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Proceedings Paper

Radiance limits of ceramic phosphors under high excitation fluxes
Author(s): Alan Lenef; John Kelso; Yi Zheng; Maxim Tchoul
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Paper Abstract

Ceramic phosphors, excited by high radiance pump sources, offer considerable potential for high radiance conversion. Interestingly, thermodynamic arguments suggest that the radiance of the luminescent spot can even exceed that of the incoming light source. In practice, however, thermal quenching and (non-thermal) optical saturation limit the maximum attainable radiance of the luminescent source. We present experimental data for Ce:YAG and Ce:GdYAG ceramics in which these limits have been investigated. High excitation fluxes are achieved using laser pumping. Optical pumping intensities exceeding 100W/mm2 have been shown to produce only modest efficiency depreciation at low overall pump powers because of the short Ce3+ lifetime, although additional limitations exist. When pump powers are higher, heat-transfer bottlenecks within the ceramic and heat-sink interfaces limit maximum pump intensities. We find that surface temperatures of these laser-pumped ceramics can reach well over 150°C, causing thermal-quenching losses. We also find that in some cases, the loss of quantum efficiency with increasing temperature can cause a thermal run-away effect, resulting in a rapid loss in converted light, possibly over-heating the sample or surrounding structures. While one can still obtain radiances on the order of many W/mm2/sr, temperature quenching effects ultimately limit converted light radiance. Finally, we use the diffusion-approximation radiation transport models and rate equation models to simulate some of these nonlinear optical pumping and heating effects in high-scattering ceramics.

Paper Details

Date Published: 25 September 2013
PDF: 20 pages
Proc. SPIE 8841, Current Developments in Lens Design and Optical Engineering XIV, 884107 (25 September 2013); doi: 10.1117/12.2023498
Show Author Affiliations
Alan Lenef, OSRAM SYLVANIA Inc. (United States)
John Kelso, OSRAM SYLVANIA Inc. (United States)
Yi Zheng, OSRAM SYLVANIA Inc. (United States)
Maxim Tchoul, OSRAM SYLVANIA Inc. (United States)


Published in SPIE Proceedings Vol. 8841:
Current Developments in Lens Design and Optical Engineering XIV
R. Barry Johnson; Virendra N. Mahajan; Simon Thibault, Editor(s)

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