Ceramic Phosphors for Light Conversion in LEDs

Raukas, M.; Kelso, J. F.; Zheng, Yi; Bergenek, K.; Eisert, D.; Linkov, A.; Jermann, F.

doi:10.1149/2.023302jss

Cited by 145 publications

(73 citation statements)

References 23 publications

(27 reference statements)

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“…9 But the main advantage compared to silicone-based converters is the high thermal conductivity of the ceramic (.5 W/mK) that allows an efficient dissipation of the heat caused by the Stokes losses within the phosphor, thus diminishing the thermal effects on the optical performance. Most recently, the optical properties of transparent, polycrystalline YAG: Ce ceramics were discussed in the literature and Raukas et al 9 described that the intrinsic scattering by pores induces backscattering, thus leading to absorption within the converter or the LED chip, which should be reduced to achieve a maximum optical conversion efficiency (CE). On the other hand, scattering is required for a homogeneous mixing of transmitted blue and converted yellow light and can be achieved by extrinsic scattering at a rough or structured surface.…”

Section: Introductionmentioning

confidence: 99%

Influence of sample thickness and concentration of Ce dopant on the optical properties of YAG:Ce ceramic phosphors for white LEDs

2014

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Translucent, polycrystalline YAG:Ce disks with 0.1, 0.5, and 1 mol% concentrations of cerium as well as different resulting thicknesses of 0.5 and 0.8 mm were prepared by reaction sintering of yttria, alumina, and cerium oxide under vacuum at a temperature of 1800 °C. The obtained samples displayed a microstructure with a Y3Al5O12 main phase interrupted by an intended scattering phase of alumina. Furthermore, the total forward transmittance was between 75 and 78% with the typical absorption bands of cerium at wavelengths of 330 and 460 nm. Phosphor conversion light-emitting diodes (LEDs) with 0.88 W power dissipation have been prepared from these YAG:Ce ceramic disks as converters and blue 455 nm LED chips for excitation. Their color coordinates in the CIE (Commission Internationale de l’Eclairage) diagram determined by spectral photometry depend on the concentration of the Ce dopant and the ceramic converter thickness. The highest luminous flux of 276 lm with an efficiency of 76.6 lm/W was measured for a converter with 0.5 mol% dopant concentration and 0.8 mm thickness emitting a yellowish white light

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Section: Introductionmentioning

confidence: 99%

Influence of sample thickness and concentration of Ce dopant on the optical properties of YAG:Ce ceramic phosphors for white LEDs

2014

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“…The simulation parameters used were a molar Ce concentration of 0.5%, a quantum efficiency of 0.90, leading to a wavelength averaged power conversion efficiency of 73.4% of converted to absorbed blue pump, a pore diameter of 350 nm (comparable to estimates in Ref. 38), and platelet thickness of 110 μm. Pores are assumed to be uniformly distributed throughout the combined LED and ceramic phosphor slab volume.…”

Section: Ecs Journal Of Solid State Science and Technology 7 (1) R32mentioning

confidence: 99%

Thermodynamics of Light Extraction from Luminescent Materials

Lenef

Piquette

Kelso

2018

ECS J. Solid State Sci. Technol.

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Light extraction from luminescent materials, where luminescence generated in a high refractive index medium must be coupled to a lower index medium, is a complex problem with significant ramifications for efficient LED and phosphor converted LED lighting. We derive thermodynamic arguments which show that light transmission for incident Lambertian light through arbitrary structured or non-structured surfaces is always limited by the ratio of incident to output étendues. Numerical simulations of various strongly scattering surfaces in the wave-optic regime are made to confirm the surface extraction results. The results are also extended to arbitrary angular radiance distributions of incident light as in Lenef, et al. [Opt. Lett., 39, 3058 (2014)], but also generalized to cases of restricted angular output emission. Furthermore, we show how cavity effects and scattering are both needed to overcome the thermodynamic surface extraction limits. Examples of both surface scattering and a converted LED with volume scattering are given. Finally, a derivation of the Lambertian light transmission theorem is developed from scalar wave-optics to highlight the physics of the thermodynamic result and to provide limits of applicability of the surface extraction limit.

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“…More recent color converter technologies use ceramics (Raukas et al, 2013) or glass-ceramics to overcome the problems of ageing and reliability (Bae et al, 2013). Table 1c shows principle technologies and material compositions of color conversion layers (Cangeloso, 2012;Chang et al, 2016;Dong et al, 2015;George et al, 2013;J€ ustel, 2013;Khanna, 2014;Li et al, 2016;McKittrick et al, 2013;McKittrick and Shea-Rohwer, 2014;Park et al, 2015;Patent, 2010;Tang et al, 2015;Wang et al, 2015;Ye et al, 2010;Yi et al, 2015).…”

Section: Led Color Converter Materialsmentioning

confidence: 99%

Critical review on life cycle inventories and environmental assessments of LED-lamps

Franz

Wenzl

2017

Critical Reviews in Environmental Science and Technology

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Resource scarcity, hazardous waste, and climate change are the driving forces for developing energy efficient and low-toxic lighting sources. Currently, solid state lighting based on lightemitting diodes is expected to become the most dominant lighting technology of the future, mostly driven by its advantage with respect to energy efficiency. Parallel to the ongoing development of light-emitting diode-based lighting sources, a number of single case and comparative life cycle assessment studies of LED-lamps and components in varying study settings were carried out. However, these studies mostly rely to specific lamp designs, which limits general conclusions. This work includes a summary of the global market of lighting and LEDlamp technologies, followed by a comprehensive review and comparison of published life cycle assessment studies. In addition, we take also some aspects, which are relevant for the well-being of an end-user and which are usually not treated in life cycle assessment studies, like glare and health issues, into consideration. A critical interpretation of the assumptions and outcomes of these studies is given and questions that remain unsettled and therefore should be addressed in future studies are discussed.

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Ceramic Phosphors for Light Conversion in LEDs

Cited by 145 publications

References 23 publications

Influence of sample thickness and concentration of Ce dopant on the optical properties of YAG:Ce ceramic phosphors for white LEDs

Influence of sample thickness and concentration of Ce dopant on the optical properties of YAG:Ce ceramic phosphors for white LEDs

Thermodynamics of Light Extraction from Luminescent Materials

Critical review on life cycle inventories and environmental assessments of LED-lamps

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