Abstract
A solution to develop high-brightness incoherent sources consists in luminescent concentration. Indeed, the absorption/emission process in a high index medium allows us to circumvent the brightness conservation law by the confinement of the light in 1 or 2 dimensions. In practice, Ce-doped luminescent concentrators pumped with InGaN LED exceed LED's brightness by one order of magnitude. This work shows how light confinement in 3 dimensions increases the brightness by an additional order of magnitude. Thanks to an analytical approach validated by experimental results, this concept gives new degrees of freedom for the design of luminescent concentrators and paves the way to a generation of incoherent sources among the brightest ever designed.
Highlights
One can basically sort light sources in two categories: incoherent light sources which can deliver high powers with a limited brightness and coherent light sources which are able to deliver high brightness at limited powers
The brightness is intrinsically related to the emission process which is isotropic for incoherent sources or direction selective for lasers and synchrotrons
This work demonstrates theoretically and experimentally that the brightness of a luminescent concentrator can be improved by an additional order of magnitude
Summary
One can basically sort light sources in two categories: incoherent light sources which can deliver high powers with a limited brightness and coherent light sources which are able to deliver high brightness at limited powers. The brightness of laser can be degraded to solve this problem either by diffusion [1], random lasing [2] or by secondary emission in phosphors [3] These sources are power-limited compared to incoherent sources. Providing that the emitters are partially transparent or partially reflective, this redirected light can be added to the direct emission resulting in a brightness enhancement. It is worth to note that the brightness enhancement in lamps and LEDs is intrinsically limited by the absorption of the emitters : absorption of the plasma in arc lamps, absorption of the filament in light bulbs, absorption of the semi-conductor in LEDs. To go further with light recycling, one must choose emitting media with low losses.
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