Angle-resolved photoluminescence spectrum of a uniform phosphor layer

Abstract

A photoluminescence spectrum depends on an emission angle due to self-absorption in a phosphor material. Assuming isotropic initial emission and Lambert-Beer’s law, we have derived simple expressions for the angle-resolved spectra emerging from the top and bottom surfaces of a uniform phosphor layer. The transmittance of an excitation light through the phosphor layer can be regarded as a design parameter. For a strongly-absorbing phosphor layer, the forward flux is less intense and more red-shifted than the backward flux. The red-shift is enhanced as the emission direction deviates away from the plane normal. When we increase the transmittance, the backward flux decreases monotonically. The forward flux peaks at a certain transmittance value. The two fluxes become similar to each other for a weakly-absorbing phosphor layer. We have observed these behaviors in experiment. In a practical application, self-absorption decreases the efficiency of conversion and results in angle-dependent variations in chromaticity coordinates. A patterned phosphor layer with a secondary optical element such as a remote reflector alleviates these problems.

Position-sensitive detectors based on redshifts in photoluminescence spectra

“…We fabricated a planar FWG with a mixture of Coumarin 6 (Sigma-Aldrich), UV-curable resin (NOA81) and two 50 mm × 50 mm × 4 mm acrylic plates, according to the method described in Ref. 17. Briefly, we sandwiched the mixture with two rectangular acrylic plates and cured the resin.…”

“…For a uniform luminescent layer where scattering events can be neglected, it causes an emission spectrum to vary with the emission angle. 17 It complicates the measurement of quantum yield of luminescent materials.…”

Extending the concept of edge collection function to polygonal and curved planar luminescent waveguides

“…The factor 1 2π has been added to the expressions in Ref. 28 to account for the light spreading in the azimuthal angle in the current three-dimensional analysis.…”

“…In the single-spot excitation experiment described in Ref. 28, re-emission events were directly observed because they were spatially separated from the initial emission. The camera was placed 20 cm away from the 5-cm-square LWG.…”

“…The re-emission intensity distribution peaks at the radius equal to l tan θ c , where l is the LWG thickness and θ c is the critical angle for TIR. 28 Because the intensity diminishes at a larger radius, the total pixel value in the circular ROI reaches an asymptotic value. This value divided by the exposure time is proportional to the number of re-emitted photons in addition to that of the initial PL photons.…”