state lighting using laser diodes is an exciting new development that requires new phosphor geometries to handle the greater light fluxes involved. The greater flux from the source results in more conversion and therefore more conversion loss in the phosphor, which generates self-heating, surpassing the stability of current encapsulation strategies used for light-emitting diodes, usually based on silicones. Here, we present a rapid method using spark plasma sintering (SPS) for preparing ceramic phosphor composites of the canonical yellow-emitting phosphor Ce-doped yttrium aluminum garnet (Ce:YAG) combined with a chemically compatible and thermally stable oxide, α-AlO. SPS allows for compositional modulation, and phase fraction, microstructure, and luminescent properties of ceramic composites with varying compositions are studied here in detail. The relationship between density, thermal conductivity, and temperature rise during laser-driven phosphor conversion is elucidated, showing that only modest densities are required to mitigate thermal quenching in phosphor composites. Additionally, the scattering nature of the ceramic composites makes them ideal candidates for laser-driven white lighting in reflection mode, where Lambertian scattering of blue light offers great color uniformity, and a luminous flux >1000 lm is generated using a single commercial laser diode coupled to a single phosphor element.

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

“…Cozzan et al. also prepared a series of Al 2 O 3 –YAG:Ce composite ceramics and gave new insights into the relationships among the relative density, thermal conductivity, and the phosphor temperature during the laser‐driven process, highlighting the crucial role of Al 2 O 3 . The Al 2 O 3 –YAG:Ce composite ceramics with the YAG:Ce concentration of 25–100% were sintered by the SPS technique.…”

“…The generated white light with k) the composite ceramic and m) the single crystal, respectively. Reproduced with permission . Copyright 2018, American Chemical Society.…”

Conversionless efficient and broadband laser light diffusers for high brightness illumination applications

“…Both these loss mechanisms scale with temperature 10 (e.g., as a result of illumination) and therefore phosphor luminescence suffers from saturation 10 , aging 11 , and thermal quenching 10 , limiting the irradiance tõ 5 kW cm −2 and thus the overall light output. Even though new concepts such as glass encapsulation 12,13 , phosphor monoliths 14 , or composite ceramic phosphors [15][16][17] can increase the irradiance level up to~10-20 kW cm −2 , the true potential of lasers for highbrightness lighting applications, with possible light outputs of several MW cm −2 , still remains unemployed.…”

Bulk polycrystalline ceria–doped Al2O3 and YAG ceramics for high-power density laser-driven solid-state white lighting: Effects of crystallinity and extreme temperatures

“…using bulk ceramic or single crystal Ce:YAG [7] and 3) using high-thermally conductivity passive ceramics as a phosphor encapsulant, i.e. an Al2O3/Ce:YAG composite [8]- [11] , which result in a higher composite thermal conductivity. The management can be addressed by using different heat sink materials for the LED packaging [12] .…”