How to distinguish elastically scattered light from Stokes shifted light for solid-state lighting?

Abstract

We have studied the transport of light through phosphor diffuser plates that are used in commercial solid-state lighting modules (Fortimo). These polymer plates contain ${\mathrm{YAG}:\mathrm{Ce}}^{+3}$ phosphor particles that elastically scatter light and Stokes shifts it in the visible wavelength range (400-700 nm). We excite the phosphor with a narrowband light source, and measure spectra of the outgoing light. The Stokes shifted light is separated from the elastically scattered light in the measured spectra and using this technique we isolate the elastic transmission of the plates. This result allows us to extract the transport mean free path $l_{\mathrm{tr}}$ over the full wavelength range by employing diffusion theory. Simultaneously, we determine the absorption mean free path $l_{\mathrm{abs}}$ in the wavelength range 400 to 530 nm where ${\mathrm{YAG}:\mathrm{Ce}}^{+3}$ absorbs. The diffuse absorption ${\mu }_{\mathrm{a}}=\frac{1}{l_{\mathrm{abs}}}$ spectrum is qualitative similar to the absorption coefficient of ${\mathrm{YAG}:\mathrm{Ce}}^{+3}$ in powder, with the ${\mu }_{\mathrm{a}}$ spectrum being wider than the absorption coefficient. We propose a design rule for the solid-state lighting diffuser plates.

References in corpus (2)

• Interplay between multiple scattering, emission, and absorption of light in the phosphor of a white light-emitting diode
• Control of mesoscopic transport by modifying transmission channels in opaque media

Cited by in corpus (4)

• 3D spatially-resolved optical energy density enhanced by wavefront shaping
• Analytical modeling of light transport in scattering materials with strong absorption
• Systematic design of the color point of a white LED
• Energy density distribution of shaped waves inside scattering media mapped onto a complete set of diffusion modes